Glow Discharge Decomposition Of SiH4 Research Articles

Compositional characterization of a-SiC:H films by infra-red spectroscopy

Amorphous Si1−xCx:H films (0 < x < 0.6) deposited on c-Si substrates by r.f. plasma-enhanced chemical vapour deposition were studied as functions of the material composition and hydrogen content by infra-red reflectivity and transmission spectroscopy. The films were prepared by glow discharge decomposition of SiH4 and CH4 gases at 50 W r.f. power, 20 Pa of pressure and 300°C of substrate temperature. From analysis of the CH and SiH stretching absorption bands it is shown that the content of hydrogen atoms bonded to Si is not appreciably affected by the precursor CH4/SiH4 flow ratio. On the contrary, the fraction of hydrogen incorporated in CH bonds increases with the relative CH4 to SiH4 flow rate. We analysed the evolution of the refractive index with the growth conditions. In particular, we found that the contribution of the hydrogen content to the minima of the interference fringes in the IR reflectivity spectra is negligible, and all changes in the absolute value are directly attributed to changes in the material composition. This gives a measure of the composition of the film, when comparing the refractive index and the carbon content obtained by X-ray photoelectron spectroscopy.

Structural Study of Amorphous SiNx:H Films Produced by Plasma-Enhanced Chemical Vapor Deposition

The structure of amorphous SiNx:H films prepared by glow discharge decomposition of SiH4 and NH3 has been investigated by measurements of X-ray diffraction intensity. The first peak in atomic density function obtained by analysis of diffraction intensity indicates a nearest-neighbor distance of 1.74 Å which corresponds to the Si–N bond length of 1.730–1.745 Å in β-Si3N4 crystal. We have also estimated the Si–N–Si–N bond configuration by comparing the corrected observed scattering intensity with the scattering intensity calculated using a simple bonding model. It has been shown that a Si atom bonded to a N atom with a coplanar bond has two tetrahedral bonds in the plane of the coplanar bonds.

Effect of Annealing on Photoluminescence Spectra and Film Structure in a-SiNx:H

The change of photoluminescence (PL) spectra and structure in hydrogenated amorphous silicon-nitrogen alloy films deposited by glow-discharge decomposition of SiH4 and NH3 with various mixture ratios has been investigated as a function of annealing temperature. The PL spectra have a single broad band in the visible range and its peak energy shifts toward lower energy for NH3/SiH4≤6.0 and higher energy for NH3/SiH4≥6.8 by annealing at 600°C. The PL-peak energy varies linearly with optical band gap. Annealing at temperatures higher than 400°C breaks Si–H and N–H bonds to form Si–N bonds for all samples. The Si–Si bond concentration decreases with annealing for NH3/SiH4≥7.5, while it is considered to increase for NH3/SiH4=5. The change observed in the PL-peak energy and the optical band gap with annealing is associated with the variation in the concentration not only of Si–N but also of Si–Si bonds.

Structure of high-photosensitivity silicon-oxygen alloy films

Amorphous silicon-oxygen alloy films with various composition have been prepared by r.f. glow discharge decomposition of SiH4 and CO2 gas mixtures. The analysis of infrared absorption spectra and x-ray photoemission spectra shows that the film consists of two phases, a silicon-rich phase and an oxygen-rich phase. We suggest that this two-phase structure results in the high photoconductivity with wide optical gap in these films.

Piezoelectric Effect on Plasma Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films

As a potential method for controlling the surface reaction of plasma CVD, mechanical vibration generated by a piezoelectric device was applied on the substrate during glow discharge decomposition of SiH4. The application of 2MHz vibration dramatically improved the photoconductivity of a-Si:H films prepared at a substrate temperature of 120°C. IR and CPM spectra for the films revealed that the piezoelectric vibration remarkably modulated the amorphous network structure and reduced the defect density to 4.3x1014cm −3 which is the best among the values ever reported.

High-fluidity chemical vapor deposition of silicon dioxide

Silicon dioxide has been deposited by the glow discharge decomposition of SiH4 and O2 at substrate temperatures below −80 °C, where the thermal reaction on the surface was basically suppressed. Ion flux onto the growth surface was significantly reduced by employing a triode reactor. Oxide deposition onto surfaces with narrow features proceeds from the bottom of a trench or groove and results in planarization of the topography. Such high-fluidity chemical vapor deposition is inferred to occur through the formation of liquified precursors on the cooled surface.

High Quality a-SiO:H Films and Their Application to a-Si Solar Cells

ABSTRACTHydrogenated amorphous silicon oxide (a-SiO:H) films were prepared by rf glow discharge decomposition of SiH4, CO2 and H2 gas mixture. These films showed better properties than a-SiC:H films. By applying the a-SiO:H to the p-layer, we attained an efficiency of 12.5% for 1cm2 single junction solar cells and a total-area efficiency of 10.1% for 30cm × 40cm tandem submodules.

