Electron energy distributions from GaP with negative electron affinity. I. Emission properties of thermalized electrons

Abstract

Photoelectron energy distributions are measured on negative electron affinity (NEA) GaP (100) surfaces for near‐band‐gap photon energy as a function of the activation conditions with Cs or Cs and O₂. X electrons in NEA GaP have a low escape probability unless Cs‐O activation is used and the work function reduced to less than 1 eV. Measured energy distribution curves are much broader than for GaAs, up to 0.8 eV (FWHM); their widths are limited by the work function. These results are interpreted by taking into account electron reflection at the surface which enhances the probability of inelastic scattering in the space‐charge region. High surface reflection is attributed to the noncentral conduction‐band minima of GaP and to Bloch‐wave matching conditions at the surface. A multivalley transport model in the space‐charge region is presented which includes these effects. Energy distribution widths given by this model are in reasonable agreement with experiment.