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  • 1.
    Deng, R.
    et al.
    Jilin University.
    Yao, B.
    Jilin University.
    Li, Y.F.
    Changchun Institute of Optics.
    Li, B.H.
    Changchun Institute of Optics.
    Zhang, Z.Z.
    Changchun Institute of Optics.
    Zhao, H.F.
    Changchun Institute of Optics.
    Zhang, J.Y.
    Changchun Institute of Optics.
    Zhao, D.X.
    Changchun Institute of Optics.
    Shen, D.Z.
    Changchun Institute of Optics.
    Fan, X.W.
    Changchun Institute of Optics.
    Yang, Li Li
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Surface morphology, structural and optical properties of polar and non-polar ZnO thin films: A comparative study2009In: Journal of Crystal Growth, ISSN 0022-0248, Vol. 311, no 19, p. 4398-4401Article in journal (Refereed)
    Abstract [en]

    The polar and non-polar ZnO thin films were fabricated on cubic MgO (1 1 1) and (0 0 1) substrates by plasma-assisted molecular beam epitaxy. Based on X-ray diffraction analysis, the ZnO thin films grown on MgO (1 1 1) and (1 0 0) substrates exhibit the polar c-plane and non-polar m-plane orientation, respectively. Comparing with the c-plane ZnO film, the non-polar m-plane ZnO film shows cross-hatched stripes-like morphology, lower surface roughness and slower growth rate. However, low-temperature photoluminescence measurement indicates the m-plane ZnO film has a stronger 3.31 eV emission, which is considered to be related to stacking faults. Meanwhile, stronger band tails absorbance of the m-plane ZnO film is observed in optical absorption spectrum.

  • 2.
    Hsiao, Ching-Lien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Junaid, Muhammad
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. 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.
    Chen, Li-Chyong
    National Taiwan University, Taiwan .
    Chen, Kuei-Hsien
    National Taiwan University, Taiwan Academic Sinica, Taiwan .
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Room-temperature heteroepitaxy of single-phase Al1-xInxN films with full composition range on isostructural wurtzite templates2012In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 524, p. 113-120Article in journal (Refereed)
    Abstract [en]

    Al1-xInxN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al1-xInxN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (similar to 13% mismatch), heteroepitaxy is achieved. However, RT-grown Al1-xInxN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al1-xInxN structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al1-xInxN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegards rule is applicable to determine x in the RT-grown Al1-xInxN epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.

  • 3.
    Jacob, AP
    et al.
    Chalmers.
    Zhao, QX
    Chalmer.
    Willander, Magnus
    Chalmers.
    Ferdos, F
    Chalmers.
    Sadeghi, M
    Chalmers.
    Wang, SM
    Chalmers.
    Hydrogen passivation of self assembled InAs quantum dots2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 11, p. 6794-6798Article in journal (Refereed)
    Abstract [en]

    A systematic study on the hydrogen passivation of nonradiative centers in InAs quantum dots grown on GaAs substrates is presented. The samples used in this study were grown by molecular beam epitaxy. The structures contain an InxGa1-xAs insertion layer between the InAs quantum dots layer and the GaAs cap layer. The thickness and In concentration of the InxGa1-xAs are varied to achieve the emission wavelength at 1.3 mum. The samples after the H-2 plasma treatment show a significant increase of the photoluminescence intensity. The experimental results show that the quality of the InAs quantum dot structures does not degrade after the hydrogen (H-2) plasma treatments. The enhancement of the photoluminescence intensity from the InAs quantum dots is thought to be due to the passivation of nonradiative centers like defects in the structures. High resolution x-ray diffraction rocking curves are used to correlate photoluminescence results.

  • 4.
    Jacob, AP
    et al.
    Chalmers University of Technology & Gothenburg University.
    Zhao, QX
    Chalmers University of Technology & Gothenburg University.
    Willander, Magnus
    Chalmers University of Technology & Gothenburg University.
    Yang, CS
    Chung Yuan University.
    Chou, WC
    Chung Yuan University.
    Room temperature luminescence from ZnSe1-xTex (x less than 1%) epilayers grown on (001) GaAs2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 4, p. 2337-2340Article in journal (Refereed)
    Abstract [en]

    Photoluminescence experiments have been performed to systematically study the effect of thermal processing on ZnSe1-xTex (xless than1%) epilayers. Our results show that, a ZnSeTe epilayer under proper post growth thermal annealing can emit light in the visible range of 5500-7000 Angstrom at room temperature. Thus by systematically processing these samples, they could be used for II-VI laser diodes that can operate at room temperature. The results from hydrogen passivation study done on these samples are consistent with the previous reports that the broadband emission is related to an isoelectronic defect, i.e., excitons bound to the Te clusters.

  • 5.
    Klason, P.
    et al.
    Laboratory of Physical Electronics and Photonics, Department of Physics, Göteborg University, Göteborg, Sweden.
    Magnusson, Karin
    Laboratory of Physical Electronics and Photonics, Department of Physics, Göteborg University, Göteborg, Sweden.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Synthesis and structural and optical properties of ZnO micro- and nanostructures grown by the vapour-liquid-solid method2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 53-56Article in journal (Refereed)
    Abstract [en]

    ZnO micro- and nanostructures have been grown by the catalytic vapour - liquid - solid method on silicon and silicon carbide. These micro- and nanostructures were characterized by scanning electron microscope, x-ray diffraction and photoluminescence measurements. The characterization shows that the ZnO nano- and microrods grown have diameters of around 200 nm on the Si substrates and 600 nm when using the SiC substrates. The length ranges from 0.5 to 10 mu m.

  • 6. Klason, P.
    et al.
    Nur, O.
    Zhao, Qing Xiang
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Magnusson, K.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Growth and characterization of ZnO nanostructures2005In: SEMINANO-2005 Brag,2005, 2005, p. 19-Conference paper (Refereed)
  • 7.
    Klason, Peter
    et al.
    Department of Physics, Göteborg University, SE-412 96 Göteborg, Sweden.
    Borseth, Thomas Moe
    Physics Department/Centre of Material Science and Nanotechnology, University of Oslo, P. O. Box 1126 Blindern, 0318 Oslo, Norway.
    Zhao, Qing X
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Svensson, Bengt G
    Physics Department/Centre of Material Science and Nanotechnology, University of Oslo, P. O. Box 1126 Blindern, 0318 Oslo, Norway.
    Kuznetsov, Andrej Yu
    Physics Department/Centre of Material Science and Nanotechnology, University of Oslo, P. O. Box 1126 Blindern, 0318 Oslo, Norway.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology. Department of Physics, Göteborg University, Göteborg, Sweden.
    Temperature dependence and decay times of zinc and oxygen vacancy related photoluminescence bands in zinc oxide2008In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 145, no 5-6, p. 321-326Article in journal (Refereed)
    Abstract [en]

    A photoluminescence study was performed at different temperatures on bulk ZnO samples annealed in zinc- and oxygen-rich atmospheres. The different annealing conditions create oxygen and zinc vacancies in a controlled way in the ZnO samples. These defects are both involved in the deep band emission (DBE) that is often observed in ZnO but exhibit different optical characteristics promoting defect identification. In particular, when decreasing the PL measurement temperature the energy peak position of the -related band decreases while that of  increases. Secondly, phonon replicas are clearly observed in the DBE spectra in the sample containing . Finally, the characteristics of the DBE decay time for - and -enriched samples are also different. Specifically, for the -enriched sample the decay curves show strong wavelength dependence and generally slower decay components as compared to the sample enriched with .

