Microscopic structure of a VH${}_{4}$ center trapped by C in Si

Microscopic structure of a VH $_{4}$ center trapped by C in Si

Chao Peng, Haoxiang Zhang, Michael Stavola, W. Beall Fowler, Benjamin Esham, Stefan K. Estreicher, Andris Docaj, Lode Carnel, and Mike Seacrist

Phys. Rev. B 84, 195205 – Published 28 November 2011

Abstract

The Si materials typically used to fabricate solar cells often contain high concentrations of carbon and hydrogen impurities. One of the more thermally stable defects in Si that contains both C and H gives rise to a Si-H vibrational line at 2184.3 cm $^{- 1}$ . We show that this center also gives rise to additional weak Si-H and C-H lines at 2214.4 and 2826.9 cm $^{- 1}$ (4.2 K). When D is partially substituted for H, rich isotopic splittings of these IR lines are produced. An analysis of these data reveals that the 2184.3, 2214.4, and 2826.9 cm $^{- 1}$ lines are due to a VH $_{4}$ defect bound to a substitutional C impurity, i.e., a VH $_{3}$ -HC center.

Received 9 September 2011

DOI:https://doi.org/10.1103/PhysRevB.84.195205

Authors & Affiliations

Chao Peng¹, Haoxiang Zhang¹, Michael Stavola^1,*, W. Beall Fowler¹, Benjamin Esham^1,†, Stefan K. Estreicher², Andris Docaj², Lode Carnel³, and Mike Seacrist⁴

¹Department of Physics and the Sherman Fairchild Laboratory, Lehigh University, Bethlehem, Pennsylvania 18015, USA
²Texas Tech University, Lubbock, Texas 79409, USA
³REC Wafer AS, NO-3908 Porsgrunn, Norway
⁴MEMC Electronic Materials, St. Peters, Missouri 63376, USA

^*michael.stavola@lehigh.edu
^†Present address: Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

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Vol. 84, Iss. 19 — 15 November 2011

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Images

Figure 1
IR absorption spectrum (4.2 K) of a Si sample that had been hydrogenated by annealing in an H $_{2}$ ambient at 1250 °C followed by a rapid quench to room temperature. The sample was made from cast, mc-Si with a carbon concentration of [C] = 8.8 × 10 $^{17}$ cm $^{- 3}$ . The inset shows the structures of $H_{2}^{*}$ defects trapped by substitutional carbon in Si. The 2210 and 2688 cm $^{- 1}$ lines have been assigned to the SiH $_{bc}$ CH $_{ab}$ structure shown on the left (Refs. 6, 10, and 11). The 1922 and 2752 cm $^{- 1}$ lines have been assigned to the CH $_{bc}$ -SiH $_{ab}$ structure on the right (Refs. 9, 10, 11).Reuse & Permissions
Figure 2
IR spectra (4.2 K) of a mc-Si sample into which H had been introduced by an anneal at 1250 °C in an H $_{2}$ ambient followed by a rapid quench to room temperature. This sample was annealed sequentially for 30 min at the temperatures shown (in degrees Celsius).Reuse & Permissions
Figure 3
IR spectra (4.2 K, 0.3 cm $^{- 1}$ resolution) of mc-Si samples into which H (or H $+$ D) had been introduced by an anneal at 1250 °C in an H $_{2}$ (or H $_{2}$ $+$ D $_{2}$ ) ambient followed by a rapid quench to room temperature. These samples were subsequently annealed at 550 °C for 30 min to produce the hydrogen centers of interest. Spectrum (i) is for a sample that contained H alone. Spectrum (ii) is for a sample that contained H $+$ D with H > D. Spectrum (iii) is for a sample that contained H $+$ D with H < D. (a) Si-H stretching region. The Si-H lines are labeled by their VH $_{3 - n}$ D $_{n}$ -HC assignments. Each of the Si-H lines is split into a closely spaced doublet. The component of the doublet at lower frequency is for the center containing C-H. The component at higher frequency is for the center containing C-D. (b) C-H stretching region. The C-H components are labeled by the number $n$ of Si-D bonds in the VH $_{3 - n}$ D $_{n}$ -HC center.Reuse & Permissions
Figure 4
An expansion of the spectra shown in Fig. 3 that reveals the splittings of the Si-H stretching modes in the frequency range 2182–2188 cm $^{- 1}$ for samples with H > D and H < D.Reuse & Permissions
Figure 5
The isochronal (30 min) annealing dependence of the integrated intensities of the IR lines at 2223 and 2183.4 cm $^{- 1}$ . These hydrogen centers were produced by a thermal treatment (1250 °C, 1 h) in an H $_{2}$ ambient. (a) Si sample grown by the floating-zone method and with a carbon concentration of [C] = 0.2 × 10 $^{17}$ cm $^{- 3}$ . (b) Cast, mc-Si sample with a carbon concentration of [C] = 8.8 × 10 $^{17}$ cm $^{- 3}$ .Reuse & Permissions
Figure 6
The structure (Ref. 28) of the VH $_{3}$ -CH center predicted by crystal06 (Ref. 19). The C relaxes away for the vacancy by 0.29 Å, and each Si relaxes away by 0.18 Å. A H attached to Si is 1.83 Å from another H attached to Si, and it is 2.25 Å from the H attached to C.Reuse & Permissions

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