Calculated electron energy distribution of negative electron affinity cathodes

G Vergara,A Herrera-Gómez,W.E Spicer

doi:10.1016/s0039-6028(99)00612-3

G Vergara, A Herrera-Gómez + Show 1 more

https://doi.org/10.1016/s0039-6028(99)00612-3

Copy DOI

Export

Save

Cite

Abstract
Full-Text
Similar Papers

Abstract

Listen

In this paper we present a model whose purpose was to study the electron energy distribution curves (EDC) of high efficiency negative electron affinity (NEA) GaAs photocathodes and to explain the features of earlier experimental data. The EDCs were calculated for transmission mode cathodes using the Monte Carlo method. The influence of parameters such as the surface potential barrier shape, p-doping concentration, vacuum level (VL), and temperature on the EDC broadening was studied. Using our model, we found that the experimental electron energy spread could be explained by the extra time the electrons spend inside the semiconductor due to multiple bouncing at the surface before escaping. There is no need to invoke electron interaction with surface trapping states. The difference between the effective electron mass in the semiconductor and the mass in the vacuum causes a refraction effect that narrows the escape angle around the surface normal. In accordance with the dipole model for NEA, the surface barrier was modeled in two sections: a triangular barrier at the surface and a flat plateau outside the semiconductor at the vacuum level. The magnitude of the energy distribution width of the experimental data studied indicates that the electrons spend a long time in the band bending region before escaping, which in turn indicates that the electrons are quantum reflected at the surface barrier a number of times before their final escape. This barrier is very sensitive to surface preparation details. The experimental data indicates that, for the high yield cathode considered, the vacuum level lies ∼0.1 eV below the bulk conduction band minimum and that the modeled triangular potential at the surface barrier was approximately 1.5 A thick and 4 eV high. In the case of this barrier, the escape probability for electrons hitting the surface with energy between the vacuum level and 0.2 eV above was smaller than 0.2.

Full Text