Epitaxial 3C-SiC Research Articles

Correlation between Q-Factor and Residual Stress in Epitaxial 3C-SiC Double-Clamped Beam Resonators

In this work, we investigate the correlation between tensile residual stress and Q-factor of double-clamped beams fabricated on epitaxial 3C-SiC layers grown on both <100> and <111> silicon substrates, using a completely optical measurement setup to measure the Q-factor of the resonators and the residual stress of the layers by means of purposely designed micromachined test structures. From the measurements, a clear correlation appears between the residual stress of the SiC layer and the Q-factor of the resonators, with Q-factor values above half a million for resonators fabricated on <111> substrates, showing residual stress around 1 GPa.

A 3C-SiC-on-Insulator-Based Integrated Photonic Platform Using an Anodic Bonding Process with Glass Substrates.

Various crystalline silicon carbide (SiC) polytypes are emerging as promising photonic materials due to their wide bandgap energies and nonlinear optical properties. However, their wafer forms cannot readily provide a refractive index contrast for optical confinement in the SiC layer, which makes it difficult to realize a SiC-based integrated photonic platform. In this paper, we demonstrate a 3C-SiC-on-insulator (3C-SiCoI)-based integrated photonic platform by transferring the epitaxial 3C-SiC layer from a silicon die to a borosilicate glass substrate using anodic bonding. By fine-tuning the fabrication process, we demonstrated nearly 100% area transferring die-to-wafer bonding. We fabricated waveguide-coupled microring resonators using sulfur hexafluoride (SF6)-based dry etching and demonstrated a moderate loaded quality (Q) factor of 1.4 × 105. We experimentally excluded the existence of the photorefractive effect in this platform at sub-milliwatt on-chip input optical power levels. This 3C-SiCoI platform is promising for applications, including large-scale integration of linear, nonlinear and quantum photonics.

Formation of epitaxial 3C-SiC layers on Si by rapid vacuum thermal processing

The results of a study of the structure and phase composition of epitaxial layers of silicon carbide (SiC) formed on silicon substrate with orientation (100) under rapid vacuum thermal processing are presented. Planar-view transmission electron microscopy investigation revealed the formation of epitaxial layers of cubic polytype SiC (3C-SiC) on silicon in the process of carbidisation at 1100 °C during 30 s, using a gas mixture of propane (10 %) and argon (90 %) as a carbon source. The formation of a monocrystalline 3C-SiC with polycrystalline inclusions and twins on all possible planes {111} was found. A rather narrow band of 793 cm–1 transverse optical phonon mode SiC on Raman spectra confirms the formation of a cubic polytype SiC. It is noted that the presence of a 180 cm–1 spectral line and a 793 cm–1 half-width band on Raman spectra indicate the presence of deformation defects in SiC.

Crystal Growth of Epitaxial 3C-SiC Thin Film on Si Substrate by Chemical Vapor Deposition using Single Precursor of Vinylsilane

We have examined the formation of 3C SiC thin films on Si substrates by chemical vapor deposition (CVD) method using vinysilane as a single precursor. The epitaxial 3C-SiC film was successfully grown on Si(111) substrate at a lower temperature of 1000 °C. In addition, in-situ phosphorus doping for polycrystalline 3C-SiC was achieved using tri-ethyl-phosphorus as a dopant source. The active dopant concentration as high as 8.2×1019 cm−3 and the resistivity as low as 1.9×10−2 Ωcm was obtained. This resistivity value is comparable to the epitaxial 3C-SiC film formed on Si substrate ever reported at the same dopant concentration region. The fact that resistivity as low as single crystalline films can be obtained at a low temperature of 900°C promises that CVD-grown 3C-SiC films using a single precursor of vinylsilane is a suitable material for a wide range of applications.

