Electrical and optical properties of deep levels in MOVPE grown GaAs

Abstract

In this paper we present a characterization and suggest an identification of deep levels that are present in our MOVPE grown GaAs. The undoped material is n-type with carrier concentrations of 3 − 7 × 10 15 cm -3. From low temperature photoluminescence we identify carbon as the dominant shallow acceptor impurity. Deep Level Transient Spectroscopy (DLTS) investigations show a dominant electron trap ≈0.74 eV below the conduction band edge. This level is known in the literature as the “O”-level, EL2 etc. The concentration of this defect is in our material in the range 5 × 10 13 − 3 × 10 14 cm -3, while other deep electron traps are present in concentrations ≲3 × 10 12 cm -3. In n-doped layers we also observe the 1.2 eV luminescence band corresponding to a level positioned ≈0.2 eV from the valence band edge. This band is not detectable in undoped material. The n-doping incorporation and the deep acceptor concentration in n-type material are found to be in agreement with recent calculations by Hurle. For the “O”-level concentration we have, for the first time, found a unique dependence on the AsH 3 partial pressure, N T ∝ P 1 /2 AsH 3 . Comparison with theoretical calculations suggests that the “O”-level is directly related to gallium vacancies.