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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}
}
  • This paper presents results of studies on carrier-induced metastable defect creation in hydrogenated amorphous silicon. The metastable defects were studied by measuring the threshold voltage shifts on thin-film amorphous silicon transistors and capacitors as a function of time, temperature, and bias. The kinetics (time, temperature, bias, and doping dependence) of these defects as well as most other metastable-defect processes are quantitatively explained by hydrogen diffusion and the creation of defects due to the presence of excess band-tail carriers.
  • The role of hydrogen in the creation and annealing kinetics of the light-induced metastable defects in hydrogenated amorphous silicon is investigated using electron spin resonance. Deuterated and hydrogenated films exhibited the same defect creation rate and nearly identical distributions of annealing energies. Implications of these results for various microscopic models for the creation of metastable defects are discussed.
  • In this paper the authors review paramagnetic point defects in amorphous silicon nitride thin films. We will discuss two intrinsic paramagnetic defects: a trivalent silicon center, named the K-center, and the recently observed nitrogen dangling-bond center. We examine the structural identification, and the electronic properties of the K-center, as well as consider why a SiN{sub x}:H is generally a very effective charge trapping dielectric. In addition, this paper compares and contrasts special features of the structure and electronic role of the paramagnetic point defects in both silicon dioxide and silicon nitride thin films; this may provide insight for further studiesmore » on the physics and chemistry of these dangling-bond centers in both materials.« less
  • The application of tritiated amorphous silicon as an intrinsic energy conversion semiconductor for radioluminescent structures and betavoltaic devices is presented. Theoretical analysis of the betavoltaic application shows an overall efficiency of 18% for tritiated amorphous silicon. This is equivalent to a 330 Ci intrinsic betavoltaic device producing 1 mW of power for 12 years. Photoluminescence studies of hydrogenated amorphous silicon, a-Si:H, show emission in the infra-red with a maximum quantum efficiency of 7.2% at 50 K; this value drops by 3 orders of magnitude at a temperature of 300 K. Similar studies of hydrogenated amorphous carbon show emission in themore » visible with an estimated quantum efficiency of 1% at 300 K. These results suggest that tritiated amorphous carbon may be the more promising candidate for room temperature radioluminescence in the visible. 18 refs., 5 figs.« less