Experimental requirements for quantitative mapping of midgap flaw concentration in semi-insulating GaAs wafers by measurement of near-infrared transmittance

Abstract

The experimental properties are critiqued that relate the midgap flaw concentration in semi-insulating GaAs, and the resulting near-infrared transmittance of a polished wafer. Since quantitative information of such flaw concentrations is desirable even for an optical thickness αt≪1, a highly stable and accurate experimental arrangement is described, which permits a meaningful evaluation even when αt≂0.01. (The transmittance is then almost Tmax, as set by the substantial reflectance losses.) This system permits mapping over a wafer’s area, by translation of the wafer with respect to the optical path. Calibration of absorption into flaw concentration is discussed for the midgap EL2 donor defect, and (in an appendix) for chromium-doped GaAs. Representative wafer maps for EL2 are used as illustrations, some as mosaic grey-scale matrix plots, and others as pseudo-three-dimensional contour plots.