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  • 1.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gällström, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep levels in tungsten doped n-type 3C-SiC2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 15, p. 152104-Article in journal (Refereed)
    Abstract [en]

    Tungsten was incorporated in SiC and W related defects were investigated using deep level transient spectroscopy. In agreement with literature, two levels related to W were detected in 4H-SiC, whereas only the deeper level was observed in 6H-SiC. The predicted energy level for W in 3C-SiC was observed (E-C-0.47 eV). Tungsten serves as a common reference level in SiC. The detected intrinsic levels align as well: E1 (E-C-0.57 eV) in 3C-SiC is proposed to have the same origin, likely V-C, as EH6/7 in 4H-SiC and E7 in 6H-SiC, respectively.

  • 2.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lin, Y.-C.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gällström, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep levels in iron doped n- and p-type 4H-SiC2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, p. 123701-1-123701-5Article in journal (Refereed)
    Abstract [en]

    Deep levels were detected in Fe-doped n- and p-type 4H-SiC using deep level transient spectroscopy (DLTS). One defect level (EC 0.39 eV) was detected in n-type material. DLTS spectra of p-type 4H-SiC show two dominant peaks (EV + 0.98 eV and EV + 1.46 eV). Secondary ion mass spectrometry measurements confirm the presence of Fe in both n- and p-type 4H-SiC epitaxial layers. The majority capture process for all the three Fe-related peaks is multi-phonon assisted. Similar defect behavior in Si indicates that the observed DLTS peaks are likely related to Fe and Fe-B pairs.

  • 3.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J
    University of Tsukuba.
    Morishita, N
    Japan Atomic Energy Agency.
    Ohshima, T
    Japan Atomic Energy Agency.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bistable defects in low-energy electron irradiated n-type 4H-SiC2010In: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, ISSN 1862-6254, Vol. 4, no 8-9, p. 227-229Article in journal (Refereed)
    Abstract [en]

    Epitaxial n-type 4H-SiC layers were irradiated at room temperature by low-energy electrons. During the annihilation process of the irradiation induced defects EH I and EH3, three new bistable centers, labeled EB centers, were detected in the DLTS spectrum. The reconfigurations of the EB centers (I -andgt; II and II -andgt; I) take place at room temperature with a thermal reconfiguration energy of about 0.95 eV. The threshold energy for moving the Si atom from its site in the SiC crystal structure is higher than the applied irradiation energy; therefore, the EB centers are attributed to carbon related complex defects.

  • 4.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J
    University of Tsukuba, Japan .
    Morishita, N
    Japan Atom Energy Agency, Japan .
    Ohshima, T
    University of Tsukuba, Japan .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Capacitance transient study of a bistable deep level in e(-)-irradiated n-type 4H-SiC2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 45Article in journal (Refereed)
    Abstract [en]

    Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H-SiC. In configuration A, the deep level known as EH5 (E-a = E-C - 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be T-A -andgt; B andgt; 730K and for the opposite process T-B -andgt; A approximate to 710 K. The energy needed to conduct the transformations were determined to be E-A(A -andgt; B) = (2.1 +/- 0.1) eV and E-A(B -andgt; A) = (2.3 +/- 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A -andgt; B and a charge carrier-emission dominated process in the case of B -andgt; A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.

  • 5.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J.
    University of Tsukuba.
    Morishita, N.
    Japan Atomic Energy Agency.
    Ohshima, T.
    University of Tsukuba.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Defects in low-energy electron-irradiated n-type 4H-SiC2010In: Physica Scripta, vol. T141, IOP Publishing , 2010, p. 014006-Conference paper (Refereed)
    Abstract [en]

    The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation increased the DLTS signals of the intrinsic defects Z(1/2) and EH6/7 and introduced the frequently observed defects EH1 and EH3. After the M-center is annealed out at about 650K without bias and at about 575K with bias applied to the sample during the annealing process, a new bistable defect in the low temperature range of the DLTS spectrum, the EB-center, evolves. Since low-energy irradiation affects mainly the carbon atoms in SiC, the M-center and the newly discovered EB-center are most probably carbon-related intrinsic defects.

  • 6.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, Junichi
    University of Tsukuba.
    Morishita, Norio
    Japan Atomic Energy Agency.
    Ohshima, Takeshi
    Japan Atomic Energy Agency.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Metastable defects in low-energy electron irradiated n-type 4H-SiC2010In: Materials Science Forum, Vols. 645-648, Trans Tech Publications , 2010, Vol. 645-648, p. 435-438Conference paper (Refereed)
    Abstract [en]

    After low-energy electron irradiation of epitaxial n-type 4H-SiC, the DUES peak amplitudes. of the defects Z(1/2) and EH6/7, which were already observed in as-grown layers, increased and the commonly found peaks EH1 and EH3 appeared. The bistable M-center, previously seen in high-energy proton implanted 4H-SiC, was detected. New bistable defects, the EB-centers, evolved after annealing out of the M-center, and EF3. The reconfiguration energies for one of the two EB-centers were determined to be about 0.96 eV for both transitions: from configuration I to II and from configuration II to I. Since low-energy electron irradiation (less than220 keV) affects mainly the carbon atom in SiC, both the M- and EB-centers are likely to be carbon related defects.

  • 7.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, Junichi
    Graduate School of Library, Information and Media Science, University of Tsukuba, 1-2 Kasuga,Tsukuba, Ibaraki 305-8850, Japan.
    Morishita, Norio
    Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Observation of Bistable Defects in Electron Irradiated N-Type 4H-SiC2011In: Materials Science Forum Vols. 679-680 (2011) pp 249-252, Trans Tech Publications Inc., 2011, p. 249-252Conference paper (Refereed)
    Abstract [en]

    DLTS measurements show bistable behavior of the previously reported EH5 peak in low- and high-energy electron irradiation 4H-SiC. Both reconfiguration processes (A ! B and B ! A) take place above 700 ±C. By isothermal annealing, the reconfiguration rates were determined and the reconfiguration energy was calculated to EA = 2.4±0.2 eV. Since the defect is present already after low-energy electron irradiation, which mainly affects the C atom in SiC, the EH5 peak may be related to defects associated with C-vacancies or C-interstitials.

