Hopping ε2 conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature

Zvyagin, I. P.; Kurova, I. A.; Nalgieva, M.; Ormont, N. N.

doi:10.1134/s1063782606010192

Cited by 5 publications

(8 citation statements)

References 9 publications

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“… Work functions Φ of the metals ( a ) Ag, ( b ) Cu, ( c ) Au and ( d ) Pt and that of hydrogen-terminated Si in vacuum [ 65 , 66 , 67 , 68 , 69 , 70 ]; the difference in work functions Δ E ; the Fermi energy level E F and that of the valence and conduction band of hydrogen-terminated silicon [ 71 ] ( E v (Si–H) or E c (Si–H) ) and of bulk silicon [ 72 , 73 ] ( E V (Si bulk ) or E c (Si bulk ) ); the energy levels of the valence bands at the metal–silicon contact ( E v (Si bulk /Me-Si ) or E v (Si–H/Me-Si) ); the Schottky barrier E sb ; the redox levels of the Me z+ /Me half-cells E (Me z+ /Me) ; and the equilibrium potentials of the 2H 3 O + /H 2 half-cells at the metal surface Equation Pot. (2H 3 O + /H 2 ) .…”

Section: Figurementioning

confidence: 99%

The Kinetics and Stoichiometry of Metal Cation Reduction on Multi-Crystalline Silicon in a Dilute Hydrofluoric Acid Matrix

Schönekerl

Acker

2020

Nanomaterials

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In this study, the process of metal cation reduction on multi-crystalline silicon in a dilute hydrofluoric acid (HF) matrix is described using Ag(I), Cu(II), Au(III) and Pt(IV). The experimental basis utilized batch tests with various solutions of different metal cation and HF concentrations and multi-crystalline silicon wafers. The metal deposition kinetics and the stoichiometry of metal deposition and silicon dissolution were calculated by means of consecutive sampling and analysis of the solutions. Several reaction mechanisms and reaction steps of the process were discussed by overlaying the results with theoretical considerations. It was deduced that the metal deposition was fastest if the holes formed during metal ion reduction could be transferred to the valence bands of the bulk and surface silicon with hydrogen termination. By contrast, the kinetics were lowest when the redox levels of the metal ion/metal half-cells were weak and the equilibrium potential of the H3O+/H2 half-cells was high. Further minima were identified at the thresholds where H3O+ reduction was inhibited, the valence transfer via valence band mechanism was limited by a Schottky barrier and the dissolution of oxidized silicon was restricted by the activity of the HF species F−, HF2− and H2F3−. The findings of the stoichiometric conditions provided further indications of the involvement of H3O+ and H2O as oxidizing agents in addition to metal ions, and the hydrogen of the surface silicon termination as a reducing agent in addition to the silicon. The H3O+ reduction is the predominant process in dilute metal ion solutions unless it is disabled due to the metal-dependent equilibrium potential of the H3O+/H2 half-cell and the energetic level of the valence bands of the silicon. As silicon is not oxidized up to the oxidation state +IV by the reduction of the metal ions and H3O+, water is suspected of acting as a secondary oxidant. The stoichiometric ratios increased up to a maximum with higher molalities of the metal ions, in the manner of a sigmoidal function. If, owing to the redox level of the metal half-cells and the energetic level of the valence band at the metal–silicon contact, the surface silicon can be oxidized, the hydrogen of the termination is the further reducing agent.

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Section: Figurementioning

confidence: 99%

The Kinetics and Stoichiometry of Metal Cation Reduction on Multi-Crystalline Silicon in a Dilute Hydrofluoric Acid Matrix

Schönekerl

Acker

2020

Nanomaterials

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“…The redox strength of the Ag + /Ag half-cell must be at least at the energetic level of the valence bands of the bulk silicon or hydrogen-terminated silicon at the silver/silicon contact to enable the valence transfer. The energetic level of the valence band of the bulk silicon without metal contact in the vacuum state is E V (Si bulk ) = −0.41 eV [ 26 , 80 , 81 ] and that of the hydrogen-terminated silicon is E V (Si-H x ) = −0.68 eV [ 19 , 82 ] ( Figure 2 a). After the initial silver/silicon contacting, band bending of the conduction and the valence bands of silicon occurs due to Fermi energy alignment at the contact.…”

