Silicon Carbide Thin Films Research Articles

Optoelectronic Properties of Hydrogenated Amorphous Substoichiometric Silicon Carbide with Low Carbon Content Deposited on Semi‐Transparent Boron‐Doped Diamond

Hydrogenated amorphous substoichiometric silicon carbide (a‐Si1−xCx:H, x < 0,1) thin films and diodes with low carbon content are prepared from a mixture of H2, SiH4, and CH4 by plasma‐enhanced chemical vapor deposition at a relatively high temperature of 400 °C on semi‐transparent boron‐doped nanocrystalline diamond (B‐NCD) electrodes with an underlying Ti grid. Vibration spectra indicate that CH4 prevents Si crystallization at elevated deposition temperatures and confirm an increasing carbon content up to x = 0.1 for samples grown with SiH4/CH4 flows up to 1:3. Dark current–voltage characteristics of B‐NCD/a‐Si1−xCx:H diodes show a rectifying ratio of about four orders at ±1 V. However, under white light illumination, an energy conversion efficiency of 4% is limited by a high serial resistivity of the B‐NCD electrode and S‐shaped photocurrent near the open‐circuit voltage.

Silicon Heterojunction Solar Cells with p-Type Silicon Carbon Window Layer

Boron-doped hydrogenated amorphous silicon carbide (a-SiC:H) thin films are deposited using high frequency 27.12 MHz plasma enhanced chemical vapor deposition system as a window layer of silicon heterojunction (SHJ) solar cells. The CH4 gas flow rate is varied to deposit various a-SiC:H films, and the optical and electrical properties are investigated. The experimental results show that at the CH4 flow rate of 40 sccm the a-SiC:H has a high band gap of 2.1 eV and reduced absorption coefficients in the whole wavelength region, but the electrical conductivity deteriorates. The technology computer aided design simulation for SHJ devices reveal the band discontinuity at i/p interface when the a-SiC:H films are used. For fabricated SHJ solar cell performance, the highest conversion efficiency of 22.14%, which is 0.33% abs higher than that of conventional hydrogenated amorphous silicon window layer, can be obtained when the intermediate band gap (2 eV) a-SiC:H window layer is used.

Dual ion beam grown silicon carbide thin films: Variation of refractive index and bandgap with film thickness

Amorphous SiC thin films on a silicon substrate (Si) with different film thicknesses (about 20–450 nm) were deposited using dual ion beam sputtering deposition (DIBSD) at room temperature. These SiC thin films were of high quality showing high coverage (>90%) and low surface and interface roughness (<5 Å). The structure and morphology of these SiC/Si systems were explored by x-ray reflectivity, x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The bonding configuration and compositional details of the SiC films were examined by Fourier-transform infrared and Raman spectroscopy. The optical constants (complex dielectric function and refractive index) and the bandgap of SiC thin films were analyzed through spectroscopic ellipsometry in the 0.55–6.3 eV energy range. An increase in the bandgap (5.15–5.59 eV) and a corresponding decrease in the refractive index (2.97–2.77) were noticed with the increase of SiC film thickness from about 20–450 nm. This thickness dependent trend in optical properties is attributed to the increase of the C to Si atomic concentration ratio in DIBSD grown SiC thin films with increasing film thickness, as observed from energy dispersive x-ray analysis measurements. The unique properties of amorphous SiC have already placed it as a suitable candidate for solar cells and photovoltaic applications in its thin film form. The results developed in this study for thickness dependent optical properties of SiC thin films can be used for further optimizing the performance of SiC in various applications through tuning of optical properties.

