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  • 1.
    Bergsten, Johan
    et al.
    Chalmers Univ Technol, Sweden.
    Thorsell, Mattias
    Chalmers Univ Technol, Sweden.
    Adolph, David
    Chalmers Univ Technol, Sweden.
    Chen, Jr-Tai
    SweGaN AB, SE-58330 Linkoping, Sweden.
    Kordina, Olof
    SweGaN AB, SE-58330 Linkoping, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Rorsman, Niklas
    Chalmers Univ Technol, Sweden.
    Electron Trapping in Extended Defects in Microwave AlGaN/GaN HEMTs With Carbon-Doped Buffers2018In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 65, no 6, p. 2446-2453Article in journal (Refereed)
    Abstract [en]

    This paper investigates AlGaN/GaN high-electron mobility transistors (HEMTs) fabricated on epistructures with carbon (C)-doped buffers. Metalorganic chemical vapor deposition is used to grow two C-doped structures with different doping profiles, using growth parameters to change the C incorporation. The C concentration is low enough to result in n-type GaN. Reference devices are also fabricated on a structure using iron (Fe) as dopant, to exclude any process related variations and provide a relevant benchmark. All devices exhibit similar dc performance. However, pulsed I-V measurements show extensive dispersion in the C-doped devices, with values of dynamicRON 3-4 times larger than in the dc case. Due to the extensive trapping, the devices with C-dopedbuffers can only supply about half the outputpower of the Fe-doped sample, 2.5 W/mm compared to 4.8 W/mm at 10 GHz. In drain current transient measurements, the trap filling time is varied, finding large prevalence of trapping at dislocations for the C-doped samples. Clusters of C around the dislocations are suggested to be the main cause for the increased dispersion.

  • 2.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Abdalla, Hassan
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, Faculty of Science & Engineering.
    Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Lilja, Louise
    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, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime2016In: Physical Review Applied, ISSN 2331-7019, Vol. 6, no 1, p. 1-15, article id 014010Article in journal (Refereed)
    Abstract [en]

    We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4H-SiC and their 6H-SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n- and p-type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

  • 3.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Abdalla, Hassan
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology.
    Lilja, L.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    ul-Hassan, Jawad
    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.
    Sveinbjörnsson, Einar
    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.
    Oxidation induced ON1, ON2a/b defects in 4H-SiC characterized by DLTS2014In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 281-284Conference paper (Refereed)
    Abstract [en]

    The deep levels ON1 and ON2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.

  • 4.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hassan, Jawad
    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, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Electron and hole capture cross sections of deep levels accessible by DLTS and MCTS in p-type 4H-SiCManuscript (preprint) (Other academic)
    Abstract [en]

    The effective electron (σn(T)) and hole (σn(T)) capture cross sections of the electrically active deep levels HK0, HK2, LB1 and EM1 found in as-grown, high temperature annealed and oxidized p-type 4H-SiC were measured by deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS) and optical-electrical MCTS and DLTS (OE-MCTS and EO-DLTS) in an effort to determine the potential recombination centers in p-type material. Additionally, we also find the D-center, and the deep levels EH6/7, ON1 and ON2 in our samples, while the levels HK1, HK3 and HK4, reported in literature, are always below the detection limit. We further compare deep level concentrations and the timeresolved photoluminescence (TRPL) measured low injection (τLI) in samples annealed at up to 1920 °C. None of the detected deep levels possess σp(T):σn(T) ratios which could enable them to act as efficient recombination centers in the annealed epilayers, where τLI ranges from 1.2·10-6 s to less than 100·10-9 s. However, a clear anti-correlation between τLI and the EH6/7 concentration is found, which is linked to the main lifetime limiting center in n-type material, Z1/2, via their common origin, the carbon vacancy. Due to their large σp(T):σn(T) ratio, the Z1/2 deep levels are not detected by frontside illumination MCTS in p-type material. We thus conclude that the main lifetime limiting deep level(s) in p-type 4HSiC appear to be located in the upper half of the bandgap and are most likely either Z1/2, or other deep levels of intrinsic or partially intrinsic origin with a similar σp(T):σn(T) ratio.

  • 5.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stenberg, Pontus
    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, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Carrier lifetime in p- and n-type 4H-SiCManuscript (preprint) (Other academic)
    Abstract [en]

    Temperature-dependent time-resolved photoluminescence measurements made in the temperature range from 77 K to 1000 K on free-standing as grown n-type 4H-SiC and p-type 4H-SiC epilayers, which are either as-grown or annealed at 1000 °C, 1400 °C or 1700 °C, are analyzed. The development of the instantaneous carrier lifetime over temperature, calculated from the decay curves of all n- and p-type samples, is found to be identical in the entire temperature range. With increasing annealing temperature only the magnitude of the lifetime in p-type 4H-SiC decreases while the trend remains identical to that in the as-grown n-type sample. Annealing thus only increases the density of the main recombination center which appears to control lifetime in as-grown n- and p-type material. The results implies that the lifetime in all samples may be governed by the same intrinsic defect, which we suggest to be Z1/2.