Epitaxial growth and electrical performance of graphene/3C–SiC films by laser CVD

High electrical conductivity graphene/epitaxial-3C–SiC (G/epi-3C–SiC) composite films have the potential to the applications such as micro-electro-mechanical systems, distributed Bragg reflectors, solar cells, and photocatalysis in harsh environments. In this study, G/epi-3C–SiC composite films were prepared through laser chemical vapor deposition (LCVD) using hexametyldisilane (HMDS) as a safe single precursor. The electrical conductivity (σ) of the composite films reached 2.23 × 104 S/m, which is 2.2 times of the highest σ reported for G/epi-3C–SiC composite. The deposition rate (Rdep) of the composite film with the highest σ is 8.2 times of that of the G/epi-3C–SiC with the highest σ ever reported. σ of the pure epitaxial 3C–SiC film is only 81.2 S/m, which is the lowest value reported to date of 3C–SiC prepared through CVD using HMDS as a single precursor. Elimination of carbon is beneficial for increasing the breakdown field intensity and decreasing the leakage current of heterojunction when epitaxial 3C–SiC is used as semiconductor material.

Growth of 3C-SiC(111) on AlN/off-axis Si(110) hetero-structure and formation of epitaxial graphene thereon

A cubic silicon carbide (3C-SiC) film was fabricated by pulsed laser deposition on an aluminum nitride layer grown on an off-axis Si(110) substrate. This is the first report about the use of off-axis Si(110) substrates for manufacturing SiC/AlN/Si multilayers. A high-quality epitaxial 3C-SiC(111) film without rotation domains or twins, as evidenced by reflection high-energy electron diffraction (RHEED) measurements, was successfully obtained by using a wurtzite AlN(0001)/off-axis Si(110) substrate. On this 3C-SiC film, graphene was formed through annealing in ultrahigh vacuum at 1200 °C and its structure and chemical bonding were investigated via in situ RHEED and X-ray photoelectron spectroscopy; the full width at half maximum of the C 1s core level peak and the root-mean-square surface roughness were 0.60 eV and 0.14 nm, respectively, which were substantially lower than those (0.73 eV and 1.44 nm) previously reported for a graphene sample with similar thickness but formed on a SiC/AlN/on-axis Si(110) substrate.

Stable single photon sources in the near C-band range above 400 K

The intrinsic characteristics of single photons became critical issues since the early development of quantum mechanics. Nowadays, acting as flying qubits, single photons are shown to play important roles in the quantum key distribution and quantum networks. Many different single photon sources (SPSs) have been developed. Point defects in silicon carbide (SiC) have been shown to be promising SPS candidates in the telecom range. In this work, we demonstrate a stable SPS in an epitaxial 3C-SiC with the wavelength in the near C-band range, which is very suitable for fiber communications. The observed SPSs show high single photon purity and stable fluorescence at even above 400 K. The lifetimes of the SPSs are found to be almost linearly decreased with the increase of temperature. Since the epitaxial 3C-SiC can be conveniently nanofabricated, these stable near C-band SPSs would find important applications in the integrated photonic devices.

A Study of the Influence Exerted by Structural Defects on Photoluminescence Spectra in n-3C-SiC

Photoluminescence (PL) spectra have been studied in 3C-SiC/4H-SiC heterostructures and 3C‑SiC single crystals. It was shown that epitaxial 3C-SiC layers grown on 4H-SiC substrates have a markedly poorer crystal perfection than do 3C-SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3C-SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3C-SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

Effect of hydrogen flow on microtwins in 3C–SiC epitaxial films by laser chemical vapor deposition

Epitaxial 3C–SiC films were fabricated on Si(001) by laser chemical vapor deposition using hexamethyldisilane as the precursor source and H2 as the dilution gas. The effect of the H2 flow rate on the density of microtwins in 3C–SiC films was investigated. Crystallographic defects were mainly composed of {111} twins, which tilted 15.8° to the surface of the substrate and refer to the multiple twins mirrored by the first-order twins; these defects were characterized by pole figure. With the flow rate of H2 increased from 1.0 to 3.0 slm (standard liter per minute), the relative twin density first decreased from 24.0 to 1.2 and then increased to 16.0. The mechanism of the formation and elimination of the defects is also discussed.

3D 3C-SiC/Graphene Hybrid Nanolaminate Films for High-Performance Supercapacitors.

