Amorphous Silicon Carbide Films Research Articles

Effect of discharge power and silicon content on optical and mechanical properties of carbon-rich amorphous silicon carbide films obtained by PECVD

We studied optical and mechanical properties of a-SixC1-x:H films prepared by the PECVD technique from the mixture of CH4, SiH4, H2 and Ar. RF discharge power and silane flow rate were chosen as parameters of the film deposition process that allowed to vary film properties. It was shown that variations of silane flow rate (10, 20 sccm) and discharge power in the 100–300 W range allow to obtain films with the following characteristics: optical bandgap 2.5–4.1 eV; refractive index of 1.8–2.1; hardness (H) 8.6–14.8 GPa; Young modulus (E) 64–143 GPa. The film deposition rate varied from 10 to 35 nm/min. By selecting deposition regimes, we deposited films with high ratio between film hardness and Young modulus (H/E = 0.13). The variations of optical and mechanical properties of the films by changing discharge power and silane flow are interpreted within a model accounting film composition and phase-structural transformations. Good combination of optical and mechanical properties of the developed films makes them promising for application as protective, passivation and anti-reflection coatings.

Third-order optical nonlinearity in nonstoichiometric amorphous silicon carbide films

This study investigated the third-order nonlinear optical properties of amorphous silicon carbide (SiC) films prepared via magnetron sputtering at room temperature (RT) and annealed at 200 °C–800 °C. The third-order optical nonlinearity was investigated by Z-scan measurement at a wavelength of 1064 nm and a pulse duration of 25 ps. The self-defocusing behaviour was observed in a large nonlinear refractive index n2 ∼10−14 m2/W, which was five orders of magnitude larger than the value of SiC crystals. By fitting the open-aperture data of the Z-scan, we determined the two- and three-photon absorption in the SiC films prepared at RT and in the annealed samples, respectively. The different nonlinear absorption behaviour was probably ascribed to the intermediate states between the conduction and valence bands.

Correlation study of photoluminescence properties and mechanism of hydrogenated amorphous silicon carbide films

Hydrogenated amorphous silicon carbide (a-SiCx:H) films have been deposited by plasma enhanced chemical vapor deposition (PECVD) system with different radio-frequency (RF) powers. The microstructure and optical properties of the films deposited at different RF powers have been studied. The results show that the sp2/sp3 ratio and the average size of sp2-C rich domains increase while the hydrogen content and the density of sp2-C rich domains in the film decreases with increasing RF power. In addition, the sp2 carbon domains are observed by HR-TEM, and a possible photoluminescence (PL) mechanism is also suggested: the strong PL emission originates from radiative recombination of excitons within sp2-C rich domains and CSi/CC random network. As RF power increases, the change of the PL properties can be attributed to the influence of RF power on the sp2-C rich domains and the CSi/CC random network. The corresponding color coordinates of PL spectra also show that the film has great application potential in white light emission.

High-rate, room-temperature synthesis of amorphous silicon carbide films from organo-silicon in high-density helicon wave plasma

In this study, amorphous silicon carbide (α-SiC) films were synthesized on 316L stainless steel by low pressure, high density helicon wave plasma (HWP), using tetramethylsilane (TMS) as the single-source precursor which is organometallic compound. The influence of the substrate bias voltage (Vs) on the surface morphology, structure, chemical composition, and mechanical properties of the α-SiC films is investigated. The increase of VS from 0 to 200 V causes the removal of organic moieties from the film and results in the formation condition for α-SiC. The maximum deposition rate of the coating is up to 250 nm/s, which is related to the high-density (>1019 m−3) plasma production of HWP [1]. The X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometer (FTIR) results imply that the film is mainly composed of SiC. The films deposited at VS = 200 V appear to be high-hardness (up to 33.6 GPa) materials with very small surface roughness (∼0.5 nm). Considering the easy control of the bias voltage, our work provides a new method for achieving α-SiC films with high-yield at room temperature.

