Characterization of EL2 distribution on semi-insulating GaAs wafer by optically assisted imperfection profile

An improved nondestructive characterization technique is developed to measure the relative density distribution of the EL2 level in undoped semi-insulating (SI) GaAs wafers at room temperature. Experimentally, the resistance of a small area of the wafer is measured twice, first with greater than band-gap illumination outside a small masked area and then with a narrow-band optical filter centered at 1074 nm in place of the masked area. The difference of the two measured resistances is shown to be proportional to the density of the EL2 level. By moving the masked area across the wafer while taking resistance measurements, the relative density variation of EL2 can be determined. A theoretical discussion based on the commonly used compensation model for undoped SI GaAs materials is presented to interpret the experimental data. A technique for applying electrical contacts to SI GaAs materials by ultrasonic soldering has been developed to achieve reproducible measurements. Although only GaAs materials were investigated, this optically assisted imperfection profile can be applied to study other high-resistivity semiconductors.