An AlGaN/GaN high-electron-mobility transistor with an AlN sub-buffer layer

The AlGaN/GaN high-electron-mobility transistor requires a thermally conducting, semi-insulating, substrate to achieve the best possibie microwave performance. The semi-insulating SiC substrate is currently the best choice for this device technology; however, fringing fields which penetrate the GaN buffer layer at pinch-off introduce significant substrate conduction at modest drain bias if channel electrons are not well confined to the nitride structure. The addition of an insulating AIN sub-buffer on the semi-insulating SiC substrate suppresses this parasitic conduction, which results in dramatic improvements in the AlGaN/GaN transistor performance. A pronounced reduction in both the gate-lau and the gate-leakage current are observed for structures with the AIN sub-buffer layer, These structures operate up to 50 V drain bias under drive, corresponding to a peak voltage of 80 V. for a 0.30 mum gate length device. The devices have achieved high-efficiency operation at 10 GHz (>70% power-added efficiency in class AB mode at 15 V drain bias) and the highest output power density observed thus far (11.2 W mm(-1)). Large-periphery devices (1.5 mm gate width) deliver 10 W (continuous wave) of maxi-mum saturated output power at 10 GHz. The growth, processing, and performance of these devices are briefly reviewed.