The effect of Al (as an iso-electronic dopant), upon deep-level defects in GaAs that had been grown by molecular beam epitaxy, was investigated by means of deep-level transient spectroscopy. Samples of Ga1-xAlxAs, with x = 0.001, 0.01 or 0.03, were studied. At least 9 different deep levels were detected. These were compared with the M levels which were normally found in molecular beam epitaxial n-type GaAs. The emission rates of deep levels were found to shift to higher values with decreasing Al content. This was attributed to lattice strain and random alloy effects. The relative concentrations of deep levels underwent large changes as the Al concentration was increased from 0.1 to 1%. Doping with Al to up to 0.1% did not appear to reduce the deep-level concentration; unlike other isovalent dopants, such as In and Sb, in molecular beam epitaxial GaAs. A further increase in Al doping to 1% led to a pronounced increase in the overall deep-level concentration, such that 3%Al-doped material failed to yield good Schottky junctions. These results were confirmed by preliminary photoluminescence data.

U.S.Qurashi, M.Z.Iqbal, N.Baber, T.G.Andersson: Materials Science Forum, 1995, 196-201, 1767-72