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% (2.5X10(-2)), 40% (1X10(-3)), and 60% (1.5x10(-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 (similar to 10(4) cm(3)) ultrahigh vacuum chamber, is intended as a test facility for characterizing candidate photocathode materials for spin polarized electron sources. (C) 1995 American Institute of Physics.