Near-threshold photoemission characterization of K2CsSb photocathodes

We present a near-threshold photoemission study of K2CsSb photocathodes, examining the quantum efficiency (QE), mean transverse energy (MTE), and electron energy distributions (EEDs) over a wide range of photon energies. The work function is determined to be 1.65 ± 0.1 eV from EED measurements. Near threshold, both QE and the high-energy tail of the emitted-electron distribution exhibit a universal exponential dependence characterized by an energy scale of ∼38.5 meV. A direct comparison with Cs3Sb reveals strikingly similar near-threshold features in QE and MTE spectral response, and energy-distribution shapes. Our results demonstrate that near-threshold photoemission in alkali-antimonide photocathodes is governed by the combined effects of disorder and electron–phonon coupling-induced band-tail states along with transport scattering-driven energy redistribution.