Microwave field-effect transistors from sulphur-implanted GaAs

Sulphur implanation into semi-insulating Cr doped GaAs has been used to fabricate MESFETs with 1.5 μm gatelength showing microwave gain equivalent to epitaxial FETs (MAG = 9 dB at 10 GHz) but higher noise. Room temperature implantation of S at an energy of 30 keV and a dose of 5 × 10¹² cm^?2, sputtered SiO₂ and Si₃N₄ as encapsulants and heat treatments from 820 to 900°C have been used. Electrical activation was found to depend critically on the substrate material. Si₃N₄-encapsulation gave slightly higher electrical activation than SiO₂.