Thin SiC Layer Research Articles

Synthesis of Ultra-Thin Two-Dimensional SiC Using the CVD Method

Two-dimensional materials have shown great potential for applications in many research areas because of their unique structures, and many 2D materials have been investigated since graphene was discovered. Ultra-thin SiC layers with thicknesses of 8–10 nm and multi-layer SiC films were designed and fabricated in this study. First, the multi-layer SiC films were obtained by the chemical vapor deposition (CVD) method with the addition of boron elements. We found that boron additives showed novel effects in the CVD process. Boron can promote the formation and crystallization of SiC films at low temperatures (1100 °C), resulting in the separation of SiC films into multi-layers with thicknesses of several nanometers. In addition, a formation mechanism for the 2D SiC layers is proposed. The boron mostly aggregated spontaneously between the thin SiC layers. Photoluminescence spectroscopy results showed that the SiC films with multi-layer structures had different bandgaps to normal SiC films. The present work proposes a potential method for fabricating 2D SiC materials with convenient experimental parameters and shows the potential of 2D SiC materials for use in electronics.

Structural and thermal analysis of polycrystalline diamond thin film grown on GaN-on-SiC with an interlayer of 20 nm PECVD-SiN

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on the SiC substrate with a 20-nm SiN dielectric. A 4.9% increase in 2DEG density after the diamond growth due to the increase in tensile strain of the GaN layer is confirmed by micro-Raman measurements. The interfacial analysis through the transmission electron microscopy and electron energy loss spectroscopy shows a thickness reduction in the SiN layer of ∼1.7 nm, which converts to a thin SiC layer at the diamond/SiN interface, and no carbon diffusion is found in the SiN layer after the diamond growth. Device simulation using the thermal properties extracted by time domain thermoreflectance predicts a temperature drop of 17.1 °C when the diamond only covers the device access region and reveals that the improvement of thermal boundary resistance is much more effective than that of the diamond thermal conductivity for the top-side heat spreading, which is mainly due to the limited thickness of the top diamond film.

Pulsed laser deposition of multilayer diamond-like carbon film grown on stainless steel

The amorphous SiC layers played an essential role of improving adhesive property in the pulsed laser deposition-grown multilayer DLC coating. Comparison of several experiments exhibited that the adhesive SiC layer enhanced the adhesive strength of the DLC layer on the transitional Ti layer. Meanwhile, the ‘inserted’ buffer thin SiC layers, which had strong binding force with the DLC layers, divided the thick DLC layer (about 1.2 μm) into several relatively thin layers. It's thought that the buffer SiC layers reduced accumulation of internal stress in each finite thickness and then prevented the cracking of the DLC layer. And the total thickness of optimized multilayer DLC coating reached to 2 μm. The multilayer DLC coating with the adhesive SiC layer and buffer SiC layers showed an excellent adhesive performance on the stainless steel. The similar tribological property of SiC layer to the DLC layer conferred this multilayer DLC coating a low friction coefficient and a low wear rate.

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiCw) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiCw/RBSC composites in this study. The microstructures and properties of the PyC-SiCw/RBSC composites under different mass fraction of nano carbon black and PyC-SiCw were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiCw, reached a high value of 5.28 MPa m1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiCw. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiCw were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiCw bridging and pullout to improve the bending strength and toughness of the SiCw/RBSC composites.

Crystalline Interlayers for Reducing the Effective Thermal Boundary Resistance in GaN-on-Diamond.

