Cathodoluminescence of homogeneous cubic GaN/GaAs(001) layers

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Abstract
The cathodoluminescence (CL) of cubic (c-) GaN epitaxial layers is investigated at temperatures between 50 K and 300 K. The low temperature CL spectra show three well resolved emission lines (3.26 eV, 3.17 eV and 3.08 eV) which are due to excitonic, donor-acceptor and free to acceptor transitions. Spatially resolved measurements of the intensity of the excitonic emission demonstrate the homogeneity of the layers which are free of microcrystalline inclusions. The room temperature CL of the layers has a full width at half maximum of 56 meV and is due to excitonic recombination as is concluded from the zero-shift of the line position when the excitation intensity is varied over some orders of magnitude. The intensity of a broad emission band at 2.4 eV shows a strong nonlinear variation of the intensity at high excitation levels. Using a rate equation model for the near band edge and the deep 2.4 eV emission we are able to describe the intensity variation of these radiative transitions as a function of the excitation intensity. Depth resolved CL measurements reveal a homogeneous depth distribution of deep recombination centres responsible for the deep 2.4 eV luminescence band.