Phosphorous coimplantation effect on threshold voltage uniformity of GaAs transistors

Abstract

Phosphorous coimplantation effect on electrical uniformity of Si-implanted GaAs active layer is investigated for undoped as-grown, undoped ingot-annealed, and In-doped substrates. Pairs of field-effect transistors, fabricated with and without P coimplantation, are placed on whole 3-in.-diam substrates at a 200-μm interval. Threshold voltage measurements reveal that a concentration of 1018 /cm3 coimplanted P reduces the standard deviation in threshold voltage for undoped as-grown substrates to 1/2.5. Undoped ingot-annealed substrates achieve the same uniformity of threshold voltage as In-doped substrates, which showed the best data. Moreover, this method reduces the variation in the mean threshold voltage among substrates by one-half. These results indicate that P coimplantation successfully suppresses the change of As to Ga vacancy concentration ratio.