WSi_0.11 Schottky gates for GaAs metal semiconductor field-effect transistors

Schottky gates for self-aligned GaAs metal semiconductor field-effect transistors (MESFETs) have been formed by dc magnetron sputtering of WSi 0.11 onto sputter-cleaned GaAs surfaces. The WSi0.11/GaAs diodes showed good current-voltage and capacitance-voltage characteristics after annealing at 800 °C. Schottky barrier heights measured by current-voltage were φI-VB ≅0.73 eV with an ideality factor n≅1.14 for large diodes and φI-VB ≅0.67 eV with n≅1.3 for 1×10 μm gates without a self-aligned n+ implant. The n+ self-aligned implant was found to cause leakage current, which was interpreted as a parallel small-area, low-barrier diode at the gate edge. FETs formed with this gate material showed good threshold voltage uniformity with a standard deviation as low as 31 mV for 1 μm enhancement-mode FETs and 49 mV for 1 μm depletion-mode FETs on a 51-mm wafer.