Properties of Au/W/GaAs Schottky barriers

The electrical and chemical properties of r.f. sputtered Au/W Schottky barriers on GaAs studied by Auger electron spectroscopy are reported. There is considerable interest in such work at present owing to the refractory nature and the thermal stability of tungsten on GaAs. The built-in potential of tungsten on GaAs was measured to be about 0.65 eV by both I–V and C–V techniques. Although tungsten alone has been reported to be stable on GaAs even at elevated temperatures of up to 500°C, the presence of a gold overlay and/or pinholes in the r.f. sputtered tungsten reduces its refractory nature. W/Au Schottky barriers annealed at 475 and 575°C for 10 min showed no appreciable degradation in their electrical properties. Samples annealed at 475°C for 2 h and 800°C for 15 min showed some degradation and migration of gold through the tungsten film. GaAs field effect transistors (FETs) with tungsten gates 0.7 μm long showed a maximum measured gain of 14 dB at 8 GHz.