SiC Buffer Research Articles

AFM-sMIM Characterization of the Recombination-Enhancing Buffer Layer for Bipolar Degradation Free SiC MOSFETs

Due to the expansion of defects like single Shockley-type Stacking Faults inside the SiC epitaxial drift layer, during high current stress, classical SiC MOSFETs can be victims of the degradation of their electrical characteristics. The introduction of an epitaxial SiC buffer layer between the substrate and the n- drift epilayer, called recombination-enhancing buffer layer, was shown to avoid this degradation. In this paper, TCAD simulations of the electrical behavior of such a commercial SiC MOSFET device with varying buffer layer thickness are studied, indicating only small modifications of the electrical characteristics. These simulations are combined with the characterization of the local electrical properties using an AFM-sMIM technique, allowing to determine the real thickness of the different layers of the device. These measurements highlight an inhomogeneous conductivity in the SiC substrate, being probably compensated by the introduction of the SiC buffer layer.

Thermodynamics and kinetics of Pb intercalation under graphene on SiC(0001)

SiC-supported graphene intercalated by a two-dimensional Pb monolayer can provide an appealing platform for spintronic applications. Such a monolayer structure is thermodynamically ultrastable, as observed in recent experiments. However, important fundamentals such as the structure of intercalated phases, locations of intercalated atoms, thermodynamic preference for intercalation, and intercalation pathways for this system have not yet been understood conclusively. In this work, extensive density functional theory calculations are performed to assess Pb intercalation thermodynamics and kinetics under graphene on SiC(0001). We find that intercalation of isolated Pb atoms is strongly disfavored over adsorption on top of graphene. However, intercalation of complete Pb layers in the gallery between SiC and graphene buffer layer is strongly favored over supported Pb monolayers and moderately favored over formation of supported large three-dimensional Pb islands. We also find that initiation of intercalation either by individual Pb atoms directly penetrating graphene or by hopping under a static graphene step edge is energetically prohibitive at experimental temperatures. Consequently, more complex intercalation pathways are operative and further analyzed. We demonstrated that once an intercalated Pb monolayer forms around a graphene step edge, a facile Pb mass transport by Pb vacancy-mediated diffusion can be triggered for continued growth of the intercalated monolayer.

Imaging and measuring the electronic properties of epitaxial graphene with a photoemission electron microscope

A photoemission electron microscope (PEEM) was recently commissioned at the NIST. To benchmark its capabilities, epitaxial graphene on 4H-SiC (0001) was imaged and analyzed in the PEEM and compared to other complementary imaging techniques. We determine our routine spatial resolution to be about 50 nm. Using the well-known electronic structure of graphene as a reference, we outline a procedure to calibrate our instrument in energy and momenta in the micrometer-angle-resolved photoemission spectroscopy (μ-ARPES). We also determine the energy and momenta resolution to be about 300 meV, 0.08 Å−1 (ky), and 0.2 Å−1 (kx), respectively. We identify distinct regions of the graphene surface based on intensity contrast rising from topographic and electronic contrasts as well as μ-ARPES. These regions are one layer graphene, one SiC buffer layer, and ≥2 layers of graphene (or graphite). These assignments are confirmed using confocal laser scanning microscopy and Raman spectroscopy. Finally, the PEEM instrument had enough sensitivity to observe the flatband in monolayer epitaxial graphene, which we attribute to the presence of compressive strain, −1.2%, in the graphene sample.

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.

TEM investigation of microstructure of semipolar GaN layers grown on nano-patterned Si(001) substrates

The synthesis of III-nitride binary compounds on commercial standard (001) silicon wafers by vapour-phase epitaxy is one of the promising directions for III-nitride technology development. However, the difference between crystal symmetry of Si(001) and wurzite (0001) surface structures is challenge that hinders the development. A use of silicon substrates with nano-patterned surface is one of the solutions to the problem. In this paper we present a transmission electron microscopy study of polar and semipolar GaN layers grown by halide vapour-phase epitaxy and metalorganic vapour-phase epitaxy on nano-patterned silicon (001) substrate. Crystallographic orientation relationships between the silicon substrate and GaN layers is identified. For GaN layers grown by metalorganic vapour-phase epitaxy an effect of SiC buffer layer synthesized by original growth method on their microstructure and surface morphology is under consideration.

The structure and mechanism of large-scale indium-intercalated graphene transferred from SiC buffer layer

It is reported that indium-coated SiC buffer layer can be directly transferred into graphene layer during low temperature annealing, forming as indium-intercalated graphene (InG). Atomic structures of InG as well as transformation mechanism are investigated by scanning tunneling microscopy (STM), Raman and X-ray photoelectron spectroscopy (XPS). InG on top of one-layered intercalated indium (called O-InG) exhibits Moiré patterns with period of 3.2 nm, and the atomic arrangement of indium atoms is detected. While, no Moiré patterns are observed on InG intercalated by two-layer of indium atoms (called T-InG). Both the two InG regions bind perfectly with the already existing epitaxial graphene (EG), exhibiting as an unbroken sheet of quasi-free-standing graphene layer. This finding provides a simple strategy and benefits to industrial fabrication of large-scale InG with regular SiC steps.

