Hot-wire Chemical Vapor Deposition Method Research Articles

Distribution of charge carrier concentrations in epitaxial Ge and GeSn layers grown on n-=SUP=-+-=/SUP=--Si(001) substrates

Heteroepitaxial Ge or Ge1-xSnx layers were grown by hot-wire chemical vapor deposition on Si(001) substrates doped heavily with a donor (As or Sb) impurity. The same layers were also grown on high-resistance Si(001) substrates for comparison. The depth profiles of carrier concentration were measured in both types of layers using the capacitance-voltage method, and carrier mobilities were measured additionally by the Hall effect method in layers on high-resistance silicon. It was found that the layers grown on high-resistance substrates were p-type, while the layers grown in the same regimes on heavily doped substrates were n-type with electron concentration n=(4-9)·1016 cm-3 in Ge layers and n=(2-4)·1017 cm-3 in GeSn layers. It was established experimentally and theoretically that the effect of autodoping of Ge and GeSn layers is lacking in the hot-wire chemical vapor deposition method. In our view, the growth of n-type Ge and GeSn layers on n+-Si(001) substrates doped heavily with a donor (As or Sb) impurity is associated with the segregation of this impurity in the process of growth of a buffer Si layer and its subsequent incorporation into growing Ge or GeSn layers. Keywords: epitaxy, doping, Ge, Si, Sn, concentration.

Effect of SiH<sub>4 </sub>Flow Rates on the Structures and Properties of Si-Rich Silicon Nitride Films Prepared by Hot Wire Chemical Vapor Deposition

Silicon-rich silicon nitride thin films were deposited on the P type (100) of silicon and Corning7059 glass by hot-wire chemical vapor deposition method using SiH4and NH3as reaction gas source. The effects of SiH4flow rate on the structures and optical properties of the thin films were studied under optimizing other deposition parameters. The structures, band gap width and surface morphology of the thin films were characterized by Fourier transform infrared absorption spectroscopy (FTIR), ultraviolet-visible (UV-VIS) light transmittance spectra and scanning electron microscope (SEM), respectively. The experiment results show that, with increasing of the SiH4flow rate, the content of N and Si atoms in the thin films increases, and the Si-N bond density increases gradually, and the optical band gap of the films shows a trend of increasing. When the silane flow rate is less than 0.9sccm, there is no Si-H bond stretching vibration absorption peak, and silicon atoms mainly bond with nitrogen atoms. As the SiH4flow rate decreases, silicon clusters embedded in silicon nitride matrix gradually become smaller. When SiH4flow rate is 0.4sccm, we prepared the silicon cluster nanoparticles with an average diameter of about 50nm embedded in silicon nitride thin films matrix. Therefore, properly reduction of the SiH4flow rate is favorable for preparing the smaller silicon cluster nanoparticles in silicon rich silicon nitride thin films. The results lay the foundation for the preparation of silicon quantum dots thin film materials.

A-SiOx:H passivation layers for Cz-Si wafer deposited by hot wire chemical vapor deposition

In order to get the high photoelectric conversion efficiency a-Si:H/c-Si solar cells, high quality intrinsic hydrogenated passivation layer between the a-Si:H emitter layer and the c-Si wafer is necessary. In this work, hot wire chemical vapor deposition (HWCVD) is used to deposite intrinsic oxygen-doped hydrogenated amorphous silicon (a-SiOx:H) and hydrogenated amorphous silicon (a-Si:H) films as the intrinsic passivation layer for a-Si:H/c-Si solar cells. The passivation effect of the films on the c-Si surface is shown by the effective lifetime of the samples that bifacial covered by the films with same deposition parameters, tested by QSSPC method. The imaginary part of dielectric constant (ε2) and bonds structure of the layers are analyzed by Spectroscopic Ellipsometry(SE) and Fourier Transfom Infrared Spectroscopy(FTIR). It is concluded that: (1) HWCVD method can be used to make a-SiOx:H films as the passivation layer for a-Si:H/c-Si cells and the oxidation of the filament can be overcome by optimizing the deposition parameters. In our experiments, the lowest surface recombination velocity of the c-Si wafer is 3.0cm/s after a-SiOx:H films passivation. (2) Oxygen-doping in the amorphous silicon layers can increase H content and the band-gap of films, similar as the phenomenon of the films deposited by PECVD.

