Experimental determination of positron-related surface characteristics of 6H-SiC

The positron work function of 6H-SiC was determined to be –2.1±0.1 eV from an analysis of the energy spectrum of
positrons reemitted from the surface. The positron reemission yield, highest in the sample inserted into vacuum after
atmospheric exposure and cleaning with ethanol, was significantly reduced after sputtering with 3 keV, 125 µA min Ne+ ions.
The yield was not recovered even after annealing at 900 °C, presumably due to the stability of sputter induced defects.
Sputtering at lower energies caused a smaller decrease in the reemission yield that was largely recovered after annealing at 850 °C. Analysis using electron induced Auger electron spectroscopy and positron-annihilation-induced Auger electron spectroscopy indicated that the surface was Si enriched after sputtering and C enriched after subsequent annealing. Values of positron diffusion length and mobility in the unsputtered material were extracted from the dependence of the reemission yield on the beam energy. The application of SiC as a field-assisted positron moderator is discussed.