Low energy Mott polarimetry of electrons from negative electron affinity photocathodes

We present data on the spin polarization P and quantum yield Y of electrons photoemitted from negative electron affinity semiconductors, including GaAs(100), GaAsP(100) alloy, and strained GaAs layer epitaxially grown on a GaAsP(100) buffer. Near photothreshold the following values for P(Y) are, respectively, obtained: 26% (2.5×10−2), 40% (1×10−3), and 60% (1.5×10−4). We describe in detail the apparatus used containing a low energy (10–25 keV) Mott polarimeter. The system, completely fitted in a small volume (∼104 cm3) ultrahigh vacuum chamber, is intended as a test facility for characterizing candidate photocathode materials for spin polarized electron sources.