Amorphous Silicon Carbon Alloy Films Research Articles

Emitting properties of a-Si:C:H films with a gold submicron grating

In this study reflection and photoluminescence spectra of a-Si:C:H thin film with gold grating on it was examined theoretically and experimentally. The hydrogenated amorphous amorphous silicon-carbon alloy films were fabricated by the PECVD technique. Arrays of gold stripes with different gold width were created by lift-off e-beam lithography. Reflection, and PL spectra has been measured by a Fourier imaging spectroscopy. The theoretical calculations are in a good agreement with experimental results. From the PL spectra it follows, that the TE polarization gives sharper and more efficient PL signal than the TM polarization, and PL efficiency almost does not depend on gold stripes widths. It was shown that only in TE modes the PL outcouples from the gratings owing to the fact that there is no plasmon’s affect in this polarization.

UV–VISIBLE, FTIR AND RAMAN SPECTRA FROM LARGE BAND-GAP HYDROFLUORINATED AMORPHOUS SILICON–CARBON THIN FILMS

Hydrofluorinated amorphous silicon–carbon alloy films (a-Si,C:H,F) were grown by a CVD glow-discharge method. The samples were prepared from SiH4 , H2 and CF4 source gas mixtures. The structural and bonding characterstics of the materials were studied using FTIR and Raman spectroscopy. In addition to hydrogen passivation, the inclusion of fluorine in the films is found to further suppress undesirable disorder states. The optical band gap E opt of the materials was determined from the Tauc relation for the optical absorption spectra. They were found to increase from about 2 eV to 3.5 eV with increasing carbon content in the samples.

Comparative study of annealing and oxidation effects in a-SiC:H and a-SiC thin films deposited by radio-frequency magnetron sputtering

Thermal annealing and oxidation effects in hydrogenated (a-SiC:H) and nonhydrogenated (a-SiC) amorphous silicon–carbon alloy films deposited by radio-frequency magnetron sputtering have been studied. The a-SiC:H and a-SiC films were thermally treated in dry Ar, wet Ar, and dry O 2 atmospheres at temperatures up to 1150 °C. The principal effects of thermal annealing in an inert atmosphere on a-SiC:H films were found to be redistribution of hydrogen bonds and formation of amorphous graphitic carbon clusters. Strong oxidation of a-SiC:H was observed after thermal treatment in oxygen at 700 °C while annealing in wet argon caused partial oxidation. Oxidation of the carbon clusters in porous a-SiC:H structures is suggested to be responsible for the higher oxidation efficiency of a-SiC:H in oxygen. In contrast, the structure of a-SiC films remained almost unchanged after annealing in dry argon up to 1000 °C. No oxidation of a-SiC was detected until 1000 °C. Water vapor was found to be more effective at oxidizing a-SiC at 1000 °C than dry oxygen, which is similar to the oxidation behavior of crystalline SiC. The high thermal and oxidation stabilities of a-SiC layers were attributed to the dense and nanovoid-free amorphous SiC network.

Correlation between structural and opto-electronic properties of a-Si 1 − xC x:H films deposited by plasma enhanced chemical vapour deposition

Hydrogenated amorphous silicon carbon alloy films of different carbon content were prepared by Plasma Enhanced Chemical Vapor Deposition using silane and methane with helium dilution and were characterized to study their opto-electronic, structural and defective properties. A linear correlation between micro structural disorder and overall disorder has been demonstrated. Further, it has been shown that the increase in the intrinsic disorder leads to an increase in the defect density while the increase in voids results in the decrease in the mass density for the studied films.

Room temperature pulsed laser deposition of Si x C thin films in different compositions

Amorphous silicon–carbon alloy films in different compositions were prepared by pulsed laser deposition from two-component targets containing pure silicon and carbon parts. The silicon–carbon ratio in the films was varied by adjusting the number of laser shots on the constituent silicon and carbon targets. The composition, optical properties, thickness, and bonding structure of the films were determined by backscattering spectrometry, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, respectively. Backscattering spectrometry data were used to determine the deposition rate of silicon and carbon. This enabled the calculation of the number of the shots onto each target to reach a predefined composition. As the film composition changed from carbon to silicon, it was shown that the microscopic and macroscopic properties of the films also changed from a diamond-like carbon phase to an amorphous silicon phase via graphite- and silicon-carbide-like composite.

Surface Plasmon Resonance on Gold and Silver Films Coated with Thin Layers of Amorphous Silicon−Carbon Alloys

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.

Spectroscopic ellipsometry study of hydrogenated amorphous silicon carbon alloy films deposited by plasma enhanced chemical vapor deposition

The optical properties of the hydrogenated amorphous silicon carbon alloy films, prepared by plasma enhanced chemical vapor deposition technique from silane and methane gas mixture diluted in helium, have been investigated using variable angle spectroscopic ellipsometry in the photon energy range from 0.73 to 4.59 eV. Tauc–Lorentz model has been employed for the analysis of the optical spectra and it has been demonstrated that the model parameters are correlated with the carbon content as well as to the structural properties of the studied films.

