Abstract
The GaAs negative electron affinity photoemission mechanism is studied using the full Bloch wave nature of the incident electron. It is found that the experimentally observed anisotropy between A and B faces is a basic result of the heteropolar nature of the GaAs, contrary to previous interpretations. The physical principles behind the numerical results are illustrated and analysed using a simple method for the scattering which illustrates the origin of the very large anisotropy observed.