Dependence on Crystalline Face of the Band Bending in Cs2 O-Activated GaAs

Abstract

Electron energy loss in the band-bending region of the p-type III–V semiconductor in a III–V photocathode is an important factor in determining the escape probability and the optimum doping. From measurements of photoelectric yield near threshold from Cs2O-activated n-type GaAs, the position of the Fermi level at the GaAs–Cs2O interface was determined for {110}, {100}, {111A}, and {111B} surfaces. Assuming the Fermi-level position at the GaAs surface to be independent of doping, the band bending for p-type GaAs is greatest for the {111A} face and least for the {111B} face. The measured escape probabilities of photoexcited electrons from different crystalline faces of optimally activated 5 × 1018/cm3 Zn-doped liquid epitaxial GaAs correlate well with the band-bending measurements. The {111B} sample has an escape probability of 0.489 and a luminous sensitivity of 1837 μA/lm.