Franck-Condon electron emission from polar semiconductor photocathodes

TL;DR

This paper develops an analytical model for phonon-mediated Franck-Condon electron emission in polar semiconductors, accurately matching experimental data and predicting emission properties based on material parameters.

Contribution

It introduces a new analytical formulation for phonon-mediated electron emission that aligns well with experimental observations of GaAs and GaN photocathodes.

Findings

Model accurately predicts quantum efficiency and transverse energy.

Good agreement with experimental emission spectra.

Surface roughness effects are minimal for polar semiconductors.

Abstract

A presented analytical formulation of (optical)phonon-mediated and momentum-resonant Franck-Condon emission of photoexcited electrons from polar semiconductors is shown to be very consistent with (i) the observed emission properties of a Cesiated GaAs(001) photocathode at 808nm [J. Phys. D: Appl. Phys. 54, 205301 (2021)] and (ii) the measured spectral emission properties of a GaN(0001) photocathode from just below its bandgap energy to 5eV. The theoretical analysis in the parabolic band approximation predicts the form of both the quantum efficiency and mean transverse energy of photoemission as a function of the photocathode's electron affinity and the electron temperature in the vicinity of its emission face. The good agreement between theory and experimental data also suggests that sub-10nm rms surface roughness effects are not significant for polar semiconductor photocathodes.