Effects of the AlN Interlayer on the Distribution and Mobility of Two-Dimensional Electron Gas in AlGaN/AlN/GaN Heterojunctions

Al 0.25 Ga 0.75 N/AlN/GaN heterojunctions with AlN interlayers of various thicknesses were grown on c-plane sapphire by metalorganic vapor phase epitaxy (MOVPE). We have revealed that the AlN interlayer hardly affects morphologies and crystal qualities; however, it prominently enhances the two-dimensional electron gas (2DEG) mobility. The optimum thickness of the AlN interlayer is 1 nm, and the corresponding room temperature Hall mobility and the sheet carrier density are 1700 cm 2 V -1 s -1 and 1.27 ×10 13 cm -2 , respectively. Self-consistent calculation results indicates that with increasing AlN thickness, i) the conduction-band discontinuity between AlGaN and GaN linearly increases; ii) the percentage of the total carriers in the AlGaN layer exponentially decreases, and content in the AlN layer exponentially increases.