Normally-on and normally-off camel diode gate GaAs field effect transistors for large scale integration

Abstract

Normally-off and normally-on camel gate GaAs field effect transistors have been fabricated from structures grown by molecular beam epitaxy. These new devices use a camel diode gate formed from n+ and p+ layers instead of a Schottky barrier gate as used in metal-semiconductor field effect transistors. The camel diode gate provides these devices with several advantages over metal-semiconductor field effect transistors, including elimination of the metallurgical difficulties of the metal-semiconductor contact, relatively easy adjustment of the built-in voltage, and the potential for improved reliability in adverse environments and under conditions of high power dissipation. Fabrication of these devices does not require precision etching, making them compatible with large scale integrated circuit technology. Fabricated devices have yielded transconductances of 80 ms/mm in long channel (3 μm gate length) normally-on and normally-off field effect transistors and of 120 ms/mm in short channel (1 μm gate length) normally-on field effect transistors. Significantly improved gate-drain breakdown voltages and, in devices with AlxGa1−xAs buffer layers, excellent saturation characteristics have been observed. A simple theory providing analytical expressions describing the performance of normally-on and normally-off camel gate field effect transistors has been developed and good agreement with experiment has been obtained.