Anisotropy in Hydrogenated Amorphous Silicon Films as Observed Using Polarized FTIR-ATR Spectroscopy
We used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate the vibrational spectra of hydrogenated amorphous silicon (a-SiH{sub x}) films 0.5-1.0 microns in thickness. We deposited the films using hot-wire or plasma-enhanced chemical vapor deposition methods (HWCVD or PECVD, respectively) on crystalline silicon and cadmium telluride substrates. Our ATR technique gave a spectral range from 2100-400 cm{sup -1}, although the Si-H wagging mode absorption band at 640 cm{sup -1} was somewhat distorted in the a-SiHx/Si samples by impurity and lattice absorption in the silicon ATR substrates. We report the identification of a Si-O-C impurity band with maximum intensity at 1240-1230 cm{sup -1}. The assignment of this band to a Si-O-C vibration is supported by secondary-ion mass spectrometry (SIMS) measurements. Our polarized FTIR-ATR spectra of HWCVD and PECVD a-SiH{sub x} films on <111> Si ATR substrates show that the impurity dipoles ar e oriented strongly parallel to the film growth direction. The wagging mode absorbance band is more intense in the film plane. This trend is less pronounced for the Si-H stretching vibrations. These observations are consistent with some degree of anisotropy or medium-range order in the films. The anisotropy in the Si-H bands may be related to residual stress in the films. Our scanning electron microscopy (SEM) analyses of the samples offer additional evidence of bulk structural anisotropy in the a-SiH{sub x}/Si films. However, the Si-O-C impurity band was not observed in the polarized ATR-FTIR spectra of the a-SiH{sub x}/CdTe samples, thus indicating that the Si substrates influence formation of the impurity in the a-SiH{sub x}/Si films.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC36-99GO10337
- OSTI ID:
- 9795
- Report Number(s):
- NREL/CP-520-26355; ON: DE00009795; TRN: US200312%%130
- Resource Relation:
- Journal Volume: 557; Conference: Presented at the Materials Research Society 1999 Spring Meeting, San Francisco, CA (US), 04/05/1999--04/09/1999; Other Information: PBD: 14 May 1999
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
ABSORPTION
ANISOTROPY
CADMIUM TELLURIDES
CHEMICAL VAPOR DEPOSITION
DIPOLES
MASS SPECTROSCOPY
REFLECTION
SCANNING ELECTRON MICROSCOPY
SILICON
SPECTRA
SPECTROSCOPY
SUBSTRATES
THICKNESS
PHOTOVOLTAICS
A-SI:H FILMS
ATTENUATED TOTAL REFLECTION
SECONDARY-ION MASS SPECTROMETRY
FOURIER TRANSFORM INFRARED SPECTROSCOPY