Study on the microstructural and overall disorder in hydrogenated amorphous silicon carbon films

Hydrogenated amorphous silicon carbon alloy films of different carbon compositions were prepared by plasma enhanced chemical vapor deposition system using silane and methane with helium dilution and were characterized by structural and optical techniques to understand the microstructural and overall disorder in amorphous semiconductors. The study demonstrates that the increase of the microstructural disorder results in an increase in the overall disorder and the local defect density induced by carbon incorporation seems to dominate the overall defect structure of the network.

Laser annealing study of PECVD deposited hydrogenated amorphous silicon carbon alloy films

The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites.

Effect of H 2 dilution on Cat-CVD a-SiC:H films

Effect of hydrogen (H 2) dilution of the Silane (SiH 4), acetylene (C 2H 2) gas mixture during the deposition of hydrogenated amorphous silicon carbon alloy (a-SiC:H) films by Cat-CVD process shows that the H 2 dilution induced additional carbon incorporation, leading to an increase of the carbon content in the films from 52% to 70% for the maximum H 2 dilution employed. A slight increase in graphitic carbon in the films deposited with H 2 dilution is also observed. A drastic increase in the optical band gap E g from 2.5 eV for zero dilution to 3.5 eV is observed for a H 2 dilution of 10 sccm. Raman spectra for the films deposited with increasing H 2 dilution indicate structural changes in the amorphous network associated with increasing graphitic carbon.

Laser induced crystallization of hydrogenated amorphous silicon-carbon alloys

Laser induced crystallization of hydrogenated amorphous silicon carbon alloy (a-Si1−xCx:H) films has been investigated by means of synchrotron x-ray diffraction. The a-Si1−xCx:H films were deposited on (100) silicon wafers by very high frequency plasma enhanced chemical vapor deposition at 100MHz in hydrogen diluted silane-methane gas mixtures. The substrate was kept at 250°C or 350°C and the stoichiometry was changed from x=0.20 to 0.63. The structural characterization of the as-grown films has been carried out by Rutherford backscattering (hydrogen concentration) and infrared spectroscopy (film ordering). The films were irradiated by a KrF excimer laser (248nm) with varying energy density and number of pulses. After irradiation, the formation of SiC crystallites has been revealed by synchrotron x-ray diffraction. Besides SiC nanocrystals, the formation of crystalline Si and graphite is observed for under- (x<0.50) and over-stoichiometric (x>0.50) samples, respectively. The essential role played by hydrogen concentration and hydrogen bonding configuration in determining the melting threshold and the consequent SiC grain formation is highlighted.

Optical bandgap and quantum well model in hydrogenated amorphous silicon carbon alloy films

Hydrogenated amorphous silicon carbon alloy (a-SiC : H) films of various composition were prepared by the rf glow discharge decomposition of acetylene and silane as well as ethylene and silane and were also annealed for various annealing temperatures. Careful and detailed IR absorption and the optical bandgap (Eopt) measurements were undertaken for a-SiC : H films of different composition (x) and annealing temperatures (Ta). Interesting variation of Eopt with x and Ta have been observed. Our study demonstrates, for the first time, that the models involving alloying or/and ordering break down and the proposed quantum well model based on heterogeneity is found to be the only model capable of explaining the observed variation of Eopt. This, consequently, may have considerable implications.

Doping of a-SiCX:H films including μc-Si:H by hot-wire CVD and their application as a wide gap window for heterojunction solar cells

Impurity doping using B 2 H 6 gas using hot-wire CVD has been tried for hydrogenated amorphous silicon-carbon (a-SiC x :H) alloy films including hydrogenated microcrystalline silicon (μc-Si:H) with carbon content, C/(Si + C), of about 28%. The dark- and photoconductivities of B-doped samples are larger than those of undoped samples. The activation energy for dark conductivity of the B-doped sample with the doping gas ratio, B 2 H 6 /(SiH 4 + CH 4 ), of about 0.054% is 0.17 eV. This value is smaller than that of the undoped sample. The P-doped samples also show larger dark- and photoconductivities and smaller activation energy than the undoped samples.

Correlation between the opto-electronic and structural parameters of amorphous semiconductors

The variation of opto electronic parameters like the optical band-gap (Tauc gap E opt and the isoabsorption gap E 04), and structural parameters like the Tauc slope parameter B, of the hydrogenated amorphous silicon carbon alloy films prepared by r.f. glow discharge decomposition of silane and acetylene as well as silane and ethylene, are discussed for various compositions and also for different annealing temperatures. We observe, for the first time, an interesting new correlation between ( E 04− E opt) and the Tauc slope parameter B of amorphous semiconductors.

Optical properties and chemical structure of ion implanted a-SiC : H

Optical contrast formation in amorphous silicon–carbon alloy films by ion implantation with Ar and group IV elements has been studied by different methods. The increased disorder and additional chemical modification of a-SiC:H, induced by the implantation of Ge or Sn, results in a considerable change of the optical properties as demonstrated by optical transmission spectra. The accompanying change in the optical gap and absorption coefficient has been derived from optical transmission and reflection measurements. The results have been related to the introduction of additional disorder and creation of new bonding configurations as suggested by Raman, infrared (IR), Mössbauer and X-ray photo-electron spectroscopy (XPS).