Section: Resultsmentioning

confidence: 99%

“…The initial platinum deposition occurs at a redox strength of the PtCl 6 2− /Pt half-cell of E (PtCl 6 2− /Pt) = 0.65 V vs. SHE at b Pt ( diss., t = 0 s) = 4.5 × 10 −7 mol∙kg −1 (example 1) in interaction with the bulk silicon. The valence band of the hydrogen-terminated silicon is not initially accessible ( E V (Si-H x ) = 0.68 eV [ 82 ], Figure 10 a). The reduction of PtCl 6 2− occurs via the intermediate PtCl 4 2− species to Pt (metal state).…”

Section: Resultsmentioning

confidence: 99%

“… ( a ) Energy diagram of Cu 2+ /Cu + and H 3 O + reduction at the Cu/Si contact with the indication of the upper and lower limits of the redox strengths of the Cu 2+ /Cu and Cu + /Cu half-cells [ 28 ] and those of the equilibrium potentials of the 2H 3 O + /H 2 half-cell [ 33 ] and energetic levels of the valence bands of the bulk and hydrogen-terminated silicon ( E V (Si bulk ) [ 26 , 80 , 81 ], E V (Si-H x ) [ 82 ]) and their bending based on the differences of Φ Cu and Φ Si-Hx [ 83 , 84 , 85 , 86 , 87 , 88 ] and the findings from [ 26 ], ( b ) amounts of Cu deposition (Δ n Cu ( diss., t = 3600 s)); ( c ) Si dissolution (Δ n Si ( diss., t = 3600 s)) and ( d ) molecular H 2 formation (Δ n H 2 ( g, t = 3600 s)) after t = 3600 s processing, as well as stoichiometric ratios of ( e ) Cu deposition and Si dissolution (Δ n Cu : Δ n Si ( diss., t = 3600 s)) and ( f ) stoichiometric ratios of molecular H 2 formation and Si dissolution (Δ n H 2 : Δ n Si ( g or diss., t = 3600 s)) relative to the initial Cu 2+ molality b Cu ( diss., t = 0 s). …”

Section: Figurementioning

confidence: 99%

“…It can be concluded from the position of the valence bands of silicon at the copper/silicon contact that the Cu 2+ /Cu and Cu + /Cu half-cells and, up to the threshold of b Cu (diss., t = 0 s) = 2.5 × 10 −4 mol•kg −1 , the 2H 3 O + /H 2 half-cell can participate in the oxidation of silicon, but not the too weak Cu 2+ /Cu + half-cell. [28] and those of the equilibrium potentials of the 2H3O + /H2 half-cell [33] and energetic levels of the valence bands of the bulk and hydrogen-terminated silicon (EV (Sibulk) [26,80,81], EV (Si-Hx) [82]) and their bending based on the differences of ΦCu and ΦSi-Hx [83][84][85][86][87][88] and the findings from [26], (b) amounts of Cu deposition (Δn Cu (diss., t = 3600 s)); (c) Si dissolution (Δn Si (diss., t = 3600 s)) and (d) molecular H2 formation (Δn H2 (g, t = 3600 s)) after t = 3600 s processing, as well as stoichiometric ratios of (e) Cu deposition and Si dissolution (Δn Cu:Δn Si (diss., t = 3600 s)) and (f) stoichiometric ratios of molecular H2 formation and Si dissolution (Δn H2:Δn Si (g or diss., t = 3600 s)) relative to the initial Cu 2+ molality b Cu (diss., t = s). [28] and those of the equilibrium potentials of the 2H 3 O + /H 2 half-cell [33] and energetic levels of the valence bands of the bulk and hydrogen-terminated silicon (E V (Si bulk ) [26,80,81], E V (Si-H x ) [82]) and their bending based on the differences of Φ Cu and Φ Si-Hx [83][84][85][86][87][88] and the findings from [26], (b) amounts of Cu deposition (∆n Cu (diss., t = 3600 s)); (c) Si dissolution (∆n Si (diss., t = 3600 s)) and (d) molecular H 2 formation (∆n H 2 (g, t = 3600 s)) after t = 3600 s processing, as well as stoichiometric ratios of (e) Cu deposition and Si dissolution (∆n Cu:∆n Si (diss., t = 3600 s)) and (f) stoichiometric ratios of molecular H 2 formation and Si dissolution (∆n H 2 :∆n Si (g or diss., t = 3600 s)) relative to the initial Cu 2+ molality b Cu (diss., t = 0 s).…”

