ELECTRICAL AND PHOTOLUMINESCENCE PROPERTIES OF UNDOPED GASB PREPARED BY MOLECULAR-BEAM EPITAXY AND ATOMIC LAYER MOLECULAR-BEAM EPITAXY

High-quality, unintentionally doped GaSb layers were grown by molecular beam epitaxy (MBE) and by atomic layer MBE (ALMBE) to study the influence of growth conditions on their transport and photoluminescence properties. While the hole mobility mu is only slightly dependent on the growth conditions, the 77 K hole concentration p shows minima at growth temperatures of similar to 450 degrees C and for Sb-4/Ga beam equivalent pressure ratios (BEPRs) of similar to 8; the concentrations of singly and of doubly ionizable acceptors and of a compensating donor have been obtained by simultaneously fitting the temperature dependence of mu and p in the 40-300 K range; from these results we show that the existence of minima of p can be related to an increased electrical compensation due to a reduced incorporation of accepters. The 15 K photoluminescence spectra are generally dominated by the donor-acceptor pair transition (A, 779 meV) involving the neutral state of the native acceptor, except when the growth is carried out at relatively low temperatures with low BEPRs. Under the latter conditions: (i) a peak (788 meV) shows at an energy 25 meV below the band-gap energy and (ii) exciton related transitions have intensities comparable to that of the A recombination.