Epitaxial Silicon Carbide Research Articles

Characterization of newly developed large area SiC sensors for the NUMEN experiment

First prototypes of large area, p–n junction, silicon carbide (SiC) detectors have been produced as part of an ongoing programme to develop a new particle identification wall for the focal plane detector of the MAGNEX magnetic spectrometer, in preparation for future NUMEN experimental campaigns. First characterizations of sensors from two wafers obtained with epitaxial silicon carbide growth and with different doping concentration are presented. Current (I–V) and capacitance (C–V) characteristics are investigated in order to determine the full depletion voltage and the doping profile. Radioactive α-sources are used to measure the energy resolution and estimate the depletion depth.

Design and analysis of novel high-performance thick epitaxial SiC radiation detector with low operating voltage by multiple p-type buried layers

In this work, epitaxial silicon carbide (SiC) radiation detectors (E-SRD) were modeled, and SiC PiN diodes with multiple p-type buried layers (PBL), named MPBL PiN, were proposed as E-SRD to address the problem that detection performance of E-SRD using convention PiN diodes (Cov. PiN) with thick epilayer is limited by its high fully depleted voltage (VFD). The charge collection efficiency (CCE), pulse height and relevant physical mechanism affecting detection performance of E-SRD were investigated. When both Cov. PiN and MPBL PiN have a 100 μm epilayer with n-type doping concentration of 3 × 1014 cm−3, the VFD of Cov. PiN reaches 2800 V, while that for MPBL PiN is only 550 V. 14 MeV neutron detection simulation results showed that, compared to Cov. PiN, the CCE, pulse height and radiation resistance of MPBL PiN improve significantly under low operating voltage within 1000 V, meanwhile its lower near-surface electric field is conducive to reducing leakage. Further, since the VFD of MPBL PiN is proportional to the thickness of the epilayer (HE) instead of to the square of the HE like Cov. PiN, the VFD of MPBL PiN with ultra-thick epilayer is much lower than that of Cov. PiN. Therefore, under commonly used operating voltage within 1000V, the sensitivity and pulse height of MPBL PiN can be proportional to the HE, while that of Cov. PiN hardly improved when HE is above 100 μm. So MPBL PiN can give full play to the high-performance detection advantages of ultra-thick epilayer, which is expected to promote the development and application of ultra-thick epilayer E-SRD with low operating voltage.

Epitaxial SiC Dosimeters and Flux Monitoring Detectors for Proton Therapy Beams.

The exceptional optoelectronic properties and high radiation resistance of epitaxial silicon carbide make this material attractive for high-energy beam dosimetry and radiation monitoring, especially when strict requirements such as high signal-to-noise ratios, high time and spatial resolutions and low detectivity levels are required. A 4H-SiC Schottky diode has been characterized as a proton-flux-monitoring detector and dosimeter under proton beams for proton therapy. The diode was composed of an epitaxial film grown on 4H-SiC n+-type substrate equipped with a gold Schottky contact. The diode was embedded in a tissue-equivalent epoxy resin and then characterized in terms of capacitance vs. voltage (C-V) and current vs. voltage (I-V) characteristics in the dark in the range of 0-40 V. The dark currents at room temperature are in the order of 1 pA, while the doping and active thicknesses extracted from the C-V are 2.5 × 1015 cm-3 and 2-4 μm, respectively. Proton beam tests have been carried out at the Proton Therapy Center of the Trento Institute for Fundamental Physics and Applications (TIFPA-INFN). They have been carried out with energies and extraction currents of 83-220 MeV and 1-10 nA, respectively, as typical for proton therapy applications, corresponding to dose rates in the range of 5 mGy/s to 2.7 Gy/s. The I-V characteristics measured under proton beam irradiation at the lowest dose rate showed a typical diode photocurrent response and a signal-to-noise ratio well above 10. Investigations with null bias evidenced a very good performance in terms of the diode's sensitivity, fast rise and decay times and response stability. The diode's sensitivity was in agreement with the expected theoretical values, and its response was linear throughout the whole investigated dose rate range.

