Properties of bonded hydrogen in hydrogenated amorphous silicon and other hydrogenated amorphous silicon alloys

doi:10.1016/0022-3093(94)00578-8

Journal of Non-Crystalline Solids

Volume 182, Issues 1–2, 1 March 1995, Pages 90-102

https://doi.org/10.1016/0022-3093(94)00578-8 Get rights and content

Abstract

This paper discusses bonding configurations of hydrogen atoms (H) in amorphous silicon and amorphous-silicon-based alloys. Recent experiments combined with theoretical calculations have identified two new aspects of bonded H that have not previously been addressed: (i) the formation of H bonds between H atoms on SiH groups and electronegative atoms or groups such as O atoms or NH groups; and (ii) an inherent metastability of H-bonded clusters as driven by the trapping of charged carriers. Both of these are shown to play important roles in (i) a photo-induced defect metastability such as the Staebler-Wronski effect, and (ii) hydrogen evolution from amorphous silicon nitrides. Finally, the concepts developed for a-Si:H alloys apply equally well to defect metastability at SiSiO₂ interfaces as in metal-oxide-semiconductor devices including insulated-gate field-effect transistors.

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Vegard's-law-like dependence of the activation energy of blistering on the x composition in hydrogenated a-Si<inf>x</inf>Ge<inf>1-x</inf>
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In this paper the average among them is used. For SiH that average is made among the data reported in the seven references [45–51] and it is ε(SiH) = 3.45 eV. As to GeH, the data of five papers are used [47,52–56] yielding an average value of ε(GeH) = 3.10 eV.
Surface quality is a key issue in semiconductor structures for device applications. Typical surface defects are blisters. Here we investigate on the relationship between the activation energy of blistering and the composition x in hydrogenated amorphous a-Si_xGe_1-x by employing layers deposited by Radio Frequency sputtering. To this aim the blistering activation energy was determined by means of Arrhenius plots in several samples with different compositions, including x = 0 and x = 1. Each sample was submitted to heat treatment up to the temperature where the onset of blistering was observed by change of the surface reflectivity. It is found that a linear dependence of the activation energy on x similar to the Vegard's law holds. The experimental result is supported by reaction kinetics modeling. It is suggested that the key step for the formation of blisters is the scission of the SiH and GeH bonds. The related energetic reaction leading to the formation of H₂ molecules in a-Si_xGe_1-x follows a linear law as a function of the x composition similarly to the activation energy.
Remote plasma-processing (RPP), medium range order, and precursor sites for dangling bond defects in "amorphous-Si(H)" alloys: Photovoltaic and thin film transistor devices
2014, Surface and Coatings Technology
Citation Excerpt :
In contrast to previous electron spin echo envelope modulation (ESEEM) studies [20], it was demonstrated that the distance between H atoms and dangling-bond defects can be well below 0.3 nm. In 1998, our group had presented several papers in which a universal mechanism for charged defect formation (i) at hydrogenated Si–SiO2 interfaces [21], and (ii) in the bulk of hydrogenated a-Si (a-Si:H) was identified [18]. The model calculations demonstrated defect metastability, and included effects of OH and NH bonding as well.
Remote plasma processing (RPP) provides pathways to the formation of photovoltaic (PV) and thin-film-transistor (TFT) devices that include buried interfaces. This is made possible by separate and independent control of (i) plasma excited O- and N-atom deposition precursors in a up-stream plasma chamber, combined with (ii) down-stream injection of Si- and Ge-atoms with control gas flow rates providing control of buried interface bonding at monolayer levels. Devices with intrinsic, B p-type and P n-type “a-Si(H)” & “a-Si,Ge(H)” layers require 10% bonded H in monolayer (SiH arrangements) and deposition and/or annealing at temperatures between 240 and 275 °C. Deposition from SiH₄ with either PH₃ or B₂H₆ dopant gasses provides spectrally reflecting films which can be annealed yielding fine-grain films for gate, or source and drain regions for TFTs or FETs.
Spectroscopic detection of medium range order in hydrogenated amorphous silicon, a-Si(H): Applications in photovolatics, thin film transistors and Si-based microelectronics
2013, Physics Procedia
