Date of Award

2011

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

First Advisor

O'Leary, Stephen (Electrical and Computer Engineering)

Keywords

Electrical Engineering.

Rights

CC BY-NC-ND 4.0

Abstract

Through the use of a general empirical model for the density of states functions, one that considers valence band band, valence band tail, conduction band band, and conduction band tail electronic states, the sensitivity of the joint density of states function to variations in the conduction band tail breadth, all other parameters being held fixed at nominal hydrogenated amorphous silicon values, is examined. It is found that when the conduction band tail is narrower than the valence band tail, its role in shaping the corresponding spectral dependence of the joint density of states function is relatively minor.This justifies the use of a simplified empirical model for the density of states functions that neglects the presence of the conduction band tail states inthe characterization of the optical response.A simplification of such an empirical model for the density of state functions associated with hydrogenated amorphous silicon is then suggested, reducing the number of independent modeling parameters from six to five as a result. As a consequence of this simplification, it is found that one is able to cast joint density of states evaluations into a dimensionless formalism, this formalism providing an elementary and effective platform for the determination of the underlying modeling parameters from experiment. This simplification is justified by showing, for reasonable hydrogenated amorphous silicon modeling parameter selections, that the joint density of states results are very similar to those determined using a more general approach.Using our dimensionless joint density of states formalism for the quantitative characterization of the optical response associated with hydrogenated amorphous silicon, a critical comparative analysis of a large number of different optical absorption data sets is then considered. When these data sets are cast into this dimensionless framework, a trend is observed that is almost completely coincident for all of the data sets considered. This suggests that there is a universal character associated with the optical absorption spectrum of hydrogenated amorphous silicon.Finally, the role that defect states play in shaping the optical response of this material are probed.

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