Uniformity of 3-in., semi-insulating, vertical-gradient-freeze GaAs wafers

We have evaluated the uniformity in [EL2], dislocation (or etch-pit) density (EPD), resistivity, mobility, and carrier concentration for 3-in., semi-insulating GaAs wafers grown by the vertical-gradient-freeze (VGF) technique. Although slight W or U patterns were observed in [EL2] and EPD along the 〈110〉 directions, for the first time, nevertheless the overall uniformity was excellent, and comparable to that in the best In-doped and whole-boule-annealed ingots grown by the liquid-encapsulated Czochralski (LEC) technique. Based on results from implant-activation studies on LEC wafers, it is estimated that the measured nonuniformities in EPD and [EL2] for the VGF wafers would contribute only about 1% to implant-activation-efficiency nonuniformities in Si-implanted wafers designed for field-effect transistor applications.