  • 8.
    Lu, W
    et al.
    Chinese Academy of Sciences.
    Ji, YL
    Chinese Academy of Sciences.
    Chen, GB
    Chinese Academy of Sciences.
    Tang, NY
    Chinese Academy of Sciences.
    Chen, XS
    Chinese Academy of Sciences.
    Shen, SC
    Chinese Academy of Sciences.
    Zhao, QX
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology.
    Enhancement of room-temperature photoluminescence in InAs quantum dots2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 21, p. 4300-4302Article in journal (Refereed)
    Abstract [en]

    We report pronounced enhancement of room-temperature photoluminescence up to 80-fold induced by proton implantation and the rapid thermal annealing process in a multilayer InAs/GaAs quantum-dot structure. This effect is studied by a combination of material methods and resulted from both proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV, resulting from the intermixing of quantum dots. Linear dependence behavior as observed for both the nonradiative recombination time and carrier relaxation time on the ion-implantation dose. Maximum enhancement of the photoluminescence is observed for a proton implantation dose of 1.0x10(14) cm(-2) followed by rapid thermal annealing at 700 degreesC. These effects will be useful for quantum dot optoelectronic devices.

  • 9.
    Nguyen, Son Tien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kuznetsov, A.
    Svensson, B.G.
    Zhao, Qing Xiang
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Morishita, N.
    Ohshima, T.
    Itoh, H.
    Isoya, J.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Recombination centers in as-grown and electron-irradiated ZnO substrates2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 9Article in journal (Refereed)
    Abstract [en]

    Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. © 2007 American Institute of Physics.

  • 10.
    Nguyen, Son Tien
    et al.
    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.
    Kuznetsov, A. Yu.
    Department of Physics, Center for Materials Science and Technology, University of Oslo, Oslo, Norway.
    Svensson, B.G.
    Department of Physics, Center for Materials Science and Technology, University of Oslo, Oslo, Norway.
    Zhao, Qing Xiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Morishita, M.N.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Ohshima, T.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Itoh, H.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Isoya, J.
    University of Tsukuba, Tsukuba, Japan.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnetic resonance studies of defects in electron-irradiated ZnO substrates2007In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 401-402, p. 507-510Article in journal (Refereed)
    Abstract [en]

    Optical detection of magnetic resonance (ODMR) was used to study defects in electron-irradiated ZnO substrates. In addition to the shallow donor and the Zn vacancy, several ODMR centers with an effective electron spin were detected. Among these, the axial LU3 and non-axial LU4 centers are shown to be dominating recombination centers. The annealing behavior of radiation-induced defects was studied and possible defect models are discussed.

  • 11.
    Pozina, Galia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yang, Li-Li
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. 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.
    Lagoudakis, P G
    University of Southampton.
    Size dependent carrier recombination in ZnO nanocrystals2010In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 97, no 13, p. 131909-Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies of fluorescence decay were performed for colloidal ZnO nanocrystals. The fluorescence lifetime reduces from 22 ps to similar to 6 ps with decreasing nanocrystal radius. We postulate that non-radiative surface states dominate the carrier dynamics in small ZnO nanocrystals and perform Monte Carlo simulations incorporating carrier diffusion and carrier recombination to model the experimental fluorescence decay dynamics. The percentage of excitons undergoing nonradiative decay due to surface trapping is as high as 84% for nanocrystals with 8 nm radius, which explains the ultrafast decay dynamics observed in small ZnO nanostructures even at low temperatures.

  • 12.
    Riaz, M.
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fulati, Alimujiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Nour, Omer
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Klason, P.
    Department of Physics, Göteborg University, SE-41296 Göteborg, Sweden.
    Buckling and mechanical instability of ZnO nanorods grown on different substrates under uniaxial compression2008In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Nanotechnology, Vol. 19, no 41Article in journal (Refereed)
    Abstract [en]

    Mechanical instability and buckling characterization of vertically aligned single-crystal ZnO nanorods grown on different substrates including Si, SiC and sapphire (a-Al2O3) was done quantitatively by the nanoindentation technique. The nanorods were grown on these substrates by the vapor-liquid-solid (VLS) method. The critical load for the ZnO nanorods grown on the Si, SiC and Al2O3 substrates was found to be 188, 205 and 130 µN, respectively. These observed critical loads were for nanorods with 280 nm diameters and 900 nm length using Si as a substrate, while the corresponding values were 330 nm, 3300 nm, and 780 nm, 3000 nm in the case of SiC and Al2O3 substrates, respectively. The corresponding buckling energies calculated from the force displacement curves were 8.46 × 10-12, 1.158 × 10-11 and 1.092 × 10-11 J, respectively. Based on the Euler model for long nanorods and the J B Johnson model (which is an extension of the Euler model) for intermediate nanorods, the modulus of elasticity of a single rod was calculated for each sample. Finally, the critical buckling stress and strain were also calculated for all samples. We found that the buckling characteristic is strongly dependent on the quality, lattice mismatch and adhesion of the nanorods with the substrate. © IOP Publishing Ltd.

  • 13.
    Sundqvist, PA
    et al.
    Göteborg University.
    Zhao, QX
    Göteborg University.
    Willander, Magnus
    Göteborg University.
    Boundary conditions for electron tunneling in complex two- and three-dimensional structures2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 16Article in journal (Refereed)
    Abstract [en]

    We present boundary conditions given in integro-differential form for the single-particle two-dimensional (2D) or 3D Schrodinger equation, which allows for a treatment of nontrivial geometries, and an arbitrary number of input and output channels. The formalism is easy to implement using standard finite element packages. We consider a resonant dot structure and transport through a ringlike waveguide without barriers. The current in the dot is focused on an ellipsoid dot via a tunneling tip. The current-voltage characteristic is calculated for this system at the temperature 4.2 K. Our results show that the current maxima appear close to the eigenstates of the quantum dot. We show, however, that only those modes which obey certain symmetry properties give rise to resonance in the dot, and current maxima are absent for antisymmetric modes at low temperatures. The current in the waveguide is shown to be a resonant function of the voltage, and the system exhibits current feedback and turbulence. Finally, we extend the formalism to other types of channels and equations other than the Schrodinger equation and we discuss some possible applications for these systems.

