Photoemission from p-GaAs(Cs,O) under transition from negative to positive electron affinity

Abstract

Abstract The evolution of the electron escape probability from p-GaAs(Cs, O) to vacuum was measured under the transition from the state of negative to the state of positive electron affinity. The transition was induced by the deposition of excess cesium or oxygen on the p-GaAs(Cs, O) surface activated to the state of negative electron affinity. Under deposition of excess cesium, the escape probability was significantly lower as compared to excess oxygen, presumably, due to reflection and scattering of electrons on two-dimensional cesium metal clusters. Under Cs-induced transition, at positive values of affinity, a new peak was observed below the band gap in the photoemission quantum yield spectra. The peak stems, presumably, from: (i) the effective capture of sub-bandgap light in the structure, which consists of the heavily doped p +-GaAs epilayer grown on the semi-insulating GaAs substrate, due to diffuse backside reflection from the rough back surface of the substrate; (ii) absorption of the captured light near the emitting p +-GaAs surface due to the Franz-Keldysh effect in the strong surface electric field; (iii) emission of the electrons generated near the surface.