Optical characteristics of intrinsic microcrystalline silicon

Abstract

We studied the optical properties of intrinsic microcrystalline silicon $(\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ deposited by very high frequency plasma-enhanced chemical-vapor deposition system at different silane concentrations (SC) by spectroscopy ellipsometry and photothermal deflection spectroscopy. The bulk property of the samples was probed because the impact of the surface layer was significantly reduced by mechanical polishing. At high SC, we extracted the optical characteristics of the disordered part by assuming a superposition of ideal $c\ensuremath{-}\mathrm{Si}$ and mathematically generated amorphous function. At low SC, we studied the reason for a large deviation of absorption coefficient in the energy range between 1.6 and 3.2 eV from the value predicted by effective medium theory. We considered the scattering loss by the inhomogeneity of $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ and introduce the dense medium radiative transfer formalism to an optical scattering simulation. We simulated the Stokes vector of p- and s-polarized light at oblique incidence. From this formalism, we could predict depolarization of p and s wave by scattered incoherent light. Further, we also suggested strain effect as the second possible reason for the enhanced absorption near the onset of the indirect transition in highly crystalline $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}.$