Relationship between the optical absorption and the density of deep gap states in microcrystalline silicon

Abstract

We have measured the subgap optical absorption of undoped microcrystalline silicon samples with photothermal deflection spectroscopy and compared it with the spin density measured by electron spin resonance. The material was prepared using the hot wire chemical vapor deposition technique with a broad range of deposition parameters, yielding materials with a wide variety of structural, optical, and electronic properties. A nearly linear correlation between the spin densities and the subgap absorption coefficient at photon energy of 0.7 eV over three orders of magnitude indicates that the optical absorption in this region is due to the dominating paramagnetic defects, likely dangling bonds. However, the structural composition of the material, determined by Raman spectroscopy, has also some influence on the optical and electronic properties, which leads to some deviation from a straightforward relationship between optical absorption and spin or defect density.