  • 14.
    Sundqvist, PA
    et al.
    University of Göteborg and Chalmers University of Technology.
    Zhao, QX
    University of Göteborg and Chalmers University of Technology.
    Willander, Magnus
    University of Göteborg and Chalmers University of Technology.
    Polarization of an exciton in a ZnO layer using a split gate potential2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 15Article in journal (Refereed)
    Abstract [en]

    In this paper we focus on structural and optical transitions of an exciton in a Zinc Oxide (ZnO) layer, which could be widely controlled by a split gate potential. We have solved the exciton problem by a self-consistent Schrodinger-Poisson technique, where the Hamiltonian includes the boundary conditions for the split gate structure. The gate voltage creates a paraboliclike potential, which at a typical threshold voltage separates or polarizes the exciton strongly. This sharp structural transition brings the exciton from being strongly correlated with a large overlap to a regime where the correlation is very small (with small overlap). The resulting structure for the exciton at negative gate voltages is a structure where the hole is located like a ring around a dotlike electron. For positive values of the gate voltage the situation is opposite. We have especially studied the ground-state binding energy and the optical transitions of the exciton. We found that the ground-state energy for ZnO could be tuned and the decrease of the ground-state energy can be as large as the double of the bulk exciton energy (60 meV for ZnO) with a gate voltage of -5 V. The ground-state energy is almost constant for small values of the gate voltage but at a typical threshold voltage (approximately -2 V) the energy suddenly changes and becomes linear with the gate voltage. We also analyze the lifetime for the exciton, which is shown to increase from nanoseconds to beyond milliseconds. This was shown to be an effect of the small overlap between the hole and the electron when the gate voltage increased above the threshold voltage. Stimulated by the long lifetime of the ground state of the exciton we also calculated the optical transition frequency and the corresponding oscillator strength for the transition between the ground state and the dominating excited (self-consistent) exciton states. The transition frequency was found to occur in the THz region and the oscillator strength in the range of 0.3-0.4 for gate voltages between -2 V and -5 V. In addition, we have also analytically described polarization and especially total charge densities for excitons in small linear electric fields.

  • 15.
    Wang, S M
    et al.
    Chalmers.
    Adolfsson, G
    Chalmers.
    Zhao, H
    Chalmers.
    Wei, Y Q
    University of Cambridge.
    Gustavsson, J
    Chalmers.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sadeghi, M
    Chalmers.
    Larsson , A
    Chalmers.
    Growth of GaInNAs and 1.3 mu m edge emitting lasers by molecular beam epitaxy2009In: JOURNAL OF CRYSTAL GROWTH, ISSN 0022-0248 , Vol. 311, no 7, p. 1863-1867Article in journal (Refereed)
    Abstract [en]

    We show that the use of a low growth rate combined with low N flux and RF power during molecular beam epitaxy (MBE) growth of dilute nitrides can efficiently enhance N incorporation while retaining good optical quality. A maximum light emission wavelength of 1.44 and 1.71 mu m has been obtained at 300 K from GaNAs and GaInNAs quantum wells, respectively. We demonstrate high-performance 1.3 pm GaInNAs multiple quantum well edge emitting lasers with record low threshold current densities, a 3 dB modulation bandwidth of 17 GHz at 300 K and capability of being modulated at 10 Gbit/s up to 110 degrees C without extra coolers. Our results show that MBE is an epitaxial technology suitable for the growth of dilute nitride materials and devices.

  • 16.
    Wang, S M
    et al.
    Chalmers.
    Zhao, H
    Chalmers.
    Adolfsson, G
    Chalmers.
    Wei, Y Q
    University of Cambridge.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Gustavsson, J S
    Chalmers.
    Sadeghi, M
    Chalmers.
    Larsson , A
    Chalmers.
    Dilute nitrides and 1.3 mu m GaInNAs quantum well lasers on GaAs2009In: MICROELECTRONICS JOURNAL, ISSN 0026-2692 , Vol. 40, no 3, p. 386-391Article in journal (Refereed)
    Abstract [en]

    We present epitaxial growth of GaInNAs on GaAs by molecular beam epitaxy (MBE) using analog, digital and N irradiation methods. It is possible to realize GaInNAs quantum wells (QWs) with a maximum substitutional N concentration up to 6% and a strong light emission up to 1.71 mu m at 300 K. High quality 1.3 mu m GaInNAs multiple QW edge emitting laser diodes have been demonstrated. The threshold current density (for a cavity of 100 x 1000 mu m(2)) is 300, 300, 400 and 940 A/cm(2) for single, double, triple and quadruple QW lasers, respectively. The maximum 3 dB bandwidth reaches 17 GHz and high-speed transmission at 10 Gb/s up to 110 degrees C under a constant voltage has been demonstrated.

  • 17.
    Willander, Magnus
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Klason, P.
    Yang, L.L.
    Al Hilli, Safaa
    Zhao, Qingxiang
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Nour, Omer
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    ZnO nanowires: chemical growth, electro-deposition and application to intracellular nano-sensors2008In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 5, no 9, p. 3076-3083Article in journal (Refereed)
    Abstract [en]

    In this paper we present our results on growth, characterization, and nano-devices based on ZnO nano-structures. The ZnO nano-structures were grown by mainly two methods, the catalytic Vapor Liquid Solid (VLS) and the low temperature chemical growth. We show that by multiple coating combined with low temperature chemical growth, well aligned with size controlled ZnO nanowires on silicon substrates can be achieved. The dissolution, due to its important on the stability of ZnO nano-structures in aqueous medium, is then discussed and some preliminary experimental results are shown. Basic Optical characteristics of ZnO nano-rods are briefly discussed. Finally, electrochemical intracellular nano-sensors based on ZnO nano-wires are demonstrated as efficient nano-sensors for monitoring the human cell activity with minute pH changes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • 18.
    Willander, Magnus
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lozovik, Y. E.
    Russian Academy of Sciences .
    Zhao, Q.X.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Science and Technology.
    Hu, Q.-H.
    Gothenburg University.
    Klason, P.
    Gothenburg University.
    Excitonic effects in ZnO nanowires and hollow nanotubes2007In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6486, no 648614Article in journal (Refereed)
    Abstract [en]

    Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of VZn and Vo on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.

  • 19.
    Willander, Magnus
    et al.
    Göteborg University.
    Nour, Omer
    Göteborg University.
    Lozovik, YE
    Russian Academy of Sciences.
    Al-Hilli, SM
    Göteborg University.
    Chiragwandi, Z
    Göteborg University.
    Hu, QH
    Göteborg University.
    Zhao, QX
    Göteborg University.
    Klason, P
    Göteborg University.
    Solid and soft nanostructured materials: Fundamentals and applications2005In: MICROELECTRONICS JOURNAL, ISSN 0026-2692, Vol. 36, no 11, p. 940-949Article in journal (Refereed)
    Abstract [en]

    The scientific work worldwide on nanostructured materials is extensive as well as the work on the applications of nanostructured materials. We will review quasi two-, one- and zero-dimensional solid and soft materials and their applications. We will restrict ourselves to a few examples from partly fundamental aspects and partly from application aspects. We will start with trapping of excitons in semiconductor nanostructures. The subjects are: physical realizations, phase diagrams, traps, local density approximations, and mesoscopic condensates. From these fundamental questions in solid nanomaterials we will move to trapping of molecules in water using nanostructured electrodes. We will also discuss how to manipulate water (create vortices) by nanostructure materials. The second part deals with nanorods (nano-wires). Particularly we will exemplify with ZnO nanorods. The reason for this is that ZnO has: a very strong excitons binding energy (60 meV) and strong photon-excitons coupling energy, a strong tendency to create nanostructures, and properties which make the material of interest for both optoelectronics and for medical applications. We start with the growth of crystalline ZnO nanorods on different substrates, both crystalline (silicon, silicon carbide, sapphire, etc) and amorphous substrates (silicon dioxide, plastic materials, etc) for temperatures from 50 degrees C up to 900 degrees C. The optical properties and crystalline properties of the nanorods will be analyzed. Applications from optoelectronics (lasers, LEDs, lamps, and detectors) are analyzed and also medical applications like photodynarnic cancer therapy are taken up. The third part deals with nano-particles in ZnO for sun screening. Skin cancer due to the exposure from the sun can be prevented by ZnO particles in a paste put on the exposed skin.

