Optical Imaging of Diffusive Electrons with Different Kinetic Energies in a Semiconductor

Abstract

Author's Summary: When electrons in a semiconductor are generated by light, they can diffuse for a certain distance before being recombined. The length of diffusion is indicative of the material quality but, unfortunately, the motions of the electrons are difficult to observe directly. The focus of this project was to find a simple and effective way to measure the diffusion length of electrons in a semiconductor material. A laser was used to generate electrons in a small area and an imaging camera was used to map their distribution through the light they emitted as they diffused. This technique can be implemented to quickly and accurately assess the quality of any semiconductor material. AbstractIn this project, a photoluminescence (PL) imaging technique was developed for probing electron diffusion in a semiconductor thin film. This technique was applied to investigate electron diffusion in GaAs for electrons of different kinetic energies. A tightly focused laser beam at 532 nm was used to generate electrons in an area of about 0.72 μm, and the spatial profile of the PL in an area much larger than that of the laser excitation site was imaged by a digital camera. Analysis of the PL images at different wavelengths indicated that the electrons maintain the same thermal distribution during diffusion and exhibit a common diffusion length of approximately 3.5 ± 0.2 μm.