We report on the characterization of bulk and epitaxial ZnO films doped by nitrogen. The ZnO thin films were grown on GaN templates and on ZnO single crystals by vapor phase deposition using Zn and NO2/N2O as precursors. Nitrogen was introduced in the epitaxial films by a mixture of ammonia in the total N2 flow and by ion implantation into the bulk crystals. The optical properties were investigated by steady state and time resolved photoluminescence (PL). We observed a well structured donor–acceptor-pair (DAP) band with a zero phonon line (ZPL) at 3.235 eV. Time resolved PL measurements allowed to conclude on the compensation. Diffusion of Ga from the GaN templates into the ZnO layers was detected by SIMS. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thick AlxGa1−xN epilayer with microcracks grown by metalorganic vapor-phase epitaxy on a GaN buffer above a (0001) sapphire substrate was comprehensively characterized by spatially and spectrally resolved cathodoluminescence (CL) and micro-Raman (μ-Raman) spectroscopy. The variation of the CL line shift and the μ-Raman measurements between the microcracks are consistent with the interpretation that AlGaN is to a large extent stressed like a two dimensional film between the microcracks with nearly full relaxation close to the cracks. A satisfactory theoretical confirmation of this stress distribution was obtained by a three-dimensional finite-element application of the elasticity theory.

The compensation and self-compensation effects in Mg-doped GaN is studied by low-temperature photoluminescence and Raman spectroscopy using a series of samples with different Mg concentrations. Strongly doped samples are found to be highly compensated in electrical measurement. The compensation mechanism is directly related to the incorporation of Mg leading to the additional formation of three different deep donor levels. Furthermore, hydrogen forms defect complexes with Mg and compensates the acceptor states. These complexes were observed as local vibrational modes in Raman spectra in the range of 2200 cm−1. The direct incorporation of Mg can be controlled by local vibrational modes in the region of GaN host phonons. Investigating the intensity dependence of the different Mg–H complexes and the LVM of activated Mg the Raman spectra give a clear direct evidence of the degree of compensation and p-conductivity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

physica status solidi (c)Volume 0, Issue 6 p. 1795-1815 Review Article Optical micro-characterization of group-III-nitrides: correlation of structural, electronic and optical properties J. Christen, Corresponding Author J. Christen juergen.christen@physik.uni-magdeburg.de Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanyPhone: +49 391 67 18668, Fax: +49 391 67 11130Search for more papers by this authorT. Riemann, T. Riemann Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorF. Bertram, F. Bertram Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorD. Rudloff, D. Rudloff Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorP. Fischer, P. Fischer Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorA. Kaschner, A. Kaschner Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorU. Haboeck, U. Haboeck Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorA. Hoffmann, A. Hoffmann Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorC. Thomsen, C. Thomsen Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this author J. Christen, Corresponding Author J. Christen juergen.christen@physik.uni-magdeburg.de Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanyPhone: +49 391 67 18668, Fax: +49 391 67 11130Search for more papers by this authorT. Riemann, T. Riemann Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorF. Bertram, F. Bertram Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorD. Rudloff, D. Rudloff Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorP. Fischer, P. Fischer Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, GermanySearch for more papers by this authorA. Kaschner, A. Kaschner Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorU. Haboeck, U. Haboeck Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorA. Hoffmann, A. Hoffmann Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this authorC. Thomsen, C. Thomsen Institut für Festkörperphysik, Technische Universität Berlin, GermanySearch for more papers by this author First published: 27 August 2003 https://doi.org/10.1002/pssc.200303125Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract For a detailed understanding of complex semiconductor heterostructures and the physics of devices based on them, a systematic determination and correlation of the structural, chemical, electronic, and optical properties on a micro- or nano-scale is essential. Luminescence techniques belong to the most sensitive, non-destructive methods of semiconductor research. The combination of luminescence spectroscopy with the high spatial resolution of a scanning electron microscope, as realized by the technique of cathodoluminescence microscopy, provides a powerful tool for the optical nano-characterization of semiconductors, their heterostructures as well as their interfaces. Additional access to the local electronic and structural properties is provided by micro-Raman spectroscopy, e.g. giving insight into the local free carrier concentration and local stress. In this paper, the properties of group-III-nitrides are investigated by highly spatially and spectrally resolved cathodoluminescence microscopy in conjunction with micro-Raman spectroscopy. Complex phenomena of self-organization and their strong impact on the microscopic and nanoscopic properties of both binary and ternary nitrides are presented. As the ultimate measure of device performance, the microscopic properties of light emitting diodes are assessed under operation. Using micro-electroluminescence mapping in the optical microscope as well as in the near field detection mode of a scanning near field optical microscope, the microscopic origin of the macroscopic spectral red shift in light emitting diodes is identified. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Citing Literature Volume0, Issue6September 2003Pages 1795-1815 RelatedInformation

