Selective implantation of GaAs for MESFET applications

A novel selective ion-implantation technique compatible with capless annealing is described. The process consists of coating the GaAs wafer with a thin layer of titanium over which photoresist can be applied and delineated several times for a number of selective implantation steps. The use of a titanium barrier layer avoids any contamination of the GaAs surface by ion-hardened photoresist. Depletion-mode MESFETs with selectively implanted channel and n+ contacts have been fabricated using this technique. Implantation through the titanium layer produced no degradation in pinch-off voltage uniformity over 2 in-diameter wafers.