PHOTOLUMINESCENCE OF GASB GROWN BY METAL-ORGANIC VAPOR-PHASE EPITAXY

Low-temperature photoluminescence of epitaxial GaSb grown by MOVPE from TMGa and TMSb on various substrates is studied and compared with existing results for GaSb grown by other techniques. The effects of growth conditions are considered. It is found that a growth temperature of 650-degrees-C is too high, and the layers are of very poor quality, while below the optimum temperature of 600-degrees-C the growth rate slows, although the optical quality appears unaffected. Investigations into the range of III/V ratios over which good quality material could be grown indicated that this factor was more critical for GaSb than for GaAs; Sb-rich conditions produced samples with poor radiative efficiency, while samples grown under Ga-rich conditions were covered in excess Ga droplets. In addition, we found that, in common with other growth techniques, the concentration of the native defect in GaSb could be controlled using the III/V ratio, and an excellent correlation was found between electrical results and features in the photoluminescence spectra. For layers not lattice-matched to the substrate, the spectrum is red-shifted. We surmise that this is due to differential thermal contraction of the epilayer and substrate. A homoepitaxial sample was chosen for detailed study and from the dependence of the spectra on temperature and excitation intensity, a previously observed bound exciton was confirmed and an acceptor of 15 meV binding energy was found.