Analyses of recombination velocities at grain boundaries by cathodoluminescence: control of injection level and effect of grain-boundary inclination angle

Cathodoluminescence (CL) analyses of semiconductor materials are routinely employed for the determination of optoelectronic properties. By evaluating CL intensity profiles across grain boundaries (GBs) in polycrystalline semiconductors, the GB recombination velocities can be determined. However, in any CL experiment, control of the injection level is essential, and up to now, there has not been a corresponding, reliable approach. The present work provides such an approach consisting of the analysis of the CL intensity acquired at various beam energies and beam currents, combined with the simulation of the excess-charge carrier density at these beam parameters. It is shown that the CL intensity profiles and therefore, the GB recombination velocities differ strongly when acquiring CL intensities at low and at high injection. Moreover, the present work provides a model for the simulation of CL intensity profiles at GBs, taking into account an inclination angle of the GB with respect to the semiconductor surface. The simulation results show that GB recombination velocities are not affected by the GB inclination angle.