The optical properties of silicon carbide thin films prepared by HWCVD from pure silane and methane under various total gas partial pressure

Optical properties of amorphous and nanocrystalline silicon carbide (SiC) thin films prepared by hot wire chemical vapor deposition (HWCVD) from silane (SiH4) and methane (CH4) gases under various total gas partial pressures are investigated. The variation of structure and optical properties of the films as a function of total gas partial pressure are studied using FTIR spectroscopy, Raman scattering spectroscopy, and UV–vis-NIR spectroscopy. Optical constants of the SiC films such as absorption coefficient, optical band gap, and refractive index are determined, and the significant correlation between the optical, structural and chemical composition of the films are discussed. The results indicated that the total gas partial pressure and deposition pressure have a strong influence on the structure of the films and therefore significantly control their optical parameters. Consequently, suitable deposition conditions for obtaining SiC films with desired optical and structural properties could be selected.

Hydrogen evolution in hydrogenated microcrystalline silicon carbide thin films

Evolved gas analysis (EGA), infrared attenuated reflection (ATR), and Raman spectroscopy experiments are used to study hydrogen evolution in hydrogenated microcrystalline silicon carbide (μc-Si1−xCx:H) films prepared by plasma-enhanced chemical vapor deposition. The results are compared with microcrystalline silicon (μc-Si:H). The effused hydrogen and carbon-hydride groups (CH, CH2, and CH3) are measured up to 800 °C. Their EGA curves have a peak at 410 °C, attributed to the methyl groups incorporated in the amorphous matrix during the deposition process. Moreover, hydrogen evolution curves show narrow and sharp peaks centered at 425 and 520 °C, corresponding to hydrogen desorbing from silicon hydrides at grain boundaries. While its content is more important than hydrogen bonded to silicon in the amorphous and denser crystalline regions of μc-Si1−xCx:H, but remains lower than in the μc-Si:H film. Raman and ATR data indicate that the μc-Si1−xCx:H film is composed of small size silicon crystallites embedded in a hydrogenated amorphous silicon carbide matrix and confirmed that carbon is incorporated in the amorphous matrix as methyl groups (CH3), inducing a decrease in SiHx groups compared to the μc-Si:H film.

Electrophysical and optical properties of the silicon carbide device structures

The results of the research of silicon carbide thin films obtained by high-frequency magnetron sputtering on various types substrates are presented. The surface morphology of silicon carbide was studied by scanning electron microscopy. Surface roughness was measured using a profilometer. The phase composition and structural perfection of the films were determined by x-ray phase analysis and Raman scattering. The method of silicon carbide layers optical parameters calculation based on experimentally obtained spectra of natural light normal reflection from the structure and from the substrate is developed. The refractive index, extinction coefficient and specific conductivity of silicon carbide films are calculated depending on the wavelength of the incident light.

The Influence of AlN Intermediate Layer on the Structural and Chemical Properties of SiC Thin Films Produced by High-Power Impulse Magnetron Sputtering.

Many strategies have been developed for the synthesis of silicon carbide (SiC) thin films on silicon (Si) substrates by plasma-based deposition techniques, especially plasma enhanced chemical vapor deposition (PECVD) and magnetron sputtering, due to the importance of these materials for microelectronics and related fields. A drawback is the large lattice mismatch between SiC and Si. The insertion of an aluminum nitride (AlN) intermediate layer between them has been shown useful to overcome this problem. Herein, the high-power impulse magnetron sputtering (HiPIMS) technique was used to grow SiC thin films on AlN/Si substrates. Furthermore, SiC films were also grown on Si substrates. A comparison of the structural and chemical properties of SiC thin films grown on the two types of substrate allowed us to evaluate the influence of the AlN layer on such properties. The chemical composition and stoichiometry of the samples were investigated by Rutherford backscattering spectrometry (RBS) and Raman spectroscopy, while the crystallinity was characterized by grazing incidence X-ray diffraction (GIXRD). Our set of results evidenced the versatility of the HiPIMS technique to produce polycrystalline SiC thin films at near-room temperature by only varying the discharge power. In addition, this study opens up a feasible route for the deposition of crystalline SiC films with good structural quality using an AlN intermediate layer.