Integrating diamond with GaN high electron mobility transistors (HEMTs) improves thermal management, ultimately increasing the reliability and performance of high-power high-frequency radio frequency amplifiers. Conventionally, an amorphous interlayer is used before growing polycrystalline diamond onto GaN in these devices. This layer contributes significantly to the effective thermal boundary resistance (TBReff) between the GaN HEMT and the diamond, reducing the benefit of the diamond heat spreader. Replacing the amorphous interlayer with a higher thermal conductivity crystalline material would reduce TBReff and help to enable the full potential of GaN-on-diamond devices. In this work, a crystalline Al0.32Ga0.68N interlayer has been integrated into a GaN/AlGaN HEMT device epitaxy. Two samples were studied, one with diamond grown directly on the AlGaN interlayer and another incorporating a thin crystalline SiC layer between AlGaN and diamond. The TBReff, measured using transient thermoreflectance, was improved for the sample with SiC (30 ± 5 m2 K GW-1) compared to the sample without (107 ± 44 m2 K GW-1). The reduced TBReff is thought to arise from improved adhesion between SiC and the diamond compared to the diamond directly on AlGaN because of an increased propensity for carbide bond formation between SiC and the diamond. The stronger carbide bonds aid transmission of phonons across the interface, improving heat transport.

Development of SOI FETs Based on Core-Shell Si/SiC Nanowires for Sensing in Liquid Environments

Core–shell Si/SiC nanostructures appear as promising building blocks for sensing applications, thanks to the high chemical stability of SiC coupled with the semiconducting properties of Si. In order to optimize the fabrication process of such structures, Si nanowires were coated with a thin SiC layer, and integrated as back-gated field-effet transistors. Two approaches for the fabrication of the SiC shell were then investigated. The first approach involves chemical vapor deposition of amorphous SiC on Si nanowires, without the need for masking; the second approach involves carbonization of Si surfaces to produce a thin crystalline SiC layer, but requires a larger thermal budget. The resulting structures were analyzed using high-resolution transmission electron microscopy (HR-TEM), and the devices were characterized electrically. Electrical characterization shows that the carbonization approach induces a dramatic decrease in drain-to-source current associated with gate leakage, whereas the electrical performances were preserved in the case of chemical deposition.

Impact of Processing on Photoluminescence Properties of 4H-SiC for Potential Qubit Applications

Single silicon vacancies VSi in silicon carbide nanostructures hold great promise for future technological applications in scalable quantum computing and information processing for simulation, sensing, and communication. These defects are typically created by ion implantation or neutron/electron irradiation. Identification of these defects, knowledge of their characteristics, control of their concentrations, isolation of single spin defects and understanding the effects of semiconductor processing on their properties are crucial to the applications of SiC in quantum electronic and integrated photonic devices. These vacancies embedded in photonic crystal cavities (PCC) have the capability of high efficiency emission of single photons which can significantly improve the performance of on-chip photonic networks and long-distance quantum communication systems, as compared to conventional solid-state emitters. Here we investigate the impact of processing on the photoluminescence properties of PCCs fabricated using three approaches: hydrogen implantation to form thin SiC layers on an oxide layer that can be easily etched away to form an air gap under the PCC, wafer bonding and mechanical thinning of the SiC, also on an oxide layer, and selective photo-electrochemical etching of an n-p epitaxial SiC structure to form an air gap. We also assess the impact of electron irradiation for these three fabrication approaches.

Chemical Stability of Si-SiC Nanostructures under Physiological Conditions

The fast and direct detection of small quantities of biological and chemical species is of key importance for numerous biomedical applications. Extensive research has been conducted on nanoelectronic devices that can perform such detection with high sensitivity using silicon nanowires and nanostructures. However, it was recently demonstrated that Si material suffers a lack of long-term stability in physiological environments at nanometer scale [1,2], and is hence not suited for in situ sensing of biological molecules. The results presented here are two important steps toward the realization of core-shell Si-SiC NWFETs for the detection of biomolecules in liquid media. First, we show that SiC NWs exhibit higher chemical stability than Si NWs under physiological conditions. Second, we present the successful carburation of a thin film of Si resulting in a 3.6 nm thin SiC layer.

