Advances in wide-bandgap semiconductor based photocathode devices for low light level applications

摘要

Our work with GaN based photocathodes shows a strong dependence on the photo-emission response versus the carrier concentration and conductivity of the films. Films with quantum efficiency (QE) as high as 56% in opaque mode and as high as 30% in transmission mode have been made. Although surface activation plays a key role, the characteristics of the films, e.g. the thickness, film structure, minority carrier diffusion length, and doping, all play a role in affecting the photo-emission QE and especially its spectral dependence. The QE of films with the various properties is discussed and the utility of using measurements of the film properties to predict the optimal performance of the resulting photocathode is demonstrated.