  • 20.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yang, Lili
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Lorenz, M
    University of Leipzig.
    Cao, B Q
    University of Leipzig.
    Zuniga Perez, J
    University of Leipzig.
    Czekalla, C
    University of Leipzig.
    Zimmermann, G
    University of Leipzig.
    Grundmann, M
    University of Leipzig.
    Bakin, A
    Tech University Carolo Wilhelmina Braunschweig.
    Behrends, A
    Tech University Carolo Wilhelmina Braunschweig.
    Al-Suleiman, M
    Tech University Carolo Wilhelmina Braunschweig.
    El-Shaer, A
    Tech University Carolo Wilhelmina Braunschweig.
    Che Mofor, A
    Tech University Carolo Wilhelmina Braunschweig.
    Postels, B
    Tech University Carolo Wilhelmina Braunschweig.
    Waag, A
    Tech University Carolo Wilhelmina Braunschweig.
    Boukos, N
    Natl Centre Science Research Demokritos.
    Travlos, A
    Natl Centre Science Research Demokritos.
    Kwack, H S
    CNRS.
    Guinard, J
    CNRS.
    Le Si Dang, D
    CNRS.
    Zinc oxide nanorod based photonic devices: recent progress in growth, light emitting diodes and lasers2009In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 20, no 33, p. 332001-Article, review/survey (Refereed)
    Abstract [en]

    Zinc oxide (ZnO), with its excellent luminescent properties and the ease of growth of its nanostructures, holds promise for the development of photonic devices. The recent advances in growth of ZnO nanorods are discussed. Results from both low temperature and high temperature growth approaches are presented. The techniques which are presented include metal-organic chemical vapour deposition (MOCVD), vapour phase epitaxy (VPE), pulse laser deposition (PLD), vapour-liquid-solid (VLS), aqueous chemical growth (ACG) and finally the electrodeposition technique as an example of a selective growth approach. Results from structural as well as optical properties of a variety of ZnO nanorods are shown and analysed using different techniques, including high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), photoluminescence (PL) and cathodoluminescence (CL), for both room temperature and for low temperature performance. These results indicate that the grown ZnO nanorods possess reproducible and interesting optical properties. Results on obtaining p-type doping in ZnO micro- and nanorods are also demonstrated using PLD. Three independent indications were found for p-type conducting, phosphorus-doped ZnO nanorods: first, acceptor-related CL peaks, second, opposite transfer characteristics of back-gate field effect transistors using undoped and phosphorus doped wire channels, and finally, rectifying I-V characteristics of ZnO: P nanowire/ZnO:Ga p-n junctions. Then light emitting diodes (LEDs) based on n-ZnO nanorods combined with different technologies (hybrid technologies) are suggested and the recent electrical, as well as electro-optical, characteristics of these LEDs are shown and discussed. The hybrid LEDs reviewed and discussed here are mainly presented for two groups: those based on n-ZnO nanorods and p-type crystalline substrates, and those based on n-ZnO nanorods and p-type amorphous substrates. Promising electroluminescence characteristics aimed at the development of white LEDs are demonstrated. Although some of the presented LEDs show visible emission for applied biases in excess of 10 V, optimized structures are expected to provide the same emission at much lower voltage. Finally, lasing from ZnO nanorods is briefly reviewed. An example of a recent whispering gallery mode (WGM) lasing from ZnO is demonstrated as a way to enhance the stimulated emission from small size structures.

  • 21.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ryzhii, Victor
    University of Aizu.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sensing infrared and terahertz regions by functional films2009In: Functional thin Films and Nanostructures for Sensors, 2009, 1stChapter in book (Other (popular science, discussion, etc.))
    Abstract [en]

    Designing functional films and nanostructures has a key role in the performance of the infrared (IR) sensing and terahertz (THz) sensing that are based particularly on quantum well, wire, and dot structures. Sensing the electromagnetic (EM) spectra is an extremely important issue for various fields, from understanding the universe, living cells, and elementary particles to numerous applications. To give a glimpse of the field in connection to functional films and nanostructures as sensing elements, in this chapter we briefly discuss infrared (IR) sensing and terahertz (THz) sensing. For IR sensing we limit ourselves to low-dimensional semiconductor functional films. For THz sensing we discuss: (a) how strain in thin films influences THz absorption from impurities, (b) plasma effects in two-dimensional electron gas (2DEG), and (c) ultrasensitive bolometers based on metal films.

  • 22.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Wadeasa, Amal
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Klason, Peter
    Gothenburg University, Sweden.
    Yang, Lili
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Beegum, Lubuna
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Raja, Shaffeq
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao, Qiangxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Light-emitting diodes based on n-ZnO nano-wires and p-type organic semiconductors2008In: Proc. SPIE 6895: Zinc Oxide Materials and Devices III, SPIE - International Society for Optical Engineering, 2008, p. 68950O-1-68950O-10Conference paper (Other academic)
    Abstract [en]

    After our recent successful demonstration of high brightness white light emitting diodes (HB-LEDs) based on high temperature grown n-ZnO nanowires on different p-type semiconductors, we present here LEDs fabricated on n-ZnO nano-wires and p-type organic semiconductors. By employing a low temperature chemical growth (≤ 90 °C) approach for ZnO synthesis combined together with organic p-type semiconductors, we demonstrate high quality LEDs fabricated on a variety of different substrates. The substrates include transparent glass, plastic, and conventional Si. Different multi-layers of p-type organic semiconductors with or without electron blocking layers have been demonstrated and characterized. The investigated p-type organic semiconductors include PEDOT:PSS, which was used as a anode in combination with other p-type polymers. Some of the heterojunction diodes also contain an electron blocking polymer sandwiched between the p-type polymer and the n-ZnO nano-wire. The insertion of electron blocking layer is necessary to engineer the device for the desired emission. Structural and electrical results will be presented. The preliminary I-V characteristics of the organic-inorganic hybrid heterojunction diodes show good rectifying properties. Finally we also present our findings on the origin of the green luminescence band which is responsible of the white light emission in ZnO is discussed.

