A study of the evolution of morphology of diamond films grown as a function of N2 gas additions to the CH4+H2 precursor in an HF-CVD system is presented. With the increase of admixture of N2 fraction, in contrast to earlier studies, the morphology was observed first togradually change from {111}-faceted crystallites texture to that of an intermediate cubo-octahedral crystallite texture and then gradually butfinally to transform completely into that of {100}-faceted crystallites. The threshold nitrogen concentration, [N2]thr, required to bring aboutthe said transition in morphology was much larger than it was reported previously. Moreover, the morphology transition required a larger[N2]thr when a large fraction of methane was employed. Further additions of nitrogen, that just exceeded the [N2]thr, resulted in growth offilms containing slightly bigger {100}-multi-layered grains or isolated planar {100}-platelets. For extremely large nitrogen additions, thegrowth of nanocrystalline or amorphous carbon films was observed. The N2 additions more than 50 vol.% did not yield any deposition.Raman scattering and photoluminescence measurements were used respectively for characterizing the quality and nitrogen doping in thefilms. These results are attributed to the possible catalytic role of atomic nitrogen at the growing surface.

Hydrogenated amorphous silicon germanium (a-SiGe:H) films were deposited using SiH4 and GeH4 mixture without H dilution by hot wire chemical vapor deposition (HW-CVD) technique. The electrical, optical and structural of these films are systematically studied as a function of substrate temperature (Tsub). The FTIR spectroscopic studies showed that a-SiGe:H films deposited at high Tsub contain H mainly the monohydride configuration whereas the films deposited at low Tsub has H in polyhydrides or (Si–H2)n complexes form. The low CH in a-SiGe:H films indicates that the growth of film is mainly from the atomic species evaporated from the hot filament and H gets incorporated in the film via gas phase reactions and substrate–gas interactions. Raman spectroscopic studies showed that the structural order of a-SiGe:H films improve with increase in Tsub. The Tsub=300°C was found to be the optimized substrate temperature for the synthesis of device quality a-SiGe:H films.

Here, we report a study of the effect of intentional incorporation of fluorine on the growth and properties of diamond films prepared by adding CF4 gas to the source gas mixture of CH4+H2 in a hot-filament chemical vapor deposition system. The films were characterized by using the scanning electron microscopy, Raman and photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements as a function of fluorine fraction in the gas phase. The films with fluorine fractions above a critical value were found to be composed of clean cubo-octahedral diamond crystals. The XPS measurements confirmed fluorine bonding at the diamond crystallite surfaces while the increase of width of 1332 cm−1 Raman band attributed to a possible incorporation of fluorine in the bulk of the diamond crystallites. The PL spectra indicated intensity enhancement of the 1.73 eV band while the 1.683 eV band intensity decreased drastically with an increase in fluorine fraction. These PL bands are proposed to originate from the defect centers formed, respectively, by multi-vacancies and mono-vacancies in the diamond crystallites while the fluorine incorporation in the bulk is proposed to induce reduction in the mono-vacancies with proportionate increase in the multi-vacancies.

In this letter, we report narrow band gap (1.39–1.53 eV) a-SiGe:H films with high photosensitivity (∼104–105) are grown successfully by HW-CVD using a mixture of (GeH4+SiH4) at low flow rates and without hydrogen dilution with higher deposition rates (>10 Å/s). These films are characterized by Raman spectroscopy, FTIR spectroscopy and UV–Visible spectroscopy. The band gap of a-SiGe:H films can be narrowed by increasing the germane gas fraction without apparent degradation in their electronic properties. The low hydrogen content in a-SiGe:H films indicates that the growth of a-SiGe:H films is mainly from the atomic species (Si, Ge and H) evaporated from the hot filament.