Wide-Gap Polysilane Produced by Plasma-Enhanced CVD at Cryogenic Temperatures

ABSTRACTPolysilane thin films have been grown by the rf glow discharge decomposition of SiH4 at substrate temperatures ranging from -84 to -110°C. The infrared absorption spectra have shown that polysilane chains (SiH2)n are predominantly incorporated in the matrix together with SiH3 which terminates the chain. Also, the infrared absorption band at 2120∼2140 cm-1 and a distinct Raman peak at ∼430 cm-1indicates that fairly long chains (SiH2)n with n&gt;11 are produced. Polysilane prepared at -110°C has an optical bandgap of about 3.1 eV and exhibits a visible luminescence around 2.75 eV at 100 K.

Electronic and optical properties of a-Si1-xCx films prepared from a H2-diluted mixture of SiH4 and CH4

Abstract This paper deals with the electronic and optical properties of a-Si1-xCx films deposited by glow-discharge decomposition of SiH4 and CH4 mixtures, in most cases with H2 dilution. These results complement the structural and compositional data on the same specimens reported in the preceding paper. A systematic investigation of optical absorption, dark conductivity, photoconductivity and H evolution has been carried out as a function of the carbon content of specimens prepared with and without H2 dilution. It is shown that the former leads to a significant increase in the photosensitivity of specimens having optical gaps of up to 2.1 eV, in agreement with the work of Matsuda and co-workers. Further support for the improvement in electronic properties produced by H, dilution is obtained from density-of-states measurements, using the space-charge-limited current technique, and from photothermal deflection spectroscopy results, both of which show a significant decrease in the density of deep defect sta...

An XPS study of chemical order in hydrogenated amorphous silicon‐carbon alloy films

AbstractThe Si(2p) and C(ls) XPS spectra of a‐Si1‐xCx: H films are studied before and after argon ion etching. Two specimens, with x = 0.26 and x = 0.39 are prepared by glow discharge decomposition of SiH4 and CH4 gases diluted in hydrogen. The as‐prepared specimens show adsorbed free carbon and silicon oxides which are substantially removed by ion etching. Both specimens indicate a preference for bonding between Si and C atoms, even after the randomizing effect of the ions. The specimen with x = 0.39 shows essentially complete chemical order while the other specimen shows some carbon not bonded to silicon as well as a substantial amount of silicon not bonded to carbon. The results agree with electron diffraction observations on the same specimens.

Amorphous Si and Si-based alloys from glow-discharge plasma

Abstract

I n s i t u ellipsometry comparison of the nucleation and growth of sputtered and glow-discharge a-Si:H

We report the results of ellipsometry measurements performed during the growth of hydrogenated amorphous silicon (a-Si:H) thin films on crystalline silicon substrates using ion beam sputtering. The data have been compared to our earlier results for high-quality a-Si:H prepared by glow-discharge decomposition of SiH4, and significant differences in the initial nucleation and microstructural evolution have been deduced for the two types of films. For the glow-discharge a-Si:H, the in situ pseudodielectric function data provided evidence for the convergence of initial growth microstructure in the first ∼50 Å, leaving a-Si:H of near bulk Si–Si bond-packing density at the interface to the c-Si substrate. After the nucleation process, growth was found to be nearly layer by layer. The data for the sputtered a-Si:H also reveal the formation of a low-density microstructure in the initial stages of growth. However, in contrast to the glow-discharge films, the microstructure does not converge, and an extensive layer (∼200–400 Å) of bond-packing density lower than the bulk is left at the interface to the substrate. The effect of hydrogen incorporation on this and other aspects of the microstructural evolution of the sputtered films is discussed. Finally, similarities observed between the microstructural evolution of the sputtered films and poorer-quality glow-discharge films provide insights into the growth mechanisms.

Preparation of microcrystalline Si1−xCx thin films

Si1−xCx (x∼0.5) films have been prepared by glow discharge decomposition of SiH4, CH4, and H2 gas mixtures. Their structural properties are examined by infrared absorption and reflection electron diffraction. It is found that the film structure depends on the ratio of source gas to hydrogen gas [(SiH4+CH4)/H2], and microcrystalline films can be obtained even at a low temperature of 350 °C when the source gas ratio is less than 0.004.

