Composition and interface quality control of AlGaN / GaN heterostructure and their 2DEG transport properties

The effects of NH₃ flow rate and reactor pressure on Al composition and the interface of AlGaN/GaN heterostructure were studied. Equilibrium partial pressure of Ga and Al over AlGaN alloy was calculated as a function of growth pressure, NH₃ flow rate and temperature. It was found equilibrium vapor pressure of Al is significantly lower than that of Ga, thus, the alloy composition mainly controlled by Ga partial pressure. We believe that more decomposition of Ga occur at lower NH₃ flow rate and higher growth pressure leads to preferred Al incorporation into AlGaN. The alloy composition gradient became larger at AlGaN/GaN heterointerface at higher reactor pressures, higher Al composition and low NH₃ flow rate. This composition gradient lowered sheet carrier concentration and electron mobility as well. We obtained an AlGaN/GaN heterostructure with sheet carrier density of ~2×10¹³ ㎝-² and mobility of 1250 and 5000 ㎤/Vs at 300 K and 100 K, respectively.