A selective dry-etch technique for GaAs MESFET gate recessing

Reports a selective dry-etching technique for GaAs MESFET gate recessing, where a thin AlGaAs etch stop is used to precisely control the recess depth. Selective dry etching was achieved by using a CCl₂F₂/He gas mixture yielding a selectivity of >600 for GaAs over AlGaAs. A thin (35-50-Å) Al_xGa _1-xAs layer (x=0.3) was used to control the etch depth. The surface composition of the RIE (reactive ion etch) recessed AlGaAs layers was analyzed by angle-resolved X-ray photospectrometry and compared to the surface compositions of the wet-chemically recessed samples. The standard deviation of MESFET threshold voltage was as low as 20 mV across a 3-in. wafer by using this selective dry-etch technique. The MESFETs show excellent electrical characteristics with transconductance of 150 mS/mm for a 1×100 μm gate and breakdown voltages as high as 38 V