NATIVE DEFECTS IN LOW-TEMPERATURE GAAS AND THE EFFECT OF HYDROGENATION

A range of experimental techniques has been used to measure point defe ct concentrations in GaAs layers grown at low temperatures (250 degree s C) by molecular-beam epitaxy (LT-GaAs). The effects of doping on the se concentrations has been investigated by studying samples containing shallow accepters (Be) or shallow donors (Si) in concentrations of si milar to 10(19) cm(-3). Material grown under As-rich conditions and do ped with Be was completely compensated and the simultaneous detection of As-Ga(0) by near-band-edge infrared absorption and As-Ga(+) by elec tron paramagnetic resonance confirmed that the Fermi level was near th e midgap position and that compensation was partly related to As-Ga de fects. There was no evidence for the incorporation of V-Ga in this lay er from positron annihilation measurements. For LT-GaAs grown under As -rich conditions and doped with Si, more than 80% of the donors were c ompensated and the detection of Si-Ga-V-Ga pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating V-Ga defects were at least partly responsible. The presence of vacancy defe cts was confirmed by positron annihilation measurements. Increasing th e Si doping level suppressed the incorporation of As-Ga Exposure of th e Be-doped layer to a radio-frequency hydrogen plasma, generated a LVM at 1997 cm(-1) and it is proposed that this line is a stretch mode of a As-Ga-H-V-As defect complex. For the Si-doped layer, two stretch mo des at 1764 and 1773 cm(-1) and a wag mode at 779 cm(-1) relating to a H-defect complex were detected and we argue that the complex could be a passivated As antisite, The detection of characteristic hydrogen-na tive defect LVMs may provide a new method for the identification of in trinsic defects. (C) 1995 American Institute of Physics.