PIXE detection limit for aluminium thin film deposited on Si-based matrix

The aim of this work is to show the capability of the PIXE technique as a rapid, non-destructive and accurate quantification method on silicon (Si) and in Si-based matrix. For this purpose, an aluminium (Al) thin film (2.5nm) deposition on silicon and silicon carbide substrates was carried out using effect joule evaporation. In order to improve the sensitivity for Al determination, a systematic study was undertaken using proton ion beam at different energies (from 0.2 to 3MeV) with a different incident angles (0°, 60°, and 80°). Proton beam energy of 0.3MeV and 80° tilting angle permits a more accurate determination of Al/Si with high sensitivity within few minutes of acquisition time and with a LOD less than 1.2×1015at/cm2. However, the LOD of Al decreases by one order of magnitude when SiC substrate is used instead of Si. Hence, these optimal parameters were used to determine the concentration of Al doping in thin homoepitaxial SiC layer. It was found that the Al/Si ratio was varied from 0.066 to 0.36 when the incident angle varied from 0 to 80°.

Fabrication of Electrostatically Actuated 4H-SiC Microcantilever Resonators by Using n/p/n Epitaxial Structures and Doping-Selective Electrochemical Etching

We fabricated electrostatically actuated single-crystalline 4H-SiC microcantilever resonators. To realize a narrow gap between cantilevers and substrate, we etched a thin p-type SiC layer in n/p/n multilayer structure by doping-selective electrochemical etching. The resonant characteristics of the fabricated 4H-SiC microcantilevers were investigated under a vacuum condition. Electrostatic actuation of microcantilevers was successfully performed by applying 10 mVrms ac voltage with 20 mV dc bias. The quality factor of 4H-SiC microcantilevers was above 100,000, which is about ten times higher than the quality factor of Si cantilevers with the same structure. Resonant characteristics were almost identical for mechanical actuation and electrostatic actuation.

Side gate AlGaN/GaN FET on silicon and sapphire

AbstractAlGaN/GaN heterostructures were grown on sapphire and alternatively on silicon substrates covered with a thin SiC layer by MOCVD. The side gated transistors were fabricated using electron beam lithography. The conductivity of the drain‐source branch could be tuned via the side gate formed by a two‐dimensional electron gas directly connected to the source drain branch or separated by a trench.The electrical measurements of the fabricated in‐plane‐gated devices revealed unipolar transistor behavior for both types of substrates. The transconductance was 1 µA/V and the output conductance reached 1.9 µA/V for the side gate transisitor on sapphire. The transconductance and output conductance of the side gate device on silicon substrates were 6 and 18 µA/V, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optoelectronic properties of improved GaN semiconductor on Si (111) using growth approaches and different interlayer's

The crystalline quality of wider direct band gap semiconductor (3.4 eV) h-GaN epilayer grown on Si (111) is evaluated by different growth approaches and by using different interlayer's. The investigations of GaN epilayer crystal quality for the template of converted porous GaN layer formed by novel nitridation process of thin (2 and 0.5 μm) GaAs layer on Si (111) and on C+ ion implanted very thin SiC layer formed on Si (111) and grown ambient effect are made. Epilayer grown on thinner non-isoelectronic converted SiC templates is found to broaden its PL line width whereas epilayer grown on porously converted GaN layer fromed from iso- electronic GaAs (111) layer on Si (111) is found narrow line width. H2 ambient grown film better crystalline quality and higher PL Ex. peak energy is found as compared to N2 ambient grown film. Low temperature PL measurement, similarity between defect related donor-acceptor peaks (DAP) to defect related yellow band luminescence at the room temperature PL measurement is also found. Grown epilayer different characterization reveals better crystalline quality h-GaN is achieved by using thin iso-electronic GaAS interlayer on Si (111) with H2 grown ambient.

Optimization of a buffer layer for cubic silicon carbide growth on silicon substrates

A procedure for the optimization of a 3C–SiC buffer layer for the deposition of 3C–SiC/(001) Si is described. After a standard carbonization at 1125°C, SiH4 and C3H8 were added to the gas phase while the temperature was raised from 1125°C to the growth temperature of 1380°C with a controlled temperature ramp to grow a thin SiC layer. The quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface are related to the gas flow and to the heating ramp rate. In order to improve the buffer quality the SiH4 and C3H8 flows were changed during the heating ramp. On the optimized buffer no voids were detected and a high-quality 1.5μm 3C–SiC was grown to demonstrate the effectiveness of the described buffer.