Laser Assisted Doping of Silicon Carbide Thin Films Grown by Pulsed Laser Deposition

Cubic silicon carbide (3C-SiC) films were grown by pulsed laser deposition (PLD) on magnesium oxide [MgO (100)] substrates at a substrate temperature of 800°C. Besides, p-type SiC was prepared by laser assisted doping of Al in the PLD grown intrinsic SiC film. The SiC phases, in the grown thin films, were confirmed by x-ray diffraction (XRD), Si–C bond structure is identified by Fourier-transform infrared spectroscopy spectrum analysis. Measurements based on the XRD and Raman scattering techniques confirmed improvement in crystallization of 3C-SiC thin films with the laser assisted doping. The studies on I–V characteristics by two probe technique, elemental analysis by energy dispersion spectrum, binding energy by x-ray photoelectron spectroscopy and carrier concentration by Hall effect, ensured Al doping in SiC thin film. From the UV–visible NIR spectroscopic analysis, the optical bandgap of the PLD grown 3C-SiC was obtained. Numerical analysis of temperature and carrier concentration distribution is simulated to understand the mechanism of laser assisted doping.

Studying Evolution of the Ensemble of Micropores in a SiC/Si Structure during Its Growth by the Method of Atom Substitution

The time evolution of the ensemble of micropores formed in the near-surface region of silicon during the growth of thin films of silicon carbide is studied by the method of atom substitution. SiC/Si samples are studied by scanning electron microscopy, ellipsometry, and confocal Raman microscopy. The formation of the porous layer involves several characteristic stages: the emergence of single pores, their growth with the formation of dendrite-like structures, and subsequent coalescence into a continuous layer. It is shown that the thickness of the porous layer at the initial stages of the growth is proportional to the cubic root of time. The possible mechanisms of pore formation are discussed and a theoretical model is proposed to describe the dependence of the average thickness of the porous layer on time. The model is in a good qualitative agreement with the experimental results.

Active control of near-field radiative heat transfer via multiple coupling of surface waves with graphene plasmon

It is known that the surface plasmons (SPs) supported by graphene can be strongly coupled with electric SPs supported by the metamaterial and with symmetric and antisymmetric surface phonon polaritons (SPhPs) supported by silicon carbide (SiC). It has been shown that coated SiC thin films can efficiently enhance near-field radiative heat transfer between metamaterials. In this study, we theoretically investigate near-field heat transfer between graphene–SiC–graphene–metamaterial (GSGM) multilayer structures. The heat transfer between GSGM structures is significantly larger than that between SiC-coated metamaterials when the chemical potential of graphene is not very high. Moreover, the structure proposed in this study behaves much better than the previous SiC/graphene/metamaterial in enhancing the near-field radiative heat transfer. The findings in this study provide a basis for active controlling of near-field radiative heat transfer.

Optical, electrical and microstructural properties of SiC thin films deposited by reactive dc magnetron sputtering

In this study, amorphous silicon carbide (SiC) thin films of variable compositions were deposited on Si (100) and glass substrates by reactive direct current magnetron sputtering of high purity silicon target, using CH4 as reactive gas. The composition and the properties of the coatings have been modified by the change in the reactive gas flow rate from 5% to 50%. Spectrophotometer has been used to measure the optical transmittance and reflectance of silicon carbide thin films over the spectral range from 280 to 1000 nm. The optical constants such as refractive indices and the extinction coefficients of the films were calculated. The band gap values of the deposited films were further evaluated with respect to the gas flow rate. Transmittance values of SiC films changed from 85% to almost 0% in the visible light range. The optical band gap values of the films were altered from 1.7 to 2.7 eV. The activation energy was found to increase from 0.16 eV up to 1 eV and dark conductivity decreased from 7.42 × 10−4 to 1.06 × 10−9 Ω−1cm−1 while carbon concentration in the films increased. The results demonstrated that the optical and electrical properties of SiC films could easily be tailored by modifying Si and C concentrations in the coating composition, for the same film thicknesses.