  • 23.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Wadeasa, Amal
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Yang, Lili
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao,, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Photonic devices in some low dimensional sysems2009In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 16, no 41, p. 17-30Article in journal (Refereed)
    Abstract [en]

    Results of using low temperature growth approach (lower than 100 oC) to control the growth of ZnO nanowires are presented. The effect of different parameters on the growth is highlighted. Time resolved low temperature photoluminescence (PL) was used to investigate surface recombination and its relation to the nanowires diameters. Finally hybrid light emitting diodes (LEDs) based on p-type polymers and n-ZnO nanowires grown on amorphous substrates is fabricated and characterized. This hybrid organic-inorganic technology can provide a suitable replacement of conventional lighting tubes.

  • 24.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yang, Lili
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Wadeasa, A.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ali, S.U.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Asif, M.H.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Q.X.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zinc oxide nanowires: controlled low temperature growth and electrochemical and optical devices2009In: Journal of Materials Chemsitry, Vol. 19, no 7, p. 1006-1018Article in journal (Refereed)
    Abstract [en]

    In this paper we present our new findings on the growth, characterization and nano-devices based on ZnO nanowires. We will limit the scope of this article to low temperature grown ZnO nanowires, due to the fact that low temperature growth is suitable for many applications. On growth and size control we will present our methodology for the growth of ZnO nanowires on Si substrates using low temperature techniques. The effect of the annealing on these low temperature grown ZnO nanowires is investigated and discussed. We then present our results on the surface recombination velocity of ZnO nanowires. This will be followed by the demonstration of new prototype nano-devices. These nano-devices include the demonstration of two new electrochemical nano-sensors. These are the extended gate glucose sensor and the calcium ion selective sensor using ionophore membrane coating on ZnO nanowires. Finally we will present results from light emitting diodes (LEDs) based on our ZnO nanowires grown on p-type organic semiconductors. The effect of the interlayer design of this hybrid organic–inorganic LED on the emission properties is highlighted.

  • 25.
    Willander, Magnus
    et al.
    University of Gothenburg.
    Zhao, Qing Xiang
    University of Gothenburg.
    Nour, Omer
    University of Gothenburg.
    Hu, Q-H
    University of Gothenburg.
    Some silicon-based heterostructures for optical applications2005In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 34, no 5, p. 515-521Article in journal (Refereed)
    Abstract [en]

    In this paper, we will present our recent research on the growth and characterization of some Si-based heterostructures for optical and photonic devices. The heterostructures to be discussed are ZnO nanorods on Si, SiO2, and other substrates such as SiN and sapphire. We will also consider strained Si1-xGex/Si heterostructures for Si optoelectronics. The performance and functionality extension of Si technology for photonic applications due to the development of such heterostructures will be presented. We will focus on the results of structural and optical characterization in relation to device properties. The structural characterization includes x-ray diffraction for assessment of the crystallinity and stress in the films and secondary ion mass spectrometry for chemical analysis. The optical properties and electronic structure were investigated by using photoluminescence. The device application of these thin film structures includes detectors, lasers, and light emitting devices. Some of the Si-based heterostructures to be presented include devices emitting and detecting up to the blue-green and violet wave lengths.

  • 26.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zinc oxide nanostructures at the forefront of new white light- emitting technology2007Other (Other (popular science, discussion, etc.))
  • 27.
    Yang, Jinghai
    et al.
    Jilin Normal University.
    Yang, Lili
    Jilin Normal University.
    Zhang, Yongjun
    Jilin Normal University.
    Wang, Dandan
    Jilin Normal University.
    Lang, Jihui
    Jilin Normal University.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Investigation on the origin of green light emission in ZnO bulk materials2009In: INTERNATIONAL JOURNAL OF MATERIALS and PRODUCT TECHNOLOGY, ISSN 0268-1900, Vol. 34, no 3, p. 360-368Article in journal (Refereed)
    Abstract [en]

    ZnO bulk materials were implanted by O and Zn with different concentration and their photoluminescence (PL) properties were investigated in detail. The results clearly show that O and Zn implantation indeed have great influence on the green light emission. By comparing the PL spectra for the samples with different implantations, O-i, Zn-i and Cu-related defects have been excluded from the possibility of the origin of green light emission step by step. Finally, it can be concluded that V-Zn is responsible to the observed green light emission, which has good agreement with the theoretical results from first principle calculation.

  • 28.
    Yang, Li Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Israr, Muhammad Qadir
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sadaf, Jamil Rana
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yang, J. H.
    Institute of Condensed State Physics, Jilin Normal University, Siping, 136000, People's Republic of China.
    Indirect optical transition due to surface band bending in ZnO nanotubes2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed)
    Abstract [en]

    ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 nm and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

  • 29.
    Yang, Li Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Xing, G. Z.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Wang, D. D.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Wu, T.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yang, J. H.
    Institute of Condensed State Physics, Jilin Normal University, Siping, 136000, People's Republic of China.
    Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVDManuscript (preprint) (Other academic)
    Abstract [en]

    Zn0.94Mg0.06O/ZnO heterostructures were grown on 2 inch sapphire wafer by MOCVD equipment. Photoluminescence mapping demonstrated that Mg uniformly distributed on the entire wafer with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors were investigated by secondary ion mass spectrometry (SIMS). All Mg SIMS depth profiles were fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC was two order of magnitude lower than that of annealed samples, which indicated that the deposition temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

  • 30.
    Yang, LiLi
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method2009In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 469, no 1-2, p. 623-629Article in journal (Refereed)
    Abstract [en]

    Well-aligned ZnO nanorod arrays (ZNAs) with different sizes in diameter were fabricated on Si substrates by two-step chemical bath deposition method (CBD), i.e. substrate pre-treatment with spin coating to form ZnO nanoparticles layer and CBD growth. The effects of substrate pre-treatments, pH, angel (θ) between substrate and beaker bottom and growth time (t) on the structure of ZNAs were investigated in detail by X-ray diffraction (XRD), field emission scan electronic microscope (SEM) and photoluminescence (PL). The results show that substrate pre-treatment, pH, θ and t indeed have great influence on the growth of ZNAs, and their influence mechanisms have been, respectively, explained in detail. The introduction of a ZnO nanoparticle layer on the substrate not only helps to decrease the diameter but also has a strong impact on the orientation of ZNAs. Under the growth condition of pH 6, θ = 70° and t = 2 h, the well-aligned ZnO nanorod arrays with 50 nm diameter was obtained on the pre-treated Si substrates. And only a strong UV peak at 385 nm appears in room temperature PL spectrum for this sample, which indicates that as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

  • 31.
    Yang, Li-Li
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Yang, J H
    Institute of Condensed State Physics, Jilin Normal University, Siping, People's Republic of China.
    Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process2010In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 4, p. 1904-1910Article in journal (Refereed)
    Abstract [en]

    ZnO nanorods arrays are respectively prepared under different vapor pressures with opening (OZN) or sealing (SZN) of the beaker. The results from time-resolved photoluminescence measurements indicate that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 degrees C post-thermal treatment or OZN samples. The results from X-ray photoelectron spectroscopy measurements reveal that the main reason for this phenomenon is that the surfaces of the SZN samples are attached by groups related to NH3 instead of the main surface recombination centers such as OH and groups in the OZN samples. The ammonia surface treatment on both OZN and SZN samples further testifies that the absorption of the groups related to NH3 does not contribute to the surface recombination on the ZnO nanorods.

