Epitaxy of GaN by MOCVD and fabrication of AlGaN/GaN MODFET

A vertical type metal organic chemical vapor deposition (MOCVD) reactor was used to grown GaN films on c-face sapphire substrates. Ammonia and trimethylgallium were induced to the reactor separately through the specially designed shower-head. In the growth procedure, firstly, the substrate was heated in a fully hydrogen environment to 1100°C and continued for 10 minutes to diminish the surface damage. Then at 1100°C this high temperature and just before next temperature decreasing procedure, the surface nitridation was performed in a mixed hydrogen/ammonia condition for several minutes. Then the substrate temperature was decreased to 520°C to grow the GaN buffer layer on the nitridation sapphire surface. The hydrogen/ammonia flow ratio was also varied in this experiment. The nitridation effect on the quality of undoped GaN epitaxial layer was studied. the AlGaN/GaN heterojunction of 200/2000 Å was used to fabricate the modulation doped FET. The maximum drain current was above 30 mA at the gate voltage of 1 V. Knee voltage of this device was about 8 V. The maximum transconductance of the device with 2 μm gate length was 50 mS/mm at the gate voltage of 1 V