Photoelectron thermalization near the unpinned surface of GaAs(Cs,O) photocathode

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Abstract
The longitudinal component of the photoelectron energy distribtuion from a transmission mode GaAs photocathode with quantum efficiency up to 18% is accurately measaured by using Generation III image intensifier as a parallel plates retarding field electron energy analyzer. The measurements are performed within the temperature range of 77-300 K with different photon energies for photoelectron excitation above or below the band gap of semiconductor. It is shown that conduction band tails in heavily doped GaAs influence photoelectron transport near the surface during the process of emission into vacuum. The transmission coefficient of a residual surface barrier is measured as a function of electron kinetic energy above the conduction band minima and is found to be much less than unity. The obtained results demonstrate the usefulness of this technique for the investigation of the physical factors which control the quantum efficiency and other parameters of photocathodes with neagitive electron affinity.

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