skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Hopping {epsilon}{sub 2} conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature

Abstract

It is shown that the high-temperature annealing in hydrogen flow results in substantial modification of the temperature dependence of the conductivity of boron-doped and undoped a-Si:H films. For doped films subjected to annealing, the {epsilon}{sub 2} conductivity related to hopping between localized states near the valence-band edge appears in the intermediate temperature range, along with the contributions of the band conductivity and the variable-range hopping conductivity. The {epsilon}{sub 2} conductivity becomes possible due to an increase in the concentration of electrically active boron atoms and to the appreciable shift of the Fermi level after high-temperature annealing of doped films in hydrogen atmosphere. The experimentally measured parameters of the {epsilon}{sub 2} conductivity make it possible to determine the width of the energy region, in which the density of localized states near the valence band falls off nonexponentially.

Authors:
; ; ;  [1]
  1. Moscow State University (Physics Department) (Russian Federation), E-mail: ormont@phys.msu.ru
Publication Date:
OSTI Identifier:
21088605
Resource Type:
Journal Article
Resource Relation:
Journal Name: Semiconductors; Journal Volume: 40; Journal Issue: 1; Other Information: DOI: 10.1134/S1063782606010192; Copyright (c) 2006 Nauka/Interperiodica; Article Copyright (c) 2006 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; BORON; DOPED MATERIALS; FERMI LEVEL; FILMS; HYDROGEN; SILICON; TEMPERATURE DEPENDENCE

