High-electron-mobility GaN grown on free-standing GaN templates by ammonia-based molecular beam epitaxy

The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n−-GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2 × 106 cm−2 to ∼2 × 1010 cm−2) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimized GaN growth on free-standing GaN templates with a low TDD (∼2 × 106 cm−2) resulted in electron mobilities of 1265 cm2/Vs at 296 K and 3327 cm2/Vs at 113 K.