Effective masses and valence-band splittings in GaN and AlN

Full-potential (FP) linearized muffin-tin orbital (LMTO) calculations within the local density approximation are used to determine the conduction and valence-band effective mass tensors and the related Rashba-Sheka-Pikus and Kohn-Luttinger Hamiltonian parameters for wurtzite and zinc-blende GaN and AlN. Spin-orbit coupling effects are obtained from atomic-sphere approximation (ASA) LMTO calculations. The $c$-axis uniaxial strain dependence of the crystal field splitting is determined and the combined results are used to interpret experimental data on the strain dependence of exciton splittings in GaN. Corrections beyond the local density approximation on the effective masses and crystal-field splittings as well as the accuracy of the quasicubic model are discussed.