Citation Formats

Zvyagin, I. P., Kurova, I. A., Nal'gieva, M. A., and Ormont, N. N. Hopping {epsilon}{sub 2} conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature. United States: N. p., 2006. Web. doi:10.1134/S1063782606010192.
Zvyagin, I. P., Kurova, I. A., Nal'gieva, M. A., & Ormont, N. N. Hopping {epsilon}{sub 2} conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature. United States. doi:10.1134/S1063782606010192.
Zvyagin, I. P., Kurova, I. A., Nal'gieva, M. A., and Ormont, N. N. Sun . "Hopping {epsilon}{sub 2} conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature". United States. doi:10.1134/S1063782606010192.
@article{osti_21088605,
title = {Hopping {epsilon}{sub 2} conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature},
author = {Zvyagin, I. P. and Kurova, I. A. and Nal'gieva, M. A. and Ormont, N. N.},
abstractNote = {It is shown that the high-temperature annealing in hydrogen flow results in substantial modification of the temperature dependence of the conductivity of boron-doped and undoped a-Si:H films. For doped films subjected to annealing, the {epsilon}{sub 2} conductivity related to hopping between localized states near the valence-band edge appears in the intermediate temperature range, along with the contributions of the band conductivity and the variable-range hopping conductivity. The {epsilon}{sub 2} conductivity becomes possible due to an increase in the concentration of electrically active boron atoms and to the appreciable shift of the Fermi level after high-temperature annealing of doped films in hydrogen atmosphere. The experimentally measured parameters of the {epsilon}{sub 2} conductivity make it possible to determine the width of the energy region, in which the density of localized states near the valence band falls off nonexponentially.},
doi = {10.1134/S1063782606010192},
journal = {Semiconductors},
number = 1,
volume = 40,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • Low-(..cap alpha..) and high-(..beta..) temperature phases of Li/sub 3/BN/sub 2/ were prepared from mixtures of Li/sub 3/N/BN = 1.1-1.0 in molar ratio at 1070 and 1170 K, respectively. Phase relation between these phases was studied by annealing the products at various temperatures and conducting DTA in a stream of nitrogen. The phase transition temperature is at about 1135 K. The melting point of ..beta..-Li/sub 3/BN/sub 2/ is around 1189K. ..cap alpha..-Li/sub 3/BN/sub 2/ crystallizes directly from the undercooled liquid at 1160K. The structure of ..cap alpha..-Li/sub 3/BN/sub 2/, which is analyzed in the present study for the first time, hasmore » tetragonal symmetry, P4/sub 2/2/sub 1/2, a = b = 4.6435(2), c = 5.2592(5) A, Z = 2, D/sub calc/ = 1.747 Mg m/sup -3/, ..mu.. = 0.082 mm/sup -1/. The structure was determined by 208 unique X-ray reflections with F/sub 0/ > 3 sigma(F/sub 0/) and refined up to R = 0.042 by a full-matrix least-squares method. The lattice is composed of Li(1), Li(2), and linear (NBN)/sup 3 -/ ions (r(B-N) = 1.339(2) A). The Li(1) ion is also linearly coordinated by two nitrogen atoms (r(Li(1)-N = 1.945(8) A). The Li(2) ion is at the center of a tetrahedron of N atoms (r(Li(2)-N) = 2.125(18) A, delta(N-Li-N) = 103.6(2) and 112.5(9)/sup 0/). Lithium ion conductivity of 3 x 10/sup -5/ S m/sup -1/ was measured at 400 K on a polycrystalline ..cap alpha..-Li/sup 3/BN/sup 2/ specimen with an activation energy of 78 kJ/mole.« less
  • The authors have investigated the effects of elevated substrate temperature (T{sub s}) on cleaning of boron residues from silicon substrates in 1%H{sub 2}-Ar plasmas, following etching of HfO{sub 2} in BCl{sub 3} plasmas. Vacuum-transfer x-ray photoelectron spectroscopy (XPS) provided a measure of total B removal rates, as well as information on individual BCl{sub x}O{sub y} moities. B cleaning rates increased with T{sub s} in an Arrhenius manner, with an apparent activation energy of 1.7 kcal/mol. Conversely, the Si etching rate decreased with increasing substrate temperature with an apparent activation energy of -0.8 kcal/mol. Therefore, when considering selectivity with respect tomore » Si etching, it is advantageous to remove B at higher T{sub s}. For example, at T{sub s}=235 deg. C, {approx}90% of B is cleaned from Si in 10 s, while <1.5 nm of Si is removed. An apparent diffusion of H into the near-surface region of Si at higher temperatures, detected indirectly by a shift and broadening of the Si(2p) XPS peak, may limit the maximum optimum substrate temperature, however. It was also found that Si does not etch in 1%H{sub 2}/Ar plasmas if an oxide layer is present.« less
  • The present work indicates through thermodynamic considerations that YLiO{sub 2} additive is beneficial for low-temperature sintering of AlN ceramics. Pressureless sintering of commercially available AlN powders with simultaneous additions of YLiO{sub 2} and CaO resulted in materials with high thermal conductivity (170 W{center_dot}m{sup {minus}1}{center_dot}K{sup {minus}1} after sintering at 1,600 C for 6 h). It is demonstrated that improvement of thermal conductivity is possible at low firing temperature by use of sintering aids.
  • Recombination dynamics of excitons in Mg{sub 0.11}Zn{sub 0.89}O epilayers grown by laser-assisted molecular-beam epitaxy on a ScAlMgO{sub 4} substrate were investigated. By using the MgZnO high-temperature-annealed self-buffer layer (HITAB), the value of full width at half maximum of the near-band-edge (NBE) photoluminescence (PL) peak at 3.6 eV was decreased from 133 to 94 meV at 293 K, and the intensity ratio of the NBE emission to the deep emission band centered around 2.2 eV was increased by a factor of 3. Also, the PL lifetime of the NBE peak at 293 K under the excitation density of 1 {mu}J/cm{sup 2}more » was increased from 49 to 60 ps. These results suggest that HITAB gave rise to improved alloy compositional homogeneity and reduced concentration of point defects.« less
  • The electrical properties of undoped and phosphorus-doped {alpha}-Si:H films with Si nanocrystals are studied. The silicon nanocrystals are formed by a solid-solid phase transition resulting from the nanosecond effect of a XeCl excimer laser on an amorphous film. The formation of the nanocrystals in the undoped films is accompanied by an increase in the electrical conductivity by two to three orders of magnitude and a simultaneous decrease in the effective activation energy of the conductivity from 0.7 to 0.14 eV. The nanocrystal sizes range from 2 to 10 nm for various laser treatment modes and are determined from Raman scatteringmore » data and high-resolution electron microscopy. The temperature dependence of the Fermi level is obtained by calculating the energies of the localized states of electrons and holes in the nanocrystals. It is shown that, as the temperature decreases, the Fermi level tends to the energy of the states in the Si nanocrystals for a wide concentration range of the dopant. The Fermi level's location close to the states in the nanocrystals is a consequence of the fact that these states are multicharged. It is found that phosphorus effectively transforms into an electrically active state during laser treatment of the doped amorphous Si films, which is an important consideration in the fabrication of shallow p-n junctions and contacts for amorphous Si films.« less