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Title: The determinants of hydrogen concentrations in hydrogenated amorphous silicon films prepared using a triode deposition system

Abstract

It is important to reduce the hydrogen concentration, in particular, the Si-H{sub 2} bond concentration, in a hydrogenated amorphous silicon film to improve its light-soaking stability. In a previous study, we found that a triode configuration plasma enhanced chemical vapor deposition method provides high quality and a very low hydrogen concentration film; however, the origin of the hydrogen reduction has been unknown. In this article, we investigate the essential factor causing the very low hydrogen concentrations observed in the triode system. In several experiments, we observed strong influences of deposition precursors on the resulting hydrogen concentrations. We propose that due to a steric hindrance, the hydrogen elimination process during film growth is disturbed when higher silane radicals stick to a growth surface. In a triode system, corresponding with the separation of the film growth surface from the precursor generation region, the contribution of higher silane radicals to film growth is suppressed due to their short diffusion length and frequent collisions with silane molecules.

Authors:
; ;  [1];  [2];  [2]
  1. National Institute of Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2-13, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20982781
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 6; Other Information: DOI: 10.1063/1.2715671; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL VAPOR DEPOSITION; CRYSTAL GROWTH; DIFFUSION LENGTH; HYDROGEN; PRECURSOR; RADICALS; SEMICONDUCTOR MATERIALS; SILANES; SILICON; THIN FILMS

Citation Formats

Shimizu, Satoshi, Matsuda, Akihisa, Kondo, Michio, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, and National Institute of Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2-13, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568. The determinants of hydrogen concentrations in hydrogenated amorphous silicon films prepared using a triode deposition system. United States: N. p., 2007. Web. doi:10.1063/1.2715671.
Shimizu, Satoshi, Matsuda, Akihisa, Kondo, Michio, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, & National Institute of Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2-13, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568. The determinants of hydrogen concentrations in hydrogenated amorphous silicon films prepared using a triode deposition system. United States. doi:10.1063/1.2715671.
Shimizu, Satoshi, Matsuda, Akihisa, Kondo, Michio, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, and National Institute of Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2-13, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568. Thu . "The determinants of hydrogen concentrations in hydrogenated amorphous silicon films prepared using a triode deposition system". United States. doi:10.1063/1.2715671.
@article{osti_20982781,
title = {The determinants of hydrogen concentrations in hydrogenated amorphous silicon films prepared using a triode deposition system},
author = {Shimizu, Satoshi and Matsuda, Akihisa and Kondo, Michio and Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 and National Institute of Advanced Industrial Science and Technology, Research Center for Photovoltaics, Central 2-13, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568},
abstractNote = {It is important to reduce the hydrogen concentration, in particular, the Si-H{sub 2} bond concentration, in a hydrogenated amorphous silicon film to improve its light-soaking stability. In a previous study, we found that a triode configuration plasma enhanced chemical vapor deposition method provides high quality and a very low hydrogen concentration film; however, the origin of the hydrogen reduction has been unknown. In this article, we investigate the essential factor causing the very low hydrogen concentrations observed in the triode system. In several experiments, we observed strong influences of deposition precursors on the resulting hydrogen concentrations. We propose that due to a steric hindrance, the hydrogen elimination process during film growth is disturbed when higher silane radicals stick to a growth surface. In a triode system, corresponding with the separation of the film growth surface from the precursor generation region, the contribution of higher silane radicals to film growth is suppressed due to their short diffusion length and frequent collisions with silane molecules.},
doi = {10.1063/1.2715671},
journal = {Journal of Applied Physics},
number = 6,
volume = 101,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • Hydrogenated amorphous silicon (a-Si:H) films prepared using a molecular beam deposition (MBD) method show an unusually sharp, narrow infrared absorption peak at 2080-2090 cm{sup -1}, which is thought to result from surface SiH species in the a-Si:H. The sharp, narrow peak is eliminated by a bias electric field of several kilovolts during deposition. The absence or presence of incoming high-energy silicon atoms or clusters accelerated by the field seems to be crucial for the resulting network structure and hydrogen distribution in a-Si:H prepared using MBD.
  • Nearly stoichiometric, amorphous silicon carbide films with a relatively low hydrogen content were deposited from organsilanes on a variety of substrates in a microwave-generated plasma without external heating. The films undergo little weight loss upon pyrolysis to 800 [degree]C. The effect of the different deposition parameters on the film composition and the exhaust gas was established through a battery of tests including infrared Fourier transform spectroscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, ellipsometry, and mass spectroscopy. For a given power level there is a limiting feeding rate of the precursor under which operation of the system is dominated by thermodynamicsmore » and thus leads to the desired product. Beyond that limit, excessive hydrogen incorporation and carbosilane polymer formation takes place. The hydrogen content of the plasma is also an important parameter affecting the chemistry of the deposition. In the thermodynamically dominated regime the nature of the precursor has no effect on the quality of the film. It affects only the relative utilization efficiency.« less
  • Amorphous hydrogenated carbon nitride thin films (a-CN{sub x}:H) have been prepared by plasma-enhanced chemical vapor deposition of N{sub 2} and CH{sub 4} gases using a helical resonator discharge. The structural and optical properties of the deposited a-CN{sub x}:H films have been systematically studied as a function of the substrate temperature and radio frequency (rf) substrate bias. The chemical structure and elemental composition of the a-CN{sub x}:H films were characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The optical properties of the films were evaluated using transmission ultraviolet{endash}visible spectroscopy. The morphology of the films wasmore » investigated by scanning electron microscopy and atomic force microscopy. The FT-IR and XPS studies demonstrate the presence of carbon{endash}nitrogen bonds with hydrogenated components in the films. The film composition ratio N/C was found to vary from 0.127 to 0.213 depending on the deposition conditions. The Raman spectra, showing the G and D bands, indicate that the a-CN{sub x}:H films have a graphitic structure. It can be found that the optical band-gap E{sub g} of a-CN{sub x}:H films is associated with graphitic clusters, while the decrease in E{sub g} is correlated with an increase in the size and number of graphitic clusters. Combining the results of Raman and optical measurements, it can be concluded that a progressive graphitization of the films occurs with increasing the substrate temperature and rf substrate bias power, corresponding to bias voltage. {copyright} {ital 1997 American Institute of Physics.}« less
  • Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorphous hydrogenated silicon films is observed for the photoconductivity and the spectral dependence of the absorption coefficient. The temperature dependences of the photoconductivity in the films under study are found to vary with the energy of incident photons. At a photon energy of 1.3 eV, temperature quenching of photoconductivity ismore » observed. Prolonged illumination of the films led to a certain decrease in the absorption coefficient at photon energies in the range 1.2-1.5 eV. The results obtained are attributed to the possible presence of silicon nanocrystals in the structure of the films and to the influence of these nanocrystals on their photoelectric and optical properties.« less