Influence of hydrogen-bonding configurations on the physical properties of hydrogenated amorphous silicon (original) (raw)
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Infrared absorption strength and hydrogen content of hydrogenated amorphous silicon
Physical review. B, Condensed matter, 1992
We have used infrared transmission and nuclear-reaction analysis to determine the ir absorption strength of the Si-H wagging and stretching modes in hydrogenated amorphous silicon (a-Si:H). The films were deposited by plasma-assisted chemical vapor deposition and reactive magnetron sputtering.
Materials Science and Engineering: B, 1993
Highly photoconductive hydrogenated amorphous silicon films (a-Si:H) have been deposited by a new cyclic deposition method involving thermal chemical vapour deposition at substrate temperatures of around 500 °C and intermittent hydrogen plasma treatment steps. The main features of the films are the low hydrogen content of less than 5at.% and the high photoconductivity-to-dark conductivity ratio of around 105. By simply varying either the plasma power or the duration of the hydrogenation time a transition from amorphous to microcrystalline films is observed. The electronic quality and stability under illumination of the best amorphous films obtained so far by the cyclic method were comparable with those of films deposited by conventional glow discharge.
Hydrogen in amorphous and microcrystalline silicon films prepared by hydrogen dilution
Journal of applied …, 1996
Hydrogen incorporation in silicon layers prepared by plasma-enhanced chemical-vapor deposition using silane dilution by hydrogen has been studied by infrared spectroscopy ͑IR͒ and elastic recoil detection analysis ͑ERDA͒. The large range of silane dilution investigated can be divided into an amorphous and a microcrystalline zone. These two zones are separated by a narrow transition zone at a dilution level of 7.5%; here, the structure of the material cannot be clearly identified. The films in/near the amorphous/microcrystalline transition zone show a considerably enhanced hydrogen incorporation. Moreover, comparison of IR and ERDA and film stress measurements suggests that these layers contain a substantial amount of molecular hydrogen probably trapped in microvoids. In this particular case the determination of the total H content by IR spectroscopy leads to substantial errors. At silane concentrations below 6%, the hydrogen content decreases sharply and the material becomes progressively microcrystalline. The features observed in the IR-absorption modes can be clearly assigned to mono-and/or dihydride bonds on ͑100͒ and ͑111͒ surfaces in silicon crystallites. The measurements presented here constitute a further indication for the validity of the proportionality constant of Shanks et al. ͓Phys. Status Solidi B 110, 43 ͑1980͔͒, generally used to estimate the hydrogen content in ''conventional'' amorphous silicon films from IR spectroscopy; additionally, they indicate that this proportionality constant is also valid for the microcrystalline samples.
1998
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Properties of hydrogenated amorphous silicon produced at high temperature
Hydrogenated amorphous silicon thin ®lm transistors (a-Si:H TFTs) were fabricated by plasma enhanced chemical vapor deposition system. Silicon nitride and a-Si:H were deposited at 150°C. The a-Si:H TFT had ®eld eect mobility of 0.75 cm 2 /V s, sub-threshold voltage swing of 0.5 V/dec and on/o current ratio >1.5´10 6 . The hydrogen was added during the gate insulator of SiN x deposition. The deposition rate of SiN x decreased and the SiH/NH ratio increased with the increasing H 2 gas¯ow rate. The a-Si:H TFT fabricated with the gate insulator with larger SiH/NH ratio had smaller threshold voltage and less threshold voltage shift after the gate bias stress (30 V, 10 3 s). Ó
Effect of hydrogen on stability of amorphous silicon thin films
Solar Energy Materials and Solar Cells, 2002
This paper presents results of the investigation of hydrogen influence on the stability of low pressure chemical vapour deposition a-Si films. We measured boron-or phosphorus-doped films post-hydrogenated by ion implantation with different hydrogen doses. The dark conductivity after fast quenching and slow cooling and the isothermal relaxation were measured at different annealing temperatures. It was found that higher hydrogen concentration causes greater metastable changes but shorter relaxation time of defects. r
Deposition and extensive light soaking of highly pure hydrogenated amorphous silicon
Applied Physics Letters, 1996
We have developed an ultrahigh vacuum plasma-enhanced chemical-vapor deposition system, and deposited high-purity device-quality hydrogenated amorphous silicon films. High sensitivity secondary ion mass spectrometry measurements show that impurity contents in the bulk of the present films are reduced to 2ϫ10 15 cm Ϫ3 for O, 7 -10ϫ10 15 cm Ϫ3 for C, and 5ϫ10 14 cm Ϫ3 for N; these impurities are normally present at fairly high levels. Nevertheless, extensive light soaking of the films resulted in a defect density as high as 5ϫ10 17 cm Ϫ3 , which is well above the impurity content. This result excludes those models of photoinduced degradation that postulate one-to-one correlation between light-induced defects and O, C, or N impurity atoms.
International Journal of Theoretical and Applied Nanotechnology, 2021
In order to investigate various properties of hydrogenated amorphous silicon (a-Si:H) for improvement of low conversion efficiency and stability of solar cells, a series of quantum simulations based on the density functional theory combined with the tight binding model were performed for a-Si:H with various hydrogen concentrations and cooling rates. The radial distribution function (RDF) for Si-Si pairs indicates that samples with higher H concentration (20% and 25%) give a structure in better agreement with experiments, but the RDF of Si-H pairs suggests that samples with lower H concentration (14%) may give more appropriate structure. The coordination number () analysis indicates that more defects (dangling bonds and floating bonds) exist in 20% and 25% H concentration samples. Overall, a-Si:H with 14% H concentration gives most preferable structure. The cooling rate has also much effect on the structure. Sample with the slowest cooling rate is slightly more structured based on Si-Si pair RDF and. The electron transport of a-Si and a-Si:H were evaluated and the superiority of a-Si:H was confirmed.
Solar energy materials …, 2007
Hydrogenated amorphous silicon (a-Si:H) thin films were deposited from pure silane (SiH 4 ) using hot-wire chemical vapor deposition (HW-CVD) method. We have investigated the effect of substrate temperature on the structural, optical and electrical properties of these films. Deposition rates up to 15 Å s À1 and photosensitivity $10 6 were achieved for device quality material. Raman spectroscopic analysis showed the increase of Rayleigh scattering in the films with increase in substrate temperature. The full width at half maximum of TO peak (G TO ) and deviation in bond angle (Dy) are found smaller than those obtained for P-CVD deposited a-Si:H films. The hydrogen content in the films was found o1 at% over the range of substrate temperature studied. However, the Tauc's optical band gap remains as high as 1.70 eV or much higher. The presence of microvoids in the films may be responsible for high value of band gap at low hydrogen content. A correlation between electrical and structural properties has been found. Finally, the photoconductivity degradation of optimized a-Si:H film under intense sunlight was also studied. r