Residual Donor Impurities in Undoped LEC SI-GaAs Crystals

Undoped liquid encapsulated Czochralski (LEC) semi-insulating (SI) GaAs is a promising substrate for GaAs IC’s . However, high electrical uniformity across a wafer has not yet been attained. The SI mechanism is explained by the compensation of shallow levels with deep levels (1, 2). In order to improve the electrical uniformity, distribution measurements of these levels are required in the first place. However, most studies done so far were limited to the deep levels and little is known about the shallow levels. In this study, SIMS measurements have been carried out to obtain the distribution of residual shallow donor impurities such as Si, S, Se and Te in several wafers. We describe the correlation between the impurity distribution and dislocation density, and a possible origin of resistivity inhomogeneity.