Comparison of Mg and Zn gate implants for GaAs n-channel junction field effect transistors

Abstract

Zinc and magnesium implants into GaAs were profiled with secondary ion mass spectroscopy and etching capacitance-voltage to measure the as-implanted and annealed profiles for the eventual formation of shallow p+/n junction gates for junction field effect transistors (JFETs). The larger mass of the zinc ions results in shorter projected range with significantly less tailing than magnesium implants. High dose, shallow zinc implants annealed under tungsten gate metal showed good activation with negligible diffusion. The improved profile of the zinc implant, as compared to a similar magnesium implant, allowed a tighter JFET design with increased performance. Zn gated n-channel enhancement mode GaAs JFETs with 0.9 µm gate lengths showed transconductances up to 200 mS/ mm with a ft of 18 GHZ and a fmax of 37 GHz. The performance of these self-aligned fully implanted JFETs compare favorably with comparably sized implanted MESFETs.