Z. Chine

Photoreflectance and photoluminescence study of annealing effects on GaAsBi layers grown by metalorganic vapor phase epitaxy

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 GaAs0.965Bi0.035 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.

Effect of thermal annealing on structural and optical properties of the GaAs0.963Bi0.037 alloy

We have investigated the effect of thermal annealing on GaAs0.963Bi0.037 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 GaAs0.963Bi0.037 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.

Anti-Stokes photoluminescence of yellow band in GaN: evidence of two-photon excitation process

Time-dependent photoluminescence of yellow band in GaN has been investigated under various excitation conditions using a Q-switched Nd : YAG laser as an excitation source. An anti-Stokes photoluminescence of the yellow band that dominates the photoluminescence (PL) spectra has been observed under the below band-gap excitation. The intensity of the anti-Stokes PL shows a non-linear dependence on the excitation intensity. Our results suggest that the energy up-conversion is via a two-step two-photon absorption process.

Very high silicon concentration by MOVPE in GaAs

Epitaxial silicon-doped GaAs layers are grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE) using silane (SiH4) 500 ppm diluted in H2 as a dopant source gas. The grown layers are characterised by the van der Pauw method, secondary ion mass spectroscopy, room and low temperature photoluminescence experiments. The carrier concentration has a growth temperature dependence when the SiH 4 partial pressure is lower than 6.7 × 10 -2 Pa. How-ever, it has no temperature dependence for SiH4 partial pressure higher than 6.7 x 10 -2 Pa and the activation energy of Si incorporation varies from 0 to 2.2 eV. The carrier concentration of Si-doped GaAs is usually saturated at 6 × 10 18 cm -3 level. However, in this study a carrier concentration of up to 1 x 10 19 cm -3 was obtained, which in our knowledge is the highest carrier concentration ever reported for Si-doped GaAs by AP-MOVPE. Compensation ratios are firstly calculated from theoretical Hall mobility. Using room temperature photoluminescence data, theoretical fils of the photoluminescence peaks, these compensation ratios are also determined and they are compared with values obtained from mobility data.