Optoelectronic Properties of Improved GaN Semiconductor on Si(111) Using Growth Approaches And Different Interlayer′s

The crystalline quality of wider direct band gap semiconductor (3.4 eV) hexagonalGaN(h-GaN)epilayer grown on Si(111) is evaluated by using different growth approaches and interlayer’s. The investigations of GaNepilayer crystal quality for the template of converted porous GaN layer formed by novel nitridation process of thin (2 and 0.5μm) GaAs layer on Si(111) and on C+ ion implanted very thin SiC layer formed on Si(111) and grown ambient effect are made. Epilayer grown on thinner non-isoelectronic converted SiC templates is found to broaden its PL line width whereas epilayer grown on porously converted GaN layer fromed from iso- electronic GaAs (111) layer on Si(111) is found narrow line width. H2 ambient grown film better crystalline quality and higher PL Ex. peak energy is found as compared to N2 ambient grown film. Low temperature PL measurement, similarity between defect related donor-acceptor peaks (DAP) to defect related yellow band luminescence at the room temperature PL measurement is also found. Grown epilayer different characterization reveals better crystalline quality h-GaN is achieved by using thin iso-electronic GaAS interlayer on Si(111) with H2 grown ambient.

Low Temperature SiC Film Deposition Using Trichlorosilane Gas and Monomethylsilane Gas

In order to produce silicon carbide thin film through the process entirely at low temperatures, silicon carbide chemical vapor deposition on a silicon wafer surface was performed using trichlorosilane gas and monomethylsilane gas. First, the silicon thin film was formed using trichlorosilane gas at 800 degrees C and was cooled to room temperature in ambient hydrogen, in order to produce hydrogen-terminated silicon surface. Next, monomethylsilane gas was introduced at room temperature to produce silicon carbide thin film. The mirror-like appearance of the film obtained by this process was maintained after the exposure to hydrogen chloride gas at 800 degrees C. Furthermore, very thin Si-C layer was detected at the surface by means of the time-of-flight secondary ion mass spectrometry. Thus, the silicon carbide thin film was concluded to be formed through the process at temperatures below 800 degrees C.

Ambipolar Behavior in Epitaxial Graphene-Based Field-Effect Transistors on Si Substrate

In this research, ambipolar behavior, which is one of graphene's unique characteristics, is studied for the epitaxial graphene formed on 3C-SiC grown on a Si substrate. The graphene channel is believed to be unintentionally p-type-doped at Dirac-point voltages of approximately +0.11 to +0.12 V. However, as drain voltage negatively increases, Dirac point voltage shifts. The drain current in the p-channel mode of operation saturates at a lower level than that in the n-channel mode of operation. These behaviors are caused by asymmetric carrier transport throughout channel-substrate heterojunctions (i.e., graphene, thin n-type SiC layer, and p-type Si substrate) and source/drain Schottky metal contacts. The interface between the p-type Si substrate and n-type SiC has a significant effect on transport in graphene channels. The results may be helpful for understanding transport in the device and for suppressing ambipolar operation, leading to a unipolar FET operation.

A STUDY ON THE PHOTOLUMINESCENCE PROPERTIES OF POROUS 6H-SiC(p) AND SiC FILM ON p-Si SUBSTRATE

P-type porous SiC layers were fabricated by anodization of a hot-pressed p-type 6H-SiC (30 kΩcm) and a 1.6 μm SiC film was deposited onto p-type Si (100) substrate by Pulsed Laser Deposition (PLD) in HF. In order to facilitate the electrochemical etching of the substrate, ethylene glycol electrolyte has been added to the solution and a thin metallic film of aluminium ( Al ) has been deposited onto a SiC prior to anodization. The structure and properties of the porous SiC layer formed by this method were investigated by Scanning Electron Microscopy (SEM) and Photoluminescence (PL). It shows that photoluminescence spectra exhibit two emission bands centered at 2.20 eV (blue band) and an extended broad band from 2.20 to 3.22 eV (green band) from porous 6H-SiC (PSC). On the contrary, porous thin 1.6 μm SiC layer exhibits only a blue band centered at 2.95 eV. Finally, the results indicate clearly that porous SiC gives off green and blue light. Also, there is a shift to blue luminescence with the same order of magnitude when using a thin SiC layer deposited onto silicon (p- Si (100)).

