A comparison of commercial sources of epitaxial material for GaN HFETs fabrication

This paper describes a comparison of material and device results obtained f rom AlGaN/GaN epitaxial HFET wafers from three commercial sources. Although all three sources supplied material to the same nominal specification, X-r ay diffraction, Hall effect and C-V profiling revealed significant differen ces between them. Wafers from two of the suppliers showed poor inter-device isolation characteristics, indicative of a conducting buffer layer. Wafers from the third supplier showed excellent inter-device isolation, but C-V m easurements showed that the AlGaN was about twice as thick as specified, re sulting in devices with high pinch-off voltages ( similar to -16 V). For th e wafers with poor buffer isolation, RF measurements on 1.2 mum gate length devices gave values of f(T) similar to 5.0 GHz and values of f(max) from 8 .0 to 11.7 GHz (exact values depending on DC bias conditions), while for th e wafer with over-thick AlGaN the corresponding values were 8.0 and 20.0 GH z. (C) 2001 Elsevier Science B.V. All rights reserved.