Elaboration of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Device

Elaboration of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Device

Nonstoichiometric amorphous silicon carbide films as promising antireflection and protective coatings for germanium in IR spectral range

A technology for preparation of amorphous nonstoichiometric hydrogenated silicon carbide (a-SixC1-x:H) films using the PE-CVD method has been developed. Such films with refractive index n = 1.8–2.1 are suitable to obtain antireflection effect on germanium in the IR spectral region. Single- and two-sided antireflection coatings of Ge enabled to increase its optical transmission up to 65% and 96% in the maximum transmission, respectively. The obtained films have good mechanical properties (H > 12 GPa, E = 100 GPa). Presence of Si-C bonds in the a-SixC1-x:H films restricts their range of application to the spectral interval 2.5–10 μm. The prepared films are uniform in composition and have high adhesion to the substrate. Variation of deposition conditions makes it possible to obtain a-SixC1-x:H films having high hardness and Young's modulus. High deposition rate, optimal optical properties of the a-SixC1-x:H films and good combination of mechanical properties for the Ge/a-SixC1-x:H film structures make them to be promising for practical application as antireflection and protective coatings for germanium.

Study and optimization of the photoluminescence of amorphous silicon carbide thin films

ABSTRACT:In this work we report the study of the effect of the deposition parameters on the photoluminescence (PL) intensity of hydrogenated amorphous silicon-carbide (a-SiC:H) films deposited at very low temperature (150 °C) by Plasma Enhanced Chemical Vapor Deposition (PECVD). We have observed that the main deposition parameter that influences the wavelength emission peak is the methane/silane (CH4/SiH4) ratio used for the films deposition, due to a change on the film carbon content. On the other hand the deposition RF power affects the PL intensity, without a change in the PL emission peak. Also we have studied the effect of the film thickness on the PL intensity and we have observed an optimal film thickness.

Effect of oxidation on intrinsic residual stress in amorphous silicon carbide films.

The change in residual stress in plasma enhanced chemical vapor deposition amorphous silicon carbide (a-SiC:H) films exposed to air and wet ambient environments is investigated. A close relationship between stress change and deposition condition is identified from mechanical and chemical characterization of a-SiC:H films. Evidence of amorphous silicon carbide films reacting with oxygen and water vapor in the ambient environment are presented. The effect of deposition parameters on oxidation and stress variation in a-SiC:H film is studied. It is found that the films deposited at low temperature or power are susceptible to oxidation and undergo a notable increase in compressive stress over time. Furthermore, the films deposited at sufficiently high temperature (≥325 C) and power density (≥0.2 W cm-2 ) do not exhibit pronounced oxidation or temporal stress variation. These results serve as the basis for developing amorphous silicon carbide based dielectric encapsulation for implantable medical devices. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1654-1661, 2019.

Effect of Nitrogen Doping and Temperature on Mechanical Durability of Silicon Carbide Thin Films

Amorphous silicon carbide (a-SiC) films are promising solution for functional coatings intended for harsh environment due to their superior combination of physical and chemical properties and high temperature stability. However, the structural applications are limited by its brittleness. The possible solution may be an introduction of nitrogen atoms into the SiC structure. The effect of structure and composition on tribo-mechanical properties of magnetron-sputtered a-SiCxNy thin films with various nitrogen content (0–40 at.%) and C/Si close to one deposited on silicon substrates were evaluated before and after exposure to high temperatures up to 1100 °C in air and vacuum. IR transmission spectroscopy revealed formation of multiple C-N bonds for the films with N content higher than 30 at.%. Improvement of the organization in the carbon phase with the increase of nitrogen content in the a-SiCN films was detected by Raman spectroscopy. Nanoindentation and scratch test point out on the beneficial effect of the nitrogen doping on the tribo-mechanical performance of a-SiCxNy coatings, especially for the annealed coatings. The improved fracture resistance of the SiCN films stems from the formation of triple C≡N bonds for the as deposited films and also by suppression of SiC clusters crystallization by incorporation of nitrogen atoms for annealed films. This together with higher susceptibility to oxidation of a-SiCN films impart them higher scratch and wear resistance in comparison to SiC films before as well as after the thermal exposure. The best tribo-mechanical performance in term of high hardness and sufficient level of ductility were observed for the a-Si0.32C0.32N0.36 film. The enhanced performance is preserved after the thermal exposure in air (up to 1100 °C) and vacuum (up to 900 °C) atmosphere. Annealing in oxidizing atmosphere has a beneficial effect in terms of tribological properties. Harder films with lower nitrogen content suffer from higher brittleness. FIB-SEM identified film-confined cracking as the initial failure event in SiC, while it was through-interface cracking for SiCN at higher loads. This points out on the higher fracture resistance of the SiCN films where higher strains are necessary for crack formation

