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Title: Use of Tritium in the Study of defects in Amorphous Silicon

Abstract

Hydrogen is known to strongly affect the physical properties of amorphous semiconductors. Indeed hydrogen is introduced during the growth of amorphous silicon films, used in active matrix displays and solar cells, to passivate silicon dangling bonds and to relax the lattice thereby reducing the density of states in the energy gap by several orders of magnitude and giving rise to device grade material. Ideally, hydrogenated amorphous silicon (a-Si:H) is a continuous covalently bonded random network of silicon-silicon and silicon-hydrogen atoms, with the predominant nearest neighbour environment similar to that of crystalline silicon.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Laboratory for Laser Energetics, University of Rochester
Sponsoring Org.:
USDOE
OSTI Identifier:
860704
Report Number(s):
DOE/SF/19460-641
1601; 2004-22; TRN: US200721%%397
DOE Contract Number:
FC52-92SF19460
Resource Type:
Conference
Resource Relation:
Journal Name: Fusion Science and Technology; Journal Volume: 48; Conference: 7th International Conference on Tritium Science and Technology, Baden-Baden, Germany, 12-17 September 2004
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 14 SOLAR ENERGY; ATOMS; DEFECTS; ENERGY GAP; HYDROGEN; PHYSICAL PROPERTIES; SILICON; SOLAR CELLS; TRITIUM

Citation Formats

Costea, S., Pisana, S., Kherani, N.P., Gaspari, F., Kosteski, T., Shmayda, W.T., and Zukotynski, S.. Use of Tritium in the Study of defects in Amorphous Silicon. United States: N. p., 2005. Web.
Costea, S., Pisana, S., Kherani, N.P., Gaspari, F., Kosteski, T., Shmayda, W.T., & Zukotynski, S.. Use of Tritium in the Study of defects in Amorphous Silicon. United States.
Costea, S., Pisana, S., Kherani, N.P., Gaspari, F., Kosteski, T., Shmayda, W.T., and Zukotynski, S.. Mon . "Use of Tritium in the Study of defects in Amorphous Silicon". United States. doi:.
@article{osti_860704,
title = {Use of Tritium in the Study of defects in Amorphous Silicon},
author = {Costea, S. and Pisana, S. and Kherani, N.P. and Gaspari, F. and Kosteski, T. and Shmayda, W.T. and Zukotynski, S.},
abstractNote = {Hydrogen is known to strongly affect the physical properties of amorphous semiconductors. Indeed hydrogen is introduced during the growth of amorphous silicon films, used in active matrix displays and solar cells, to passivate silicon dangling bonds and to relax the lattice thereby reducing the density of states in the energy gap by several orders of magnitude and giving rise to device grade material. Ideally, hydrogenated amorphous silicon (a-Si:H) is a continuous covalently bonded random network of silicon-silicon and silicon-hydrogen atoms, with the predominant nearest neighbour environment similar to that of crystalline silicon.},
doi = {},
journal = {Fusion Science and Technology},
number = ,
volume = 48,
place = {United States},
year = {Mon Nov 28 00:00:00 EST 2005},
month = {Mon Nov 28 00:00:00 EST 2005}
}

Conference:
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  • Hydrogen is known to strongly affect the physical properties of amorphous semiconductors. Indeed hydrogen is introduced during the growth of amorphous silicon films, used in active matrix displays and solar cells, to passivate silicon dangling bonds and to relax the lattice thereby reducing the density of states in the energy gap by several orders of magnitude and giving rise to device grade material. Ideally, hydrogenated amorphous silicon (a-Si:H) is a continuous covalently bonded random network of silicon-silicon and silicon-hydrogen atoms, with the predominant nearest neighbour environment similar to that of crystalline silicon. a-Si:H typically contains about 10 atomic percent hydrogen.Tritiummore » can readily substitute for hydrogen in a-Si:H without altering the physicochemical properties of the material. Tritium decay leads to a change in the local bond structure of the material as helium detaches from bonds leaving behind dangling bonds. The decay rate of tritium and therefore the rate of dangling bond formation is determined by the half-life of tritium. Hence, tritium provides a unique avenue to dynamically study the effect of dangling bonds on the density of states in the energy gap and therefore on the optoelectronic properties of a-Si:H. Tritiated hydrogenated amorphous silicon (a-Si:H:T) was deposited using mixtures of tritium and silane gases in a dc saddle-field glow-discharge deposition system. The amount of tritium in the films was controlled by adjusting the relative flow of tritium and silane gases into the deposition chamber.Photoluminescence, isothermal capacitive transient spectroscopy and constant photocurrent spectroscopy were used to measure defect concentration as a function of time in the films. The defect concentration was found to increase between 1 and 2 orders of magnitude, in about 300 hours. Thermal annealing decreased the defect concentration. It was found that tritium permits a study of the change in the density of defect states due to dangling bond formation in a-Si:H without the uncertainties introduced by the use of multiple samples.« less
  • Photocreation mechanisms and properties of nitrogen dangling bonds in amorphous hydrogenated silicon nitride (a-SiN[sub x]:H) thin films are investigated. We find that the creation kinetics are strongly dependent on the post-deposition anneal; this thermal process can be described by a simple exponential function which yields an activation energy of 0.8 eV. The compositional dependence of the nitrogen dangling bond center suggests that its energy level lies close to the valence band edge, in agreement with theoretical calculations. This energy level position can explain why a-SiN[sub x]:H films often become conducting following a high post-deposition anneal.
  • A mechanism for charged-carrier-trapping-induced defect metastability in hydrogenated amorphous silicon (a-Si:H) and in hydrogenated amorphous silicon alloys containing relatively high concentrations of oxygen and/or nitrogen atoms (a-Si:X:H, X = O or N) is described. The experimental results that identified this defect metastability mechanism were (i) differences in the Staebler-Wronski effect in a-Si:H and a-Si:N:H alloys prepared from N{sub 2} and NH{sub 3} source gases by remote plasma-enhanced chemical-vapor deposition, and (ii) differences in defect generation at N-atom terminated Si-SiO{sub 2} interfaces prepared from NH{sub 3} and N{sub 2}O.
  • We have observed the growth of defects caused by optical illumination in liquid nitrogen. We kept the sample in liquid nitrogen over one year. After one year and half the ESR signal reached <<10{sup 18} cm{sup -3} with no evidence of saturation. After that, we step-wise annealed isochronal the sample up to room temperature, where two thirds of original defects were annealed out. After room temperature, the sample was annealing isothermally around 300 K for several months. At this temperature, the defects slowly anneal. After a hundred of hours at 295K, the defect density decreased 10x from its original valuemore » at 77K.« less
  • We report on a possible microscopic origin of the UV light-induced silicon and nitrogen dangling bonds and positive charge in TFT gate-quality N-rich amorphous silicon nitride films deposited by PECVD at the substrate temperatures of 250 and 400{degrees}C. 12 refs., 3 figs.