Эволюция ансамбля микропор в структуре SiC/Si в процессе роста методом замещения атомов

AbstractThe time evolution of the ensemble of micropores formed in the near-surface region of silicon during the growth of thin films of silicon carbide is studied by the method of atom substitution. SiC/Si samples are studied by scanning electron microscopy, ellipsometry, and confocal Raman microscopy. The formation of the porous layer involves several characteristic stages: the emergence of single pores, their growth with the formation of dendrite-like structures, and subsequent coalescence into a continuous layer. It is shown that the thickness of the porous layer at the initial stages of the growth is proportional to the cubic root of time. The possible mechanisms of pore formation are discussed and a theoretical model is proposed to describe the dependence of the average thickness of the porous layer on time. The model is in a good qualitative agreement with the experimental results.

Development of Pd-Pt functionalized high performance H2 gas sensor based on silicon carbide coated porous silicon for extreme environment applications

Present work demonstrates the hydrogen gas (H2) sensing characteristics of palladium-platinum (Pd-Pt) functionalized silicon carbide (SiC) thin film grown on porous silicon (PSi) substrate for high temperature applications. Nano-crystalline SiC thin film was deposited by RF magnetron sputtering on anodized PSi substrate. The loading of discrete ultra-thin Pd-Pt bimetallic catalytic layer was carefully controlled by varying the sputtering parameters. The proposed device architecture (Pd-Pt/SiC/PSi) revealed significant advantages, such as stable high sensing response, large tunable detection range (5–500 ppm), fast response/recovery time, excellent reproducibility, high selectivity, wide operating temperature regime (25–500 °C) and good durability. The observed high response may be ascribed to the combined effect of enhanced catalytic activity of bimetallic Pd-Pt layer and increased surface area of the proposed sensor.

Influence of topological constraints on ion damage resistance of amorphous hydrogenated silicon carbide

Radiation damage in materials is an important reliability issue in applications ranging from microelectronic devices to nuclear reactors. However, the influence of atomic structure and specifically topological constraints on the ion damage resistance of amorphous dielectrics has until recently been largely neglected. We have investigated the 120 keV He+ ion damage resistance for a series of amorphous hydrogenated silicon carbide (a-SiC:H) thin films. Changes in elemental composition and atomic structure induced by He+ ion irradiation were monitored using nuclear reaction analysis, Rutherford backscattering spectroscopy, transmission Fourier-transform infrared spectroscopy, and transmission electron microscopy while changes in mechanical properties were investigated using nanoindentation measurements. We show that for 120 keV He+ ion doses producing up to one displacement per atom, significant hydrogen loss, bond rearrangement, film shrinkage, and mechanical stiffening were induced for films with mean atomic coordination (〈r〉) ≤ 2.7, while comparatively minor changes were observed for films with 〈r〉 > 2.7. The observed radiation hardness threshold at 〈r〉rad > 2.7 is above the theoretically predicted rigidity percolation threshold of 〈r〉c = 2.4. Based on the observed elimination of terminal CH bonds and SiCH2Si linkages, the higher radiation hardness threshold is interpreted as evidence that these bonds are too weak to function as constraints in high-energy ion collisions. Eliminating these constraints increased 〈r〉c to 2.7, in agreement with the observed 〈r〉rad = 2.7. These results demonstrate the key role of topological constraints in ion damage resistance and provide additional criteria for the design of ion-damage-resistant amorphous materials.

