Experiments to determine the mean depth scale of positrons in silicon: Slow positron beam measurements on MBE-grown silicon layers on silicon oxide

Molecular beam deposited silicon layers of different thicknesses on thermally grown SiO2, were studied using a slow positron beam. The layer thickness was determined by scanning electron microscopy cross-section images. Positron data were modelled by means of VEPFIT with subsequently changed mean depth parameters A and n. The results were compared with the known layer thickness. It was found that a reasonable fit can be obtained only from a small set of parameters. This corresponds to a positron mean depth scale in silicon like (z) over bar = [2.75(0.25) mu g cm(-2) keV(-1.7))/rho]E-1.7(0.05). These results are in good agreement with recent Monte-Carlo calculations.