Impact of electron beam irradiation on the cathodoluminescence intensity for ZnO and GaN

We have studied the effect of the electron beam irradiation on ZnO and GaN by using cathodoluminescence (CL). The bandedge emissions of ZnO and GaN usually decrease during CL observation, but they can increase in certain cases, such as Zn-plane in ZnO. These variations depend on not only the specimens and the electron beam conditions but also the nature of the luminescence centers and the chemical nature of the material surface. This work suggests that the electron beam induces some modifications near the surface region.