Photoinduced transient spectroscopy and photoluminescence studies of copper contaminated liquid-encapsulated Czochralski-grown semi-insulating GaAs

Abstract

Photoinduced transient spectroscopy (PITS) studies of samples of copper contaminated annealed semi-insulating GaAs in the temperature range of 274–384 K show two dominant levels at about Ev +0.5 eV and about Ec −0.59 eV in addition to the EL2 levels at about Ec −0.80 eV. Depth profiling using chemical etching followed by PITS measurements shows a competing process between the defects responsible for the level at Ev +0.5 eV and that at Ec −0.59 eV. The former is predominantly found near the surface and the latter is dominant in the interior. From the depth profiling results, we have determined that the diffusion constants for these two types of defects are about 4.7×10−10 cm2 s−1 and 5.2×10−10 cm2 s−1, respectively. We propose that the level at Ev +0.50 eV is due to a copper related complex and the level at Ec −0.59 eV is due to native defects. The copper related level at about Ev +0.50 eV is different from the often seen copper related defect level at around Ev +0.40 eV. The presence of these two levels would explain the variety of results reported by different workers on the deep levels attributed to copper. Photoluminescence measurements on a copper contaminated sample at 4.2 K show a peak at 1.36 eV which is due to CuGa acceptor level. This peak appears even after repeated etching of the sample, showing the presence of copper throughout the sample. Comparison data were also obtained for both ‘‘copper-free’’ annealed and unannealed samples.