Synthesis of Cubic Nanocrystalline Silicon Carbide (3C-SiC) Films by HW-CVD Method

Cubic nanocrystalline silicon carbide (3C-SiC) films have been deposited by using the hot wire chemical vapor deposition (HW-CVD) method at a low substrate temperature and at high deposition rate. Structural, optical and electrical properties of these films have been investigated as a function of H2 dilution ratio. The formation of 3C-SiC films has been confirmed from low angle XRD analysis, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and dark and photoconductivity measurements. The FTIR spectroscopy analysis revealed that the bond densities of Si-H and C-H decrease while that of Si-C increases with increase in the H2 dilution ratio. The total hydrogen content decreases with increase in H2 dilution ratio and was found < 15 at. % over the entire range of H2 dilution ratio studied whereas the band gap show an increasing trend with increase in the H2 dilution ratio.

Ellipsometric, XPS and FTIR study on SiCN films deposited by hot-wire chemical vapor deposition method

SiCN films were deposited by hot-wire chemical vapor deposition (HWCVD) method using hexamethyldisilazane (HMDS). These films contain a lot of oxygen. Using HMDS with NH3, low oxygen content films can be obtained. It is found from the structure determination that Si‐N bonds are the vital bonds of SiCN films. It is also found that the highest amount of Si‐N bonds content SiCN has the highest amount of nitrogen and the amount of nitrogen is directly related to the properties of the films. The amount of oxygen, film density, the refractive index and optical band gap are strong functions of the amount of nitrogen in the films. With increasing nitrogen, the amount of oxygen decreases and with decreasing nitrogen, the amount of oxygen increases. The film density and optical band gap also increase with increasing nitrogen. On the other hand with increasing nitrogen, the refractive index decreases.

Impact of dilution gases on structure, properties and growth of hydrogenated nanocrystalline silicon (nc-Si:H) prepared by HW-CVD method

In this work we present a detailed structural, optical and electrical characterization of hydrogenated nanocrystalline silicon (nc-Si:H) thin films grown by hot wire chemical vapor deposition (HW-CVD) as a function of hydrogen (H2), argon (Ar) and helium (He) dilution of silane. A variety of analysis techniques such as Raman spectroscopy (RS), x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy and conductivity measurements were used to characterize the grown films. We observed that these properties are greatly influenced by dilution of silane with H2,Ar and He. Characterization of these films by Raman spectroscopy and low angle x-ray diffraction revealed that the increase in H2 andAr dilution of silane endorses the growth of crystallinity in the films whereas increase in He dilution of silane deteriorates the film properties.An attempt has beenmade to explain the fundamental differences in nanocrystallization growth mechanism by addition of H2, Ar and He in silane.

Highly Conducting Phosphorous Doped nc-Si:H Thin Films Deposited at High Deposition Rate by Hot-Wire Chemical Vapor Deposition Method

In this paper, we report the synthesis of highly conducting phosphorous doped hydrogenated nanocrystalline silicon (nc-Si:H) films at substantially low substrate temperature (200 degrees C) by hot-wire chemical vapor deposition (HW-CVD) method using pure silane (SiH4) and phosphine (PH3) gas mixture without hydrogen dilution. Structural, optical and electrical properties of these films were investigated as a function of PH3 gas-phase ratio. The characterization of these films by low-angle X-ray diffraction, Raman spectroscopy and atomic force microscopy revealed that, the incorporation of phosphorous in nc-Si:H induces an amorphization in the nc-Si:H film structure. Fourier transform infrared spectroscopy analysis indicates that hydrogen predominately incorporated in phosphorous doped n-type nc-Si:H films mainly in di-hydrogen species (Si-H2) and poly-hydrogen (Si-H2)n bonded species signifying that the films become porous, and micro-void rich. We have observed high band gap (1.97-2.37 eV) in the films, though the hydrogen content is low (< 1.4 at.%) over the entire range of PH3 gas-phase ratio studied. Under the optimum deposition conditions, phosphorous doped nc-Si:H films with high dark conductivity (sigma Dark -5.3 S/cm), low charge-carrier activation energy (E(act) - 132 meV) and high band gap (- 2.01 eV), low hydrogen content (- 0.74 at.%) were obtained at high deposition rate (12.9 angstroms/s).

