Effect of pressure on exciton energies of homoepitaxial GaN

Optical reflectance spectra of a homoepitaxial gallium nitride layer were measured under high pressure (0-10 GPa) at low temperature (10 K). The layer was grown by metalorganic chemical vapor deposition on a GaN single crystal. The pressure dependencies of the A, B and C exciton resonance energies have been determined. A value of dE(g)/dP = 43.2(6) meV GPa(-1) is obtained for the linear pressure coefficient of the lowest band gap energy of GaN. Eased on changes of energy splittings between the A, B and C excitons, we conclude that the pressure dependence of the crystal field splitting parameter of GaN is very weak (0.4 meV GPa(-1)). This is indirect evidence that the atom coordination remains close to perfectly tetrahedral under hydrostatic pressure. (C) 1998 Elsevier Science Ltd. All rights reserved.