Investigation of surface properties of Si-doped GaN films by electric force microscopy and photoluminescence

Results of the electric force microscopy (EFM) and photoluminescence (PL) measurements in a set of Si-doped GaN films are presented. The EFM measurements indicate that substantial surface states exist in GaN thin films and the density of surface states is reduced with the Si doping concentration. It is found that this result strongly correlates with the optical properties of the epifilms. We show that the ratio of near-band edge luminescence of the front-side and back-side PL spectra increases with the doping concentration. This behavior manifests the effects of the surface states on the luminescent properties of GaN. Our investigation therefore not only shows the important role of surface states on the optical properties of GaN, but it also reveals that the combination of EFM and optical techniques is a very powerful way to understand the physical properties of a thin film.