  • 8.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J.
    University of Tsukuba.
    Morishita, N.
    Japan Atom Energy Agency.
    Ohshima, T.
    Japan Atom Energy Agency.
    Annealing behavior of the EB-centers and M-center in low-energy electron irradiated n-type 4H-SiC2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 10, p. 103703-Article in journal (Refereed)
    Abstract [en]

    After low-energy electron irradiation of epitaxial n-type 4H-SiC with a dose of 5 x 10(16) cm(-2), the bistable M-center, previously reported in high-energy proton implanted 4H-SiC, is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is confirmed, and an enhanced recombination process is suggested. The annihilation process is coincidental with the evolvement of the bistable EB-centers in the low temperature range of the DLTS spectrum. The annealing energy of the M-center is similar to the generation energy of the EB-centers, thus partial transformation of the M-center to the EB-centers is suggested. The EB-centers completely disappeared after annealing temperatures higher than 700 degrees C without the formation of new defects in the observed DLTS scanning range. The threshold energy for moving Si atom in SiC is higher than the applied irradiation energy, and the annihilation temperatures are relatively low, therefore the M-center, EH1 and EH3, as well as the EB-centers are attributed to defects related to the C atom in SiC, most probably to carbon interstitials and their complexes.

  • 9.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep levels in hetero-epitaxial as-grown 3C-SiC2010In: AIP Conference Proceedings, Vol. 1292, 2010, p. 63-66Conference paper (Refereed)
    Abstract [en]

    3C-SiC grown hetero-epitaxially on 4H- or 6H-SiC using a standard or a chloride-based CVD process were electrically characterized using IV, CV and DLTS. The reverse leakage current of the Au-Schottky diodes was  reduced to lower than 10-8 A at -2V by a thermal oxidation step using UV-light illumination at 200oC. The Schottky barrier height of the Ni and Au contacts were determined by IV measurement to be ØB = 0.575  eV and ØB = 0.593 eV, respectively, for a contact diameter of about 150 mm. One dominant DLTS peak was observed in the 3C-epilayers independently of the substrate at about EC0:60 eV which is attributed to W6-level in 3C-SiC. This deep level is thought to be related to an intrinsic defect.

  • 10.
    Carlsson, Fredrik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Storasta, Liutauras
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Electroluminescence from implanted and epitaxially grown pn-diodes2000In: Materials Science Forum, Vols. 338-343, Trans Tech Publications Inc., 2000, Vol. 338-3, p. 687-690Conference paper (Refereed)
    Abstract [en]

    The electroluminescence from pn-diodes with (1) aluminum doped epitaxially grown, (2) aluminum implanted or (3) aluminum and boron implanted p-layer have been investigated. The temperature dependence for both the spectra and the decays of the major spectral components have been investigated at temperatures from 80 K to 550 K. The implanted diodes show implantation damage in the form of the D-1 center and lack of emission from the aluminum center. The epitaxial diodes show luminescence from the aluminum center. The band edge luminescence is visible above 150 K for the epitaxial diode and above 300 K for the implanted. The emission from deep boron can be seen in the aluminum and boron co-implanted diode and in the epitaxially grown diode that have an unintentional boron doping below 10(17) cm(-3).

  • 11.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Amano, Hiroshi
    Department of Electrical Engineering and Computer Science, Nagoya University, Chikusa-ku, Nagoya, Japan.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy2016In: Physical Review B, ISSN 2469-9950, Vol. 94, no 4, article id 045206Article in journal (Refereed)
    Abstract [en]

    Deep levels in Mg doped GaN have been studied using deep level transient spectroscopyand minority charge carrier transient spectroscopy. Two traps are revealed in the investigatedtemperature range. In the substrate, one electron trap labelled ET1 (EC – 0.158 eV) is observedand in the Mg-doped layer, one hole trap labelled HT1 has been revealed. By varying theelectric field, it is found that the hole trap HT1 exhibits an electric field enhanced hole emissionrate. Using four theoretical models based on 3-dimensional Coulombic Poole-Frenkel effect, 3-dimensional square well Poole-Frenkel effect, phonon assisted tunneling, and 1-dimensionalCoulombic Poole-Frenkel effect including phonon assisted tunneling, the experimental data arefitted in order to justify the field enhanced emission process. It is found that the 1-dimensionalCoulombic Poole-Frenkel model including phonon assisted tunneling is consistent with theexperimental data. Since the trap exhibits Poole-Frenkel effect, we suggest it is acceptor like.From the theoretical model, the zero field activation energy of HT1 and an estimate of the holecapture cross section have been determined as Ev+0.57 eV and 1.9x10-15 cm2, respectively.Since the level is only observed in Mg-doped material, it is suggested that the trap can beassociated with a Mg related defect.

  • 12.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 15Article in journal (Refereed)
    Abstract [en]

    Electron traps in thick free standing GaN grown by halide vapor phase epitaxy were characterized by deep level transient spectroscopy. The measurements revealed six electron traps with activation energy of 0.252 (E1), 0.53 (E2), 0.65 (E4), 0.69 (E3), 1.40 (E5), and 1.55 eV (E6), respectively. Among the observed levels, trap E6 has not been previously reported. The filling pulse method was employed to determine the temperature dependence of the capture cross section and to distinguish between point defects and extended defects. From these measurements, we have determined the capture cross section for level E1, E2, and E4 to 3.2 × 10−16 cm2, 2.2 × 10−17 cm2, and 1.9 × 10−17 cm2, respectively. All of the measured capture cross sections were temperature independent in the measured temperature range. From the electron capturing kinetic, we conclude that trap E1, E2, and E3 are associated with point defects. From the defect concentration profile obtained by double correlated deep level transient spectroscopy, we suggest that trap E4 and E6 are introduced by the polishing process.