  • 6.
    Booker, Ian Don
    et al.
    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, Faculty of Science & Engineering.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stenberg, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Donor and double donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 23, article id 235703Article in journal (Refereed)
    Abstract [en]

    Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp 0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn 2+(T) ≈ 1 × 10−14 cm2, σn +(T) ≈ 1 × 10−14 cm2, and σp 0(T) ≈ 9 × 10−18 cm2 for EH6 and σn 2+(T) ≈ 2 × 10−14 cm2, σn +(T) ≈ 2 × 10−14 cm2, σp 0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

  • 7.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ul Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lilja, Louise
    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.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, J. Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sveinbjörnsson, Einar
    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.
    Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC2014In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 8, p. 4104-4110Article in journal (Refereed)
    Abstract [en]

    4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.

  • 8.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdanfar, Milan
    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, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Shallow boron, the deep D-center and their influence on carrier lifetime in n- and p-type 4H-SiCManuscript (preprint) (Other academic)
    Abstract [en]

    The shallow boron and deep D-center are analyzed by minority carrier transient spectroscopy (MCTS), deep level transient spectroscopy (DLTS) and optical-electrical MCTS in n-type 4H-SiC with varying concentrations of boron, and in p-type 4H-SiC. MCTS, using high resolution correlation functions, shows the D-center to be composed of two closely overlapping peaks, referred to as D(a) and D(b), both most likely originating from the same defect located on inequivalent lattice sites. The hole capture cross sections of the D center are derived from DLTS filling pulse measurements in p-type material. The electron capture behavior of the D-center is analyzed by optical-electrical MCTS, and we find the center to be a pure hole trap, unable to act as a recombination center, with electron capture cross sections smaller than 1·10-23 cm2. The shallow boron peak is found to be composed of two or more overlapping levels in high resolution MCTS spectra. The shallow levels are further demonstrated to produce minority carrier trapping and detrapping effects in n-type 4H-SiC, which result in long time-resolved photoluminescence (TRPL) transients with microsecond decay constants, even in material containing high concentrations of the lifetime killing center Z1/2.

  • 9.
    Karhu, Robin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Magnusson, Bjorn
    Norstel AB, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    CVD growth and properties of on-axis vanadium doped semi-insulating 4H-SiC epilayers2019In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 125, no 4, article id 045702Article in journal (Refereed)
    Abstract [en]

    Highly resistive homoepitaxial layers of 4H-SiC have been grown on the Si-face of nominally on-axis, n-type substrates using chemical vapor deposition. Vanadium tetrachloride has been used as the V-dopant which is responsible for the high resistivity of the epilayers. 100% 4H-polytype was reproduced in the epilayers using the optimized on-axis growth process. The upper limit of vanadium tetrachloride flow rate was also established to achieve high resistivity epilayers free of 3C polytype inclusion. A resistivity of more than 1 x 10(5) Omega cm has been achieved in epilayers with a very low concentration of V (1 x 10(15) cm(-3)). Owing to the low concentration of V, superior epilayer structural quality was achieved compared to V-doped and standard high purity semi-insulating bulk grown material of similar resistivity. Epitaxial layers with varying vanadium tetrachloride flow have also been grown to study the influence of V concentration on the polytype stability, structural quality, and optical and electrical properties of epilayers. A clear correspondence has been observed in the flow-rates of vanadium tetrachloride, the atomic concentration of V, and electrical, optical, and structural properties of epilayers. Published under license by AIP Publishing.

  • 10.
    Khosa, R. Y.
    et al.
    Univ Iceland, Iceland; Univ Educ Lahore, Pakistan.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Pålsson, K.
    Univ Iceland, Iceland.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, N.
    Chalmers Univ Technol, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Electrical properties of 4H-SiC MIS capacitors with AlN gate dielectric grown by MOCVD2019In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 153, p. 52-58Article in journal (Refereed)
    Abstract [en]

    We report on the electrical properties of the AlN/4H-SiC interface using capacitance- and conductance-voltage (CV and GV) analysis of AlN/SiC MIS capacitors. The crystalline AlN layers are made by hot wall MOCVD. CV analysis at room temperature reveals an order of magnitude lower density of interface traps at the AlN/SiC interface than at nitrided SiO2/SiC interfaces. Electron trapping in bulk traps within the AlN is significant when the MIS capacitors are biased into accumulation resulting in a large flatband voltage shift towards higher gate voltage. This process is reversible and the electrons are fully released from the AlN layer if depletion bias is applied at elevated temperatures. Current-voltage (IV) analysis reveals that the breakdown electric field intensity across the AlN dielectric is 3-4 MV/cm and is limited by trap assisted leakage. By depositing an additional SiO2 layer on top of the AlN layer, it is possible to increase the breakdown voltage of the MIS capacitors significantly without having much impact on the quality of the AlN/SiC interface.

