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We present measurements of the transverse and longitudinal energy spread of photoelectrons emitted from a GaAsP photocathode as a function of its degradation state. The cathode was initially activated to a state of negative electron affinity in our photocathode preparation facility, achieving a quantum efficiency of 3% at a wavelength of 532 nm. It was then transferred under XHV conditions to our transverse energy spread spectrometer, where energy spread measurements were made while the photocathode was progressively degraded through a controlled exposure to oxygen. Data have been collected under photocathode illumination at 532 nm, and the changing photoelectron energy distribution associated with the changes in the level of electron affinity due to quantum efficiency degradation through an exposure to 0.25 L of oxygen has been demonstrated. Our experiments have shown that GaAsP boasts a significantly higher resilience to degradation under exposure to oxygen than a GaAs photocathode, though it does exhibit a higher level of mean transverse energy. Coupled with the favourable published data on GaAsP photoemission response times, we conclude that GaAsP is a viable candidate material as a particle accelerator electron source.

Long-wavelength shift and enhanced room temperature photoluminescence efficiency in GaAsSb/InGaAs/GaAsbased heterostructures emitting in the spectral range of 1.0-1.2 μm due to increased charge carrier's localization

The evolution of surface band bending and surface photovoltage was monitored in situ by photoreflectance spectroscopy during activation of the surface of epitaxial GaAs to the state of negative electron affinity by successive deposition of cesium and oxygen in a standard ‘‘yo-yo’’ technique. Considerable variations of the band bending (by approximately 0.3 eV) and surface photovoltage (by three orders of magnitude) were observed. It was found that the maximum of photoemission quantum yield corresponded to unexpectedly small value of the band bending φs=0.3 eV, as compared to widely accepted value of approximately 0.5 eV.