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Journal ArticleDOI

Amorphous and microcrystalline silicon films deposited by hot-wire chemical vapor deposition at filament temperatures between 1500 and 1900 °C

01 Jun 1996-Journal of Applied Physics (American Institute of Physics)-Vol. 79, Iss: 11, pp 8748-8760
TL;DR: The optical, electronic and structural properties of thin films deposited by Hot-Wire chemical vapor deposition with filament temperatures, Tfil, between 1500 and 1900 C from silane and hydrogen are studied in this paper.
Abstract: The optical, electronic and structural properties of thin films deposited by Hot‐wire chemical vapor deposition with filament temperatures, Tfil, between 1500 and 1900 °C from silane and hydrogen are studied. The substrate temperature, Tsub, was kept constant at 220 °C. Amorphous silicon films (a‐Si:H) are obtained at high filament temperatures, low deposition pressures and low hydrogen‐to‐silane flow rate ratio (Tfil∼1900 °C, p<30 mTorr and FH2/FSiH4≤1). At these deposition conditions, high growth rates are observed (rd≥10 As−1) both with and without hydrogen dilution, and no silicon deposition was observed on the filaments. However, if a lower filament temperature is used (Tfil∼1500 °C) a transition from a‐Si:H to microcrystalline silicon (μc‐Si:H) occurs as the pressure is decreased from above 0.3 Torr to below 0.1 Torr. The highest dark conductivity and lowest activation energy, of ∼1 Scm−1 and <0.1 eV, respectively, were observed for μc‐Si:H deposited at p∼50 mTorr. In this Tfil regime, μc‐Si:H growt...
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors describe how high-quality intrinsic hydrogenated amorphous silicon (a-Si: H), as well as purely intrinsic single-phase hydrogenated polycrystalline silicon (poly-Si, H), can be obtained by hot-wire chemical vapour deposition (HWCVD).
Abstract: We describe how high-quality intrinsic hydrogenated amorphous silicon (a-Si: H), as well as purely intrinsic single-phase hydrogenated polycrystalline silicon (poly-Si: H), can be obtained by hot-wire chemical vapour deposition (HWCVD). The deposition parameter space for these different thin-film materials has been optimized in the same hot-wire deposition chamber. A review of the earlier work shows how such high-quality films at both ends of the amorphous-crystalline scale have evolved. We incorporated both the amorphous and the polycrystalline silicon films in n-i-p solar cells and thin-film transistors (TFTs). The solar cells, with efficiencies in excess of 3%, confirm the material quality of both the a-Si: H and the poly-Si: H i-layer materials, but more work is needed to improve the interfaces with the doped layers. The TFTs made with a-Si: H and poly-Si: H channels show quite similar characteristics, such as a field-effect mobility of 0·5cm2 V−1 s−1, indicating that the channel region has a...

109 citations

Journal ArticleDOI
TL;DR: In this paper, a-Si:H TFTs with a current switching ratio of 5×105, a threshold voltage of 6.3 V, and an electron field effect mobility in the saturation regime of 0.6 cm2/V
Abstract: Hydrogenated amorphous silicon, a-Si:H, prepared with the hot-wire chemical vapour deposition technique is incorporated in thin-film transistors (TFTs). High-quality TFTs are fabricated with this type of a-Si:H, which we deposited at a rate of 17 A/s. TFTs with a current switching ratio of 5×105, a threshold voltage of 6.3 V, and an electron field-effect mobility in the saturation regime of 0.6 cm2/V s are obtained. These TFTs do not show any threshold voltage shift upon prolonged gate voltage application, in contrast to conventional a-Si:H TFTs. This has been achieved by optimizing the electronic properties of the hot-wire layer, and by optimizing the interface between the gate dielectric and the hot-wire layer.

52 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe direct detection of gaseous free radicals produced as a function of filament temperature in the hot-wire chemical vapor deposition (HW-CVD) of amorphous silicon from silane.

45 citations

Journal ArticleDOI
TL;DR: In this article, Boron-doped hydrogenated microcrystalline silicon (μc-Si:H) films were prepared using hot-wire chemical vapor deposition (HWCVD) technique Structural, electrical and optical properties of these thin films were systematically studied as a function of B2H6 gas (diborane) phase ratio.

