High hole mobility in AlN from negative crystal-field splitting

Group-III nitrides are key semiconductors for power electronics and optoelectronics. Among them, AlN is particularly promising since it possesses an ultrawide bandgap, high breakdown field, and excellent thermal conductivity. In anticipation of the experimental realization of p-doped AlN, we report a state-of-the-art first-principles study of the hole mobility in AlN, and a comparison with the more established GaN. We compute phonon- and impurity-limited mobilities using the ab initio Boltzmann transport equation, and include spin-orbit coupling, long-range dipole and quadrupole corrections, and GW quasiparticle bands. We obtain a theoretical hole mobility of 178 cm2/Vs at room temperature along the c axis, significantly higher than the hole mobility of GaN. The superior mobility of AlN originates from its negative crystal-field splitting, which places the split-off holes at the top of the valence bands and far above the heavy holes.