CATHODOLUMINESCENCE IMAGING OF QUANTUM-WELLS - THE INFLUENCE OF EXCITON TRANSFER ON THE APPARENT ISLAND SIZE

We demonstrate the influence of lateral exciton transfer on the resolution in cathodoluminescence images and thereby the apparent island size in monolayer-flat (ML-flat) areas in quantum wells (QW's). The QW used in this study exhibits two peaks originating in regions of two different QW thicknesses, differing by 1 ML. A variation of the exciton transfer is achieved by altering the temperature. When the temperature is increased from 20 to 120 K, the ratio between the low-energy and the high-energy peak is increased by over a factor of 5, caused by an increased lateral transfer. At 20 K the images of the two peaks show a high degree of complementary behavior and features of about 0.5 μm can be resolved. The contrast and the complementary behavior is reduced with increased temperature, i.e., increased transfer, and at 110 K the smallest features observed are about 1 μm. We also suggest a model, where the ML-flat areas in reality are clusters of microislands. These clusters appear to be extended islands of a single thickness, due to a one-way transfer of excitons from thinner to thicker microislands. The sizes of these apparently extended islands are discussed in terms of a diffusion-length-dependent critical density of microislands. © 1994 The American Physical Society.