Correlation of dielectric and vibrational properties of amorphous hydrogenated Si for photovoltaic applications: modeling and experiment

Demand on high quality amorphous hydrogenated Si (a- Si:H) for thin film solar cell or microelectronics applications necessitates microscopic and in-situ access to various processes in this fundamentally interesting material. We demonstrate that such access can be provided by combining first principles computational simulations with commonly used infrared vibrational spectroscopy and still rarely utilized optical ellipsometry in the infrared (IR) range. To achieve this goal we developed computational approaches to comprehensively track hydrogen behaviour in both ordered and disordered (non-crystalline) materials. Theoretical computational tools include ab-initio Car-Parrinello molecular dynamics, an improved signal processing technique, computer visualization, calculations of the temperature dependent electron band structure, electron density of states (DOS) and dielectric function, all used to interpret available experimental data. Correlation of the temperature dependent electronic, dynamical, vibrational and optical properties with quality, stability, details of hydrogen bonding, and diffusion in a-Si:H are discussed. In particular, in the infrared range this study provides information about the localized states inside the a-Si:H mobility gap, the unsaturated Si dangling bonds and the role of the technologically important effect of hydrogen passivation of the defects in the amorphous network.