Surface Kinetic Mechanisms of Epitaxial Chemical Vapour Deposition of 4H Silicon Carbide Growth by Methyltrichlorosilane-H2 Gaseous System.

The chemical vapour deposition (CVD) technique could be used to fabricate a silicon carbide (SiC) epitaxial layer. Methyltrichlorosilane (CH3SiCl3, MTS) is widely used as a precursor for CVD of SiC with a wide range of allowable deposition temperatures. Typically, an appropriate model for the CVD process involves kinetic mechanisms of both gas-phase reactions and surface reactions. Here, we proposed the surface kinetic mechanisms of epitaxial SiC growth for MTS-H2 gaseous system where the MTS employed as the single precursor diluted in H2. The deposition face is assumed to be the Si face with a surface site terminated by an open site or H atom. The kinetic mechanisms for surface reactions proposed in this work for MTS-H2 gaseous system of epitaxial growth of SiC by CVD technique from mechanisms proposed for H-Si-C-Cl system are discussed in detail. Predicted components of surface species and growth rates at different mechanisms are discussed in detail.

MicroRaman Study of Nanostructured Ultra-Thin AlGaN/GaN Thin Films Grown on Hybrid Compliant SiC/Por-Si Substrates

In our study, for the first time we demonstrate the advantages of using a compliant hybrid substrate of porSi/SiC to grow high-quality ultra-thin nanostructured AlxGa1−xN/GaN heterostructures using molecular beam epitaxy with plasma-activated nitrogen. Comparison of our experimental results obtained by micro-Raman spectroscopy, deconvolution, and the fitting of the experimental Raman spectra and subsequent calculations with information from already established literature sources show that the use of such a hybrid SiC/porSi substrate has a number of undeniable advantages for the growth of ultra-thin AlxGa1−xN/GaN nanoheterostructures without requiring the use of thick AIIIN buffer layers. Direct growth on a hybrid compliant substrate of SiC/porSi leads to a substantial relaxation in the elastic stresses between the epitaxial film, porous silicon, and silicon carbide, which consequently affects the structural quality of the ultra-thin AlxGa1−xN/GaN epitaxial layers. The experimental and computational data obtained in our work are important for understanding the physics and technology of AlxGa1−xN/GaN nanoheterostructures and will contribute to their potential applications in optoelectronics.

Comparative study of nanostructured ultra-thin AlGaN/GaN heterostructures grown on hybrid compliant SiC/porSi substrates by molecular beam epitaxy with plasma nitrogen activation

This study demonstrates the advantages of using a hybrid compliant substrate containing a porous silicon (porSi) layer, obtained through electrochemical etching of the original silicon substrate, and a silicon carbide (SiC) layer, formed on its surface through the Kukushkin method, to grow high-quality, ultra-thin nanostructured AlхGa1-xN/GaN heterostructures with nanocolumnar morphology by molecular beam epitaxy with plasma-activated nitrogen.Comparison of our experimental results with information from prior literature illustrates that the use of such a hybrid SiC/porSi substrate has a number of undeniable advantages for the growth of ultra-thin AlхGa1-xN/GaN nanoheterostructures without the use of thick AIIIN buffer layers. Direct growth on a hybrid compliant substrate and SiC/porSi leads to a substantial relaxation of elastic stresses between the epitaxial film, porous silicon, and silicon carbide; this consequently affects the structural quality and optical characteristics of AIIIN nitride-based transistor ultra-thin structures.The experimental and computational data obtained in our research are important for understanding the physics and technology of AlхGa1-xN/GaN nanoheterostructures, and they will contribute to their potential applications in optoelectronics.

Analysis of the Gas Phase Epitaxy of Silicon Carbide as a Basic Process for the Technology of Power Electronics

Analysis of the Gas Phase Epitaxy of Silicon Carbide as a Basic Process for the Technology of Power Electronics

A new method for creating nanoprofiled epitaxial silicon carbide surfaces on silicon

In the presented work, the method of substitution of atoms was used to form an epitaxial nanostructured profiled SiC layer with a given geometry on a Si crystal. The found conditions for the synthesis of the SiC layer with the initial geometry and morphology of the Si surface preserve the initial state, covering layered SiC, completely repeating the profile of the initial Si surface.

