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Analysis of Compositionally and Structurally Graded Si:H and Si1−xGex:H Thin Films by Real Time Spectroscopic Ellipsometry

Published online by Cambridge University Press:  01 February 2011

Nikolas Podraza ,
Jing Li ,
Christopher R. Wronski ,
Mark W. Horn ,
Elizabeth C. Dickey  and
Robert W. Collins
Nikolas Podraza
Affiliation:
[email protected], The Pennsylvania State University, Materials Research Institute, 272 Materials Research Lab, University Park, PA, 16802, United States
Jing Li
Affiliation:
[email protected], The Pennsylvania State University, Materials Research Institute, University Park, PA, 16802, United States
Christopher R. Wronski
Affiliation:
[email protected], The Pennsylvania State University, Materials Research Institute, University Park, PA, 16802, United States
Mark W. Horn
Affiliation:
[email protected], The Pennsylvania State University, Materials Research Institute, University Park, PA, 16802, United States
Elizabeth C. Dickey
Affiliation:
[email protected], The Pennsylvania State University, Materials Research Institute, University Park, PA, 16802, United States
Robert W. Collins
Affiliation:
[email protected], University of Toledo, Department of Physics and Astronomy, Toledo, OH, 43606, United States
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Abstract

Silicon-germanium (Si1−x Gex :H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating intermediate and low H2-dilution material layers, which have been designed to produce predominately amorphous films with a controlled distribution of microcrystalline particles. The compositional evolution of alloy-graded a-Si1−x Gex :H has been studied as well using similar methods. In each case, depth profiles of microcrystalline content, f μc , or Ge content, x, have been extracted. Additionally, real time spectroscopic ellipsometry has been used to monitor post-deposition exposure of a-Si:H, a-Si1−xGex:H, and a-Ge:H films to a hydrogen plasma in situ in order to determine sub-surface amorphous film modification similar to that which would occur when a highly H2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhanced performance of Si:H based solar cells, through controlled bandgap grading using compositionally graded amorphous binary alloys (a-Si1−xGex :H) or the incorporation of controlled fractions of microcrystallites into bulk amorphous i-layer materials, and by providing a fundamental understanding of the modification of component layers during the deposition of subsequent layers in multilayer stacks.

Keywords

Sioptical propertiesplasma-enhanced CVD (PECVD) (deposition)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1066: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology—2008 , 2008 , 1066-A10-01
Copyright
Copyright © Materials Research Society 2008

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References

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