Microstructure related optical characterization of technologically relevant hydrogenated silicon thin films (original) (raw)
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The Eighth International Conference on Advanced Semiconductor Devices and Microsystems, 2010
The paper deals with the hydrogenated amorphous silicon (a-Si:H) films about 300 nm in thickness prepared by using rf-PECVD with hydrogen dilution R = 10 of the silane source gas in the amorphous growth regime onto clean Corning Eagle 2000 glass substrates at different deposition temperatures ranging from 50 to 200 °C. Structural and optical properties of the films were obtained from X-ray diffraction and UV-Vis spectrophotometry. The full width at half maximum of the first scattering peak decreases with increasing of the deposition temperature up to 150 °C and then remains constant. Optical band-gaps are from 1.65 to 1.76 eV, which slightly decrease with increasing deposition temperature, whereas the refractive index increases with increasing deposition temperature. This indicates that the density of the films at higher temperature has increased.
2012
Hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared in a home-built radio-frequency (rf) plasma enhanced chemical vapour deposition (PECVD) system have been studied. The rf powers were fixed in the range of 5 W-80 W. The optical properties and crystallinity of the films were studied by X-ray diffraction (XRD), Micro-Raman scattering spectroscopy, high resolution transmission electron microscope (HRTEM), and optical transmission and reflection spectroscopy. The XRD and Micro-Raman scattering spectra were used to investigate the evidence of crystallinity in order to determine the crystallite sizes and crystalline volume fraction in the films. The HRTEM image of the film was used to correlate with the crystallinity that was determined from XRD and Micro-Raman scattering spectra. Optical constants such as refractive index, optical energy gap, Tauc slope, Urbach energy and ionic constants were obtained from the optical transmission and reflectance spectra. From the results, it was interesting to found that the optical constants showed a good correlation with the crystallinity within the variation of rf power. Also, the ionic constants of the films showed an indication of the degree of crystallinity in the films. The variation of the optical energy gap with the rf power based on structure disorder and the quantum confinement effect is discussed. (C) 2011 Elsevier Ltd. All rights reserved.
Solar Energy Materials and Solar Cells, 2008
Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited from pure silane (SiH 4) and hydrogen (H 2) gas mixture by conventional plasma enhanced chemical vapour deposition (PE-CVD) method at low temperature (200 1C) using high rf power. The structural, optical and electrical properties of these films are carefully and systematically investigated as a function of hydrogen dilution of silane (R). Characterization of these films with low angle X-ray diffraction and Raman spectroscopy revealed that the crystallite size in the films tends to decrease and at same time the volume fraction of crystallites increases with increase in R. The Fourier transform infrared (FTIR) spectroscopic analysis showed at low values of R, the hydrogen is predominantly incorporated in the nc-Si:H films in the mono-hydrogen (Si-H) bonding configuration. However, with increasing R the hydrogen bonding in nc-Si:H films shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H 2) and (Si-H 2) n complexes. The hydrogen content in the nc-Si:H films decreases with increase in R and was found less than 10 at% over the entire studied range of R. On the other hand, the Tauc's optical band gap remains as high as 2 eV or much higher. The quantum size effect may responsible for higher band gap in nc-Si:H films. A correlation between electrical and structural properties has been found. For optimized deposition conditions, nc-Si:H films with crystallite size 7.67nmhavinggooddegreeofcrystallinity(7.67 nm having good degree of crystallinity (7.67nmhavinggooddegreeofcrystallinity(84%) and high band gap (2.25 eV) were obtained with a low hydrogen content (6.5 at%). However, for these optimized conditions, the deposition rate was quite small (1.6 Å /s).
Thin Solid Films, 1984
The electronic and optical properties of a-Si:H films prepared by the r.f. glow discharge method from a mixture of SiH4 and H2 were studied. The effects of variation in the concentration of H2 in the mixture were also investigated. The dark conductivity of a-Si:H films reaches a minimum at a low concentration of H2 and then increases with increasing concentration of H2. In addition, the photoconductive gain shows a maximum at a low concentration of H2. The band gap, however, remains virtually constant up to 25% H2 and then increases significantly as the H2 concentration is increased further. The activation energy increases slowly with H2 concentration up to 25% and then decreases with a further increase in the H2 concentration. IR vibrational spectra show an increase in the amount of Si—H bonding as the H2 concentration increases to 25% and then a decrease with a further increase in the H2 concentration.
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.
Vacuum, 2009
Thin film silicon Medium-range order Grain size Hydrogen dilution Microstructure X-ray diffraction Raman analysis FTIR spectrometry a b s t r a c t Plasma enhanced chemical vapour deposition (PECVD) has been used to prepare hydrogenated amorphous silicon (a-Si:H) thin films at different hydrogen dilution of silane source gas. The films were deposited on Corning glass 1737 substrate and on (100) oriented c-Si wafers and characterized by XRD diffraction, micro-Raman and FTIR spectrometry. Experimental data show evolution from amorphous to nanocrystalline silicon and contain the medium-range order (MRO) with varying hydrogen dilution during deposition. From X-ray diffraction and Raman analysis, it is found that the presence of crystalline phase depends on the kind of substrate and on the dilution scale.
Low Temperature Growth of Hydrogenated Silicon Prepared by PECVD from Argon Diluted Silane Plasma
Crystal Structure Theory and Applications, 2012
In order to contribute to the understanding of the optoelectronics properties of hydrogenated nanocrystalline silicon thin films, a detailed study has been conducted. The samples were deposited by 13.56 MHz PECVD (Plasma-Enhanced Chemical Vapor Deposition) of silane argon mixture. The argon dilution of silane for all samples studied was 96% by volume. The substrate temperature was fixed at 200˚C. The influence of depositions parameters on optical proprieties of samples was studied by UV-Vis-NIR spectroscopy. The structural evolution was studied by Raman spectroscopy and X-ray diffraction (XRD). Intrinsic-layer samples depositions were made in this experiment in order to obtain the transition from the amorphous to crystalline phase materials. The deposition pressure varied from 400 mTorr to 1400 mTorr and the rf power from 50 to 250 W. The structural evolution studies show that beyond 200 W, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing rf power and working pressure. Films near the amorphous to nanocrystalline transition region are grown at reasonably high deposition rates (~10 Å/s), which are highly desirable for the fabrication of cost effective devices. The deposition rate increases with increasing rf power and process pressure. Different crystalline fractions (21% to 95%) and crystallite size (6 -16 nm) can be achieved by controlling the process pressure and rf power. These structural changes are well correlated to the variation of optical proprieties of the thin films.