Synthesis of transfer-free graphene on cemented carbide surface

Direct growth of spherical graphene with large surface area is important for various applications in sensor technology. However, the preparation of transfer-free graphene on different substrates is still a challenge. This study presents a novel approach for the transfer-free graphene growth directly on cemented carbide. The used simple thermal annealing induces an in-situ transformation of magnetron-sputtered amorphous silicon carbide films into the graphene matrix. The study reveals the role of Co, a binding phase in cemented carbides, in Si sublimation process, and its interplay with the annealing temperature in development of the graphene matrix. A detailed physico-chemical characterisation was performed by structural (XRD analysis and Raman spectroscopy with mapping studies), morphological (SEM) and chemical (EDS) analyses. The optimal bilayer graphene matrix with hollow graphene spheres on top readily grows at 1000 °C. Higher annealing temperature critically decreases the amount of Si, which yields an increased number of the graphene layers and formation of multi-layer graphene (MLG). The proposed action mechanism involves silicidation of Co during thermal treatment, which influences the existing chemical form of Co, and thus, the graphene formation and variations in a number of the formed graphene layers.

Electrochemical characteristics of amorphous silicon carbide film as a lithium-ion battery anode.

The electrochemical reactions of SiC film with Li+ have been investigated by electrochemical characterization and X-ray photoelectron spectroscopy. The SiC film is prepared by inductively-coupled-plasma chemical-vapor-deposition (ICP-CVD) technique and displays an amorphous state due to the low processing temperature (∼350 °C). An irreversible reaction of SiC with Li+ occurs with the formation of lithium silicon carbide (LixSiyC) and elemental Si, followed by a reversible alloying/dealloying reaction of the elemental Si with Li+. The 500 nm SiC film shows an initial reversible specific capacity of 917 mA h g−1 with a capacity retention of 41.0% after 100 cycles at 0.3C charge/discharge current, and displays much better capacity retention than the Si film (5.2%). It is found that decreasing the SiC thickness effectively improves the specific capacity by enhancing the reaction kinetics but also degrades the capacity retention (for 250 nm SiC, its initial capacity is 1427 mA h g−1 with a capacity retention of 25.7% after 100 cycles). The better capacity retention of the 500 nm SiC anode is mainly because residual SiC exists in the film due to its incomplete reaction caused by its lower reaction kinetics, and it has high hardness and can act as a buffer matrix to alleviate the anode volume change, thus improving the mechanical stability and capacity retention of the SiC anode.

Effect of ALD-Al2O3 Passivated Silicon Quantum Dot Superlattices on p/i/n+ Solar Cells

The photovoltaic (PV) nature of the silicon (Si) quantum dot super lattice (QDSL) is studied with an atomic-layer-deposited aluminum oxide film (ALD-Al2O3) and a conventional sputtered-grown amorphous silicon carbide film (a-SiC). The QDSL structures act as an intermediate layer in a p/i/n+ Si solar cell. The QDSL consists of 4-nm Si on 2-nm SiC nanodisks (NDs) arrayed in an ALD-Al2O3 and a-SiC passivation matrix. Formation of Si-NDs was confirmed by bright field scanning transmission electron microscope. A significant PV response in generating a high photocurrent density $\mathit {J_{sc}}$ of 30.15 mA/cm $^{2}$ , open circuit voltage $\mathit {V_{oc}}$ of 0.50 V, fill factor FF of 0.61, and efficiency $\eta $ of 9.12% was observed in ALD-Al2O3/QDSL solar cell with respect to a-SiC/QDSL solar cell with $\mathit {J_{sc}}$ of 26.94 mA/cm $^{2}$ , $\mathit {V_{oc}}$ of 0.50 V, FF of 0.47, and $\eta $ of 6.42%. A wide range of photo-carrier transports by the ALD-Al2O3/QDSL structure is possible in the external quantum efficiency spectra with respect to a-SiC/QDSL solar cell. The enhanced PV performance of the QD solar cells was clarified in terms of simulating the absorption contributions for all possible transitions in the nanostructure with different passivation films.

