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A method by which negative electron affinity GaAs photocathodes can be made to recover their photoyield following decay is reported. The source of decay can be either an oxidizer in the background gas or gas introduced through deliberate dosing. Conventional methods employ the use of the alkali Cs as the photoyield recovery agent. This work describes an alkali application-free method, similar to electron stimulated desorption, for photoyield recovery.

Amorphous silicon and amorphous silicon germanium photoemitters grown via radio frequency plasma enhanced chemical vapor deposition have been investigated to determine their usefulness as photoinjector electron sources. Characterized properties include activation process, wavelength dependent photoyield, germanium induced photoyield shift, background gas and ion sensitivities, and average transverse emission energy. While overall lower in yield than the GaAs photoemitter, many of their properties are comparable. The amorphous silicon photoemitter robustness upon gas and ion exposure is superior to that of GaAs. The combined properties of amorphous silicon germanium photoemitters make them ideal candidates for low cost photoinjector sources or as protective photoemitting layers on more sensitive photogenerating materials.

Negative electron affinity GaAs photoemitters require ultrahigh vacuum conditions to achieve the best performance and to maintain the quantum yield. This limits their utility in applications where the background pressure is high. The authors have developed an activation procedure by which the reactivity to CO2, a principal cause of yield decay, is greatly reduced. The use of a second alkali in the activation process is responsible for the increased immunity of the activated surface. The best immunity was obtained by using a combination of Cs and Li without any loss in near band gap yield.

An anisotropy in the quantum efficiency (QE) has been observed in photoemission from strained GaAs photocathodes excited by linearly polarized light. The wavelength dependence of the anisotropy is closely correlated with that of the electron-spin polarization. Based on a theoretical analysis, we show that the QE anisotropy is caused by an in-plane strain anisotropy arising from anisotropic strain relaxation. The QE anisotropy calculated from the in-plane strain anisotropy measured with X-ray diffraction and the measured QE anisotropy are in good agreement.

The successful operation of a GaAs‐based polarized electron source utilizing a DC high voltage gun for the SLC program at SLAC has raised the prospects for a similar source for next generation linear colliders (NGLC). A major challenge in meeting the NGLC requirements is to produce ≳1012 electrons per macrobunch from the cathode. The physics issues that are involved in limiting charge extraction from a GaAs‐type cathode and the prospects of realizing a NGLC polarized electron source based on an SLC‐type gun will be discussed.