Native defects in low-temperature GaAs and the effect of hydrogenation

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Abstract
A range of experimental techniques has been used to measure point defect concentrations in GaAs layers grown at low temperatures (250 °C) by molecular-beam epitaxy (LT-GaAs). The effects of doping on these concentrations has been investigated by studying samples containing shallow acceptors (Be) or shallow donors (Si) in concentrations of ∼1019 cm−3. Material grown under As-rich conditions and doped with Be was completely compensated and the simultaneous detection of As0Ga by near-band-edge infrared absorption and As+Ga by electron paramagnetic resonance confirmed that the Fermi level was near the midgap position and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer from positron annihilation measurements. For LT-GaAs grown under As-rich conditions and doped with Si, more than 80% of the donors were compensated and the detection of SiGa–VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating VGa defects were at least partly responsible. The presence of vacancy defects was confirmed by positron annihilation measurements. Increasing the Si doping level suppressed the incorporation of AsGa. Exposure of the 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 AsGa–H–VAs defect complex. For the Si-doped layer, two stretch modes 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-native defect LVMs may provide a new method for the identification of intrinsic defects.