We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition (CVD) containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy (SIMS), was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm−1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD.

The strong three-dimensional modulation of the optical and structural properties due to the self-organized formation of Ga-rich AlGaN microdomains is directly imaged by spectrally and spatially resolved cathodoluminescence microscopy. The 5-μm-thick, crack-free AlGaN was grown on patterned GaN/sapphire templates periodically structured into trenches and terraces. During initial AlGaN overgrowth, the modulation of the local AlGaN stochiometry results in marble-like striations of Ga accumulation clearly reflecting the pattern periodicity. In contrast, after subsequent overgrowth, a homogeneous emission wavelength, i.e., a homogeneous aluminum content, is found near the sample surface. However, the strong rise of quantum efficiency directly above the trenches indicates a drastic improvement of material quality.

We analyze the influence of annealing on compositional fluctuations in InGaAsN quantum wells by means of composition-sensitive high-resolution transmission electron microscopy and photoluminescence. In as-grown samples, we find In-concentration fluctuations of ±5% on a length scale of 20 nm in a two-dimensional grown quantum well. No indications for N concentration fluctuations are found within the limits of resolution. Annealing homogenizes the In distribution within the well and causes diffusion of N out of the quantum well. According to our compositional analysis, the blueshift in the photoluminescence can in part be attributed to reduction in N concentration inside the well. The more homogeneous In distribution leads to a reduction in linewidth and Stokes shift.

We have carried out spatially resolved micro-Raman spectroscopy, cathodoluminescence microscopy and scanning capacitance microscopy in order to obtain a comprehensive understanding about the properties of different domains formed in epitaxial laterally-overgrown GaN. For this purpose a spherical pit was fabricated into the sample by mechanical grinding and polishing, penetrating through to the buffer layer at its center. We found areas showing sharp excitonic luminescence corresponding to local free-carrier concentrations n below 1017 cm—3 as well as domains exhibiting broad luminescence originating from recombination of a doping plasma with n reaching 1019 cm—3. Simultaneously, we observed in the scanning microscopy investigations a substructure which could be explained by the existence of internal space charge regions.

We report on spatially-resolved low-temperature luminescence and Raman experiments on ZnO epilayers grown on GaN templates by vapor phase deposition. Our investigations reveal that the peak luminescence position of the free and bound exciton lines of ZnO depends on the distance from the substrate. Different acceptor and donor species become locally dominant. Furthermore, a strong red shift occurs directly at the interface, indicating strong local internal electric fields. From Raman experiments we determined the spatial evolution of the compressive strain in the ZnO epilayer and the induced tensile strain in the GaN templates.

We study the incorporation of nitrogen into ZnO. A series of samples grown by chemical vapour deposition (CVD) containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy (SIMS), was investigated. Nitrogen forms a shallow acceptor in ZnO and leads to typical excitonic emission and donor-acceptor pair band recombination. Binding energies of ~16 meV for the exciton and ~165 meV for the nitrogen acceptor are obtained. The Raman spectra revealed local vibrational modes at 275, 510, 582, 643 and 856 cm in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen. This hints to the origin of compensated acceptor states detected in PL measurements. The compensation mechanisms may be similar to those reported for GaN:Mg.

With in situ micro-Raman measurements during the electrochemical reduction of WO3 thin films, the influence of the intercalated cation (H+/Li+) and an addition of water to the aprotic lithium electrolyte was investigated. The Raman spectra of lithium bronzes LixWO3 show two main results: (i) the intercalation of hydrogen can be clearly distinguished in situ from the intercalation of lithium with this technique and (ii) even with an addition of 500 ppm of water to the lithium electrolyte no hydrogen intercalation was observed.