  • 13.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Thermal behavior of irradiation-induced-deep levels in bulk GaN2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Bulk GaN grown by halide vapor phase epitaxy and irradiated by 2 MeV electrons at a fluence of 5×1016 cm-2 were studied by deep level transient spectroscopy. After irradiation, two new peaks labelled D0 (EC – 0.18 eV) and D1 (EC – 0.13 eV) are observed. From isochronal annealing studies in the temperature range of 350 - 600 K, it is observed that peak D0 is completely annealed out already at 550 K while the broad peak D1 has a more complex annealing behavior. The concentration of D1 is decreasing during annealing and its peak position is shifted to higher temperatures, until a relatively stable peak labelled D2 (EC – 0.24 eV) is formed. From an isothermal annealing study of D2, it is concluded that the annealing process can be described by a first order annealing process with an activation energy and prefactor of 1.2 eV and 6.6 × 105 s-1, respectively. From the large pre-factor it is concluded that the annihilation of D2 is governed by a long-range migration process. From its annealing behavior, it is suggested that trap D2 may be related to the VGa.

  • 14.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 9Article in journal (Refereed)
    Abstract [en]

    By minority carrier transient spectroscopy on as-grown n-type bulk GaN produced by halide vapor phase epitaxy (HVPE) one hole trap labelled H1 (EV + 0.34 eV) has been detected. After 2 MeV-energy electron irradiation, the concentration of H1 increases and at fluences higher than 5×1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV) increases. By studying the increase of the concentration versus electron irradiation fluences, the introduction rate of T1 and T2 using 2 MeV-energy electrons was determined to 7X10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1 and the low threading dislocation density in the HVPE bulk GaN material, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the trap H1 suggests that the H1 defect is associated with a primary intrinsic defect or a complex.

  • 15.
    Duc Tran, Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Japan Atomic Energy Agency, Takasaki, Japan.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Electronic properties of defects in high-fluence electron irradiated bulk GaN2016In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 3, p. 521-526Article in journal (Refereed)
    Abstract [en]

    Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.

  • 16.
    Duc, Tran Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency (JAEA), Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Capture cross section of electron-irradiation-induced defects in bulk GaN grown by halide vapor phase epitaxy2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Electron-irradiation-induced defects in GaN grown by halide vapor phase epitaxy is studied by deep level transient spectroscopy in which the capture cross section and its temperature dependence of the deep levels was determined by the filling pulse method. Before irradiation, one trap level, labelled ET4 (EC – 0.244 eV), was observed. After performing electron irradiation with an energy of 2 MeV at a fluence of 5 × 1016 cm-2, four deep trap levels, labelled ET1 (EC – 0.178 eV), ET2 (EC – 0.181 eV), ET3 (EC – 0.256 eV) and ET5 appeared. After annealing at 650K for 2 hours, only two irradiation induced deep levels, ET1 and ET3, were observed. By varying the rate windows, the temperature dependence of the capture cross section of the two deep levels ET1 and ET2 and ET3 was studied. The temperature behavior of ET2 and ET3 capture cross section is independent on temperature whereas the capture cross section of the deep level ET1 depends strongly on the temperature. It is suggested that electron capturing is govern by a multiphonon process to the level ET1.

  • 17.
    Duc, Tran Thien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atomic Energy Agency (JAEA), Takasaki, Japan.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 10, p. 102103-Article in journal (Refereed)
    Abstract [en]

    Defects induced by electron irradiation in thick free-standing GaN layers grown by halide vapor phase epitaxy were studied by deep level transient spectroscopy. In as-grown materials, six electron traps, labeled D2 (E-C-0.24 eV), D3 (E-C-0.60 eV), D4 (E-C-0.69 eV), D5 (E-C-0.96 eV), D7 (E-C-1.19 eV), and D8, were observed. After 2MeV electron irradiation at a fluence of 1 x 10(14) cm(-2), three deep electron traps, labeled D1 (E-C-0.12 eV), D5I (E-C-0.89 eV), and D6 (E-C-1.14 eV), were detected. The trap D1 has previously been reported and considered as being related to the nitrogen vacancy. From the annealing behavior and a high introduction rate, the D5I and D6 centers are suggested to be related to primary intrinsic defects.

  • 18. Ellison, A.
    et al.
    Magnusson, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnusson, W.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Storasta, Liutauras
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Henelius, N.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    HTCVD Growth of Semi-Insulating 4H-SiC Crystals With Low Defect Density2001In: Mat. Res. Soc. Symp. Proc., Vol. 640, 2001, p. H1.2-Conference paper (Refereed)
  • 19.
    Ellison, A
    et al.
    Linkoping Univ, IFM, SE-58183 Linkoping, Sweden Linkoping Univ, Okmetic AB, SE-58183 Linkoping, Sweden ABB Corp Res, SE-72178 Vasteras, Sweden.
    Zhang, J
    Magnusson, W
    Linkoping Univ, IFM, SE-58183 Linkoping, Sweden Linkoping Univ, Okmetic AB, SE-58183 Linkoping, Sweden ABB Corp Res, SE-72178 Vasteras, Sweden.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Fast SiC epitaxial growth in a chimney CVD reactor and HTCVD crystal growth developments2000In: Materials science Forum, Vols. 338-342, Trans Tech Publications Inc., 2000, Vol. 338-3, p. 131-136Conference paper (Refereed)
    Abstract [en]

