Ground-state characteristics of an acceptor center in wide-gap semiconductors with a weak spin-orbit coupling

Spin-orbit splitting, strain-potential constants, and the g factor of the acceptor-center ground state described by a superposition of a Coulomb and a central-cell potential have been calculated for wide-band-gap semiconductors, such as GaN. Analytical expressions for these parameters, which depend only on the light-to heavy-hole mass ratio, have been obtained within the zero-range potential model. It is shown that the differences between these parameters for the limiting cases of purely Coulomb and zero-range potentials do not exceed 7%, thus permitting one to use for estimates simple analytical expressions. Calculation of the acceptor-center ground state made for the hexagonal modification of GaN suggests a strong anisotropy of the g factor, whereas measurements yield a practically isotropic value of g close to that of a free electron. This contradiction is removed if a spontaneous strain due to the Jahn-Teller effect appears perpendicular to the C 6 axis of the crystal near the acceptor center.