Cathodoluminescence study of undoped GaN films: Experiment and calculation

In this paper, we report the theoretical and experimental results of cathodoluminescence (CL) from GaN layers grown at 800 °C by metal organic vapor phase epitaxy (MOVPE) on silicon substrate. The CL spectra recorded at room temperature reveal the near band-edge emission at 3.35–3.42 eV and a broad yellow luminescence at 2.2 eV. The CL depth analysis at constant power excitation shows inhomogeneous CL distribution in depth of these emissions as the electron beam increases from 3 to 25 keV. There appears a blue shift of the CL band-edge peaks with increasing sample depth. This behavior is explained by a change of the fundamental band gap due to residual strain and the local temperature rise under high electron beam excitation. The simulation of the CL excitation and intensity is developed using a consistent two-dimensional (2-D) model based on the electron beam energy dissipation and taking into account the effects of carrier diffusion, internal absorption and the recombination processes in GaN. The influence of electron beam local heating and respective strain effects on the CL signal are also discussed. A comparative study between experimental and simulated CL spectra at room temperature was performed.