Photoionization cross-sections and energy levels of gold, iron, platinum, silver, and titanium in silicon

Abstract

The photoionization cross-sections of various deep impurities of interest in solar-grade silicon for photovoltaic cells, and the corresponding energy levels, have been determined by steady state photo-induced currents in pn junctions or Schottky barrier junctions irradiated simultaneously with two wavelengths of light. Light of about half the band-gap energy controls the occupancy of the deep impurity level and the spectral dependence of the photocurrent on a higher photon energy light source then provides, via the Lucovsky model, the photo-cross-section and the impurity energy level. The results obtained for Au and Pt in Si are in agreement with those of Braun and Grimmeiss and the energy levels for Fe, Ti, and Ag obtained optically are in agreement with those obtained by other methods.