We have investigated the effect of thermal annealing on GaAs 0.963 Bi 0.037 layers grown by atmospheric pressure metalorganic vapour phase epitaxy. High resolution x-ray diffraction (HRXRD) patterns show high crystalline quality and remarkable stability against thermal annealing up to 700 • C. When the annealing temperature reaches 750 • C, the GaAs 0.963 Bi 0.037 alloy is no longer stable, and the HRXRD pattern reveals the presence of other peaks. Atomic force microscopy images show a surface accumulation of Bi islands which disappear at 750 • C. The photoluminescence (PL) is clearly improved after annealing, but no shift of the PL peak was observed. The optimal annealing temperature is found to be ∼700 • C.

The optical properties of GaAsBi layers grown by atmospheric pressure metalorganic vapor phase epitaxy on p-type GaAs substrates and annealed at different temperatures are investigated by photoreflectance and photoluminescence spectroscopies. Photoreflectance spectra show no significant shift in the band gap energy of GaAs 0.965 Bi 0.035 with annealing temperature except 600 • C for which the band gap energy reaches a minimum value corresponding to a red shift of 60 meV. The low temperature photoluminescence spectra of GaAsBi layers show a broad band centered at ∼1.36 eV. The temperature dependence of the 1.36 eV emission band in addition to the increasing intensity of this band with bismuth flow suggests that it is originated from Bi clusters or from complex defects probably located at the surface/interface of the GaAsBi epilayer.

We report a study by photoluminescence (PL), Raman scattering, and highly resolved X‐ray diffraction (HRXRD) of a series of Si‐doped n‐type GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire (0001) with the carrier concentration of 2.3 × 1017 – 9 × 1018 cm–3. We found that the band gap reduction deduced from the PL spectra analysis is due to both band gap narrowing (BGN) effect and change of the nature of stress in the GaN:Si layers. The HRXRD spectra show that at high Si‐doping levels (>1.6 × 1018 cm–3) the GaN films become under tensile stress. Progressive decreases of the E2 Raman mode frequency with Si concentration confirm this observation. The stress induced E2 mode frequency shift is estimated to 1.6 cm–1/GPa. Additionally, dislocation densities are determined by HRXRD by employing a model that uses the line width of X‐ray rocking curves. Atomic force microscopy (AFM) is also used to investigate the defect surface structures of GaN:Si layers which are dominated by pinned steps and surface depressions related to threading dislocations. We find that dislocation densities given by AFM measurements are in agreement with those obtained from rocking curve line widths. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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