表面粗さのオージェプロファイルへの影響

The effect of surface roughness on depth profile in Auger Electron Spectroscopy (AES) has been experimentally studied. Films of a-Si : H were prepared by the glow discharge decomposition of SiH4 on substrates with various roughness and characterized by AES analysis. In AES depth profiles, the broadening width of a-Si : H/substrate interface increased with enhancing the roughness of the substrate. On the other hand, the decrease in Auger peak to peak intensity of a-Si : H layer is not observed. These results show that the broadening of iprofile is caused not by the sputter induced roughness, but by the surface roughness of the substrate. Consequently the broadening width (ΔW) of the interface is confirmed to be explained by expression as a function of X, such as ΔW=a·exp (b · X), where X is the roughness of substrate, and, a and b are coefficient.

Structure and Defects in Amorphous Si–O Films

Amorphous Si–O films prepared by magnetron sputtering and glow discharge decomposition were investigated by infrared (IR) absorption, electron spin resonance and photoconductivity measurements. Amorphous Si–O films prepared by a glow discharge decomposition of SiH4+O2 gas mixture has a high photoconductivity with a wide optical gap, suggesting that hydrogenated amorphous Si–O films are not inferior to hydrogenated amorphous Si–C and Si–N as widegap materials. The compositional dependence of the peak position of the Si–O–Si stretching mode in the IR absorption spectrum for films prepared with various deposition conditions reveals that under a low substrate temperature Si and O atoms tend to be randomly mixed without O–O bonds while under a high substrate temperature they tend to be phaseseparated into Si and SiO2.

Properties of Hydrogenated Amorphous Si-N Prepared by Various Methods

The results of optical absorption, infrared absorption, electron spin resonance and photoluminescence measurements are presented for hydrogenated amorphous Si-N films prepared by three different methods; magnetron sputtering of an Si target in an Ar+N2+H2 gas mixture, glow-discharge decomposition of SiH4+N2, and glow-discharge decomposition of SiH4+NH3. The improvement in the properties of films prepared by the third method, e.g., the sharp band tail and low dangling-bond density, is explained mainly in terms of the structual softening due to the existence of N-H bonds. The fatigue of the photoluminescence due to illumination is found to be more prominent and the recovery due to annealing less prominent in N-incorporated film than in a-Si:H.

Electronic and Optical Properties of A—(Si, Ge):H Alloys

AbstractWe describe the preparation and electronic and optical properties of amorphous (Si, Ge) alloys. A—(Si, Ge):H alloys were prepared by glow discharge decomposition of SiH4 and GeH4. The bandgap was varied between 1.78 and 1.42 eV by changing the GeH4:SiH4 ratio in the gas phase. We find a distinct influence of growth temperature on electronic properties. Films grown at low temperatures (200–250C) tendto have much lower photo conductivity than films grown at higher temperatures (300–325C). The electron (μ τ) products of high temperature films are general&gt; 1X10–7 cm2/V. We also obtain very sharp valence band tails in a—(Si, Ge):H alloys, with slopes of ∼ 40 meV. The hole (μ τ) product is generally ∼1–2X10–8 cm2/V. All these properties suffer a catastrophic decline when bandgap is reduced below about 1.5 eV.

Reactive sputtering of amorphous silicon in Ne, Ar, and Kr

We have characterized hydrogenated amorphous silicon films prepared by rf diode sputtering in varying partial pressures of Ne, Ar, and Kr. The mechanisms of ion bombardment of growing film surface due to large negative floating potentials at low gas pressures can explain the observed film characteristics. These inert gas effects are in contrast to those seen in inert gas dilution studies of glow discharge decomposition of SiH4. These differences are examined and lead to general conclusions about the effect of bombardment in minimizing microstructure, and in producing electronically-active defects. Other bombardment processes are also discussed.

High current post-hydrogenated chemical vapor deposited amorphous silicon p-i-n diodes

Amorphous silicon p-i-n diodes have been fabricated for the first time by chemical vapor deposition and post-hydrogenation in a hydrogen plasma. By analyzing the current-voltage characteristics we obtain current densities up to 50 A/cm2 and rectification ratios better than 107 for 3-V applied bias. A characteristic reversible breakdown voltage is observed up to voltages of ∼20 V. These results are compared with those obtained on amorphous silicon p-i-n diodes prepared by glow discharge decomposition of SiH4.

Electrophotographic Properties of RF Glow Discharge-Produced Amorphous Si: H Film

Amorphous silicon film with extremely high dark resistivity, 1013–1014 ohm-cm, at room temperature is prepared for the first time by glow discharge decomposition of SiH4 with suitable doping by B2H6 and a slight content of oxygen. The a-Si: H film exhibits an excellent photoconductive sensitivity in visible wavelength range. Room temperature electron and hole drift mobilities are found to be almost the same in a-Si: H film deposited at 200°C of the substrate temperature and 10-3 B2H6/SiH4 doping gas ratio. These unique properties of a-Si: H films are utilized for bi-chargable monolayer electrophotographic photoreceptor, and positive and negative reproduced images have been firstly demonstrated by utilizing a-Si: H deposited drum.