    The epitaxial growth of SiC is investigated in a CVD process based on a vertical hot-wall, or "chimney", reactor geometry. Carried out at increased temperatures (1650 to 1850 degreesC) and concentrations of reactants, the growth process enables epitaxial rates ranging from 10 to 50 mum/h. The growth rate is shown to be influenced by two competing processes: the supply of growth species in the presence of homogeneous gas-phase nucleation, and, the etching effect of the hydrogen carrier gas. The quality of thick (20 to 100 mum) low-doped 4H-SiC epitaxial layers grown at rates ranging between 10 and 25 mum/h are discussed in terms of thickness uniformity, surface morphology and purity. The feasibility of high voltage Schottky rectifiers (V-BR from 2 to similar to3.8 kV) on as-grown chimney CVD epilayers is reported. In a second part, recent developments of the High Temperature Chemical Vapor Deposition (HTCVD) technique for SiC crystal growth are described. Using pure gases (SiH4 and C2H4) as source material and growth temperatures of 2100-2300 degreesC, this technique enables at present growth rates ranging from 0.4 to 0.8 mm/h. 6H and 4H-SiC crystals of thickness up to 7 mm and diameters up to 40 mm have been grown. We report micropipe densities of similar to 80 cm(-2) over areas of 0.5 cm(2) in 35 mm diameter 4H-SiC wafers sliced from HTCVD grown crystals. Undoped wafer demonstrators exhibit semi-insulating behavior with a bulk resistivity higher than 7.10(9) Omega cm at room temperature.

  • 20.
    Forsberg, Mathias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Amano, Hiroshi
    Department of Electrical Engineering and Computer Science, Nagoya University, Japan.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Dynamic properties of excitons in ZnO/AlGaN/GaN hybrid nanostructures2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, no 7889, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Hybrid samples based on ZnO colloidal nanocrystals (NCs) deposited on AlGaN/GaN quantum well (QW) structures with different top barrier thickness d = 3, 6 and 9 nm are studied by time-resolved photoluminescence. Thermal behavior of the QW exciton lifetime in the hybrids and in the bare QW structures has been compared and it has been found that the QW exciton recombination rate increases in the hybrid having d = 3 nm and decreases in the hybrid with d = 6 nm, while no change has been observed for the structure with d = 9 nm. It is suggested that non-radiative resonance energy transfer from the QW excitons to the ZnO NCs and a variation of the surface potential can both influence the QW exciton lifetime in the hybrids.

  • 21.
    Forsberg, Mathias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Amano, Hiroshi
    Nagoya University, Japan.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Time-resolved photoluminescence properties of hybrids based on inorganic AlGaN/GaN quantum wells and colloidal ZnO nanocrystals2015In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 87, p. 38-41Article in journal (Refereed)
    Abstract [en]

    Dynamic properties are studied for the AlGaN/GaN quantum well (QW) structures with and without the coating of colloidal ZnO nanocrystals (NCs). The QW exciton recombination rate was reduced in such hybrids compared to the bare QW structure only in the sample with the thinnest cap layer of 3 nm. Assuming that one of the recombination mechanisms in this hybrid is non-radiative resonant energy transfer (NRET) between the QW and the energy acceptor material i.e. ZnO NCs, the maximum pumping efficiency was estimated to be similar to 42% at 60 K. The NRET effect is, however, vanished after several months despite that the hybrid structures are composed of chemically stable components. (C) 2015 Published by Elsevier Ltd.

  • 22. Gogova, D.
    et al.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Talik, E.
    Kruczek, M.
    Tuomisto, F.
    Saarinen, K.
    Investigation of the structural and optical properties of free-standing GaN grown by HVPE2005In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 38, no 14, p. 2332-2337Article in journal (Refereed)
    Abstract [en]

    The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 νm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm-3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized. © 2005 IOP Publishing Ltd.

  • 23.
    Gogova, D.
    et al.
    Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany; Central Laboratory of Solar Energy and New Energy Sources at the Bulgarian Academy of Sciences, Blvd. Tzarigradsko shose 72, 1784 Sofia, Bulgaria.
    Siche, D.
    Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany.
    Kwasniewski, A.
    Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany.
    Schmidbauer, M.
    Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany.
    Fornari, R.
    Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Central Laboratory of Solar Energy and New Energy Sources at the Bulgarian Academy of Sciences, Blvd. Tzarigradsko shose 72, 1784 Sofia, Bulgaria.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    HVPE GaN substrates: growth and characterization2010In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 7, no 7-8, p. 1756-1759Article in journal (Refereed)
    Abstract [en]

    GaN substrates with low dislocation densities were prepared by halide vapor-phase epitaxy (HVPE) on c-plane sapphire and by means of a post-growth laser-induced lift-off or natural stress-induced (self-) separation process. The HVPE growth on InGaN/GaN buffer layers and subsequent self-separation method was seen as advantageous, in comparison with the laser-induced lift-off one, in terms of lower cost and better crystalline quality of the GaN material obtained. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • 24.
    Gogova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kasic, A.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Tuomisto, F.
    Laboratory of Physics, Helsinki University of Technology, Finland .
    Saarinen, K.
    Laboratory of Physics, Helsinki University of Technology, Finland .
    Dobos, L.
    Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Science, Hungary .
    Pécz, B.
    Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Science, Hungary .
    Gibart, P.
    LUMILOG, 2720, Chemin de Saint Bernard, France .
    Beaumont, B.
    LUMILOG, 2720, Chemin de Saint Bernard, France .
    Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 1, p. 799-806Article in journal (Refereed)
    Abstract [en]

    Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ∼2.5×107 cm−2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm−3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm−1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. © 2004 American Institute of Physics.

  • 25.
    Gällström, Andreas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnusson, Björn
    Norstel AB, Norrköping, Sweden.
    Beyer, Franziska
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Budapest University of Technology and Economics and Hungarian Academy of Science, Budapest, Hungary .
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, Ivan G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Electronic Configuration of Tungsten in 4H-, 6H-, and 15R-SiC2012In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 211-216Conference paper (Refereed)
    Abstract [en]

    A commonly observed unidentified photoluminescence center in SiC is UD-1. In this report, the UD-1 center is identified to be tungsten related. The identification is based on (i) a W-doping study, the confirmation of W in the samples was made using deep level transient spectroscopy (DLTS), (ii) the optical activation energy of the absorption of UD-1 in weakly n-type samples corresponds to the activation energy of the deep tungsten center observed using DLTS. The tungsten-related optical centers are reported in 4H-, 6H-, and 15R-SiC. Further, a crystal field model for a tungsten atom occupying a Si-site is suggested. This crystal field model is in agreement with the experimental data available: polarization, temperature dependence and magnetic field splitting.