(Invited) Epitaxy of Silicon Carbide for Power Devices

We observe an evolution how electric power is generated, converted, distributed and used. The world making an attempt to move away from fossil fuels towards a more renewable, energy efficient and electrified energy ecosystems, and therefor efficiency in power conversion processes becomes critically important. As the most prominent example, various wide band gap semiconductor materials are entering the power electronics in electric and hybrid vehicles. Among them is a Silicon Carbide (SiC). A major benefit of its characteristics, comparing to Silicon (Si), in terms of switching speed, heat loss and size of power electronic devices, is at least 50 % reduction in energy loss in the form of heat. This saving translates into more efficient power electronics and more energy for an electric motor and therefore for longer mileage with the same battery. Therefore, SiC offers an opportunity to move power electronics beyond the boundaries set by the material limits of Si. From production point of view, SiC is especially attractive because of its compatibility with Si manufacturing technologies.Modern semiconductor power electronic devices are fabricated out of epitaxial thin films of semiconductors, creating a desired device’s layers stack. Therefore, the epitaxy is absolutely essential for creation of such devices.SiC is a fascinating material with excellent physical properties. It is a wide band gap semiconductor with high thermal conductivity. It is resistant to chemical etchants and radiation. It has high mechanical strength and biocompatible. SiC is the only Group IV compound semiconductor. And finally one of its polytypes, cubic silicon carbide (3C-SiC), can be grown on Si. There are over 200 polytpes of SiC. All of them are formed from 50% Si and C and consist of hexagonal SiC bilayers. Different stacking sequences of C-Si bilayers produces different crystal structures. Different polytypes have different properties and challenges. Due to this epitaxy is very challenging. Among all known polytypes only 3C-, 4H- and 6H- have been very well researched. Hexagonal polytypes of SiC such as 4H- and 6H-SiC already have commercial applications in power electronics and also used as substrates for gallium nitride (GaN). SiC substrates can be formed from these two polytypes, which can then be used for homoepitaxial growth at high temperatures for device applications. These substrates are extremely expensive, limited to 150 mm diameters and epitaxial growth requires very high temperatures (~1700-1800 °C), which are only achievable in specially designed, hot-walled chemical vapor deposition (CVD) reactors. 3C-SiC is the only polytype of SiC which possesses a zinc-blende crystal structure and can be grown on a Si substrate, below the Si melting point (1410 °C). Epitaxy state of the art and challenges for these polytypes and their application will be reviewed.

The Influence of Tri-Defects of Epitaxial Layers on the Performance of 4H-Sic Diodes

The triangular defect is a common defect in the 4H-SiC epitaxy, which is also one of the killer defects to the 4H-SiC devices. In this paper, the 4H-SiC epitaxial wafer was grown by chemical vapor deposition (CVD). The formation mechanism of triangular defects in silicon carbide epitaxy was analyzed, and the solutions were proposed. Then, the diodes were fabricated on the wafer, and the influence of triangular defects on the forward and reverse I-V characteristics of 4H-SiC diodes was analyzed by tracking the defects map. The results show that the presence of triangular defects can lead to the reduction of the reverse voltage by about 40%, an increase of the leakage current by four orders of magnitude, and an increase of the forward conduction resistance.

Low-Temperature Growth of the CdS Cubic Phase by Atomic-Layer Deposition on SiC/Si Hybrid Substrates

A new method for epitaxial growth of cadmium sulfide (CdS) films in the metastable cubic phase by atomic-layer deposition on silicon substrates with a buffer layer of epitaxial silicon carbide has been developed. The growth of this CdS phase is provided by the low growth temperature (~180°C). The cubic phase was identified both by X-ray diffraction analysis and by spectral ellipsometry because the main peak of light absorption by CdS is split into two peaks, at 4.9 and 5.4 eV, in the hexagonal phase and is unsplit (degenerate) at 5.1 eV in the cubic phase.

