Amorphous Silicon Carbide Films Research Articles

Investigation of amorphous-SiC thin film deposition by RF magnetron sputtering for optical applications

Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV–Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 μm in the range 2.50–2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C–C bond concentration.

Effect of annealing in air on the properties of carbon-rich amorphous silicon carbide films

Thermal stability of thin carbon-rich Si carbide films was studied. Air anneals at the temperatures up to 700 °C were used to model the operation thermal conditions of the films in photoelectronic devices such as solar cells covered by Si carbide antireflection coatings. Si carbide films with different carbon-to-silicon ratios were studied. Annealing in air was shown to lead to consecutive film oxidation and transformation from Si carbides to oxidized Si carbide composites. The oxidized composites demonstrated the changes in thickness, element composition and optical properties as compared to the non-annealed films. At this, the films with higher Si content showed better stability of the optical properties at increased temperatures. During annealing, the increase of the film thickness by Si oxide formation competed with the thickness decrease by formation and evaporation of carbon oxide.

High-Quality Amorphous Silicon Carbide for Hybrid Photonic Integration Deposited at a Low Temperature.

Integrated photonic platforms have proliferated in recent years, each demonstrating its unique strengths and shortcomings. Given the processing incompatibilities of different platforms, a formidable challenge in the field of integrated photonics still remains for combining the strengths of different optical materials in one hybrid integrated platform. Silicon carbide is a material of great interest because of its high refractive index, strong second- and third-order nonlinearities, and broad transparency window in the visible and near-infrared range. However, integrating silicon carbide (SiC) has been difficult, and current approaches rely on transfer bonding techniques that are time-consuming, expensive, and lacking precision in layer thickness. Here, we demonstrate high-index amorphous silicon carbide (a-SiC) films deposited at 150 °C and verify the high performance of the platform by fabricating standard photonic waveguides and ring resonators. The intrinsic quality factors of single-mode ring resonators were in the range of Qint = (4.7-5.7) × 105 corresponding to optical losses between 0.78 and 1.06 dB/cm. We then demonstrate the potential of this platform for future heterogeneous integration with ultralow-loss thin SiN and LiNbO3 platforms.

Structural properties and optical modeling of thermally annealed silicon carbide thin films

Non–hydrogenated amorphous silicon carbide films were processed by electron beam-physical vapour deposition on c-Si (100) and glass substrates. The films were isochronally annealed at varying temperatures. FTIR and Raman spectroscopies as well as XRD studies were used for structural investigation. For the pristine sample, it is found that the film is Si rich in an amorphous SiC matrix and that the observed graphitization is exclusively described by a single broad D-band in Raman. During the annealing process, a start of rearrangement of the network is observed at low temperatures of annealing but the amorphous phase still dominates in the microstructure. Still at low temperatures, the graphitization band broadens and expands to the G-bands region while at higher temperatures, an improved stochiometric crystalline SiC phase is achieved and distinct graphitic D and G bands are resolved. The induced crystalline network through annealing is prone to oxidation both in Si-O, bridged oxygen Si-O-Si and/or to silicon oxycarbide SiCx -O groups. An optical model based on effective medium approximation (EMA) theory is proposed in order to extract the optical properties of the material. It is established, from the evolution of the bandgap, that the films become transparent over a wider region of the visible spectrum as the temperature of annealing is increased to high values.

Synthesis of thin‐film materials using nonthermal plasma at a higher degree of dissociation

AbstractLower flow rates of precursor molecules are favorable for the synthesis of thin‐film materials using nonthermal plasma at a higher degree of dissociation and sufficiently high deposition rate. These deposition conditions can be used for both continuous wave (CW) and pulsed plasmas and result in higher consumption of precursor molecules, which is beneficial for industrial applications due to cost reduction. A wider range of power can be used to control the chemical and physical properties of thin‐film materials based on power‐dependent plasma chemistry. Hydrogenated amorphous silicon carbide films deposited in CW and pulsed plasma are used as an example. The different kinetics of film growth and the role of self‐bias voltage in both types of plasma are discussed.

Enhanced Red Emission from Amorphous Silicon Carbide Films via Nitrogen Doping.

