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Development of Deposition Phase Diagrams for Thin Film Si:H and Si1-xGex:H Using Real Time Spectroscopic Ellipsometry

Published online by Cambridge University Press:  01 February 2011

N. J. Podraza ,
G. M. Ferreira ,
C. R. Wronski  and
R. W. Collins
N. J. Podraza
Affiliation:
Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606;
G. M. Ferreira
Affiliation:
Department of Electrical Engineering and Center for Thin Film Devices, The Pennsylvania State University, University Park,PA 16802
C. R. Wronski
Affiliation:
Department of Electrical Engineering and Center for Thin Film Devices, The Pennsylvania State University, University Park,PA 16802
R. W. Collins
Affiliation:
Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606;
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Abstract

The growth of hydrogenated silicon (Si:H) and silicon-germanium alloys (Si1-xGex:H) by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) substrates has been studied by real time spectroscopic ellipsometry (RTSE). The motivation is to develop deposition phase diagrams that can provide greater insight into the optimization of amorphous Si1-xGex:H (a-Si1-xGex:H) for multijunction photovoltaics. In initial studies, the phase diagram for bottom cell a-Si1-xGex:H (Eg ˜ 1.4 eV) is found to exhibit fundamental similarities to that for Si:H when both materials are prepared under standard PECVD conditions that optimize pure a-Si:H. These similarities suggest directions for optimizing a-Si1-xGex:H by identifying conditions under which a smooth, stable surface is obtained to the largest possible bulk layer thickness. In phase diagram development for PECVD Si1-xGex:H on c-Si, it has been found that the highest surface stability and smoothest surfaces are obtained using cathodic deposition (self bias: ˜-20 V) with a H2-dilution level just below that of the amorphous-to-(mixed-phase microcrystalline) [→(a+μc)] transition for a thick layer. Due to the promising nature of these results, full phase diagrams are compared for cathodic and anodic Si1-xGex:H as well as for cathodic and anodic Si:H, all on c-Si substrates. The cathodic phase diagram for Si1-xGex:H reveals a narrow range of significant improvement in surface structural evolution near the →(a+μc) transition, and for a-Si:H reveals an extension of the ultrasmooth protocrystalline regime to a much wider range of thickness.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 862: Symposium A – Amorphous and Nanocrystalline Silicon Science and Technology–2005 , 2005 , A16.3
Copyright
Copyright © Materials Research Society 2005

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