  • 32.
    Yang, Li-Li
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology. Institute of Condensed State Physics, Jilin Normal University, Siping, People's Republic of China.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Yang, J H
    Institute of Condensed State Physics, Jilin Normal University, Siping, People's Republic of China.
    Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 11, p. 3592-3597Article in journal (Refereed)
    Abstract [en]

    The surface composition of as-grown and annealed ZnO nanorods arrays (ZNAs) grown by a two-step chemical bath deposition method has been investigated by X-ray photoelectron spectroscopy (XPS). XPS confirms the presence of OH bonds and specific chemisorbed oxygen on the surface of ZNAs, as well as H bonds on (1 0 (1) over bar 0) surfaces which has been first time observed in the XPS spectra. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Annealing can largely remove the OH and H bonds and transform the composition of the other chemisorbed oxygen at the surface to more closely resemble that of high temperature grown ZNAs, all of which suppresses surface recombination according to time-resolved photoluminescence measurements.

  • 33.
    Yang, Li-Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yang, J H
    Jilin Normal University.
    Ivanov , Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Annealing effects on optical properties of low temperature grown ZnO nanorod arrays2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 5, p. 053503-Article in journal (Refereed)
    Abstract [en]

    Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 degrees C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 degrees C.

  • 34.
    Yang, Li-Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yang, J.H.
    Institute of Condensed State Physics, Jilin Normal University, Siping, 136000, People's Republic of China.
    Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition2009In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 4, p. 1046-1050Article in journal (Refereed)
    Abstract [en]

    The diameter of well-aligned ZnO nanorod arrays (ZNAs) grown on Si substrates has been well controlled from 150nm to 40nm by two-step chemical bath deposition method (CBD), i.e. substrate pretreatment with spin coating to form ZnO nanoparticles seed layer and CBD growth. The effects of ZnO nanoparticles density and diameter on size and alignment of ZNAs were investigated in detail by atomic force microscope (AFM), X-ray diffraction (XRD), scan electronic microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL). The results indicate that both diameter and density of ZnO nanoparticles which were pre-coated on the substrates will influence the size and alignment of ZNAs, but the density will play a key role to determine the diameter of ZNAs when the density is higher than the value of 2.3×108cm-2. Moreover, only a strong UV peak at 385 nm appears in room temperature PL spectrum for these samples, which indicates that  as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

  • 35.
    Yang, L.L.
    et al.
    Jilin Normal University.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Xing, G.Z.
    Nanyang Technology University.
    Wang, D.D.
    Nanyang Technology University.
    Wu, T.
    Nanyang Technology University.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yang, J.H.
    Jilin Normal University.
    A SIMS study on Mg diffusion in Zn(0.94)Mg(0.06)O/ZnO heterostructures grown by metal organic chemical vapor deposition2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 20, p. 8629-8633Article in journal (Refereed)
    Abstract [en]

    Zn(0.94)Mg(0.06)O/ZnO heterostructures have been grown on 2 in. sapphire wafer using metal organic chemical vapor deposition (MOCVD). Photoluminescence (PL) mapping demonstrates that Mg distribution on the entire wafer is very uniform (standard deviation of Mg concentration/mean Mg concentration = 1.38%) with average concentration of similar to 6%. The effect of annealing on the Mg diffusion in Zn(0.94)Mg(0.06)O/ZnO heterostructures has been investigated in detail by using secondary ion mass spectrometry (SIMS). All the Mg SIMS depth profiles have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn(0.94)Mg(0.06)O layer deposited at 700 degrees C is two orders of magnitude lower than that of annealed samples, which clearly indicates that the deposition temperature of 700 degrees C is much more beneficial to grow ZnMgO/ZnO heterostructures and quantum wells.

  • 36.
    Zhao, H
    et al.
    Chalmers University.
    M Wang, S
    Chalmers University.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    H Lai, Z
    Chalmers University.
    Sadeghi, M
    Chalmers University.
    Larsson , A
    Chalmers University.
    Comparison of optical and structural quality of GaIn(N) As analog and digital quantum wells grown by molecular beam epitaxy2008In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 23, no 12, p. 125002-Article in journal (Refereed)
    Abstract [en]

    A set of Ga0.625In0.375(N) As single quantum well (QW) samples with the identical total amounts of Ga and In and QW thicknesses was designed and grown by both the analog and the digital methods using molecular beam epitaxy. The N exposure time in the GaInNAs samples was kept the same. The inter-band gap recombination in the analog and the digital InGaAs QWs appears in a similar transition energy range as a result of In segregation. Temperature-dependent photoluminescence (PL) measurements were performed on the GaInNAs samples. An S-shaped dependence of the transition energy on temperature was observed in the digital GaInNAs QWs but not in the analog GaInNAs QW. Post-growth rapid thermal annealing had remarkably different effects on the PL intensity: an increase for the analog InGaAs QW and for the analog and digital GaInNAs QWs, but a decrease for the digital InGaAs QW with increasing annealing temperature. The GaIn(N) As samples grown by the digital method showed weaker PL intensities and smaller wavelength blue-shifts than the similar samples grown by the analog method. Possible strain relaxation mechanisms are discussed.

  • 37.
    Zhao, H
    et al.
    Chalmers.
    Wang, S M
    Chalmers.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sadeghi, M
    Chalmers.
    Larsson , A
    Chalmers.
    Growth and characterization of GaInNAs by molecular beam epitaxy using a nitrogen irradiation method2009In: JOURNAL OF CRYSTAL GROWTH, ISSN 0022-0248 , Vol. 311, no 7, p. 1723-1727Article in journal (Refereed)
    Abstract [en]

    We propose an innovative technique, making use of the In segregation effect, referred as the N irradiation method, to enhance In-N bonding and extend the emission wavelength of GaInNAs quantum wells (QWs). After the formation of a complete In floating layer, the growth is interrupted and N irradiation is initiated. The majority of N atoms are forced to bond with In atoms and their incorporation is regulated independently by the N exposure time and the As pressure. The effect of the N exposure time and As pressure on the N incorporation and the optical quality of GaInNAs QWs were investigated. Anomalous photoluminescence (PL) wavelength red shifts after rapid thermal annealing (RTA) were observed in the N-irradiated samples, whereas a normal GaInNAs sample revealed a blue shift. This method provides an alternative way to extend the emission wavelength of GaInNAs QWs with decent optical quality. We demonstrate light emission at 1546 nm from an 11-nm-thick QW, using this method and the PL intensity is similar to that of a 7-nm-thick GaInNAs QW grown at a reduced rate.