Studies on the effects of intentionally doped Si and N impurities on the growth and structural characteristics of diamond films prepared by hot-filament chemical vapor deposition are reported. The Si-doped diamond films exhibit enhancement of crystallite size whereas N-doped films indicate large changes in nucleation density and morphology. Both impurities were observed to show disorder effects at higher concentrations. The photoluminescence band at 1.683 eV was observed to enhance with increase in concentration of both impurities while it was expected to disappear when N alone was doped. The origin of the 1.683-eV band is correlated to the monovacancies stabilized by the impurity atoms.

The electrical, structural and optical properties of hydrogenated amorphous silicon (a-Si:H) films deposited from pure silane (SiH4) using hot wire chemical vapor deposition (HW-CVD) technique are systematically studied as a function of silane flow rate FSiH4 between 5 and 30 sccm. We found that the properties are greatly affected by the silane flow rate over the range we studied. The device quality a-Si:H films with a photosensitivity >105 were deposited by HW-CVD at a deposition rate >10 Å s−1 using low silane flow rate. However, a-Si:H films deposited at higher silane flow rate and/or higher deposition rates show degradation in their structural and electrical properties. The FTIR studies indicate that the hydrogen bonding in a-Si:H films shifts from mono-hydrogen (Si–H) to di-hydrogen (Si–H2) and (Si–H2)n complexes when films were deposited at higher silane flow rate. The hydrogen content in the a-Si:H films increases with increase in silane flow rate and was found to be less than 10 at.%. The Raman spectra show increase in disorder and the Rayleigh scattering with increase in silane flow rate. The optical band gap also shows an increasing trend with silane flow rate. Therefore, only the hydrogen content cannot be accounted for the increase in the optical band gap. We think that the increase in the optical band gap may be due to the increase in the voids. These voids reduce the effective density of material and increase the average Si–Si distance, which is responsible for the increase in the band gap. Silane flow rate of 5 sccm, appears to be an optimum flow rate for the growth of mono-hydrogen (Si–H) bonded species having low hydrogen content (∼4.25 at%) in a-Si:H films at high deposition rate (∼12.5 Å s−1), high photosensitivity (∼105) and small structural disorder.

The electrical, structural and optical properties of undoped and phosphorus doped μc-Si:H films prepared by a HW-CVD technique have been studied. The hydrogen (H2) dilution of silane has been varied carefully to produce undoped μc-Si:H films. The amorphous-to-microcrystalline transition was observed for a hydrogen dilution ratio >0.75. The phosphorus doped μc-Si:H films were deposited by varying the phosphine (PH3) gas flow rate. The structural properties of these films have been investigated by Raman spectroscopy, low angle X-ray diffraction spectroscopy and Fourier transform infrared vibrational spectroscopy. Electrical characterization has been carried out by dark conductivity and charge carrier activation energy measurements. The phosphorus doped μc-Si:H films showed that the addition of PH3 to the source gases promotes the growth of crystallinity. The increase in crystallite size and crystalline volume fraction with the addition of PH3 to the source gases indicates that it enhances the crystallization of the μc-Si:H film. Low angle XRD studies shows that the PH3 doped μc-Si:H does not show any preferential orientation crystallites. For optimized deposition conditions PH3 doped μc-Si:H films with high dark conductivity (0.4 S/cm), low activation energy (0.03 eV) and high band gap (1.82 eV) were obtained with a high deposition rate (13 Å/s). However, for these optimized conditions, the hydrogen content was relatively large (8.3 at.%).

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 (Variation in B2H6 gas phase ratio, dopant gas being diluted in hydrogen, affected the film properties through variation in doping level and hydrogen dilution). Characterization of these films from low angle X-ray diffraction and Raman spectroscopy revealed that the high conductive film consists of mixed phase of microcrystalline silicon embedded in an amorphous network. Even a small increase in hydrogen dilution showed marked effect on film microstructure. At the optimized deposition conditions, films with high dark conductivity (0.08 (Ωcm)−1) with low charge carrier activation energy (0.025eV) and low optical absorption coefficient with high optical band gap (∼2.0eV) were obtained. At these deposition conditions, however, the growth rate was small (6Å/s) and hydrogen content was large (9at%).

