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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.

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High‐temperature GaN films were grown at 1120 °C and 1080 °C by atmospheric pressure metalorganic vapor phase epitaxy on silicon nitride (SiN)‐treated sapphire using a GaN buffer layer grown at 600 °C. The effect of a SiN interlayer has been investigated. We have varied the silane (SiH4) flow from 4 to 20 sccm and the duration of SiN treatment from 60 s to 180 s. These layers have been characterized in‐situ by laser reflectometry and ex‐situ by atomic force microscopy (AFM) and low‐temperature photoluminescence. AFM revealed that GaN grown with optimized SiN treatment shows a terrace‐like structure with a reduced density of dislocations of about 5 × 108 cm−2 compared to GaN without SiN treatment. The I2 line is very intense with a 4 meV full width at half maximum. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)