Spin polarized photoemission from molecular beam epitaxy-grown Be doped GaAs

We have made a comparative study of the performance of spin polarized photocathodes based on molecular beam epitaxy (MBE) grown GaAs with Be-doping and on liquid phase epitaxy (LPE) grown GaAs with Zn-doping. The experiments were performed on GaAs (100), (110), and (111) surfaces atT-300 K. The photoelectron spin polarization (P) of the MBE-photocathodes is face dependent reaching 49% for the (111) surface, a value close to P=50% predicted by theory. In contrast for the LPE-photocathodes P is significantly lower (19≲P≲36%). Possible causes for the higher polarization of the MBE-photocathodes are investigated. The influence of the Zn- and Be-dopant is elucidated by theoretical model calculations which shows that replacing the Zn-dopant by Be reduces significantly the depolarization at very low temperatures, but not at room temperature. It is therefore concluded that theinterface region between the GaAs substrate and the MBE-GaAs layer grown on top of it strongly influences the performance of the source.