Hydrogen plasma treatment of stacking layers in a layer-by-layer (LBL) growth scheme effectively modulates the network structure from the surface into the bulk through the growth zone by abstraction of hydrogen from the Si:H matrix. It is an efficient way of reducing the microcrystalline transition layer so that virtual saturation of the crystallization may be obtained at a significantly low thickness of the sample compared to that obtained by a continuous mode of deposition. The growth of a highly conducting undoped µc-Si:H film at a stacked layer thickness of ∼650 Å is described. The film has a dark conductivity, σD, of ∼4×10-3 S·cm-1 and exhibits a very high crystallinity, as determined by Raman scattering and transmission electron microscope studies.

We report here enhancement of nucleation and growth of diamond films deposited by hot filament (HF) chemical vapour deposition (CVD) technique on as-received mirror-polished and scratched silicon substrates coated with In–Sn–O (ITO) buffer layers. The nucleation density (ND) for variously pretreated substrates is found to improve by a factor greater than 500 when they were coated with ITO layer. The role of scratches is shown to be mainly that of particle traps whereas their topographical features appear to have no role in nucleation.

Diamond films have been deposited using a chemical vapour deposition (CVD) technique involving a hybridization of the hot filament and the capacitively coupled radio-frequency (RF) plasma. The changes produced in the surface morphology and Raman spectra of these films are investigated as a function of the magnitude of RF power and deposition chamber pressure. The coupling of low levels of RF power with the hot filament CVD is observed to improve the growth rate as well as quality of the diamond films while higher levels of RF power decreased the growth rate and produced porous films containing needle-shaped microcrystals. These changes are attributed to the ion bombardment of the growing film due to the self-biasing effect of the RF plasma. (C) 1998 Elsevier Science S.A. All rights reserved.

Hydrogenated amorphous silicon carbide (a-SiC:H) films were deposited by using a combination of radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) and heated filament techniques with the objective of improving the quality of the films due to the possible beneficial effect of the latter technique. The atomic hydrogen produced via electron (emitted from the filament) impact dissociation of the process gases plays a significant role in improving the properties of the film such as the structure and bonding configuration. The electrons emitted from the hot filament also help in dissociation of methane molecules into different types of radicals. From the characterization of the films thus produced it is seen that by the combination of the two methods of deposition under optimised condition carbon is incorporated more as a Si–C bond which is structurally better. These results in better opto-electronic properties at high band gap of a-SiC:H which also shows lower light induced degradation than those of the films produced by only using the RF PECVD method.

The role of substrate pretreatments in the nucleation of CVD diamond on non-diamond substrates is not clearly understood. The CVD diamond nucleation on polished Si(100) pretreated with ultrasonication and patterned Si(100) without and with the identical pretreatment was studied. It was concluded that nucleation on pretreated surfaces occurs predominantly on the diamond residue, but the surface features produced play an important role as traps for diamond particulates during pretreatment, leading to more effective diamond seeding.

Diamond films have been deposited using a chemical-vapour-deposition (CVD) technique involving a hybridization of the hot filament and the capacitively coupled radio-frequency (r.f.) plasma at a reactor pressure of less than 2Torr. The changes produced in surface morphology and Raman spectra of these films are investigated as a function of the magnitude of r.f. power and the concentration of methane in hydrogen. The plasma excited by low levels of r.f. power was observed to improve the overall growth rate, whereas the medium level of r.f. power improved the quality. High levels of r.f. power, however, did not yield any deposition. The growth mechanism is suggested to involve an atomic H-induced etching process along with self-bias-induced energetic electron or ion bombardment of the growing film surface when different electrode geometries were used.

