In this letter, the excitonic emissions from ZnO epilayers were studied by depth-resolved cathodoluminescence (CL) microanalysis. An excellent agreement between the redshift of the experimental depth-resolved CL emission and theoretically simulated values was observed, which clearly identified its origin to be the strong internal absorption in ZnO epilayer. Moreover, the rigorous Monte Carlo simulated CL generation profiles with the correction of self-absorption exhibit the reasonable correspondence with the measured CL intensities. The intensity discrepancies for low and high excitation cases have been interpreted by the occurrence of the excess carrier nonradiative recombination on the surface space charge layer and the exciton nonradiative quenching processing by defects or structural disorders near the interface of ZnO and sapphire.
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The recorded CL spectra have been corrected by the overall detection system response factor. Moreover, the additional CL measurements show that the intensity of CL NBE emission exhibits almost linear dependence on excitation current with fixed beam energy (, ). It means that no saturation effects will occur in the range of beam current used in this study, which is applicable for the depth-resolved microanalysis.
