Non–monotonic behaviour in the mean transverse energy of electrons emitted from a reflection–mode p-GaAs(Cs,O) photocathode during its QE degradation through oxygen exposure

Abstract We present a study on the evolution of both transverse and longitudinal energy distributions due to oxygen–induced quantum efficiency degradation in the electrons emitted from a reflection–mode p-GaAs(Cs,O)-photocathode over an effective electron affinity range of χ *∼ −0.1 eV to χ *∼ +0.3 eV under illumination wavelengths λ = 808, 635 and 532 nm. For λ = 635 and 532 nm, we found that the mean transverse energy of electrons emitted as the photocathode effective electron affinity increased has a non–monotonic character. Our proposed fitting model links the measured response to changes in the relative number of thermalised and non–thermalised electrons in the total emitted photocurrent.