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Title: Metastable Defects in Tritiated Amorphous Silicon

Abstract

The appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to {sup 3}He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half-life of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 10{sup 16} to 10{sup 17}/cm{sup 3}, which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value ofmore » 3 x 10{sup 19}/cm{sup 3} after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2 x 10{sup 20}/cm{sup 3}). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
979834
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Amorphous and Polycrystalline Thin-Film Silicon Science and Technology - 2007: Proceedings of the Materials Research Society Symposium, 9-13 April 2007, San Francisco, California; Related Information: Paper No. 0989-A02-04
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; ANNEALING; BETA DECAY; BETA PARTICLES; DECAY; DEFECTS; ENERGY SPECTRA; HALF-LIFE; HELIUM; HYDROGEN; INTERSTITIALS; NITROGEN; RESONANCE; SATURATION; SHAPE; SILICON; SPECTROSCOPY; SPIN; STORAGE; TRITIUM; Solar Energy - Photovoltaics; Silicon Materials and Devices

Citation Formats

Ju, T., Whitaker, J., Zukotynski, S., Kherani, N., Taylor, P. C., and Stradins, P. Metastable Defects in Tritiated Amorphous Silicon. United States: N. p., 2007. Web. doi:10.1557/PROC-0989-A02-04.
Ju, T., Whitaker, J., Zukotynski, S., Kherani, N., Taylor, P. C., & Stradins, P. Metastable Defects in Tritiated Amorphous Silicon. United States. doi:10.1557/PROC-0989-A02-04.
Ju, T., Whitaker, J., Zukotynski, S., Kherani, N., Taylor, P. C., and Stradins, P. Mon . "Metastable Defects in Tritiated Amorphous Silicon". United States. doi:10.1557/PROC-0989-A02-04.
@article{osti_979834,
title = {Metastable Defects in Tritiated Amorphous Silicon},
author = {Ju, T. and Whitaker, J. and Zukotynski, S. and Kherani, N. and Taylor, P. C. and Stradins, P.},
abstractNote = {The appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to {sup 3}He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half-life of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 10{sup 16} to 10{sup 17}/cm{sup 3}, which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3 x 10{sup 19}/cm{sup 3} after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2 x 10{sup 20}/cm{sup 3}). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.},
doi = {10.1557/PROC-0989-A02-04},
journal = {Amorphous and Polycrystalline Thin-Film Silicon Science and Technology - 2007: Proceedings of the Materials Research Society Symposium, 9-13 April 2007, San Francisco, California},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}