45 citations

Journal ArticleDOI
TL;DR: In this paper, the removal of hydrogen from the growth surface during silane plasma deposition of silicon is correlated with the transition from amorphous to micro-crystalline film structure.
Abstract: Removal of hydrogen from the growth surface during silane plasma deposition of silicon is correlated with the transition from amorphous to microcrystalline film structure. Plasma deposition experiments were performed using a pulsed gas technique, where repeated steps of thin amorphous silicon film deposition, and atomic hydrogen (or deuterium) exposure are used to form microcrystalline and polycrystalline thin films at substrate temperatures below 250 °C. Infrared absorption and Raman spectroscopy are used to estimate the silicon-hydrogen bonding concentrations, and characterize crystal structure, respectively. Hydrogen elimination probed using real-time differentially pumped mass spectroscopy demonstrates that during atomic deuterium exposure, hydrogen abstraction by deuterium, rather than silicon etching, is the primary mechanism for hydrogen removal from the depositing surface. Polycrystalline material, with no shoulder at 480 cm−1 in the Raman spectrum, and grain sizes greater than 1000 A, as determin...

44 citations

References
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Journal ArticleDOI
TL;DR: In this article, the optical constants of amorphous Ge were determined for the photon energies from 0.08 to 1.6 eV, and the absorption is due to k-conserving transitions of holes between the valence bands as in p-type crystals.
Abstract: The optical constants of amorphous Ge are determined for the photon energies from 0.08 to 1.6 eV. From 0.08 to 0.5 eV, the absorption is due to k-conserving transitions of holes between the valence bands as in p-type crystals; the spin-orbit splitting is found to be 0.20 and 0.21 eV in non-annealed, and annealed samples respectively. The effective masses of the holes in the three bands are 0.49 m (respectively 0.43 m); 0.04 m, and 0.08 m. An absorption band is observed below the main absorption edge (at 300 °K the maximum of this band is at 0.86 eV); the absorption in this band increases with increasing temperature. This band is considered to be due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties and which are considered to be associated with vacancies. The absorption edge has the form: ω2ϵ2∼(hω−Eg)2 (Eg = 0.88 eV at 300 °K). This suggests that the optical transitions conserve energy but not k vector, and that the densities of states near the band extrema have the same energy-dependence as in crystalline Ge. A simple theory describing this situation is proposed, and comparison of it with the experimental results leads to an estimate of the localization of the conduction-band wavefunctions.

8,184 citations

MonographDOI
R. A. Street1
30 Aug 1991
TL;DR: In this article, the electronic density of states of amorphous silicon and their electronic states have been investigated in terms of defect reactions, thermal equilibrium and metastability, as well as their electronic properties.
Abstract: 1. Introduction 2. Growth and structure of amorphous silicon 3. The electronic density of states 4. Defects and their electronic states 5. Substitutional doping 6. Defect reactions, thermal equilibrium and metastability 7. Electronic transport 8. Recombination of excess carriers 9. Contacts, interfaces and multilayers 10. Amorphous silicon device technology.

2,003 citations

Journal ArticleDOI
TL;DR: In this article, the formation kinetics of μc-Si:H has been investigated through the film depositions and plasma diagnoses in widely-scanned glow discharge plasma conditions; RF power density, SiH 4 /H 2 ratio and substrate temperature.
Abstract: The formation kinetics of μc-Si:H has been investigated through the film depositions and plasma diagnoses in widely-scanned glow discharge plasma conditions; RF power density, SiH 4 /H 2 ratio and substrate temperature. The roles of H and SiH x adsorbed on the surface as well as impinging ions have been discussed in relation to volume fraction and crystallite size of μc films, and continuous control of crystallite size has been demonstrated using a triode system. Hall mobility of the deposited μc-Si:H films has also been presented as a function of the volume fraction of μc.

531 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device-quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament.
Abstract: Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

464 citations

Journal ArticleDOI
TL;DR: It is suggested that the enhancement of the scattering cross section, which scales with the observed optical-absorption coefficient and diffuse elastic light scattering, is due to enhanced coupling of the electromagnetic field of the incident light to the charge-density fluctuations at the grain boundaries of the quasi-isolated crystallites.
Abstract: The intensity of the Raman-active ${\ensuremath{\Gamma}}_{25\mathcal{'}}$ mode of nanometer-sized crystalline silicon, nc-Si, normalized to that of calcium fluoride, ${\mathrm{CaF}}_{2}$, at 322 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was measured for samples deposited under controllably varied conditions. Changes of the intensity by a factor of up to approximately 6.7 were found. These are correlated with the lattice expansion and with the compressive stress in thin films of the material. It is suggested that the enhancement of the scattering cross section, which scales with the observed optical-absorption coefficient and diffuse elastic light scattering, is due to enhanced coupling of the electromagnetic field of the incident light to the charge-density fluctuations at the grain boundaries of the quasi-isolated crystallites.

397 citations