The influence of methane flow rate on microstructure and surface morphology of a-SiC:H thin films prepared by plasma enhanced chemical vapor deposition technique

Hydrogenated amorphous silicon carbide (a-SiC:H) films, which contain sp3 hybridized carbon phase embedded in a-SiC:H matrix were fabricated by a radio frequency (13.56MHz) plasma enhanced chemical vapor deposition (PECVD) system with methane and silane mixture (silane diluted by H2, volume ratio: 90% H2+10% SiH4) as reactive precursor gases. It was found that under the deposition conditions of fixed the RF power density, pressure, deposition temperature and silane mixture flow rate, the flow rate of methane (R) had a large impact on the content of sp3 hybridized carbon phase and surface morphology of the a-SiC:H thin films. The research shows that the silicon bonding environment didn't change with increasing R and the H bonded to sp3 hybridized carbon phase mainly derived from the CHn radicals generated by decomposition of CH4 rather than H2. Simultaneously, the methane flow rates can control the deposition rate and surface morphology of the a-SiC:H films and make the films become more compact and uniform.

Formation of high conductive nano-crystalline silicon embedded in amorphous silicon-carbide films with large optical band gap

High conductive phosphorus-doped nano-crystalline Si embedded in Silicon-Carbide (SiC) host matrix (nc-Si:SiC) films were obtained by thermally annealing doped amorphous Si-rich SiC materials. It was found that the room conductivity is increased significantly accompanying with the increase of doping concentrations as well as the enhanced crystallizations. The conductivity can be as high as 630 S/cm for samples with the optical band gap around 2.7 eV, while the carrier mobility is about 17.9 cm2/ V·s. Temperature-dependent conductivity and mobility measurements were performed which suggested that the carrier transport process is strongly affected by both the grain boundaries and the doping concentrations.

Forming cylindrical light beams with axially symmetric polarization distribution by using a light-emitting silicon-carbide-based planar waveguide

Plasma-chemical gas-phase deposition has been used to fabricate a luminescent asymmetric planar waveguide based on an amorphous silicon carbide film of micron thickness deposited on a circular quartz substrate with a transparent cylindrical side surface. When photoluminescence is excited in an asymmetric planar waveguide, peaks of linearly polarized (P and S) radiation are recorded in the emission spectra from the side surface of the substrate, caused by emission in the leaky modes of the planar waveguide. A spherical mirror converted the radiation coming out of the side surface of the sample substrate located at the center of the mirror into a cylindrical light beam. The spectra of the P- and S-polarized radiation have been studied at different points of the cross section of the cylindrical beam. It is shown that the cylindrical beam possesses radial and azimuthal polarizations.

High Temperature Nanoindentation Testing of Amorphous SiC and B<sub>4</sub>C Thin Films

Amorphous silicon carbide (a-SiC) and boron carbide (a-B4C) thin films were deposited using reactive magnetron sputtering of SiC and B4C target, respectively. Nanoindentation tests performed up to 450 °C in air were performed to explore and compare their hardness and elastic modulus.Hardness of a-B4C film decreases at smaller rate in comparison to a-SiC film up to 450 °C. Similarly, elastic modulus value of B4C is more stable with temperature than that of a-SiC.

