Nominally undoped layers which had been grown by means of molecular beam epitaxy were investigated by using temperature-dependent and frequency-dependent admittance spectroscopy. Deep-level transient spectroscopy was inapplicable because the space-charge region, which was needed for the detection of deep defects, existed only at low frequencies. Two deep defect levels were identified in molecular beam epitaxially grown layers. The thermal activation energies were 0.45 and 0.63eV, respectively. These deep traps were familiar from deep-level transient spectroscopic and thermally stimulated conductivity studies.

A.Krtschil, H.Witte, M.Lisker, J.Christen, U.Birkle, S.Einfeldt, D.Hommel: Journal of Applied Physics, 1998, 84[4], 2040-3