Highly conducting boron-doped microcrystalline silicon carbide (μc-SiC:H) thin films have been prepared by mercury sensitised photochemical vapor deposition. The chamber pressure was identified as one of the most crucial parameters governing the microcrystalline growth as well as the dopant incorporation in the microcrystalline thin films. Raman studies show the crystalline size and volume fraction decreases with increasing pressure. Transmission electron microscopy of such films reveal that the crystalline phase contains silicon only, so that carbon is incorporated only in the amorphous phase. The presence of carbon in these films was confirmed by secondary ion mass spectroscopy. There is an optimum pressure (0.5 Torr), depending upon the other deposition parameters, for which the conductivity of p-type μc-SiC:H film is highest (1.2×10−4 S cm−1).

Highly conductive n-type hydrogenated microcrystalline silicon (c-Si:H) films have been prepared by a radio-frequency plasma-enhanced chemical vapour deposition technique in an ultra-high-vacuum deposition system, using a mixture of hydrogen, silane and phosphine gases under a low RF power. The electrical, optical and structural properties of films of various thicknesses have been studied and correlated. Comparisons between n-type Si:H films deposited under high (120 mW ) and low (30 mW ) powers have been made. A conductivity as high as 7.5 S has been achieved for 180 Å thick films. Their crystallinity was confirmed by transmission electron microscopy and Raman spectroscopy. Changes in optical absorption at various thicknesses have been studied using photothermal deflection spectroscopy.

a-SixGe1−x:H films have been produced by employing the hot-filament assisted chemical vapour deposition (HF-CVD) technique for investigation of their structural characteristics using Raman scattering technique. We show here that the HF-CVD technique can be used to produce a-SixGe1−x:H alloy films of desired composition by using extremely low concentrations of GeH4 gas in SiH4 gas leading to what is termed as GeH4 starving filament condition. The mechanism responsible for the growth of the alloy films is discussed and the Raman results have been used to show that the films grown by the HF-CVD technique are structurally better ordered compared to those grown by using the plasma and sputter deposition techniques.

In situ two-step hot filament chemical vapor deposition (HFCVD) was developed to synthesize diamond films on aluminum oxide (Al2O3) substrates. The first step at higher temperature leads to precipitation of diamond-like carbon (DLC) and aluminum carbide (Al4C3) phases on the substrate surface, which promote enhanced nucleation of diamond growth during the subsequent second step of deposition. The presence of carbide phase in the interface region is found to lead to [100] oriented growth of diamond as well as enhanced adhesion properties.

Enhanced nucleation of polycrystalline diamond has been achieved on Si(100) with an intermediate layer of carbonitride. The carbonitride film was formed by an ion beam assisted deposition method and was characterized by Rutherford backscattering, X-ray photoelectron and laser Raman spectroscopies. The diamond deposition was accomplished using a hot filament chemical vapor deposition technique. Diamond film quality was examined with the help of laser Raman spectroscopy and scanning electron microscopy.

Hydrogenated amorphous silicon (a-Si:H) films were deposited by hot-filament-assisted chemical vapour deposition (HF-CVD), r.f. glow discharge CVD (GD-CVD) and their hybrid version (HF-GD-CVD). The films were characterized in terms of their structural disorder, H bonding, optical band gap and photoconductivity. These parameters for the HF-CVD films were compared with those of the GD-CVD and HF-GD-CVD films. The structural disorder in all the films was found to be mainly a linear function of the growth rate, although the degree of change varied depending on the technique used. The HF-CVD films appeared to be structurally better ordered than those of GD-CVD and HF-GD-CVD. The improved order in the HF-CVD films was attributed to the absence of charged particle bombardment and to the improved ratio of SiH species to SiH2 species. At higher growth rates, this ratio decreased and the disorder increased. At low growth rates, the structural and electronic qualities of the HF-CVD films were independent of the H content. The growth rate thus appeared to be the limiting factor in controlling the quality of a-Si:H films; this limiting value was higher in HF-CVD.