Normally-Off GaAs FET Monolithic Technology.

Al.5Ga.5As gate heterojunction field-effect transistors HJFETs have been fabricated using organometallic OM epitaxy and tested. Growth of the FET active layer on an undoped buffer layer has been shown to produce less velocity degradation at the channel-substrate interface than if the active layer is grown directly on a Cr-doped substrate. HJFETs have been fabricated by growing the p-Al.5Ga.5As and p-GaAs OM gate layers on mesa-etched vapor-phase epitaxy VPE active layers and also by growing all three layers by OM epitaxy. Electrical measurements on normally-on and normally-off HJFETs indicated a problem at the p-Al.5Ga.5Asn-GaAs interface, later confirmed by the finding of significant amounts of oxygen in the Al.5Ga.5As. Microwave small signal and large signal switching measurements were made on HJFETs with 2x300 micron gates and on Schottky barrier FETs SBFETs with 1x200 micron Al gates intended to simulate normally-off HJFETs. Circuit models were derived from the small-signal measurements and gate propagation delays were derived from the switching measurements. A 2-micron gate normally-on HJFET had 47 psec gate propagation delay while a 1-micron gate SBFET simulated normally-off HJFET had 27 psec gate propagation delay. Author