A MODFET PROCESS FOR MICROMETER SCALE STRAINED-LAYER ISLANDS

Previous studies have demonstrated that the density of misfit dislocat ions can be reduced by growth of strained layers on patterned substrat es. In this paper, a new process sequence for the fabrication of pseud omorphic modulation-doped field effect transistors (MODFETs) on patten ed GaAs substrates is presented. Semi-insulating GaAs substrates were patterned and dry etched using chemically assisted ion beam etching (C AIBE) to define a series of mesas prior to epitaxial layer growth. Dou ble-doped, pseudomorphic MODFET layers were then grown on the substrat es by molecular beam epitaxy. Using a planarization technique based on SiO2/photoresist, MODFETs with vacuum-passivated T-gates which bridge across up to 20 mesas were fabricated. Current-voltage measurements o f these MODFETs show high output currents and good pinch-off character istics.