High-performance supercapacitors feature big and stable capacitances and high power and energy densities. To fabricate high-performance supercapacitors, 3D 3C-SiC/graphene hybrid nanolaminate films are grown via a microwave plasma-assisted chemical vapor deposition technique. Such films consist of 3D alternating structures of vertically aligned 3C-SiC and graphene layers, leading to high surface areas and excellent conductivity. They are further applied as the capacitor electrodes to construct electrical double layer capacitors (EDLCs) and pseudocapacitors (PCs) in both aqueous and organic solutions. The capacitance for an EDLC in aqueous solutions is up to 549.9 µF cm-2 , more than 100 times higher than that of an epitaxial 3C-SiC film. In organic solutions, it is 297.3 µF cm-2 . The pseudocapacitance in redox-active species (0.05 Fe(CN)6 3-/4- ) contained aqueous solutions is as high as 62.2 mF cm-2 . The capacitance remains at 98% of the initial value after 2500 charging/discharging cycles, indicating excellent cyclic stability. In redox-active species (0.01 m ferrocene) contained organic solutions, it is 16.6 mF cm-2 . Energy and power densities of a PC in aqueous solution are 11.6 W h kg-1 and 5.1 kW kg-1 , respectively. These vertically aligned 3C-SiC/graphene hybrid nanolaminate films are thus promising electrode materials for energy storage applications.

Investigating positive oxide charge in the SiO2/3C-SiC MOS system

This paper investigates the origin of the fixed positive oxide charge often experimentally observed in Metal Oxide Semiconductor (MOS) structures of SiO2 formed on cubic silicon carbide (3C-SiC). The electrical properties of MOS structures including either thermally grown SiO2 or deposited SiO2 by Plasma Enhanced Chemical Vapour Deposition (PECVD) on epitaxial 3C-SiC layers grown directly on Si are investigated. MOS structures with a range of oxide thickness values subjected to different thermal treatments were studied. It was found that both thermally grown and deposited SiO2 on 3C-SiC exhibit similar positive charge levels indicating that the charge originates from interface states at the 3C-SiC surface and not from the oxide. The nature of this surface charge in the SiO2/3C-SiC system is also discussed based on the current data and previously published results.

Epitaxial growth of 3C–SiC on Si(111) and (001) by laser CVD

AbstractEpitaxial 3C–SiC films have been deposited on Si(111) and Si(001) substrates via laser CVD with deposition rate of 12.32 and 15.56 μm/h, respectively. The activation energy of 3C–SiC on Si(111) and Si(001) was 80 and 160 kJ/mol, and the root mean square (RMS) roughness (w) as a function of the film thickness (h) follows power laws of w~h0.31 and w~h0.06, respectively. The growth mechanisms of epitaxial 3C–SiC films on Si(111) and Si(001) was investigated based on the structural analysis and roughness evolution.

Unintentionally Doped Epitaxial 3C-SiC(111) Nanothin Film as Material for Highly Sensitive Thermal Sensors at High Temperatures

There is a growing interest and demand to develop sensors that operate at high temperatures. In this work, we investigate the temperature sensing properties of unintentionally doped n-type single crystalline cubic silicon carbide (SiC) for high temperatures up to 800 K. A highly sensitive temperature sensor was demonstrated with a temperature coefficient of conductivity (TCC) ranging from ${1.96}\times {10}^{4}$ to ${5.18}\times {10}^{4}$ ppm/K. The application of this material was successfully demonstrated as a hot film flow sensor with its high signal-to-noise response to air flow at elevated temperatures. The high TCC of the single crystalline SiC film at and above 800 K strongly revealed its potential for highly sensitive thermal sensors working at high temperatures.

Influence of Growth Temperature on Site Competition Effects during Chemical Vapor Deposition of 4H-SiC Layers

After presenting an exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3CSiC films grown by chemical vapor deposition (CVD), we focalize once more on what is called site competition effects. We observed that the influence of C/Si ratio on dopant (Al, N) incorporation in SiC was qualitatively different depending on whether the growth experiments were performed in “low temperature” (LT) or “high temperature” (HT) regime. Partial explanation of observed phenomena basing on thermal evolution of carbon coverage of SiC surface is proposed.