  • 38.
    Zhao, Qing Xiang
    et al.
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology.
    Terahertz semiconductor laser structures2002In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 384-3, p. 197-204Article in journal (Refereed)
    Abstract [en]

    In this paper, we theoretically examine the possible quantum well structures that may fulfill the criterion to achieve a terahertz (THz) laser devices. Our calculations are based on well-developed effective-mass theory that accounts for valence-band mixing as well as the mismatch of band parameters and dielectric constants between well and barrier materials. The advantage of the model is that the ground and excited states of acceptors confined in strained quantum well structures can be calculated. Therefore, by calculating the splitting of the acceptor ground states in strained InxGa1-xAs/GaAs and Si1-xGex/Si quantum well structures versus well widths and alloy concentrations, our results provide a guiding to design the structures that inky be suitable for realizing THz stimulated emissions in a range between 2 and 8 THz.

  • 39.
    Zhao, Qingxiang
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Klason, P.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Jiang, W. L.
    Yang, J. H.
    Synthesis and characterization of ZnO nanostructures grown on Si substrates2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 131-134Article in journal (Refereed)
    Abstract [en]

    ZnO nanostructures were grown by thermal evaporation technique on ( 001) Si substrate and were characterized by photoluminescence measurements, scanning electron microscope and x-ray measurements. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions. By optimizing the growth conditions, orientated ZnO nanorods with a diameter of around 300 nm and lengths of 20 - 35 mu m have been achieved, and they show excellent optical properties. The laser action is observed at room temperature by using optical pumping.

  • 40.
    Zhao, Qingxiang
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Liu, Xinyu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Properties of shallow donors in ZnMgO epilayers grown by metal organic chemical vapor deposition2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 18, p. 183508-Article in journal (Refereed)
    Abstract [en]

    High quality Zn1-xMgxO epilayers have been grown by means of metal organic chemical vapor deposition technique on top of ZnO templates. The grown samples were investigated by x-ray photoelectron spectroscopy and photoluminescence. The magnesium (Mg) concentration was varied between 0% and 3% in order to study the properties of shallow donors. The free and donor bound excitons could be observed simultaneously in our high quality Zn1-xMgxO epilayers in the photoluminescence spectra. The results indicate that both built-in strain and Mg-concentration influence the donor exciton binding energy. It clearly shows that the donor exciton binding energy decreases with increasing Mg-concentration and with increasing built-in strain. Furthermore, the results indicate that the donor bound exciton transition energy increases with decreasing strength of the built-in strain if the Mg-concentration is kept the same in the Zn1-xMgxO epilayers.

  • 41.
    Zhao, Qingxiang
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Physics and Electronics.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Physics and Electronics.
    Ryzhii, Viktor
    Sensing infrared and terahertz regions by functional films2009In: Functional Thin Films / [ed] Anis Zribi, Jeffrey Fortin, editors, London: Springer Verlag , 2009, 1, p. -213Chapter in book (Other academic)
    Abstract [en]

    Designing functional films and nanostructures has a key role in the performance of the infrared (IR) sensing and terahertz (THz) sensing that are based particularly on quantum well, wire, and dot structures. Sensing the electromagnetic (EM) spectra is an extremely important issue for various fields, from understanding the universe, living cells, and elementary particles to numerous applications. To give a glimpse of the field in connection to functional films and nanostructures as sensing elements, in this chapter we briefly discuss infrared (IR) sensing and terahertz (THz) sensing. For IR sensing we limit ourselves to low-dimensional semiconductor functional films. For THz sensing we discuss: (a) how strain in thin films influences THz absorption from impurities, (b) plasma effects in two-dimensional electron gas (2DEG), and (c) ultrasensitive bolometers based on metal films.

  • 42.
    Zhao, Qingxiang
    et al.
    Göteborg University.
    Willander, Magnus
    Göteborg University.
    Wang, S.M.
    Chalmers University of Technology.
    Wei, Y.Q.
    Chalmers University of Technology.
    Gu, Q.F.
    Chalmers University of Technology.
    Sadeghi, M
    Chalmers university of Technology.
    Larsson, A
    Chalmers University of Technology.
    Optical properties of GaInNAs/GaAs quantum well structures2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 10, p. 4423-4426Article in journal (Refereed)
    Abstract [en]

    The radiative recombination in GaInNAs/GaAs quantum well structures was investigated by low temperature optical spectroscopy. In the temperature region, below 100 K, we found that the observed transition energies strongly depend on the excitation intensity and the temperature, which is indicative of carrier localization. The degree of carrier localization depends on the In-concentration but is not significantly influenced by the N-concentration when the N-concentration exceeds 1.6%. Photoluminescence studies indicate that the degree of the carrier localization decreases with increasing In-concentration at a constant N-concentration. In addition, the experimental results show that carrier localization is strongly correlated to deep level emission. Through post-growth thermal treatment at 650 °C both carrier localization and deep level emission can be eliminated.

  • 43.
    Zhao, Qingxiang
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Physics and Electronics.
    Yang, Li-Li
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sernelius, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Physics and Electronics.
    Surface recombination in ZnO nanorods grown by chemical bath deposition2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 7, p. 073526-Article in journal (Refereed)
    Abstract [en]

    Verticallywell-aligned ZnO nanorods on Si substrates were prepared by atwo-step chemical bath deposition (CBD) method. The optical properties ofthe grown ZnO nanorods were investigated by time resolved photoluminescencespectroscopy. It was found that the effective decay time ofthe near bandgap recombination in the CBD grown ZnO nanorodsstrongly depends on the diameter of the ZnO nanorods. Typically,the decay curves obtained from these ZnO nanorods show acombination of two exponential decays. The experimental results show thatthe fast exponential decay is related to the surface recombinationand the slow decay is related to the “bulk” decay.The measured decay time of the effective surface recombination decreaseswith decreasing diameter, while the bulk decay time remains unchanged.The results also show that an annealing treatment around 500 °Csignificantly reduces the surface recombination rate. A simple carrier andexciton diffusion equation is also used to determine the surfacerecombination velocity, which results in a value between 1.5 and4.5 nm/ps.

  • 44.
    Zhao, Qingxiang
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Yang, Li-Li
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Surface Recombination in ZnO Nanorods Grown by Aqueous Chemical Method2009In: PHYSICS OF SEMICONDUCTORS: 29th International Conference on the Physics of Semiconductors / [ed] Marília J. Caldas, Nelson Studart, Melville, N.Y, USA: American Institute of Physics (AIP), 2009, p. 319-320Conference paper (Refereed)
    Abstract [en]

    ZnO nanorods on Si substrates were prepared by either a two-steps chemical bath deposition (CBD) method or thermal evaporation technique. 11 was found that the effective decay time of the near bandgap recombinations strongly depends on the method, which was used to grow the ZnO nanorods. ZnO nanorods grown by the CBD exhibit characteriristic two-exponential decay curves, while ZnO nanorods grown by thermal evaporation technique show single exponential decays. The experimental results show that the fast exponential decay from the CBD grown ZnO nanorods is related to the surface recombination, while the slow decay is related to the "bulk" decay. The results also show that an annealing treatment around 500 degrees C to 700 degrees C significantly reduces the surface recombination rate.