  • 26.
    Gällström, Andreas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnusson, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Beyer, Franziska
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Budapest University of Technology and Economics, Hungary.
    Son Tien, Nguyen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Optical identification and electronic configuration of tungsten in 4H-and 6H-SiC2012In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, no 10, p. 1462-1466Article in journal (Refereed)
    Abstract [en]

    Several optically observed deep level defects in SiC are still unidentified and little is published on their behavior. One of the commonly observed deep level defects in semi-insulating SiC is UD-1. less thanbrgreater than less thanbrgreater thanThis report suggests that UD-1 is Tungsten related, based on a doping study and previously reported deep level transient spectroscopy data, as well as photo-induced absorption measurements. The electronic levels involved in the optical transitions of UD-1 are also deduced. The transitions observed in the photoluminescence of UD-1 are from a Gamma(C3v)(4), to two different final states, which transform according to Gamma(C3v)(5)circle plus Gamma(C3v)(6) and Gamma(C3v)(4), respectively.

  • 27.
    Hemmingsson, Carl
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Boota, M
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Rahmatalla, R O
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Junaid, M
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Health Sciences.
    Monemar , Bo
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth and characterization of thick GaN layers grown by halide vapour phase epitaxy on lattice-matched AlInN templates2009In: JOURNAL OF CRYSTAL GROWTH, ISSN 0022-0248 , Vol. 311, no 2, p. 292-297Article in journal (Refereed)
    Abstract [en]

    We have investigated the feasibility to use GaN lattice-matched Al0.82In0.18N as a starting layer for growth of thick GaN using halide vapor phase epitaxy (HVPE). The buffer, which consisted of Al0.82In0.18N(0 0 0 1) on a 50-nm-thick TiN(1 1 1) seed layer, was grown by magnetron sputter epitaxy (MSE) on a 2 Al2O3(0 0 0 1) substrate. It was found that the surface morphology of the GaN strongly depends on the choice of carrier gases. Using a mixture of hydrogen and nitrogen results in a rough morphology, while growth in pure nitrogen gives layers of good morphology and high transparency. For a 30-pm-thick GaN film, the threading dislocation (TD) density, as determined by cathodoluminescence, is about similar to 3 x 10(8) cm(-2). By transmission electron microscopy (TEM), it was revealed that the threading dislocations originate from the buffer layer and the GaN/Al0.82In0.18N interface. The GaN/Al0.82In0.18N interface is roughened during growth due to a chemical incompatibility between the HVPE process and the Al0.82In0.18N layer. Additionally, the GaN layers are cracked due to tensile strain indicating initial growth of crystallites which eventually coalesce and hence build up a tensile stress in the film.

  • 28.
    Hemmingsson, Carl
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Metastable defects in 6H-SiC: Experiments and modeling2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 3, p. 1324-Article in journal (Refereed)
    Abstract [en]

    [No abstract available]

  • 29.
    Hemmingsson, Carl
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    Schineller, B.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Growth of bulk GaN in a vertical hydride vapour phase epitaxy reactor2006In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 40, no 4-6 SPEC. ISS., p. 205-213Article in journal (Refereed)
    Abstract [en]

    Using the hydride vapour phase epitaxy technique, we have grown 2-inch diameter bulk GaN material with a thickness up to 2 mm. The growth was performed in a vertical hot-walled reactor at atmospheric pressure. In this geometry, the process gases are distributed from the bottom upwards through the reactor. We present recent results on growth and characterization of the bulk GaN material. The structural and optical properties of the layers have been studied using decorative etching, optical microscopy, scanning electron microscopy, X-ray diffraction, cathodoluminescence, and low temperature photoluminescence. © 2006 Elsevier Ltd. All rights reserved.

  • 30.
    Hemmingsson, Carl
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    Aixtron AG, D-52072 Aachen, Germany.
    Schineller, B.
    Aixtron AG, D-52072 Aachen, Germany.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hydride vapour phase epitaxy growth and characterization of thick GaN using a vertical HVPE reactor2007In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 1, p. 32-36Article in journal (Refereed)
    Abstract [en]

    Growth of 2-inch diameter bulk GaN layers with a thickness up to 2 mm is demonstrated in a vertical hydride vapour phase growth reactor. Morphology, dislocations, optical and electrical properties of the material have been investigated using atomic force microscopy, optical microscopy, decorative etching in hot H3PO4, Hall measurements and low-temperature photoluminescence. Atomic force microscopy reveals a two-dimensional step flow growth mode with step bunching for layers with a thickness of 250 µm. As the growth proceeds, the morphology is changed to a hill and valley structure. The EPD was determined to 5×105 cm-2 for a 2 mm thick layer. The Hall mobility and the carrier concentration were determined. For a 1.7 mm thick layer at 300 K the mobility and the carrier concentration is 520 cm2/V s and about 4×1017 cm-3, respectively. Low-temperature photoluminescence spectra measured on a 350 µm thick freestanding layer show the DBE line at 3.4707 eV with a full-width half-maximum of 1 meV, confirming a stress free GaN layer. © 2006 Elsevier B.V. All rights reserved.

