University of Illinois Urbana-Champaign

Density functional study of hydrogen in amorphous silicon

Tuttle, Blair R.

This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.

Permalink

https://hdl.handle.net/2142/30769

Description

Title
Density functional study of hydrogen in amorphous silicon
Author(s)
Tuttle, Blair R.
Issue Date
1997
Director of Research (if dissertation) or Advisor (if thesis)
Adams, James B.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • amorphous silicon
  • photovoltaics
  • defects
  • hydrogen bonding
  • hydrogen diffusion
  • molecular dynamics (MD) simulations
Language
en
Abstract
Hydrogenated amorphous silicon is a relatively new material with device applications including photovoltaics. Intrinsic and light-induced electronic defects reduce the efficiency of a-Si:H solar cells. Although hydrogen is implicated in these defects, microscopic understanding of the structure and energetics of hydrogen in a-Si:H has been limited. The current limits are in part do to the lack of reliable theoretical calculations. Here we apply density functional methods to study H in a-Si:H. First, we develop a new atomistic model for a-Si:H. Then, using molecular dynamics simulations, we compare several currently available atomistic models. Finally, we calculate the properties of hydrogen in these models, including the geometric environments, the energetics, the electronic structure and the vibrational properties. Our most important conclusions are presented below. Our calculations are consistent with the following microscopic picture for long range diffusion of H in a-Si:H. Clustered Si-H bonds constitute the dominant trapping species. Upon the dissociation of 2 H atoms, a Si-Si bond forms leaving a nominally 4-fold coordinated weak bond complex. The 2 H atoms move away separately along Si-Si bond center sites until trapped at another weak bond complex. The calculated activation energy is found in agreement with established experimental results. Also, our calculations are successfully applied to observations of H evolution, hydrogendeuterium exchange and long range diffusion in p-type amorphous silicon. Our calculations clarify the role of H during electronic defect formation. We calculate the energetics for H to move from a variety of Si-H bonds to the bulk chemical potential. For isolated Si-H bonds (i.e. in micro-cavities without any bond reconstruction) the energetics are not consistent with observations. However, if the remaining Si reconstructs with a nearby silicon creating a 5-fold coordinated defect then the energetics are in agreement with observations. Therefore, our results indicate that the dangling bond model for intrinsic defects in amorphous silicon should be revisited.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/30769
Copyright and License Information
Copyright 1997 Blair R.Tuttle

Owning Collections

Dissertations and Theses - Physics PRIMARY
Dissertations in Physics