Enhancement/Depletion-Mode Selectively-Doped GaAs/AlGaAs Heterostructure Devices Fabricated Using A Self-Aligned Refractory Gate Process.
29 October 1987
An initial demonstration of a GaAs/AlGaAs enhancement/depletion process using self-aligned refractory gates and molecular beam epitaxially grown selectively doped heterostructures is reported. EFETs and DFETs are formed simultaneously after GaAs and AlGaAs cap and etch stop layers are removed on selected areas of the wafer. Control of FET parameters is obtained by maintaining layer thickness and doping uniformity of ultra-thin layers during MBE growth and subsequent device processing. Threshold voltage standard deviations of 20 and 50 mV have been achieved across a 40x40 mm sup 2 area of a 3 in. wafer for EFETs and DFETs, respectively. Inter-wafer threshold voltage uniformity was 40 mV for EFETs and 90 mV for DFETs on similar areas of five wafers.