Influence of In-Situ Annealing of Si-Rich Silicon Carbide Thin Films

Si-rich Silicon carbide thin films have grown popularity in the past decade for various opto-electronic applications. Post processing of these thin films at temperature higher than 1000oC usually lead to phase transformations to form Si nanoclusters embedded in amorphous SiC deposited by sputtering on thin films. However, the processing technique is crucial to avoid contaminants, and obtain good quality films. Therefore, a novel in-situ annealing approach within the deposition chamber is carried out at temperatures lower than usual. The influence of in-situ annealing on the material property is meticulously studied by means of Spectroscopic Ellipsometry (SE), Diffused Reflectance Spectroscopy (DRS), and Fourier Transform Infrared Spectroscopy (FTIR). In SE, the spectra are fitted using various models; the refractive index values confirm the Si-richness of the film. The band gap (2.5 to 1.5 eV) is extracted from UV spectra using Tauc plot, which confirms the coexistence of the multiphase structure with the possibility of having Si-NC with different dimensions. The results obtained are promising for optoelectronic device applications.

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.

Synthesis and structural evolution of hydrogenated amorphous silicon carbide thin film with carbon nanostructures

A new hydrogenated amorphous silicon carbide (a-SiCx:H) thin film with carbon nanostructure is grown through plasma enhanced chemical vapor deposition (PECVD) method. The structural evolution and growth mechanism of the as deposited a-SiCx:H thin film are explored and further discussed with different substrate temperatures. The results show that the structure of the a-SiCx:H thin film is a multiphase structure of carbon nanostructures embedded into CSiO(H) amorphous matrix, and the carbon nanostructure is a spheroidal graphite-like structure. With increasing substrate temperature, the carbon nanostructure gradually grows up through incorporation with surrounding nanostructures. When the substrate temperature increases further to 300 °C, the ultrafine basic structure units of graphite are found within the carbon nanostructure. In addition, the disorder of the thin film first increases and then decreases with increasing substrate temperature, which give rise to band tail states among the π-π⁎ band gap. The change of structure of as synthesized a-SiCx:H thin film with different substrate temperatures supports the sub-plantation model. Furthermore, a tunable optical band gap depended on structure of the carbon nanostructures is demonstrated at different substrate temperatures, which may bring about a potential of application.

Improvement of Electrical Properties of Carbon Nanowall by the Deposition of Thin Film.

In this study, the improvement of the electrical properties of carbon nanowalls (CNWs) by the deposition of nonmetallic thin films such as carbon (C), silicon (Si), and silicon carbide (SiC) was investigated. The CNWs were synthesized on a Si wafer substrate using microwave-plasma-enhanced chemical vapor deposition (PECVD). The thin films were deposited through RF magnetron sputtering with a 4-inch target (C, Si, and Sic) on the grown CNWs. The surficial and cross-sectional conditions were examined using the images obtained from a field emission scanning electron microscope (FESEM). The structural characteristics were analyzed through Raman analysis. The analysis of the electric characteristics confirmed that the resistivity decreased for the nonmetallic-thin-film-coated samples, and that the mobility increased in the order of the as-deposited sample and the C-, SiC-, and Si-thin film-deposited samples. It was also confirmed that the deposition of the SiC thin films resulted in the lowest resistivity at 13.6 × 10-3 Ωcm, and that the deposition of the Si thin films showed the highest mobility at 304 cm2/VS.

Simultaneous Determination of Young’s Modulus and Residual Stress in PECVD a-SiC from Postbuckling Vibration of MEMS Beams

For design of MEMS structures, an accurate measurement of material properties of thin films is necessary, which vary considerably due to process variations. In addition, performance of MEMS devices are often affected due to process induced residual stresses and even dimensional variations. Thus, it is essential that we develop techniques to determine these important material and structural properties from each complete fabrication process. In this work, we exploit the invariance of even modes of buckled beams w.r.t. change in stress for decoupling effects of modulus and stress on dynamic characteristics of MEMS beams. This enables simultaneous estimation of Young’s modulus and residual stress. The technique is demonstrated by estimating modulus and stress in amorphous silicon carbide thin films deposited by PECVD. Use of post-buckling analysis makes this technique useful for thin films with high compressive stresses. Since the proposed method does not involve electrostatic actuation, it is equally applicable to dielectric thin films.

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