  • 45.
    Zhao, QX
    et al.
    Chalmers University of Technology and Göteborg University.
    Jacob, AP
    Chalmers University of Technology and Göteborg University.
    Willander, Magnus
    Chalmers University of Technology and Göteborg University.
    Wang, SM
    Chalmers University of Technology.
    Wei, YQ
    Chalmers University of Technology.
    Ferdos, F
    Chalmers University of Technology.
    Sadeghi, M
    Chalmers University of Technology.
    Larsson, A
    Chalmers University of Technology.
    Yang, JH
    Jilin Normal University.
    Nonradiative centers in InAs dots grown on GaAs substrates for 1.3 mu m emission2003In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 315, no 02-Jan, p. 150-155Article in journal (Refereed)
    Abstract [en]

    Nonradiative centers in InAs dots grown on GaAs substrates are investigated in this study. The emission from InAs dots close to 1.3 mum is monitored under different excitation densities and different excitation energy. The used samples were also treated by hydrogen plasma in order to suppress the nonradiative centers. The purpose of this work is to study how nonradiative centers influence the efficiency of InAs dots emission and whether the nonradiative centers can be reduced. Our results clearly illustrate that there indeed exist nonradiative centers, both at the interface between the InAs dots and surrounding layers and in the GaAs layers, which can be suppressed by H-treatments. A technique to estimate relative amount of nonradiative centers is also discussed.

  • 46.
    Zhao, QX
    et al.
    Göteborg University.
    Klason, P
    Göteborg University.
    Willander, Magnus
    Göteborg University.
    Zhong, HM
    Chinese Academy of Sciences.
    Lu, W
    Chinese Academy of Sciences.
    Yang, JH
    Chinese Academy of Sciences.
    Deep-level emissions influenced by O and Zn implantations in ZnO2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 21Article in journal (Refereed)
    Abstract [en]

    A set of bulk ZnO samples implanted with O and Zn at various densities were investigated by photoluminescence. The implantation concentration of O and Zn is varied between 1x10(17)/cm(3) and 5x10(19)/cm(3). The samples were thermally treated in an oxygen gas environment after the implantation. The results clearly show the influence of O and Zn implantations on the deep-level emission. By comparing the photoluminescence spectra for the samples with different implantations, we can conclude that the V-Zn is responsible to the observed deep-level emission. In addition, a novel transition at the emission energy of 3.08 eV at 77 K appears in the O-implanted sample with 5x10(19)/cm(3) implantation concentration. The novel emission is tentatively identified as O-antisite O-Zn.

  • 47.
    Zhao, QX
    et al.
    Chalmers University of Technology.
    Wang, SM
    Chalmers University of Technology.
    Sadeghi, M
    Chalmers University of Technology.
    Larsson, A
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology.
    Yang, JH
    Chalmers University of Technology.
    Effects of nitrogen incorporation on the properties of GaInNAs/GaAs quantum well structures2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 7Article in journal (Refereed)
    Abstract [en]

    We report results from theoretical and experimental investigations of GaInNAs/GaAs quantum well structures. Optical transition energies for samples with different In and N concentrations were determined by photoluminescence measurements. The results show that the reduction of the ground-state transition energy by the introduction of N decreases with increasing In concentration. The experimental data are compared with calculations using the effective-mass approximation. Modifications of the band-gap energy due to N incorporation were accounted for using the two-level repulsion model. Proper effective-mass and band offset values, based on recent experimental work, were used. Calculated and measured transition energies show good agreement. The critical thickness, lattice constant, strain, and optical transition energies are discussed for GaInNAs/GaAs quantum well structures tuned for emission at 1.3 and 1.55 mu m, in particular. Such a simple model, within the effective-mass approximation, is a very useful guide for device design. (C) 2005 American Institute of Physics.

  • 48.
    Zhao, QX
    et al.
    Chalmers University of Technology and Göteborg University.
    Wang, SM
    Chalmers University of Technology.
    Wei, YQ
    Chalmers University of Technology.
    Sadeghi, M
    Chalmers University of Technology.
    Larsson, A
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology and Göteborg University.
    Effect of growth temperature and post-growth thermal annealing on carrier localization and deep level emissions in GaNAs/GaAs quantum well structures2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 12Article in journal (Refereed)
    Abstract [en]

    We report results from investigation of the optical properties of GaNAs/GaAs quantum well structures. The structures were grown by molecular-beam epitaxy at different temperatures, and subsequently postgrowth thermal treatments at different temperature were performed. The results show that the carrier localization is smaller in a structure grown at a temperature of 580 degrees C in comparison with a structure grown at 450 degrees C. Both structures also show a broaden deep level emission band. Furthermore, the deep level emission band and the carrier localization effect can be removed by thermal annealing at 650 degrees C in the structure grown at 450 degrees C. The structure quality and radiative recombination efficiency are significantly improved after annealing. However, annealing under the same condition has a negligible effect on the structure grown at 580 degrees C. (C) 2005 American Institute of Physics.

  • 49.
    Zhao, QX
    et al.
    Chalmers University of Technology.
    Wang, SM
    Chalmers University of Technology.
    Wei, YQ
    Chalmers University of Technology.
    Sadeghi, M
    Chalmers University of Technology.
    Larsson, A
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology.
    Radiative recombination of localized excitons and mobility edge excitons in GaInNAs/GaAs quantum wells with strong carrier localization2005In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 341, no 04-Jan, p. 297-302Article in journal (Refereed)
    Abstract [en]

    The radiative recombination in InxGa1-xN0.01As0.99/GaAs quantum well structures exhibiting strong carrier localization was investigated by optical spectroscopy. For In-concentration from 0 to 30%, the results indicate that the degree of carrier localization decreases with increasing In-concentration. At temperatures below 100 K, the mobility edge excitons as well as localized excitons are identified and their transitions energies strongly depend on the excitation intensity. At elevated temperatures the localized excitons become quenched. The temperature dependence of the photoluminescence emission energy shows different behaviors at different excitation intensities.

  • 50.
    Zhao, QX
    et al.
    Chalmers University of Technology and Göteborg University.
    Willander, Magnus
    Chalmers University of Technology and Göteborg University.
    Morjan, RE
    Chalmers University of Technology and Göteborg University.
    Hu, QH
    Chalmers University of Technology and Göteborg University.
    Campbell, EEB
    Chalmers University of Technology and Göteborg University.
    Optical recombination of ZnO nanowires grown on sapphire and Si substrates2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 1, p. 165-167Article in journal (Refereed)
    Abstract [en]

    ZnO nanowires have been grown on sapphire and Si substrates using catalytic growth. A strong near-band-gap ultraviolet emission is observed at room temperature. By carefully studying the temperature dependence of ZnO wire emission, we found that the room-temperature UV emission contains two different transitions; one is related to the ZnO free exciton and the other is related to the free-to-bound transition. The bound state has a binding energy of about 124 meV. The results from optical measurements show that a high quality of ZnO nanowires grown on sapphire and Si substrates has been achieved.

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