Transverse effective charge and its pressure dependence in GaN single crystals

The pressure dependence of the A(1)(TO) and A(1)(LO) phonon modes of bulk, single crystals of wurtzite GaN has been measured by Raman scattering in a diamond-anvil cell up to 40 GPa. The measured phonon frequencies have been used to determine the LO and TO phonon-mode Gruneisen parameters and also t he value of effective transverse charge e(T)* = 2.6 and its pressure deriva tive de(T)*/dP = -2.4x10(-3) GPa(-1). The experimentally obtained values ar e compared with results of calculations by means of tight-binding formalism combined with ab initio linear muffin-tin orbital calculations. [S0163-182 9(99)05027-4].