The influence of OMVPE growth pressure on the morphology, compensation, and doping of GaN and related alloys

Growth pressure has a dramatic influence on the grain size, transport chara cteristics, optical recombination processes, and alloy composition of GaN a nd AlGaN films. We report on systematic studies which have been performed i n a close spaced showerhead reactor and a vertical quartz tube reactor, whi ch demonstrate increased grain size with increased growth pressure. Data su ggesting the compensating nature of grain boundaries in GaN films is presen ted, and the impact of grain size on high mobility silicon-doped GaN and hi ghly resistive unintentionally doped GaN films is discussed. We detail the influence of pressure on AlGaN film growth, and show how AlGaN must be grow n at pressures which are lower than those used for the growth of optimized GaN films. By controlling growth pressure, we have grown high electron mobi lity transistor (HEMT) device structures having highly resistive (105 Ohm-c m) isolation layers, room temperature sheet carrier concentrations of 1.2 x 10(13) cm(-2) and mobilities of 1500 cm(2)/Vs, and reduced trapping effect s in fabricated devices.