Depth-Resolved and Excitation Power Dependent Cathodo-Luminescence of MBE Grown Cubic GaN Epilayers

Abstract

AbstractWe present a detailed investigation of the cathodoluminescence (CL) of MBEgrown cubic GaN (c-GaN) epitaxial layers. Under high excitation conditions the room temperature CL-spectrum is dominated by a single excitonic emission band at about 3.21 eV with a full width at half maximum of 55 meV. Under low electron beam excitation a second, deep emission band at 2.4 eV is observable. A strong variation of the ratio between the deep luminescence intensity and the near band edge luminescence intensity ratio is observed with increasing excitation intensity. Using a simple model based on bimolecular rate equations the concentration of defects involved in this transition is estimated to be about 1015 cm−3. CL-measurements with varying excitation intensity reveal that these recombination levels have only minor influence on the performance of high injection optoelectronic devices like laser diodes. Depth resolved measurements and CL-images from a cleaved c-GaN/GaAs reveal that the deep recombination centers are homogeneously distributed within the epilayer, however the concentration of nonradiative recombination centers is increasing towards the GaN/GaAs interface.