Electron energy distributions from GaP with negative electron affinity. II. Near-uv photoemission and secondary emission

Abstract

Near‐uv photoelectron energy distributions and spectral quantum yields are measured on high‐efficiency carbon‐free (100) GaP epitaxial layers activated to negative electron affinity (NEA) with Cs or Cs and O₂. Energy distributions show that near‐uv photoelectrons thermalize at both X and L conduction‐band minima even for electrons excited by direct Γ^v₁₅→Γ^c₁ transitions. A two‐valley diffusion model gives an accurate quantitative description of the quantum yields and is consistent with the observed energy distribution curves. Secondary‐electron energy distributions are given. Thermalization effects at X and L conduction‐band minima are also obvious here, but the proportion of hot electrons is higher than has generally been suspected up to now. The hot electron distributions show structure which corresponds to maxima and minima of the density of states in the conduction band at the surface. This can be used in a simple experiment to measure the amount of band bending at the surface. 1.65 and 1.4 eV are obtained for Cs and Cs‐O activated surfaces, respectively.