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Characterization of Monolayer-Level Composition and Optical Gap Profiles in Amorphous Silicon-Carbon Alloy Bandgap-Modulated Structures

Published online by Cambridge University Press:  15 February 2011

H. Fujiwara ,
Joohyun Koh ,
C. R. Wronski  and
R. W. Collins
H. Fujiwara
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802.
Joohyun Koh
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802.
C. R. Wronski
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802. Department of Electrical Engineering, andThe Pennsylvania State University, University Park, PA 16802.
R. W. Collins
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802. Department of Physics, The Pennsylvania State University, University Park, PA 16802.
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Abstract

Over the past few years we have applied real time spectroscopie ellipsometry (RTSE) to characterize the structural, compositional, and optical gap profiles in continuously-graded amorphous silicon-carbon alloy films (a-Si1-xCx:H). Most recently, we have extended the RTSE methods to their monolayer sensitivity and resolution limits. In this study, continuous triangular variations in the carbon content × (0.02≤x≤0.24) within ∼25 to 130 Å thick graded layers were introduced at the i/p interfaces of the n-i-p solar cell structures using continuous variations in the flow ratio z=[CH4]/{[SiH4]+[CH4]} during rf plasma-enhanced chemical vapor deposition (PECVD). A virtual interface approximation has been applied to interpret the RTSE data collected during the growth of the graded interface layers. This analysis yields C-content depth-profiles with monolayer-level resolution and a compositional uncertainty of ±0.004. Even compositional gradients in which x changes by >0.2 within a few monolayers’ thickness are readily characterized. Lastly, a continuous increase in open circuit voltage with increasing graded interface layer thickness, saturating at ΔVoc=0.1 V after 100 Å, is observed in the n-i-p solar cells with graded layers. These results demonstrate the importance of the RTSE analysis in assessing bandgap engineered device designs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 467: Symposium A – Amorphous and Microcrystalline Silicon Technology - 1997 , 1997 , 531
Copyright
Copyright © Materials Research Society 1997

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References

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