Characterization of amorphous silicon:hydrogen based materials for thin film device applications

This thesis presents a methodology to investigate a-Si:H material properties using a self-consistent approach. The aim is to evaluate experimental data based on a density of states (DOS) model composed of extended states and localized states. This approach incorporates results obtained from several characterization techniques and the derived DOS parameters cover a wide energy range. The self-consistency in evaluating the results from different techniques ensures that a reliable, unified set of material parameters are obtained.;The optical gap and the densities of extended states are determined from analyzing the optical constants obtained by using ex situ ellipsometry as well as transmission and reflection measurements. The representation of an optical gap in a-Si:H is examined using the proposed distribution of extended states. Results of different a-Si:H based materials are presented and discussed. The mobility gap is characterized by using internal photoemission of both electrons and holes into a-Si:H. The parabolic distribution of extended states and the amorphous nature of a-Si:H are taken into account in the analysis.;The photoconductivity in a-Si:H is governed by the defect states in the gap which can be resulted from structural disorder or dangling bonds present in the material. The recombination kinetics in a-Si:H and the distributions of gap states are characterized by steady state and dual-beam photoconductivity (DBP) measurements. The densities and capture cross sections of these states are extracted by using a Subgap Absorption Modeling (SAM) program that fits model predictions to the photoconductivity data and DBP spectra.;Material parameters obtained from film studies are used to predict the p-i-n solar cell characteristics using a device modeling program (AMPS). The results are compared with the experimental data obtained on cells made from these materials. This approach allows a diagnostic analysis on the correlation between material properties and device characteristics.