Chemical Behavior of Byproduct Layer in Exhaust Tube Formed by Silicon Carbide Epitaxial Growth in a System Using Chlorides

This study evaluated the chemical behavior of an oily byproduct which was formed in the exhaust tube during the silicon carbide epitaxial growth process using various precursors, such as silanes, chlorosilanes, propane, hydrogen chloride and hydrogen. Most of the precursors were spontaneously emitted from the oily byproduct, when the oily byproduct was kept under a nitrogen gas flow at atmospheric pressure and at room temperature. When the oily byproduct was exposed to 2-5 % chlorine trifluoride gas in ambient nitrogen at room temperature, various gaseous fluorides were produced, accompanying a slight temperature increase.

Epitaxial 4H–SiC based Schottky diode temperature sensors in ultra-low current range

This work reports highly sensitive and linear temperature sensors based on epitaxial silicon carbide (SiC). Circular shaped Ni/4H-nSiC Schottky barrier diode (SBD) temperature sensors of area 3.140 mm2 have been fabricated and characterized in forward current (If) and temperature range from 10 pA to 5 nA and 233 K–473 K, respectively. The highest value of absolute thermal sensitivity |S| has been achieved as 3.425 mV/K at the lowest If = 10 pA. The sensors show best performance at If = 0.1 nA with lowest root mean square error, temperature error and highest coefficient of determination as 5.341 mV, 1.620 K and 99.96%, respectively, with |S| = 3.295 mV/K. Moreover, for If ≤ 20 pA, sensors reach their maximum operating temperature point, i.e., 448 K. The highest value of self-heating in the sensors have been calculated as 1.623 nK. Moreover, asymmetry has been observed between experimental and the theoretical values of |S| which are explained using variation in the barrier height patches (probably caused by defects at the interface) parameter like their effective area, radius, number, barrier height at the saddle point, with the temperature.

Oxygen intercalated graphene on SiC(0001): Multiphase SiOx layer formation and its influence on graphene electronic properties

Low-dimensionality materials are highly susceptible to interfaces. Indeed, intercalation of different chemical species in between epitaxial graphene and silicon carbide (SiC), for instance, may decouple the graphene with respect to the substrate due to the conversion of the buffer layer into a graphene layer. O-intercalation is known to release the strain of such 2D material and to lead to the formation of high structural quality AB-stacked bilayer graphene. Nonetheless, this interface transformation concomitantly degrades graphene electronic transport properties. In this work we employed different techniques in order to better understand the structure of the graphene/SiC interface generated by O-intercalation and to elucidate the origin of the poor electronic properties of graphene. Experimental results revealed the formation of a SiO2 rich layer with a defective transition layer in between it and the SiC, which is characterized by the existence of silicon oxycarbide structures. Scanning tunneling spectroscopy measurements revealed an extensive presence of electronic states just around the Fermi level all over the sample surface, which may suppress the charge carriers mobility around this region. According to theoretical calculations, such states are mainly due to the formation of silicon oxicarbides within the interfacial layer.

Investigation of Al- and N-implanted 4H–SiC applying visible and deep UV Raman scattering spectroscopy

Effects of aluminum (Al) and nitrogen (N) implantation performed at room and at elevated (500 °C) temperatures on epitaxial n-type 4H polytype silicon carbide as well as post-implantation annealing have been studied by Raman scattering spectroscopy. The amorphization of 4H–SiC is observed because of ion implantation effects. The Raman analysis showed that the recovery of the crystallinity increased with an increase in the annealing temperature. However, for samples implanted with high doses, the full crystal recovery was not complete even with annealing temperatures up to 1800 °C, and crystal defects were still present in the recrystallized layer, which was confirmed by transmission electron microscopy. Raman scattering spectra were collected at room temperature using a micro-Raman spectrometer. The visible (488 nm) and deep ultraviolet (266 nm) lasers were used as excitation sources. For the DUV laser, the optical penetration depth is less than the implanted layer thickness, and the area near the surface layer can be exactly probed. In contrast, the visible Raman spectrum shows bands characteristic of bulk 4H–SiC, which arise from the underlying non-implanted region. Based on the analysis of the longitudinal optical phonon–plasmon coupled mode, the electrical parameters for N2+ implanted samples were evaluated, where electron concentration n = 3.05 × 1018 cm−3 and mobility μ = 50 cm2/V s, respectively. The results are consistent with the parameters measured by the Hall method.

Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy.

Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are 'half van der Waals' metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.

Низкотемпературный рост кубической фазы CdS методом атомно-слоевого осаждения на гибридных подложках SiC/Si

A new method has been developed for the epitaxial growth of cadmium sulfide CdS films in a metastable cubic phase on silicon substrates with a buffer layer of epitaxial silicon carbide by atomic layer deposition. This CdS phase is achieved due to the low growth temperature (~ 180 ℃). The cubic phase was identified by both X-ray diffraction (XRD) and spectral ellipsometry due to the fact that the main peak of CdS absorption is split into two peaks in the hexagonal phase (4.9 eV and 5.4 eV) and is a singlet in the cubic phase (5.1 eV).

Structure and Hardness Evolution of Silicon Carbide Epitaxial Layers Irradiated with He+} Ions

Structure and Hardness Evolution of Silicon Carbide Epitaxial Layers Irradiated with He⁺} Ions

Effect of Defects in Silicon Carbide Epitaxial Layers on Yield and Reliability

Inline metrology tools are widely used to detect defects in SiC epitaxial layers. The defect statistics are used in a variety of ways to determine quality, pass/fail and screen affected die. In this work, we document the automated detection and classification of various epitaxial defects based on type and origin. We further classify these categories into killer and non-killer defects and compare them to the electrical yield of Schottky Diodes. The origins of these defects are determined in broad categories, resulting in a clustering and yield-scaling model, which agrees very closely to experimental data. Further, we look at on-wafer screening techniques of potential weak die by both defect tagging and unclamped inductive switching (UIS) stress testing. Successful 1000-hr reliability tests show the robustness of our detection and screening methods.

Anisotropic and plane-selective migration of the carbon vacancy in SiC: Theory and experiment

We investigate the migration mechanism of the carbon vacancy $({V}_{\text{C}})$ in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The ${V}_{\text{C}}$, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for ${V}_{\text{C}}$ removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that ${V}_{\text{C}}$ migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, ${V}_{\text{C}}(h)$, and pseudocubic, ${V}_{\text{C}}(k)]$ and their consequences for ${V}_{\text{C}}$ migration have not been considered so far. The first part of the paper presents a theoretical study of ${V}_{\text{C}}$ migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for ${V}_{\text{C}}$ migration. In 3C-SiC, ${V}_{\text{C}}$ is found to migrate with an activation energy of ${E}_{\text{A}}=4.0$ eV. In 4H-SiC, on the other hand, we anticipate that ${V}_{\text{C}}$ migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of ${E}_{\text{A}}=4.2$ eV, and a striking preference for basal migration within the $h$ plane with a barrier of ${E}_{\text{A}}=3.7$ eV, to the detriment of the $k$-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of ${V}_{\text{C}}$ in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the ${\mathrm{Z}}_{1/2}$ electron trap in annealed samples that were subject to ion implantation. Activation energies of ${E}_{\text{A}}=(4.4\ifmmode\pm\else\textpm\fi{}0.3)$ eV and ${E}_{\text{A}}=(3.6\ifmmode\pm\else\textpm\fi{}0.3)$ eV were found for ${V}_{\text{C}}$ migration along the $c$ and $a$ directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of ${D}_{0}=0.54\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}/\mathrm{s}$ and 0.$017{\mathrm{cm}}^{2}/\mathrm{s}$ are in line with a simple jump process, as expected for a primary vacancy point defect.