Enhanced optical absorption in hydrogenated microcrystalline silicon: an absorption model

In this study we investigate the optical absorption and structural properties of hydrogenated microcrystalline silicon prepared by the hot wire deposition technique (hw-mu c-Si:H). To understand the enhanced optical absorption present in the material, we describe the correlation between the structural properties and the optical absorption in the framework of a novel absorption model. The structure of the hw-mu c-Si:H is assumed to consist of crystalline grains surrounded by grain boundaries and embedded in an amorphous matrix. The absorption coefficient, alpha, for the microcrystalline films is derived from the superposition of the absorption coefficients for amorphous, alpha(a), crystalline, alpha(c) and grain boundary, alpha(gb), regions weighted by their appropriate volume fractions. Taking into account the variation of alpha(gb) with the hydrogen content at the grain boundaries, the dependence of the absorption coefficient, alpha, on the average crystallite size, L, is obtained in accordance with our experimental results. In this paper we consider the absorption at a photon energy of 1.4 eV. (C) 1998 Elsevier Science B.V. All rights reserved.