Section: Copper Deposition Onto Multicrystalline Siliconmentioning

confidence: 99%

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The Role of the Molecular Hydrogen Formation in the Process of Metal-Ion Reduction on Multicrystalline Silicon in a Hydrofluoric Acid Matrix

Schönekerl

Acker

2021

Nanomaterials

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Metal deposition on silicon in hydrofluoric acid (HF) solutions is a well-established process for the surface patterning of silicon. The reactions behind this process, especially the formation or the absence of molecular hydrogen (H2), are controversially discussed in the literature. In this study, several batch experiments with Ag+, Cu2+, AuCl4– and PtCl62– in HF matrix and multicrystalline silicon were performed. The stoichiometric amounts of the metal depositions, the silicon dissolution and the molecular hydrogen formation were determined analytically. Based on these data and theoretical considerations of the valence transfer, four reasons for the formation of H2 could be identified. First, H2 is generated in a consecutive reaction after a monovalent hole transfer (h+) to a Si–Si bond. Second, H2 is produced due to a monovalent hole transfer to the Si–H bonds. Third, H2 occurs if Si–Si back bonds of the hydrogen-terminated silicon are attacked by Cu2+ reduction resulting in the intermediate species HSiF3, which is further degraded to H2 and SiF62–. The fourth H2-forming reaction reduces oxonium ions (H3O+) on the silver/, copper/ and gold/silicon contacts via monovalent hole transfer to silicon. In the case of (cumulative) even-numbered valence transfers to silicon, no H2 is produced. The formation of H2 also fails to appear if the equilibrium potential of the 2H3O+/H2 half-cell does not reach the energetic level of the valence bands of the bulk or hydrogen-terminated silicon. Non-hydrogen-forming reactions in silver, copper and gold deposition always occur with at least one H2-forming process. The PtCl62– reduction to Pt proceeds exclusively via even-numbered valence transfers to silicon. This also applies to the reaction of H3O+ at the platinum/silicon contact. Consequently, no H2 is formed during platinum deposition.

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Electrical transport mechanisms in three dimensional ensembles of silicon quantum dots

Balberg

2011

Journal of Applied Physics

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In this review, we try to derive a comprehensive understanding of the transport mechanisms in three dimensional ensembles of Si quantum dots (QDs) that are embedded in an insulating matrix. This understanding is based on our systematic electrical measurements as a function of the density of Si nanocrystallites as well as on a critical examination of the available literature. We conclude that in ensembles of low density QDs, the conduction is controlled by quantum confinement and Coulomb blockade effects while in the high density regime, the system behaves as a simple disordered semiconductor. In between these extremes, the transport is determined by the clustering of the QDs. In view of the clustering, two types of transitions in the electrical and optical properties of the system are identified. In order to understand them, we introduce the concept of “touching.” The application of this concept enables us to suggest that the first transition is a local carrier deconfinement transition, at which the concentration of the non “touching” QDs reaches its maximum, and that the other transition is associated with the onset of percolation in a continuous disordered network of “touching” QDs. It is hoped that our conclusions for the entire possible density range will provide guidance for the discussion and understanding of the transport in ensembles of semiconductor QDs in general and in ensembles of Si and Ge QDs in particular.

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Hopping ε2 conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature

Cited by 5 publications

References 9 publications

The Kinetics and Stoichiometry of Metal Cation Reduction on Multi-Crystalline Silicon in a Dilute Hydrofluoric Acid Matrix

The Kinetics and Stoichiometry of Metal Cation Reduction on Multi-Crystalline Silicon in a Dilute Hydrofluoric Acid Matrix

The Role of the Molecular Hydrogen Formation in the Process of Metal-Ion Reduction on Multicrystalline Silicon in a Hydrofluoric Acid Matrix

Electrical transport mechanisms in three dimensional ensembles of silicon quantum dots

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