Second harmonic generation of GaN(0001)

Second harmonic generation (SHG) spectra of the Ga- and N-terminated GaN(0001) surfaces have been studied by using the first-principles full potential linearized augmented plane-wave method, Equilibrium surface geometries are determined through the total-energy minimization method. The calculated SHG spectra in the low-energy spectral range are dominated by the two-photon resonances associated with the surface states, while in the high energy range the SHG responses are contributed from the bulk states. Adsorption of Ga on the N-terminated GaN(0001) surface results in a substantial evolution of the surface related SHG features.