Ultra-high strain in epitaxial silicon carbide nanostructures utilizing residual stress amplification

Strain engineering has attracted great attention, particularly for epitaxial films grown on a different substrate. Residual strains of SiC have been widely employed to form ultra-high frequency and high Q factor resonators. However, to date, the highest residual strain of SiC was reported to be limited to approximately 0.6%. Large strains induced into SiC could lead to several interesting physical phenomena, as well as significant improvement of resonant frequencies. We report an unprecedented nanostrain-amplifier structure with an ultra-high residual strain up to 8% utilizing the natural residual stress between epitaxial 3C-SiC and Si. In addition, the applied strain can be tuned by changing the dimensions of the amplifier structure. The possibility of introducing such a controllable and ultra-high strain will open the door to investigating the physics of SiC in large strain regimes and the development of ultra sensitive mechanical sensors.

3C-SiC Epitaxy on Deeply Patterned Si(111) Substrates

The growth morphology of epitaxial 3C-SiC crystals grown on hexagonal pillars deeply etched into Si (111) substrates is presented. Different growth velocities of side facets let the top crystal facet evolve from hexagonal towards triangular shape during growth. The lateral size and separation between Si pillars determine the onset of fusion between neighboring crystals during growth at a height tailoring of which is crucial to reduce the stacking fault (SF) density of the coalesced surface. Intermediate partial fusion of neighboring crystals is shown as well as a surface of fully coalesced crystals.

Characterization of a n+3C/n−4H SiC heterojunction diode

We report on the fabrication of n + 3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to ∼7 × 1017 cm−3 dopant impurity concentration. The conduction band off-set is about 1 V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n + 3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices.

Defect Reduction in Epitaxial 3C-SiC on Si(001) and Si(111) by Deep Substrate Patterning

The heteroepitaxial growth of 3C-SiC on Si (001) and Si (111) substrates deeply patterned at a micron scale by low-pressure chemical vapor deposition is shown to lead to space-filling isolated structures resulting from a mechanism of self-limitation of lateral expansion. Stacking fault densities and wafer bowing may be drastically reduced for optimized pattern geometries.

High Quality 3C-SiC (111) Epitaxial Layer on Si (110) Substrate by Using Si<sub>2</sub>Cl<sub>6</sub>+C<sub>3</sub>H<sub>8</sub>

The 3C-SiC (111) layer has been grown on Si (110) substrate by using hexachloro-disilane (HCDS) and propane. The propane flow rate was controlled in the carbonization step and the growth step for obtaining SiC layer with high crystal quality. The high quality epitaxial 3C-SiC (111) layer was successfully grown at growth temperature of 1280°C and lower propane flow rate condition. Grown 3C-SiC epitaxial layers were systematically analyzed by an optical microscope, Raman spectroscopy, FE-SEM and XRD

Electrochemical properties and applications of nanocrystalline, microcrystalline, and epitaxial cubic silicon carbide films.

Microstructures of the materials (e.g., crystallinitiy, defects, and composition, etc.) determine their properties, which eventually lead to their diverse applications. In this contribution, the properties, especially the electrochemical properties, of cubic silicon carbide (3C-SiC) films have been engineered by controlling their microstructures. By manipulating the deposition conditions, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are obtained with varied properties. The epitaxial 3C-SiC film presents the lowest double-layer capacitance and the highest reversibility of redox probes, because of its perfect (001) orientation and high phase purity. The highest double-layer capacitance and the lowest reversibility of redox probes have been realized on the nanocrystalline 3C-SiC film. Those are ascribed to its high amount of grain boundaries, amorphous phases and large diversity in its crystal size. Based on their diverse properties, the electrochemical performances of 3C-SiC films are evaluated in two kinds of potential applications, namely an electrochemical capacitor using a nanocrystalline film and an electrochemical dopamine sensor using the epitaxial 3C-SiC film. The nanocrystalline 3C-SiC film shows not only a high double layer capacitance (43-70 μF/cm(2)) but also a long-term stability of its capacitance. The epitaxial 3C-SiC film shows a low detection limit toward dopamine, which is one to 2 orders of magnitude lower than its normal concentration in tissue. Therefore, 3C-SiC film is a novel but designable material for different emerging electrochemical applications such as energy storage, biomedical/chemical sensors, environmental pollutant detectors, and so on.