The enhanced red photoluminescence (PL) from Si-rich amorphous silicon carbide (a-SiCx) films was analyzed in this study using nitrogen doping. The increase in nitrogen doping concentration in films results in the significant enhancement of PL intensity by more than three times. The structure and bonding configuration of films were investigated using Raman and Fourier transform infrared absorption spectroscopies, respectively. The PL and analysis results of bonding configurations of films suggested that the enhancement of red PL is mainly caused by the reduction in nonradiative recombination centers as a result of the weak Si-Si bonds substituted by Si-N bonds.

Silicon carbide synthesized by RF magnetron sputtering in the composition of a double layer antireflection coating SiC/MgF2

In this paper, the optimal thickness of SiC film for an antireflection coating was determined by computer simulations using Lumerical FTDT and SCOUT software. The simulation was carried out for the SiC/MgF2 system, where silicon carbide films were deposited at a magnetron power of 100, 150, 200, 250 W, while the thickness of the magnesium fluoride films remained unchanged and amounted to 130 nm. The simulation results showed that the optimal parameters for the synthesis of SiC antireflection layer are 100 W/50 nm. With these parameters, the reflection is less than 3% in the widest wavelength range of 475–1020 nm. The dependence of the physical properties of the synthesized films on the power of the magnetron is investigated. Using reflection and transmission spectroscopy it was experimentally revealed that a decrease in the magnetron power from 250 to 100 W leads to a decrease in the refractive index. According to our results the best antireflection effect can be achieved with SiC/MgF2 coatings when SiC films are deposited at 100 W magnetron power. The reflectance spectra are consistent with the simulation spectra, especially in the 475–1020 nm range, where the surface reflects only 0.2–3.0% of the incident light. The obtained results are explained by the correlation between the structural properties, composition of amorphous silicon carbide films and antireflection properties.

Amorphous silicon carbide thin films doped with P or B for the photoelectrochemical water splitting devices

Photoelectrochemical water splitting devices require semiconductor photoelectrode material fulfilling a number of primary requirements such as band gap, band edge alignment and corrosion resistance to electrolyte. Amorphous silicon carbide films, undoped and doped (P or B), were deposited on Si substrates by PECVD technology. The concentration of elements in the films was determined by RBS and ERD analytical method. Raman spectroscopy study of the SiC films were performed by using a Raman microscope and chemical compositions were analyzed by FTIR, before and after immersion of samples to aqueous pH 2.0 and pH 1.0 sulphuric acid electrolyte. Electrical properties of SiC films before and after immersion of samples to aqueous pH 2.0 and pH 1.0 sulphuric acid electrolyte were studied by measurement of the I–V characteristics on structure Al/SiC/Si/Al. Differences between Raman spectra, FTIR spectra and I–V characteristics before and after immersion to electrolyte are discussed.

Thin c-Si Solar Cells Based on VOx Heterojunctions With Texturized Rear Surface

Solar cells based on thin crystalline silicon (c-Si) substrates have the potential to provide relevant efficiencies with less material. In this article, we report on the fabrication of thin solar cells starting from a 20 μ m-thick c-Si wafer. Special attention is paid to optical performance of the rear surface where we need very high internal reflection and light scattering to improve light trapping properties of the device. In this sense, we introduce a texturization of the rear surface, which is excellently passivated by aluminium oxide films. In addition, for the rear contacts we use metal-covered wide-bandgap materials to improve back reflectance with a Vanadium Oxide/c-Si heterojunction for the emitter regions while the base contacts are defined by laser processing phosphorus doped amorphous silicon carbide films. Best solar cell has a reasonable efficiency of 8.7% and, more importantly, external quantum efficiency measurements demonstrate a better performance for photons with λ > 900 nm than in the case of a flat rear surface.

Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.

