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Assignment of High Wave-number Absorption and Raman Scattering Peaks in Microcrystalline Silicon

Published online by Cambridge University Press:  01 February 2011

Erik V. Johnson ,
Laurent Kroely  and
Pere Roca i Cabarrocas
Erik V. Johnson
Affiliation:
[email protected], LPICM-CNRS, Ecole Polytechnique, 10 route de Saclay, Palaiseau, F-91128, France
Laurent Kroely
Affiliation:
[email protected], LPICM-CNRS, Palaiseau, France
Pere Roca i Cabarrocas
Affiliation:
[email protected], LPICM-CNRS, Palaiseau, France
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Abstract

In the optimization of high-growth rate hydrogenated microcrystalline silicon (μc-Si:H) for photovoltaics, the observation of the infrared (IR) absorption peaks around 2000 cm-1 - which originate from silicon hydrogen (Si-HX) bonds in the film bulk - can provide useful information about the properties of the film. If the films are deposited on IR transparent substrates, Fourier Transform infrared (FTIR) spectroscopy is the most commonly used technique to measure the absorption in this regime. The rich spectrum of Si-HX peaks that can be observed in this wavenumber region describes the distribution of the bonded hydrogen amongst the various possible SiHX configurations, and as well, the presence of a pair of narrow, twin peaks at 2085 and 2100 cm-1 is indicative of material that is porous and prone to oxidation upon exposure to air. Many of these high wavenumber peaks are also observable using Raman scattering spectroscopy, allowing one to observe films on substrates that are not IR transparent. As well, the different absorption/scattering cross sections of the two techniques provide a useful tool to understand the origins of the various peaks, and in particular, those of the twin narrow peaks. In this work, we examine the dynamics upon exposure to atmosphere of these twin peaks in μc-Si:H grown by Matrix Distributed Electron Cyclotron Resonance (MD-ECR) PECVD. This deposition technique is an extremely promising one for growing μc-Si:H thin films at high deposition rates, and has demonstrated μc-Si:H film deposition at up to 28Å/s. By using both FTIR and Raman spectroscopy to characterize these films, we examine the differences in the dynamics of each of the twin peaks according to the technique used. In addition, secondary ion mass spectrometry (SIMS) measurements on the films show the physical distribution of oxygen in the films after five months of air exposure, and XRD measurements correlate the presence of these twin peaks with a [111] preferential surface orientation. Using these observations, we assign these absorption and scattering features to specific configurations of Si-HX within the film, and explain both the dynamics of the peaks over time and the similarity of the peaks for a wide range of samples.

Keywords

SiRaman spectroscopyinfrared (IR) spectroscopy
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1245: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology-2010 , 2010 , 1245-A13-05
Copyright
Copyright © Materials Research Society 2010

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