  • 11.
    Khosa, R. Y.
    et al.
    Univ Iceland, Iceland; Univ Educ Lahore, Pakistan.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Winters, M.
    Chalmers Univ Technol, Sweden.
    Palsson, K.
    Univ Iceland, Iceland.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, N.
    Chalmers Univ Technol, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Electrical characterization of high k-dielectrics for 4H-SiC MIS devices2019In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 98, p. 55-58Article in journal (Refereed)
    Abstract [en]

    We report promising results regarding the possible use of AlN or Al2O3 as a gate dielectric in 4H-SiC MISFETs. The crystalline AlN films are grown by hot wall metal organic chemical vapor deposition (MOCVD) at 1100 degrees C. The amorphous Al2O3 films are grown by repeated deposition and subsequent low temperature (200 degrees C) oxidation of thin Al layers using a hot plate. Our investigation shows a very low density of interface traps at the AlN/4H-SiC and the Al2O3/4H-SiC interface estimated from capacitance-voltage (CV) analysis of MIS capacitors. Current-voltage (IV) analysis shows that the breakdown electric field across the AlN or Al2O3 is similar to 3 MV/cm or similar to 5 MV/cm respectively. By depositing an additional SiO2 layer by plasma enhanced chemical vapor deposition at 300 degrees C on top of the AlN or Al2O3 layers, it is possible to increase the breakdown voltage of the MIS capacitors significantly without having pronounced impact on the quality of the AlN/SiC or Al2O3/SiC interfaces.

  • 12.
    Khosa, R. Y.
    et al.
    Univ Iceland, Iceland.
    Thorsteinsson, E. B.
    Univ Iceland, Iceland.
    Winters, M.
    Chalmers Univ Technol, Sweden.
    Rorsman, N.
    Chalmers Univ Technol, Sweden.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Electrical characterization of amorphous Al2O3 dielectric films on n-type 4H-SiC2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 2, article id 025304Article in journal (Refereed)
    Abstract [en]

    We report on the electrical properties of Al2O3 films grown on 4H-SiC by successive thermal oxidation of thin Al layers at low temperatures (200 degrees C - 300 degrees C). MOS capacitors made using these films contain lower density of interface traps, are more immune to electron injection and exhibit higher breakdown field (5MV/cm) than Al2O3 films grown by atomic layer deposition (ALD) or rapid thermal processing (RTP). Furthermore, the interface state density is significantly lower than in MOS capacitors with nitrided thermal silicon dioxide, grown in N2O, serving as the gate dielectric. Deposition of an additional SiO2 film on the top of the Al2O3 layer increases the breakdown voltage of the MOS capacitors while maintaining low density of interface traps. We examine the origin of negative charges frequently encountered in Al2O3 films grown on SiC and find that these charges consist of trapped electrons which can be released from the Al2O3 layer by depletion bias stress and ultraviolet light exposure. This electron trapping needs to be reduced if Al2O3 is to be used as a gate dielectric in SiC MOS technology. (c) 2018 Author(s).

  • 13.
    Khosa, Rabia Y.
    et al.
    Science Institute, University of Iceland, Iceland.
    Chen, J. T.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pálsson, K.
    Science Institute, University of Iceland, Iceland.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Rorsman, Niklas
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden.
    Sveinbjörnsson, Einar Ö.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Science Institute, University of Iceland, Iceland.
    Electrical Characterization of MOCVD Grown Single Crystalline AlN Thin Films on 4H-SiC2019In: Silicon Carbide and Related Materials 2018, Trans Tech Publications Ltd , 2019, Vol. 963, p. 460-464Conference paper (Refereed)
    Abstract [en]

    We report on a very low density of interface traps at the AlN/4H-SiC interface estimated from capacitance-voltage (CV) analysis of metal-insulator-semiconductor (MIS) capacitors. Single crystalline aluminum nitride (AlN) films are grown by metal organic chemical vapor deposition (MOCVD). Current-voltage (IV) analysis shows that the breakdown electric field across the AlN dielectric is 3 MV/cm. By depositing an additional SiO2 layer on top of the AlN layer it is possible to increase the breakdown voltage of the MIS capacitors significantly without having pronounced impact on the quality of the AlN/SiC interface.

