Density of gap states of silicon grain boundaries determined by optical absorption

Abstract

The results of optical absorption measurements on fine-grain polycrystalline-silicon thin films indicate that the singly occupied dangling silicon bond lies 0.65±0.15 eV below the conduction-band minimum in the grain boundary. The grain boundary band gap is ∼1.0 eV and there is evidence for exponential tailing of the band edges. The optical absorption was determined by photothermal deflection spectroscopy. The dangling silicon bond density has been measured on polycrystalline-silicon thin films as a function of hydrogen passivation of the grain boundaries and on silicon-on-saphhire films. The optical absorption exhibits a defect shoulder which varies as the dangling bond density.