Growth of AlGaN/GaN heterojunction field effect transistors on semi-insulating GaN using an AlGaN interlayer

Semi-insulating (SI) GaN layers were grown on 4H-SiC substrates by inserting an AlGaN layer between the AlN buffer and the GaN layer. Secondary ion mass spectroscopy measurements showed that the AlGaN layer prevented Si from diffusing from the substrate into the GaN layer. X-ray diffraction and atomic force microscopy analyses showed that an optimized AlGaN interlayer does not degrade the crystal quality or surface morphology of the SI GaN. The room temperature mobility of an AlGaN/GaN heterostructure using this SI GaN was 2200 cm2/V s. High electron mobility transistors (HEMTs) with 0.65 μm long gates were also fabricated on these SI GaN buffers. A power density of 19.0 W/mm with a power added efficiency of 48% was demonstrated at 10 GHz at a drain bias of 78 V. These HEMTs also exhibited sharp pinch off, low leakage, and negligible dispersion