STRUCTURAL AND OPTICAL PROPERTIES OF POLYCRYSTALLINE6H-SiCAND CRYSTALLINESiCFILM GROWN ONTO SILICON SUBSTRATE BY PLD

In this paper, we present a comparative study of structural and optical properties of polycrystalline p-type 6H-SiC and thin SiC layer growth onto Si . The thin SiC layer was grown on a p-type Si(100) substrate by pulsed laser deposition (PLD) using KrF excimer laser from a 6H-SiC hot pressed target. The properties of polycrystalline 6H-SiC and thin SiC layer were investigated by scanning electronic microscopy (SEM), high resolution X-Ray Diffraction (XRD), secondary ion mass spectrometry (SIMS), FT-IR spectroscopy and photoluminescence spectrometry. XRD analysis showed that the two materials have the same hexagonal structure (6H-SiC) as identified by ASTM 72-0018. In addition, a SIMS analysis gives a ratio Si/C of the thin SiC layer around 1.15 but the ratio Si/C of the target was found equal to 1.06, whereas one should have 1.0. This is due to the higher ionization efficiency of Si by the report of C atoms and in photoluminescence, the two materials exhibit the same emission bands (blue and green). Finally, a crystalline thin SiC layer of 1.6 μm was elaborated using the PLD method at low-temperature indicating that the technique reproduces the same macroscopic property (optical, structural, mechanical, etc.) of the target.

Effect of anodization time on photoluminescence of porous thin SiC layer grown onto silicon

A porous SiC (PSC) layer was fabricated by anodization of a 1.6 μm thin SiC layer deposited onto p-type Si(1 0 0) substrate by pulsed laser deposition (PLD), using a hot-pressed 6H-SiC( p) as sputtered target. p-Type PSC layers were fabricated by anodization in HF/ethylene glycol electrolyte (1:1 by vol.) at different etching times. The properties of the PSC layer formed by this method were investigated by X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and photoluminescence (PL). The results show, that the growth layer was crystalline and PL spectra exhibit blue band emission centered at 2.95 eV. In addition, the results indicate clearly an increase in PL intensity by ten times of magnitude compared to that exhibited by the unetched sample.

Morphological, structural and optical properties of thin SiC layer growth onto silicon by pulsed laser deposition

Crystalline silicon carbide thin layers were grown on a p-type Si(1 0 0) substrate by pulsed laser deposition (PLD) using KrF excimer laser at λ=248 nm from a 6H–SiC hot-pressed target. The target “SiC” used to elaborate our SiC films is realized from a mixture of 1SiO 2 with 3C (carbon) “1SiO 2+3C” heated in an oven at 2500 °C (the target was a hot-pressed material and supplied by Goodfellow). The morphological, structural and optical properties of SiC layers were investigated by scanning electronic microscopy (SEM), high-resolution X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and UV–visible spectrophotometer. XRD analysis of the target showed that this latter is a hexagonal structure (6H–SiC). The XRD pattern shows that a 1.6 μm crystalline SiC layer was formed. In addition, a SIMS analysis gives a ratio Si/C of the thin SiC layer around 1.15 but the ratio Si/C of the target was found equal to 1.06, whereas one should have 1.0. This is due to the degree of the sensitivity of the SIMS technique and due to the higher ionization efficiency of Si compared to C atoms, all these which give different ratios. It is known that the PLD technique reproduces the same macroscopic property (optical, mechanical, structural, etc.) of the target. An optical gap ( E Gap) of the SiC layer of about 2.51 eV was obtained by reflectance measurement. Finally, a crystalline thin SiC layer of 1.6 μm was elaborated using PLD method at low-temperature deposition.