Dependences of amorphous structure on bias voltage and annealing in silicon–carbon alloys

The amorphous silicon–carbon alloy films have been obtained by filtered cathodic vacuum arc (FCVA) technique. The typical carbon composition is about 32% in the film by using a 50% target (the atomic ratio), which is characterized by X-ray photoemission spectroscopy. The films deposited with various bias voltages and annealed in different temperature were characterized by Raman spectrometer, atomic force microscope, and X-ray diffraction. The disorder of Si–C network increased with using the high bias voltages during the deposition. This high disorder in the film with high bias voltages induces the smaller nanometer crystallites after annealed in 1000°C than low bias. The Raman peaks shift to the high frequency with increasing the annealing temperature up to 750°C due to the increasing of nanometer grain size at the same bias. A sharp transition from nanocrystalline to polycrystalline can be observed when the films annealed under 1000°C.

Quantum well model and variation of the optical band gap in hydrogenated amorphous silicon carbon alloy films

In addition to the increase in the optical band gap ( E opt) with hydrogenation, interesting variation of E opt results with the increase in the carbon content ( x) and also annealing temperature ( T a) in the hydrogenated amorphous silicon carbon alloy films (a-Si 1− x C x :H). E opt increases with x, reaches a maximum and then decreases with the further increase in x while E opt initially decreases with T a and then increases with the further increase in T a. The present study demonstrates that the models based on alloying or/and ordering fail to explain both the variation of E opt with x as well as T a, and the proposed model, which is an extension of the Brodsky quantum well model (Solid State Commun. 36 (1980) 55) to hydrogenated amorphous silicon carbon alloys. However, it is the only model capable of explaining the experimental results, a fact which may have considerable implications.

Temperature effects in the hot wire chemical vapor deposition of amorphous hydrogenated silicon carbon alloy

The microstructure, composition, and bonding in hydrogenated amorphous silicon carbon alloy (a-SiC:H) films grown at different substrate temperatures were investigated by a combination of multiple internal reflection-Fourier transform infrared spectroscopy and near edge x-ray absorption fine structure measurements. Hot wire chemical vapor deposition (HW–CVD) was used to grow the thin films at substrate temperatures ranging from 200 to 600 K using mono- and trimethylsilane as precursors. It is found that raising the substrate temperature during HW–CVD leads to films depleted in the higher hydrides (namely SiH3, SiH2, and CH3) in favor of the lower hydrides (SiH and CH). This change marks a transition of the film structure from a highly methylated-polysilane backbone to a polycarbosilane backbone. In addition, some crystalline characteristics appear with increasing substrate temperature, demonstrating that the change of substrate temperature affects both the hydrogen configuration and the microstructure of the film. Temperature-dependent growth of thin a-SiC:H films by HW–CVD is compared with the method of electron cyclotron resonance plasma-enhanced (PECVD).

STRUCTURAL AND MECHANICAL PROPERTIES OF AMORPHOUS SILICON-CARBON ALLOY FILMS DEPOSITED BY FILTERED CATHODIC VACUUM ARC TECHNIQUE

Amorphous silicon-carbon alloy films have been successfully deposited by filtered cathodic vacuum are technique. The structural and mechanical properties of the films were investigated by using x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, surface profiler and nano-indenter. The silicon content in the films determined by XPS measurement varies from 2.4 to 48 at.%. Both XPS and Raman spectroscopy show the existence of silicon carbide clusters in the films containing intermediate concentration of silicon. The silicon atoms predominately substitute the carbon atom into the carbon clusters at low silicon concentration, and form amorphous silicon carbide clusters or amorphous silicon clusters at higher silicon concentration. The hardness of the films varies from 60 to 22 GPa while the stress reduces from 8.0 to 2.1 GPa.

Dependence on the C 2H 4 and SiH 4 gas mixture of the Si-C film properties obtained by excimer lamp chemical vapour deposition

Amorphous silicon-carbon alloy films were obtained by photo-chemical vapour deposition irradiating a gas mixture of ethylene and silane diluted in argon with a xenon excimer lamp ( λ = 172 nm). Films were deposited at low temperatures ( T = 200 °C) on to silicon, Corning glass and aluminium substrates. The role of the gas-phase parameters on the composition, structure and optical properties of the films is reported. Characterization by energy dispersive X-ray spectroscopy and Rutherford backscattering spectroscopy revealed that an increase in the ethylene/silane concentration ratio led to important changes in film composition. The ellipsometric measurements indicated a logarithmic decrease in the refractive index from 1.9 to 1.3. Infrared spectroscopy showed the presence of Si-C bonds as well as hydrogen bonded in different configurations to silicon and carbon atoms, with the density of C-H bonds being considerably larger than that of Si-H. Ethylene-rich gas mixtures produced a decrease in the number of Si-H bonds and a shift in their stretching frequencies towards higher wave numbers, due to compositional variations. Postdeposition oxidation of the films was also observed, as a consequence of their porous character.