  • 31.
    Hemmingsson, Carl
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Optimization of low temperature GaN buffer layers for halide vapor phase epitaxy growth of bulk GaN2013In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 366, p. 61-66Article in journal (Refereed)
    Abstract [en]

    We have studied growth and self-separation of bulk GaN on c-oriented Al2O3 using low temperature (LT) GaN buffer layers. By studying the X-ray diffraction (XRD) signature for the asymmetric and symmetric reflections versus the LT-GaN thickness and V/III precursor ratio, we observe that the peak width of the reflections is minimized using a LT buffer thickness of ∼100–300 nm. It was observed that the V/III precursor ratio has a strong influence on the morphology. In order to obtain a smooth morphology, the V/III precursor ratio has to be more than 17 during the growth of the buffer layer. By using an optimized LT buffer layer for growth of a 20 μm thick GaN layer, we obtain a XRD peak with a full width at half maximum of ∼400 and ∼250 arcs for (002) and (105) reflection planes, respectively, and with a dark pit density of ∼2.2×108 cm−2. For layers thicker than 1 mm, the GaN was spontaneously separated and by utilizing this process, thick free freestanding 2″ GaN substrates were manufactured.

  • 32.
    Hemmingsson, Carl
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    Aixtron AG, D-52072 Aachen, Germany.
    Schineller, B.
    Aixtron AG, D-52072 Aachen, Germany.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Modeling, optimization, and growth of GaN in a vertical halide vapor-phase epitaxy bulk reactor2008In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 310, no 5, p. 906-910Article in journal (Refereed)
    Abstract [en]

    In this work we are presenting growth results of thick gallium nitride (GaN), numerical modeling and optimization of a vertical hot-walled halide vapor-phase epitaxy reactor. Using a simulation model, the growth rate and thickness uniformity of the GaN layers have been predicted and optimized. The simulation results have been correlated with experiments to verify the model. Using constant precursor flows, the average growth rate over a 2 in substrate was increased with a factor of four by only optimizing the composition of N2 and H2 in the carrier gas and the carrier gas flow rates. With a simple sticking model, assuming Ga mass transport-limited growth, the growth rate and thickness uniformity could be estimated. Photoluminescence mapping of the grown layer shows that the layers have excellent optical properties and a high degree of uniformity. © 2007 Elsevier B.V. All rights reserved.

  • 33.
    Hemmingsson, Carl
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Khromov, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of GaN nanotubes by halide vapor phase epitaxy2011In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 22, no 8, p. 085602-Article in journal (Refereed)
    Abstract [en]

    We have investigated low temperature growth of GaN nanostructures using halide vapor phase epitaxy on c-oriented Al2O3 and Au coated Al2O3 substrates. Depending on the III/V ratio and the growth temperature, the shape and density of the structures could be controlled. By increasing the GaCl partial pressure, the structure changed from dot-like to nanotubes. The nanotubes, which could be open or closed, were about 1 mu m long with a diameter of typically 200 nm. In addition, it was observed that the nanostructures were spontaneously nucleated at droplets of Ga or, when using Au coated Al2O3, on droplets of Au/Ga alloy. By varying the growth temperature, the inner diameter of the nanotubes could be controlled. The experimental results suggest that this approach with pre-patterned Au coated Al(2)O(3)substrates has the potential for fabrication of well-organized nanotubes with a high density.

  • 34.
    Hemmingsson, Carl
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lindström, J.L.
    National Defense Research Institute.
    Savage, S.
    Industrial Microelectronics Center.
    Nordell, N.
    Industrial Microelectronics Center.
    Deep-Level Defects in Electron-irradiated 4H SiC Epitaxial Layers1997In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 81, no 9, p. 6155-6159Article in journal (Refereed)
    Abstract [en]

    Deep level defects in electron-irradiated 4H SiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiated p+n junctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as ≈5×1013 cm-2. Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent. © 1997 American Institute of Physics.

  • 35.
    Kasic, A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Gogova, Daniela
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bundesmann, C.
    Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany.
    Schubert, M.
    Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany.
    Micro-Raman scattering profiling studies on HVPE-grown free-standing GaN2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 12, p. 2773-2776Article in journal (Refereed)
    Abstract [en]

    Free-standing GaN of ∼330 μm thickness with low defect density was prepared by hydride vapor-phase epitaxy (HVPE) on sapphire in a vertical atmospheric-pressure reactor and a subsequent laser-induced lift-off process. The structural and optical properties of the material were assessed by various characterization techniques, like X-ray diffraction, photo- and cathodoluminescence, spectroscopic ellipsometry, positron annihilation spectroscopy, and transmission electron microscopy. Here, we focus on μ-Raman scattering profiling studies providing the vertical strain distribution and the evolution of the crystalline quality with increasing layer thickness. Profiles of the free-carrier concentration are obtained from monitoring the LO-phonon plasmon coupled mode. Comparative investigations are performed on the material before and after separation of the sapphire substrate. The GaN material presented here is well capable of serving as a substrate for further homoepitaxial strain-relaxed and crack-free growth needed for fabrication of high-quality III-nitride device heterostructures.

  • 36.
    Kasic, A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Gogova, Daniela
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Heuken, M.
    Aixtron AG, Germany .
    Characterization of crack-free relaxed GaN grown on 2″ sapphire2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 7, p. 73525-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the growth of high-quality and virtually strain-free bulklike GaN by hydride vapor-phase epitaxy in a vertical atmospheric-pressure reactor with a bottom-fed design. The 300‐μm-thick GaN layer was grown on a 2″ (0 0 0 1) sapphire substrate buffered with a ∼ 2‐μm-thick GaN layer grown by metal-organic chemical-vapor deposition. During the cool down process to room temperature, cracking was induced in the sapphire substrate, thereby allowing the bulklike GaN layer to relax without provoking cracking of itself. The crystalline quality and the residual strain in the 2″ GaN wafer were investigated by various characterization techniques. The lateral homogeneity of the wafer was monitored by low-temperature photoluminescence mapping. High-resolution x-ray diffraction and photoluminescence measurements proved the high crystalline quality of the material grown. The position of the main near-band-gap photoluminescence line and the phonon spectra obtained from infrared spectroscopic ellipsometry show consistently that the 2″ crack-free GaN is virtually strain-free over a diameter of approximately 4 cm.

