Influence of the dopant concentration on the photoemission in NEA GaAs photocathodes

Abstract The influence of impurity concentration on the photoemission from Negative Electron Affinity (NEA) GaAs photocathodes has been investigated. Experimental curves of photoemission spectral sensitivity are obtained for several dopant concentrations and when normalized to their peak value their spectral response shows three zones of well differentiated behaviour, in good agreement with theoretical predictions derived in this work. For illumination with wavelengths below ≈ 800 nm, photoemission is dominated by the escape probability. Higher concentration leads to higher normalized photoemission sensitivity. For wavelengths between ≈ 800 and 910 nm, the dominant role is played by the diffusion length of electrons in the bulk. Higher normalized sensitivity is obtained for lower concentration. For wavelengths above ≈ 910 nm, photoemission is dominated by the absorption coefficient, which depends on concentration through the value of the gap energy. The behaviour of sensitivity with concentration in this spectral zone is similar to that of wavelength shorter than 800 nm.