Characterization of Annealed Low-Temperature GaAs Layers Grown by Molecular Beam Epitaxy with n-i-n Structure

Abstract

Deep levels and resistivity in annealed low-temperature molecular beam epitaxial (LT-MBE) GaAs layers were characterized using n- i-n structure. We found that annealing at 620°C resulted in the highest attainable resistivity of LT GaAs layers. However, deep-level transient spectroscopy (DLTS) and photocapacitance quenching measurements showed no signal of the midgap (EL2) level. Only a “shallower” EL3-like level was observed in the layer of high resistivity. The fact that no midgap level was detected in the highest-resistivity LT GaAs layer means that the “compensation" mechanism does not play an important role in controlling the semi-insulating properties of LT GaAs layers. On the other hand, a midgap level appeared upon annealing at higher than 620°C, although the resistivity of LT GaAs layers decreased more than five orders of magnitude. The photoquenching measurements suggest that this level is identical to the EL2 level. These results support the “buried Schottky barrier" model.