  • 37.
    Khromov, Sergey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Amano, H
    Nagoya University.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 7, p. 075324-Article in journal (Refereed)
    Abstract [en]

    The effect of Mg doping on stacking fault (SF) formation in c-plane GaN grown by metal-organic chemical-vapor deposition has been studied for Mg concentration between 2 x 10(18) cm(-3) and 5 x 10(19) cm(-3). Transmission electron microscopy studies demonstrate a direct correlation between the increasing Mg content and the number of small (3-10-nm long) SFs present. The energy dispersive x-ray analysis (EDX) line profile of a SF shows that the Mg-impurity atom resides at a distance approximately 5 nm from the SF. Cathodoluminescence (CL) mapping reveals that the Mg-doped regions radiate at energies corresponding to known SF emission peaks. SF-related peaks in CL spectra show metastability, which may be attributed to transfer processes involving Mg acceptors and nearby associated SFs.

  • 38.
    Khromov, Sergey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Effect of C-doping on near-band gap luminescence in bulk GaN substrates grown by halide vapor phase epitaxy2013Manuscript (preprint) (Other academic)
    Abstract [en]

    Freestanding bulk C-doped GaN substrates grown by halide vapor phase epitaxy were studied by optical spectroscopy and electron microscopy. In cathodoluminescence (CL) the yellow line (YL) was more intense in samples with higher C content and stable in the temperature range 5-300 K. CL mapping in situ a scanning electron microscope revealed pitlike structure of the layers with higher YL intensity in the pits related to higher local oxygen incorporation. Near bandgap (NBG) emission studies of the pits revealed donor-bound excitons (DBE) with broad emission and no significant acceptor bound exciton (ABE) emission. Pit-free areas demonstrate two well-resolved ABEs with DBE quenched. Quenching of the DBE is explained by potential fluctuations in the vicinity of the carbon atoms in the pits-free regions lowering the ionization barrier for DBE.

  • 39.
    Khromov, Sergey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 22, p. 223503-Article in journal (Refereed)
    Abstract [en]

    Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 × 1016 cm−3 to 6 × 1017 cm−3. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at ∼3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1–2 × 1017 cm−3 is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission.

  • 40.
    Leone, Stefano
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Beyer, Franziska
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Chloride-Based SiC Epitaxial Growth toward Low Temperature Bulk Growth2010In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 8, p. 3743-3751Article in journal (Refereed)
    Abstract [en]

    In this study, chloride-based chemical vapor deposition (CVD) of SiC is used either to grow epitaxial layers at high growth rate and to facilitate homopolytypic growth on on-axis substrates or to grow bulk material at temperatures lower than 2000 °C. A vertical reactor configuration with an inlet of gas flow placed at the bottom of the reactor chamber and the exhaust at the top of it has been used. The chlorinated precursors have helped to eliminate or greatly reduce cluster formation, thereby allowing the deposition of thick SiC epilayers at growth rates exceeding 300 μm/h at 1700−1900 °C. Up to 1.5 mm thick homoepitaxial layers have been grown on up to 75 mm diameter 4H- or 6H-SiC wafers. Both on-axis and off-axis, Si-face and C-face polarities have been used. Our results show great promise for the realization of a high growth rate epitaxial process suitable for bulk growth at temperatures lower than those typically used. Such a process is interesting on account of the higher quality material and lower operating cost.

  • 41.
    Li, Xun
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Optical properties of AlGaN/GaN epitaxial layers grown on free-standing Ga-face and N-face GaN substrates2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Comparative studies have been made on AlGaN/GaN epitaxial layers grown by metalorganic chemical vapor deposition on both Ga- and N-face free-standing GaN substrates fabricated by halide vapor phase epitaxy. By time-resolved photoluminescence studies, we conclude that two-dimensional electron gas (2DEG) only appears for heterostructures grown on Ga-face. We studied the temporal behavior of the 2DEG emission, which correlates well with recombination processes in an asymmetric triangular potential well formed by an AlGaN/GaN structure grown in [0001] direction.

  • 42.
    Li, Xun
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Properties of GaN layers grown on N-face free-standing GaN substrates2015In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 413, p. 81-85Article in journal (Refereed)
    Abstract [en]

    GaN layers were homoepitaxially grown on N-face free-standing GaN substrates using a hot-wall metalorganic chemical vapor deposition method. By using optimized growth parameters, layers with a smooth morphology were obtained. The crystalline quality of epilayers was studied by a high resolution X-ray diffraction technique and compared to the substrates. Optical properties of the epilayers studied by low temperature time-resolved photoluminescence have shown longer recombination time for donor-bound exciton compared to the substrates. (C) 2014 Elsevier B.V. All rights reserved.

  • 43.
    Monemar, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Khromov, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Amano, Hiroshi
    Nagoya University, Japan.
    Avrutin, Vitaliy
    Virginia Commonwealth University, VA USA.
    Li, Xing
    Virginia Commonwealth University, VA USA.
    Morkoc, Hadis
    Virginia Commonwealth University, VA USA.
    Luminescence of Acceptors in Mg-Doped GaN2013In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 52, no 8Article in journal (Refereed)
    Abstract [en]

    Recent photoluminescence (PL) data for Mg-doped GaN at 2 K are discussed, with reference to published theoretical calculations of the electronic level structure. It is concluded that the typical PL peaks at 3.466 eV (acceptor bound exciton ABE1) and the broader 3.27 eV donor-acceptor pair (DAP) PL are the expected standard PL signatures of the substitutional Mg acceptor. Additional broader peaks at 3.455 eV (ABE2) and 3.1 eV are suggested to be related to the same acceptors perturbed by nearby basal plane stacking faults. The low temperature metastability of PL spectra is assigned to a nonradiative metastable deep level.