Role of argon in hot wire chemical vapor deposition of hydrogenated nanocrystalline silicon thin films

Structural, optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) films, deposited from silane (SiH4) and argon (Ar) gas mixture without hydrogen by hot wire chemical vapor deposition (HW-CVD) method were investigated. Film properties are carefully and systematically studied as a function of argon dilution of silane (RAr). We observed that the deposition rate is much higher (4–23Å/s) compared to conventional plasma enhanced chemical vapor deposited nc-Si:H films using Ar dilution of silane (0.5–0.83Å/s). Characterization of these films with Raman spectroscopy revealed that Ar dilution of silane in HW-CVD endorses the growth of crystallinity and structural order in the nc-Si:H films. The Fourier transform infrared spectroscopic analysis showed that with increasing Ar dilution, the hydrogen bonding in the films shifts from di-hydrogen (Si–H2) and (Si–H2)n complexes to mono-hydrogen (Si–H) bounded species. The hydrogen content in the films increases with increasing Ar dilution and was found to be <4at.% over the entire range of Ar dilutions of silane studied. However, the band gap shows decreasing trend with increase in Ar dilution of silane and it has been attributed to the decrease in the percentage of the amorphous phase in the film. The microstructure parameter was found to be >0.4 for the films deposited at low Ar dilution of silane and ~0.1 or even less for the films deposited at higher Ar dilution, suggesting that there is an enhancement of structural order and homogeneity in the film. From the present study it has been concluded that the Ar dilution of silane is a key process parameter to induce the crystallinity and to improve the structural ordering in the nc-Si:H films deposited by the HW-CVD method.

WITHDRAWN: Ellipsometric and XPS study on SiCN films deposited by hot-wire chemical vapor deposition method

WITHDRAWN: Ellipsometric and XPS study on SiCN films deposited by hot-wire chemical vapor deposition method

Polymeric nanocoatings by hot-wire chemical vapor deposition (HWCVD)

Hot-wire chemical vapor deposition (HWCVD) of polymers affords the ability to coat objects of complex shape and nanoscale features. Using hot filaments to drive the gas phase chemistry has enabled the deposition of true linear polymers rather than the highly cross-linked organic networks typically associated with plasma enhanced CVD. The HWCVD method is particularly valuable for creating ultrathin layers of insoluble polymers, such as polytetrafluoroethylene (PTFE, Teflon-TM) and polyoxymethylene (POM, Delrin-TM). Additionally, organosilicon polymers, fluoroorganosilicon copolymers, and vinyl hydrocarbon polymers have all been demonstrated by HWCVD. The object to be coated remains at room temperature, promoting the required adsorption of film forming species.

Properties of hydrogenated amorphous silicon carbide films prepared at various hydrogen gas flow rates by hot-wire chemical vapor deposition

We prepared hydrogenated amorphous silicon carbide thin films using SiH 4, CH 4 and H 2 gases by the hot-wire chemical vapor deposition method and investigated the influence of hydrogen gas flow rate, F(H 2), on their film properties. For F(H 2) between 10 and 100 sccm, two groups of films were obtained: high E g opt. (group H) and low E g opt. (group L). The E g opt. in group H decreased from 2.27 to 2.14 eV when F(H 2) increased from 10 to 100 sccm, and the E g opt. in group L decreased from 1.93 to 1.78 eV when F(H 2) increased from 50 to 100 sccm. The difference in E g opt. between the two groups resulted from differences in the electrical power applied to the W wire and deposition on the W wire.

Deposition of microcrystalline silicon prepared by hot-wire chemical-vapor deposition: The influence of the deposition parameters on the material properties and solar cell performance

Microcrystalline silicon (μc-Si:H) of superior quality can be prepared using the hot-wire chemical-vapor deposition method (HWCVD). At a low substrate temperature (TS) of 185 °C excellent material properties and solar cell performance were obtained with spin densities of 6×1015cm−3 and solar cell efficiencies up to 9.4%, respectively. In this study we have systematically investigated the influence of various deposition parameters on the deposition rate and the material properties. For this purpose, thin films and solar cells were prepared at specific substrate and filament temperatures and deposition pressures (pD), covering the complete range from amorphous to highly crystalline material by adjusting the silane concentration. The influence of these deposition parameters on the chemical reactions at the filament and in the gas phase qualitatively explains the behavior of the structural composition and the formation of defects. In particular, we propose that the deposition rate is determined by the production of reactive species at the filament and a particular atomic-hydrogen-to-silicon ratio is found at the microcrystalline/amorphous transition. The structural, optical, and electronic properties were studied using Raman and infrared spectroscopies, optical-absorption measurements, electron-spin resonance, and dark and photoconductivities. These experiments show that higher TS and pD lead to a deterioration of the material quality, i.e., much higher defect densities, oxygen contaminations, and SiH absorption at 2100cm−1. Similar to plasma enhanced chemical-vapor deposition material, μc-Si:H solar cells prepared with HW i layers show increasing open circuit voltages (Voc) with increasing silane concentration and best performance is achieved near the transition to amorphous growth. Such solar cells prepared at low TS exhibit very high Voc up to 600 mV and fill factors above 70% with i layers prepared by HWCVD.