  The anticorrelation between quantum efficiency (QE) and electron spin
polarization (ESP) from a p-doped GaAs activated to negative electron affinity
(NEA) is studied in detail using an ensemble Monte Carlo approach. The
photoabsorption, momentum and spin relaxation during transport, and tunnelling
of electrons through the surface potential barrier are modeled to identify
fundamental mechanisms, which limit the efficiency of GaAs spin-polarized
electron sources. In particular, we study the response of QE and ESP to various
parameters such as the photoexcitation energy, doping density, and electron
affinity level. Our modeling results for various transport and emission
characteristics are in a good agreement with available experimental data. Our
findings show that the behaviour of both QE and ESP at room temperature can be
fully explained by the bulk relaxation mechanisms and the time which electrons
spend in the material before being emitted.