Graphene Trails on PECVD Hydrogenated Amorphous Silicon Carbide Films SiC-a: H by Laser Writing at Room Temperature

The production of high quality graphene without the need for catalyst metals as in the case of chemical vapor deposition (CVD) techniques remain a challenge. Silicon carbide is one of the materials with potential to form graphene films on its surface through thermal decomposition when subjected to high temperatures and ultrahigh vacuum. This technique is highly desirable since it enables the elimination of corrosion and transfer steps, which can leave residues in the graphene structure and alter its quality, as well as its electrical proprieties, however it is a costly and time consuming method. In this work, we present the production of graphene trails by direct laser radiation writing at room temperature and atmospheric pressure on hydrogenated amorphous silicon carbide films (SiC-a:H) produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). Graphene trails of approximately 1cm x 4μm were obtained with patterns designed by computer Aided Design (CAD) software. Variations were made in both scanning speed and laser focal length, identifying a great dependence on the graphene quality with these two parameters. The best results of the Raman Spectroscopy Mappings showed high quality graphene with distance between point defects (LD) of 20nm, crystallite size (La) of 25nm and few layers (2-3). In addition, the electrical measurements from Au/Ti (20nm/100nm) electrodes deposited by electron beam evaporation showed high conductivity, with sheet resistances (Rs) from 0.7kΩ to 1.3 kΩ per square. This technique opens a great possibility of manufacturing devices for applications in electronics, being a fast, efficient and low cost method.

Abrasive mechanisms and interfacial mechanics of amorphous silicon carbide thin films in chemical-mechanical planarization

In this paper, the polishing process of a silicon carbide (SiC) substrate covered with a thin amorphous SiC (a-SiC) film is investigated by molecular dynamics simulation method. A diamond abrasive particle slides or rolls over the SiC workpiece surface with different depths and speeds. The results indicated that in the sliding motion, increasing the sliding depth leads to a higher force, stress, temperature, and a higher number of atoms removed. The best surface quality gains by sliding at 10 Å depth or at the depth that equal to the a-SiC layer thickness. At this polishing depth, the a-SiC plays a role as a padding layer that prevents the SiC substrate from subsurface damage. At a deeper depth, the crystalline SiC atoms at the interfacial area are transformed into the amorphous state. In sliding motion, the ploughing and cutting regimes dominate the atomic removal mechanism. Similar to the sliding motion, improving the rolling depth results in a higher force, stress, temperature, and the number of atoms removed. However, the rolling movement generates higher stress, deeper subsurface damage (SSD) zone, rougher surface and lower number of atoms removed. In rolling motion, the removal mechanism is mainly adhering to which the workpiece atoms are adhered by the abrasive surface. This report also investigates the effect of the abrasive size and the a-SiC thickness to the removal process. The bigger abrasive the higher force, stress, and the number of atoms removed. While increasing the a-SiC film thickness leads to a lower force and shallower SSD zone. Despite the differences in the abrasive size and the thickness, the sliding motion always performs a dramatically better ability to remove the workpiece atoms than the rolling one. A SiC model with the ripple structure is also constructed and analyzed. The bigger ripple mostly generates a higher force, temperature, strain, and a higher number of atoms removed. The high-temperature and high-value atomic strain areas mainly exist in the a-SiC film, at the upper side of the interface. The sliding motion again wipes out more atoms and creates a smoother groove than the rolling motion. Additionally, in the rolling motion, the large ripple can be lengthened and stuck to the substrate.

Resistive switching behaviour of amorphous silicon carbide thin films fabricated by a single composite magnetron sputter deposition method

Amorphous silicon carbide (a-SiC) films of thickness 50–300 nm are deposited by a single composite target magnetron sputtering process. Metal–SiC–metal structures are fabricated to demonstrate resistive switching. The top metal electrode is Cu, Pt or Ag and the bottom electrode is fixed as Au. Reversible resistive switching from high to low resistance states is observed for SiC films at voltages between 1 and 5 V. The interface between metal electrode and a-SiC films plays a significant role in achieving optimal switching performance. Resistance OFF/ON ratios of $$10^{8}$$ , retention times $${>}10^{4}$$ s and endurance of 50 cycles are achieved in the best devices. Cross-sectional scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy are employed to understand the mechanism of device operation. Raman spectroscopy indicates the formation of nanocrystalline graphite in these devices after a few cycles of operation.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Annealing effects on a-SiC:H and a-SiCN:H films deposited by plasma CVD methods