  • 14.
    Khosa, Rabia Y.
    et al.
    Science Institute, University of Iceland, IS-107 Reykjavík, Iceland.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, IS-107 Reykjavík, Iceland.
    Winters, Michael
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Karhu, Robin
    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, Faculty of Science & Engineering.
    Rorsman, Niklas
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden.
    Low Density of Near-Interface Traps at the Al2O3/4H-SiC Interface with Al2O3 Made by Low Temperature Oxidation of Al2017In: Silicon Carbide and Related Materials 2016, Trans Tech Publications Ltd , 2017, Vol. 897, p. 135-138Conference paper (Refereed)
    Abstract [en]

    We report on a very low density (<5×1011 cm-2) of near-interface traps (NITs) at the Al2O3/4H-SiC interface estimated from capacitance-voltage (CV) analysis of MOS capacitors at different temperatures. The aluminum oxide (Al2O3) is grown by repeated deposition and subsequent low temperature (200°C) oxidation for 5 min of thin (1-2 nm) Al layers using a hot plate. We refer to this simple method as hot plate Al2O3. It is observed that the density of NITs is significantly lower in the hot plate Al2O3 samples than in samples with Al2O3 grown by atomic layer deposition (ALD) at 300°C and in reference samples with thermally grown silicon dioxide grown in O2 or N2O ambient.

  • 15.
    Malmros, Anna
    et al.
    Chalmers Univ Technol, Sweden.
    Chen, Jr-Tai
    SweGaN, SE-58330 Linkoping, Sweden.
    Hjelmgren, Hans
    Chalmers Univ Technol, Sweden.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kordina, Olof
    SweGaN, SE-58330 Linkoping, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland.
    Zirath, Herbert
    Chalmers Univ Technol, Sweden.
    Rorsman, Niklas
    Chalmers Univ Technol, Sweden.
    Enhanced Mobility in InAlN/AlN/GaN HEMTs Using a GaN Interlayer2019In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 66, no 7, p. 2910-2915Article in journal (Refereed)
    Abstract [en]

    An enhancement of the electron mobility (mu) in InAlN/AlN/GaN heterostructures is demonstrated by the incorporation of a thin GaN interlayer (IL) between the InAlN and AlN. The introduction of a GaN IL increases mu at room temperature (RT) from 1600 to 1930 cm(2)/Vs. The effect is further enhanced at cryogenic temperature (5 K), where the GaN IL sample exhibits a mu of 16 000 cm(2)/Vs, compared to 6900cm(2)/Vs without IL. The results indicate the reduction of one or more scattering mechanisms normally present in InAlN/AlN/GaN heterostructures. We propose that the improvement in mu is either due to the suppression of fluctuations in the quantum well subband energies or to reduced Coulomb scattering, both related to compositional variations in the InAlN. HEMTs fabricated on the GaN IL sample demonstrate larger improvement in dc- and high-frequency performance at 5 K; f(max) increases by 25 GHz to 153 GHz, compared to an increase of 6 GHz to 133 GHz without IL. The difference in improvement was associated mainly with the drop in the access resistances.

  • 16.
    Sveinbjörnsson, Einar
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Science Institute, University of of Iceland, Reykjavík, Iceland.
    Gislason, O.
    Science Institute, University of of Iceland, Reykjavík, Iceland.
    Deep traps in 4H-SiC MOS capacitors investigated by deep level transient spectroscopy2014In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2 / [ed] Okumura, H; Harima, H; Kimoto, T; Yoshimoto, M; Watanabe, H; Hatayama, T; Matsuura, H; Funaki, T; Sano, Y, Stafa-Zurich. Switzerland: Trans Tech Publications , 2014, Vol. 778-780, p. 603-606Conference paper (Refereed)
    Abstract [en]

    Using Deep Level Transient Spectroscopy (DLTS) on n-type MOS capacitors we find that thermal oxidation of 4H-SiC produces deep traps at or near the SiO2/SiC interface with two well defined DLTS peaks. The traps are located ~ 0.85 V and ~ 1.0 eV below the SiC conduction band edge and are present in wet and dry oxides as well as oxides produced by sodium enhanced oxidation and oxides grown in N2O. The deep traps are located at the SiO/SiC interface after oxidation at 1150C but do extend further into the SiC epilayer after oxidation at 1240C. We identify these traps as ON1 and ON2 which been observed in epitaxial layers after oxidation at very high temperatures (1200-1500C) [1].

  • 17.
    Winters, M.
    et al.
    Chalmers, Sweden.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Iceland, Iceland.
    Melios, C.
    National Phys Lab, England; University of Surrey, England.
    Kazakova, O.
    National Phys Lab, England.
    Strupinski, W.
    Institute Elect Mat Technology, Poland.
    Rorsman, N.
    Chalmers, Sweden.
    Characterization and physical modeling of MOS capacitors in epitaxial graphene monolayers and bilayers on 6H-SiC2016In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, no 8, article id 085010Article in journal (Refereed)
    Abstract [en]

    Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 . 10(12)eV(-1)cm(-2) is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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