Surface characterization of semi-insulating GaAs wafers by room temperature photoluminescence mapping

Surfaces of semi-insulating (SI) GaAs wafers were investigated by photoluminescence (PL) spectroscopy at room temperature. PL mappings of 2-inch wafers were studied for both band-edge and EL2 emission bands under weak excitation conditions. The PL intensities are affected not only by bulk properties, but also by some surface related phenomena. We report that surface mechanical damage and its in-depth profile can be evaluated by PL mapping and successive chemical etching. Asymmetrical, nonuniform patterns of the PL intensity are sometimes observed for as-received wafers, but adequate deionized water treatment enhances the intensity and causes the appearance of a crystallographic PL intensity pattern. The intensity is at the same level as that after chemical etching. The band-edge emission is more sensitive than the EL2 emission to both surface treatment and damage. Auger analysis and ellipsometry were performed to clarify the mechanism of the deionized water treatment. The native oxide layer on a GaAs surface can be removed simply by using the deionized water treatment. Enhancement of the PL intensity after adequate water treatment is considered to be directly related to the reduction of surface states, which are induced by natural oxidation.