Hydrogenated amorphous silicon carbide (a-SiC:H) and carbonitride (a-SiCN:H) films were deposited in RF and mid-frequency (MF) discharges and electron cyclotron resonance (ECR) plasma. Annealing was performed in high vacuum up to 1000 °C and the temperature-dependent gas effusion from the films was investigated in situ by mass spectrometry. Changes of mechanical film properties, i.e. thickness, stress and Young's modulus, were determined ex situ by profilometry and nanoindentation, respectively. Using elastic recoil detection analysis, Rutherford backscattering and X-ray photoelectron spectroscopy, effects of annealing on elemental composition and chemical bonding were investigated. Annealing the a-SiC:H films significantly increased their Young's modulus and decreased their thickness by up to 25% in the case of ECR plasma deposition. The a-SiCN:H films deposited by MF and RF discharge practically retained their Young's modulus and the film thickness shrinkage was below 3%. At intermediate temperatures, these films showed a small thickness increase. For ECR-deposited a-SiCN:H, the expansion was larger and accompanied by a distinct reduction of Young's modulus. Hydrogen effusion and plastic flow under both compressive and tensile stress have a pronounced impact on the mechanical film properties. Annealing effects on film structure and properties are discussed and fundamental processes are derived.

Effect of DC negative bias on microstructure and surface morphology of amorphous silicon carbide films prepared by HWP-CVD

The effect of DC negative bias (− Vs) on microstructure and surface morphology of amorphous silicon carbide thin films prepared by helicon wave plasma chemical vapor deposition is reported. Microstructure and surface morphology were obtained by scanning electron microscope (SEM) and atomic force microscope (AFM). The results show that the increase of − Vs on the substrate make a more compact film and lower surface roughness, which can reach 0.56 nm. The XRD analysis reveals that the SiC thin films are of an amorphous structure. Percentages of carbon and silicon atoms (C/Si) were measured by energy dispersive spectrometer (EDS), and the C/Si ratio can reach 1.45. The structural properties of the films were studied by Raman spectroscopy techniques and Fourier transform infrared (FTIR). It is found that the films contain not only Si–C bonds but also Si–CHx bonds. Raman spectra results show that the proportion of disordered carbon in the films decreases with the increase of − Vs. The results of ultra-microhardness tester show that the hardness of the films increases with the increase of − Vs and the maximum mechanical hardness can reach 18.5 GPa at − Vs = − 60 V.

Pulsed laser deposition of SiC thin films and influence of laser-assisted annealing

Silicon carbide (SiC) thin films were grown by pulsed laser deposition (PLD) on Si (1 0 0) substrates at a substrate temperature of 800 °C. Besides, laser annealing was performed on the post deposited intrinsic amorphous SiC films using Nd3+:YAG 355 nm laser in the Ar environment. The laser-annealed samples showed the crystalline characteristics. Crystalline characteristics of PLD grown, laser annealed samples were identified by X-ray diffraction (XRD), Raman analysis. Numerical analysis performed on SiC/Si interface to investigate the temperature distribution, to understand the mechanism of laser assisted annealing.

Effect of plasma power on properties of hydrogenated amorphous silicon carbide hardmask films deposited by PECVD

We report the effects of plasma power on the properties of hydrogenated amorphous silicon carbide (a-SiC:H) films deposited by plasma enhanced chemical vapor deposition (PECVD). The optical and mechanical properties of the a-SiC:H films deposited with various plasma powers ranging from 100 to 1600 W were investigated. With the increase in the plasma power, both refractive indices and extinct coefficients decrease monotonically; meanwhile, the hardness and elastic modulus as well as the compressive stress are observed to increase. These properties depend primarily on the chemical structure involving different bonding configurations and the concentration of constituent elements with various plasma powers. We demonstrate that the increase in plasma power can induce a decrease in refractive index owing to the enlargement of the Si–C bonds and the carbon content of a-SiC:H films.

Conduction mechanisms in hydrogenated amorphous silicon carbide

We report on the conduction mechanisms at room temperature of hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films deposited by 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD). By analysing the current-voltage (J-V) characteristic of films with different thicknesses, it was possible to prove that space charge limited current (SCLC) enhanced by the Poole-Frenkel effect is the dominant charge transport mechanism for high electric fields. In addition, films with a variation of the Si–C ratio x (between 0.5 and 0.8) showed that higher Si content decreases the volume trap density. This result was in accordance to an observed decrease of the Urbach energy, indicating less long-range disorder.

Structural and Optical Properties of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Applications

Structural and Optical Properties of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Applications