  • 44.
    Monemar, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Gogova, Daniela
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Growth of thick GaN layers with hydride vapour phase epitaxy2005In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, p. 17-31Article in journal (Refereed)
    Abstract [en]

    In this paper we describe recent experimental efforts to produce high quality thick (⩾300 μm) GaN layers on sapphire, the removal of such a layer from the sapphire substrate, and the properties of the so obtained free-standing GaN material. The growth process is described in some detail in the vertical reactor geometry used in this work. Defects like dislocations, micro-cracks and pits produced during growth are discussed, along with procedures to minimize their concentration on the growing surface. The laser lift-off technique is shown to be a feasible technology, in particular if a powerful laser with a large spot size can be used. A major problem with the free-standing material is the typically large bowing of such a wafer, due to the built in defect concentrations near the former GaN-sapphire interface. This bowing typically causes a rather large width of the XRD rocking curve of the free-standing material, while optical data confirm virtually strain free material of excellent quality at the top surface.

  • 45.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Malinauskas, T
    Jarasiunas, K
    Gibart, P
    Beaumont, B
    Time-resolved spectroscopy of excitons bound at shallow neutral donors in HVPE GaN2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, p. 482-485Article in journal (Refereed)
    Abstract [en]

    Time-resolved photo luminescence (TRPL) data for temperatures 2-150 K are presented for two thick HVPE samples grown in two different laboratories. The samples both have residual O and Si shallow donor concentrations in the 10(16)cm(-3) range. The radiative decay time for neutral donor-bound excitons (DBEs) related to these donors is found to be about 300 ps. The decay of the DBEs at longer decay times is found to be related to feeding from the free exciton-polariton states. At elevated temperatures the decay of the DBE is very similar to the free exciton decay. (c) 2006 Elsevier B.V. All rights reserved.

  • 46.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kawashima, T.
    Amano, H.
    Akasaki, I.
    Usui, A.
    Optical properties and acceptor states in Mg doped GaN2008In: 8^th Akasaki Symposium,2008, 2008Conference paper (Other academic)
  • 47.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Toropov, A.A.
    Choubina, Tatiana
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Kawashima, T.
    Amano, H.
    Akasaki, I.
    Usui, A.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Properties of dopants and defects in GaN from bound exciton spectra2008In: Meijo International Symposium on Nitride Semiconductors 2008,2008, 2008Conference paper (Other academic)
  • 48.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Amano, H.
    Akasaki, I.
    Figge, S.
    Hommel, D.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Usiui, A.
    Mg related acceptors in GaN2010In: Phys. Status Solidi C 7, 2010, p. 1850-Conference paper (Refereed)
  • 49.
    Monemar, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Kawashima, T
    Meijo University.
    Amano, H
    Meijo University.
    Akasaki, I
    Meijo University.
    Paskova, T
    Kyma Technology Inc.
    Figge, S
    University of Bremen.
    Hommel, D
    University of Bremen.
    Usui, A
    Furukawa Co Ltd.
    Evidence for Two Mg Related Acceptors in GaN2009In: PHYSICAL REVIEW LETTERS, ISSN 0031-9007, Vol. 102, no 23, p. 235501-Article in journal (Refereed)
    Abstract [en]

    The optical signatures of Mg-related acceptors in GaN have been revisited in samples specifically grown on bulk GaN templates, to avoid strain broadening of the optical spectra. Bound-exciton spectra can be studied in these samples for Mg concentrations up to [Mg]approximate to 2x10(19) cm(-3). Contrary to previous work it is found that instabilities in the photoluminescence spectra are not due to unstable shallow donors, but to unstable Mg-related acceptors. Our data show that there are two Mg-related acceptors simultaneously present: the regular (stable) substitutional Mg acceptor, and a complex acceptor which is unstable in p-GaN.

  • 50.
    Monemar, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Khromov, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Izyumskaya, V. N.
    Virginia Commonwealth University, VA 23284 USA Virginia Commonwealth University, VA 23284 USA .
    Avrutin, V.
    Virginia Commonwealth University, VA 23284 USA Virginia Commonwealth University, VA 23284 USA .
    Li, X.
    Virginia Commonwealth University, VA 23284 USA Virginia Commonwealth University, VA 23284 USA .
    Morkoc, H.
    Virginia Commonwealth University, VA 23284 USA Virginia Commonwealth University, VA 23284 USA .
    Amano, H.
    Nagoya University, Japan .
    Iwaya, M.
    Meijo University, Japan .
    Akasaki, I.
    Meijo University, Japan .
    Properties of the main Mg-related acceptors in GaN from optical and structural studies2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 5, p. 053507-Article in journal (Refereed)
    Abstract [en]

    The luminescent properties of Mg-doped GaN have recently received particular attention, e. g., in the light of new theoretical calculations, where the deep 2.9 eV luminescence band was suggested to be the main optical signature of the substitutional Mg-Ga acceptor, thus, having a rather large binding energy and a strong phonon coupling in optical transitions. We present new experimental data on homoepitaxial Mg-doped layers, which together with the previous collection of data give an improved experimental picture of the various luminescence features in Mg-doped GaN. In n-type GaN with moderate Mg doping (less than10(18) cm(-3)), the 3.466 eV ABE1 acceptor bound exciton and the associated 3.27eV donor-acceptor pair (DAP) band are the only strong photoluminescence (PL) signals at 2 K, and are identified as related to the substitutional Mg acceptor with a binding energy of 0.225 +/- 0.005 eV, and with a moderate phonon coupling strength. Interaction between basal plane stacking faults (BSFs) and Mg acceptors is suggested to give rise to a second deeper Mg acceptor species, with optical signatures ABE2 at 3.455 eV and a corresponding weak and broad DAP peak at about 3.15 eV. The 2.9 eV PL band has been ascribed to many different processes in the literature. It might be correlated with another deep level having a low concentration, only prominent at high Mg doping in material grown by the Metal Organic Chemical Vapor Deposition technique. The origin of the low temperature metastability of the Mg-related luminescence observed by many authors is here reinterpreted and explained as related to a separate non-radiative metastable deep level defect, i.e., not the Mg-Ga acceptor. (C) 2014 AIP Publishing LLC.

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