Effects of excitation density on cathodoluminescence from GaN

Wurtzite GaN epilayers are studied by cathodoluminescence (CL) spectroscopy. Results show that the intensities of donor–acceptor pair (DAP) and yellow luminescence (YL) peaks sublinearly depend on excitation density, presumably, due to saturation effects. The intensity of near-gap emission, however, exhibits a superlinear dependence on electron-beam excitation. In contrast to photoluminescence measurements, CL studies of GaN are usually performed in a regime with a strongly nonlinear dependence of luminescence intensities on excitation due to a large difference in carrier generation rates for these two techniques. As a result, the ratios of near-gap to YL and DAP emission intensities strongly depend on electron-beam current. Moreover, electron-beam spot size (i.e., beam focusing) dramatically affects CL intensity. An understanding of such saturation effects is necessary for a correct interpretation of CL spectra from GaN.