Preparation and characterization of polymer-derived amorphous silicon carbide with silicon-rich stoichiometry

Polydihydrosilane with pendant hexyl groups was synthesized to obtain silicon-rich amorphous silicon carbide (a-SiC) films via the solution route. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage. Therefore, the polymer provides sufficient purity for the fabrication of semiconducting a-SiC. Here, we investigated the correlation of Si/C stoichiometry between the polymer and the resultant a-SiC film. The structural, optical, and electrical properties of the films with various carbon contents were also explored. Experimental results suggested that the excess carbon that did not participate in SiC configurations was decomposed and was evaporated during polymer-to-SiC conversion. Consequently, the upper limit of the carbon in resultant a-SiC film was <50at.%; namely, the polymer provided silicon-rich a-SiC, whereas the conventionally used polycarbosilane inevitably provides carbon-rich one. These features of this unusual polymer open up a frontier of polymer-derived SiC and solution-processed SiC electronics.

Fabrication of hydrogenated amorphous silicon carbide films by decomposition of hexamethyldisilane with microwave discharge flow of Ar

Hydrogenated amorphous silicon carbide films have been fabricated by the decomposition of hexamethyldisilane with a microwave discharge flow of Ar. Mechanically hard films were obtained by applying radio-frequency (RF) bias voltages to the substrate. The atomic compositions of the films were analyzed by a combination of Rutherford backscattering and elastic recoil detection, X-ray photoelectron spectroscopy (XPS), and glow discharge optical emission spectroscopy. The chemical structure was analyzed by carbon-K near-edge X-ray absorption fine structure spectroscopy, high-resolution XPS, and Fourier transform infrared absorption spectroscopy. The structural changes upon the application of RF bias were investigated, and the concentration of O atoms near the film surface was found to play a key role in the mechanical hardness of the present films.

The Synthesis and Structural Properties of Crystalline Silicon Quantum Dots upon Thermal Annealing of Hydrogenated Amorphous Si-Rich Silicon Carbide Films

Silicon quantum dots (QDs) embedded in non-stoichiometric hydrogenated silicon carbide (SiC:H) thin films have been successfully synthesized by plasma-enhanced chemical vapor deposition and post-annealing. The chemical composition analyses have been carried out by x-ray photoelectron spectroscopy (XPS). The bonding configurations have been deduced from Fourier transform infrared absorption measurements (FTIR). The evolution of microstructure with temperature has been characterized by glancing incident x-ray diffraction (XRD) and Raman diffraction spectroscopy. XPS and FTIR show that it is in Si-rich feature and there are a few hydrogenated silicon clusters in the as-grown sample. XRD and Raman diffraction spectroscopy show that it is in amorphous for the as-grown sample, while crystalline silicon QDs have been synthesized in the 900°C annealed sample. Silicon atoms precipitation from the SiC matrix or silicon phase transition from amorphous SiC is enhanced with annealing temperature increase. The average sizes of silicon QDs are about 5.1 nm and 5.6 nm, the number densities are as high as 1.7 × 1012 cm−2 and 3.2 × 1012 cm−2, and the crystalline volume fractions are about 58.3% and 61.3% for the 900°C and 1050°C annealed samples, respectively. These structural properties analyses provide an understanding about the synthesis of silicon QDs upon thermal annealing for applications in next generation optoelectronic and photovoltaic devices.

Asymmetric planar luminescent waveguide based on amorphous silicon carbide with polarized radiation in leaky modes

Plasma-enhanced chemical vapor deposition is used to fabricate asymmetric planar luminescent waveguides (APWs) based on amorphous silicon-carbide films with submicron thickness on quartz substrates. Narrow peaks of linearly (P and S) polarized radiation related to the emission in the APW leaky modes are detected in the APW emission spectra from the end surface of a substrate under excitation of photoluminescence. The dependence of the spectral positions of peaks on the angle at which the radiation is emitted from the end surface and the film thickness is analyzed. At grazing angles of emission, the radiation wavelength is almost independent of the angle. It is demonstrated that the difference between the wavelengths of the P- and S-polarized peaks in the PL spectra decreases with an increase in the waveguide thickness. The waveguide works as an optical microcavity for leaky modes. The amplitude of the S-polarized peak is higher than the amplitude of the P-polarized peak due to the fact that the Q factor for the S-polarized leaky modes is greater than the Q factor for the P-polarized leaky mode. The luminescent APWs can be used to generate optical beams with radial and azimuthal polarizations.