Effect of growth termination conditions on the performance of AlGaN/GaN high electron mobility transistors

The effect of the growth conditions of the top 2.5 nm thick AlGaN cap layer and wafer cool down conditions on AlGaN/GaN high electron mobility transis tor performance was investigated. The AlGaN/GaN heterostructures were depos ited on sapphire by metalorganic chemical vapor deposition and consisted of a 3 mum thick semi-insulating GaN layer and an 18 nm thick Al0.33Ga0.67N l ayer, the top 2.5 nm of which was deposited under various conditions. The p ower performance of the devices severely degraded for all samples where the Al content of the top 2.5 nm of AlGaN was increased and/or the ammonia flo w during growth of the top layer was decreased. A modest improvement in the output power density was observed when the growth conditions of the cap la yer were identical of those of the rest of the AlGaN layer, but when the wa fer was cooled down in pure nitrogen. (C) 2001 American Institute of Physic s.