Electronic and Phonon Deformation Potentials of GaN and AlN:Ab initio Calculations versus Experiment

The structural, electronic, and lattice-dynamical properties of homogeneously strained wurtzite GaN and AlN are studied ab initiousing a pseudopotential-plane-wave method and a linear-response approach to the density-functional theory. The elastic properties are characterized by the stiffness constants. Electronic and phonon deformation potentials as well as biaxial stress coefficients are determined. Discrepancies between experimental and theoretical results for the stress coefficients are widely due to deviating parameters and an incorrect stress–strain relation. We show that the biaxial stress coefficient of the high-frequency E2 phonon and of the electronic band gaps should be smaller than they were commonly determined so far. We find that the quasicubic approximation is not valid for the electronic deformation potentials of GaN but is reasonable for those of AlN instead.