Various experimental techniques were used to measure the point defect concentrations in layers which had been grown at 250C by means of molecular beam epitaxy. The effect of doping upon these concentrations was investigated by studying samples which contained shallow acceptors (Be) or shallow donors (Si) at concentrations of the order of 1019/cm3. It was found that material which had been grown under As-rich conditions, and doped with Be, was completely compensated. The simultaneous detection of AsGa0 by near-bandedge infra-red absorption methods, and of AsGa+ by electron paramagnetic resonance techniques, confirmed that the Fermi level was near to the mid-gap position and that compensation was partly related to AsGa defects. Positron annihilation measurements provided no evidence for the incorporation of VGa into this layer. In the case of samples which were grown under As-rich conditions and were doped with Si, more than 80% of the donors were compensated. The detection of SiGa-VGa pairs by infra-red localized vibrational mode spectroscopy indicated that compensating VGa defects were partly responsible. The presence of vacancy defects was confirmed by positron annihilation data. Increases in the Si doping level suppressed the incorporation of AsGa. Exposure of the doped layer to a radio-frequency H plasma generated a localized vibrational mode at 1997/cm. It was suggested that this line was a stretching mode of a AsGa-H-VAs defect complex. In Si-doped layers, stretching modes at 1764 and 1773/cm and a wagging mode at 779/cm, which were related to a H-defect complex, were detected. It was proposed that the complex could be a passivated As antisite, and that the detection of characteristic H-native defect localized vibrational modes could provide a new method for the identification of intrinsic defects.

R.E.Pritchard, S.A.McQuaid, L.Hart, R.C.Newman, J.Mäkinen, H.J.Von Bardeleben, M.Missous: Journal of Applied Physics, 1995, 78[4], 2411-22