IMPROVED SOURCES OF SPIN-POLARIZED ELECTRONS

PHOTOCATHODES THAT PRODUCE POLARIZED ELECTRONS ARE A VITAL COMPONENT OF THE ELECTRON COLLIDERS USED IN HIGH ENERGY PHYSICS EXPERIMENTS, SUCH AS THOSE AT THE STANFORD LINEAR ACCELERATOR CENTER (SLAC). THE YIELDS OF ELECTRONS FROM TODAY'S PHOTOCATHODES ARE LOW, REDUCING THE EFFECTIVENESS OF THESE SOPHISTICATED LINEAR ACCELERATOR INSTRUMENTS. THIS PROJECT SHOULD IMPROVE POLARIZED ELECTRON SOURCES BY OPTIMIZING THE DEPOSITION PROCESS USED TO MAKE THE PHOTOCATHODE LAYERED STRUCTURE. THE BASIC DEVICE STRUCTURE CONSISTS OF A THIN, STRAINED LAYER OF GALLIUM ARSENIDE (GAAS), ON A GALLIUM ARSENIDE PHOSPHIDE (GAASP) BUFFER REGION, ON A GAAS WAFER. CAREFUL DESIGN OPTIMIZATION IS NEEDED TO ACHIEVE MAXIMUM LAYER STRAIN, AND THEREFORE MAXIMUM YIELD OF POLARIZED ELECTRONS. TOO MUCH STRAIN RESULTS IN CRYSTAL DEFECTS WHICH SIGNIFICANTLY REDUCE PERFORMANCE. IN PHASE I, STRUCTURES WILL BE FORMED GBY METAL ORGANIC CHEMICAL VAPOR DEPOSITION (MOCVD); DEVICE PERFORMANCE WILL MEASURED AT SLAC. PHASE II WILL SEEK TO IMPROVE UPON RESULTS BY STUDYING MORE ADVANCED LAYER STRUCTURES AND DEVICE PROCESSING, AND DEPOSITION ON LARGER DIAMETER WAFERS.