Hydrogenated amorphous silicon, a-Si_1-xH_x, with ~ at.10% or x ~0.1±0.02, is used in photovoltaics (PV), and thin film transistors (TFT's). Amorphous Si (a-Si) thin films, thought to be free of H, are used as precursors for polycrystalline gate electrodes in microelectronics. PV and TFT alloys has been deposited by the glow discharge method (GD), remote plasma-enhanced chemical vapor deposition (RPECVD, and reactive magnetron sputtering (RMS) with bonded-H determined by deposition precursors and substrate temperatures. Two conditions are required for low Si dangling bond densities ~0.5 to 1x10¹⁶ cm⁻³: (i) a bonded monohydride, Si-H, concentration of ~10 at. % H, and (ii) a deposition, and/or a post-deposition anneal at ~240 °C to 300 °C. These reduce strain by introducing medium range order (MRO) as nano-meter scale aperiodically-assembled clusters. Si L_2,3 X-ray absorption spectroscopy (XAS) has been used to confirm MRO extending beyond short-range order (SRO) of continuous random networks (CRN) through observation of ligand-field split d-state features. These are associated with symmetry-adapted linear combinations (SALCs) of atomic states forming molecular orbital valence bands. XAS and photoelectron spectroscopy (PES) studies have confirmed that a-Si used for microelectronic applications also has MRO as well. This is associated with a H-transfer reaction from an Si-H bond of the cluster into a Si-H-Si bonding arrangement on near-neighbor sites. MRO has also identified by other spectroscopic techniques: spectroscopic ellipsomentry (SE), and ultra-violet or X-ray photoemission spectroscopy (UPS or XPS). The same H-atom motion induced by absorption of sun-light is responsible for the Staebler-Wronski Effect (SWE); the generation of Si-atom dangling bonds that degrade PV performance.
Electronic defect states of amorphous silicon nitride
2003, Optical Materials
Citation Excerpt :
The defect mechanisms, under light illumination and thermal annealing, involve with transitions between charged states of N and Si DBs. The fourfold coordinated N4 bond is not easily formed in a-SiNx:H. Yet, the bond energy calculations [14] have shown that the positively charged ammonium complex H2–N+–Si2 can be a stable state in a-Si:N:H films. In some heavily hydrogenated silicon nitride films [8], the N–H bond-stretching frequency is at about 3335 cm−1, which is 15 cm−1 smaller than the regular 3350 cm−1 of the NH group.
The theoretical tight-binding/cluster–Bethe-lattice method is used to study the electronic states induced by the local bonding structures in amorphous silicon nitride. The electronic density of states of the clusters containing various bonding structures are calculated. The Si dangling bond (DB) can create a deep defect states in the gap. The N DB can induce a state below the top of the valence band. The Si–Si bond induces electronic states near the top of the valence band. For the N–N bond, there is an anti-bonding p $π^{∗}$ state near the valence band edge and an anti-bonding p $σ^{∗}$ state in the energy gap. The SiH and NH bonds do not introduce defect states in the energy gap. They can give energy disorder to the band edges and contribute to the potential fluctuations. The N site of the Si₂NH₂ complex can be positively charged and form a defect pair with the negatively charged Si DB. The Si₂NH₂ complex can be a precursor for the charged N DBs before annealing.
Electron cyclotron resonance plasma enhanced chemical vapour deposition and optical properties of SiO<inf>x</inf> thin films
1998, Journal of Non-Crystalline Solids
Silicon–oxygen alloys ranging from amorphous silicon to silicon dioxide have been deposited from electron cyclotron resonance SiH₄/O₂/Ar plasmas onto radio frequency biased substrates at room temperature. Hundred Watt microwave power, a working pressure of 2 mTorr, a total gas flow rate of 20 sccm, and 13.5 Watt radio frequency bias power were used. Refractive indices of 3.8 to 1.48 were measured by ellipsometry at a wavelength of 632.8 nm. Deposition rates for different SiH₄/(SiH₄+O₂) gas flow ratios were between 4.3 and 7.5 nm min⁻¹. Fourier transform infrared spectroscopy revealed a gradual evolution of the chemical composition of the films from amorphous silicon to silicon dioxide with change in gas phase composition. For silicon dioxide films, the centre frequency of the main Si–O stretching band is 1060 cm⁻¹, whereas full width at half maximum is approximately 94 cm⁻¹. Presence of Si–OH bonds is not detectable for any of the films. The amount of hydrogen in the films is considerably less than that in similar layers deposited by radio frequency plasma enhanced chemical vapour deposition, and for amorphous silicon it does not exceed 1.5×10²² cm⁻³. The presence of a single band at 486 cm⁻¹ in the Raman spectrum of the a-Si film confirmed its amorphous structure.
Thermal stability of the optical band gap and structural order in hot-wire-deposited amorphous silicon
2009, Journal of Materials Science

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^☆: This research is supported in part by the Office of Naval Research, the NSF Engineering Center for Advanced Electronic Materials Processing at North Carolina State University, the North Carolina Sematech Center of Excellence, and the Department of Energy.

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Section 3. DefectsProperties of bonded hydrogen in hydrogenated amorphous silicon and other hydrogenated amorphous silicon alloys☆

Abstract

Phys. Rev.

J. Non-Cryst. Solids

J. Vac. Sci. Technol.

J. Vac. Sci. Technol.

J. Non-Cryst. Solids

Appl. Phys. Lett.

Phys. Rev.

Philos. Mag.

Phys. Rev.

J. Non-Cryst. Solids

J. Vac. Sci. Technol.

Phys. Rev.

Solid State Commun.

J. Phys. (Paris) C4

Phys. Rev.

Chemical Bonds and Bond Energy

Section 3. Defects
Properties of bonded hydrogen in hydrogenated amorphous silicon and other hydrogenated amorphous silicon alloys☆