Scaling analyses on the critical current density in MgB2/NbN/Si thin film

Scaling analyses are performed on the critical current density J c in MgB2/NbN/Si thin film. In our previous work on MgB2/SiC/Si film [Mat. Sci. Eng. 502 (2019) 012184], we have shown that J c data well scale on a single line with the reduced scaling formula more than 10 orders of magnitude. We extend these studies onto MgB2 film with NbN buffer layer in comparison with SiC buffer. Experimental J c data under perpendicular magnetic field to the film are reduced against transition temperature and critical field, and applicability of the comprehensive scaling formula is examined over 16 orders of magnitude. Our scaling formula is revealed to be well applicable to the NbN-buffered film as well.

Properties of Semipolar GaN Grown on a Si(100) Substrate

Semipolar GaN layers synthesized on a nanostructured Si(100) substrate are studied. It is shown that using a Si(100) nanoprofile combined with SixNy nanostrips on top of nanostructures can yield, via metal-organic chemical-vapor deposition, GaN(10 $$\bar {1}$$ 2) layers. An additional SiC buffer layer makes it possible to obtain GaN(10 $$\bar {1}$$ 1) layers with a full-width at half-maximum of the diffraction-curve of ωθ ≈ 35′ arcmin. It is found that the luminescence properties of the semipolar layers are mostly due to basal plane stacking faults BSFS-I1, in contrast to polar layers in which these properties are mostly due to the recombination of excitons.

Growing III–V Semiconductor Heterostructures on SiC/Si Substrates

A three-layer heterostructure consisting of AlN (∼0.72 μm thick), AlGaN (∼ 1.82 μm thick), and GaN (∼2.2 μm thick) layers has been grown by hydride–chloride vapor phase epitaxy (HVPE) method on a Si substrate with a SiC buffer nanolayer. The heterostructure was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and other techniques. The results showed that SiC/Si substrates can be used for growing films of III–V semiconductor compounds by HVPE at a high rate (~66 μm/h) free of cracks and with small residual elastic stresses (~160 MPa).

Epitaxy of GaN(0001) and GaN(10$$\bar {1}$$1) Layers on Si(100) Substrate

Two different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10 $$\bar {1}$$ 1) on a V-shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10 $$\bar {1}$$ 1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ωθ ~ 45 arcmin, whereas for the semipolar GaN(10 $$\bar {1}$$ 1), these values are –0.29 GPa and ωθ ~ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.

Effect of SiC buffer layer on flux pinning property of MgB2 tapes

In this paper we aimed at investigating the flux pinning property of MgB2 films on hastelloy tapes which are buffered on various thicknesses of SiC layers. We have observed that the increase in thickness of the SiC buffer layer is very closely related with the systematic improvement of the field dependence of the critical current densities (Jc) of MgB2 tapes while the values of Jc decreased. According to the analysis of the pinning force density (Fp), there exist two pinning sources both in the pure MgB2 and in the MgB2 film with the thinnest SiC buffer layer. On the while, the pinning source observed in the MgB2 films with thicker SiC buffer layers appears to be different from those previously mentioned. The different pinning behaviors of MgB2 films may suggest that there be an additional pinning center working on the MgB2 films with thick SiC buffer layers. The microstructural analyses of MgB2 films confirmed that intra-granular defects and columnar grain boundaries may be a dominant pinning mechanism in the pure MgB2 and the MgB2 film with 170 nm-thick SiC buffer layer. For the MgB2 films with thicker SiC buffer layers, carbon diffusion into the MgB2 film, which is defined by the Auger electron spectroscopy, may be the origin of the additional pinning mechanism.

Characteristics of ZrC Barrier Coating on SiC-Coated Carbon/Carbon Composite Developed by Thermal Spray Process.

A thick ZrC layer was successfully coated on top of a SiC buffer layer on carbon/carbon (C/C) composites by vacuum plasma spray (VPS) technology to improve the ablation resistance of the C/C composites. An optimal ZrC coating condition was determined by controlling the discharge current. The ZrC layers were more than 70 µm thick and were rapidly coated under all spraying conditions. The ablation resistance and the oxidation resistance of the coated layer were evaluated in supersonic flames at a temperature exceeding 2000 °C. The mass and linear ablation rate of the ZrC-coated C/C composites increased by 2.7% and 0.4%, respectively. During flame exposure, no recession was observed in the C/C composite. It was demonstrated that the ZrC coating layer can fully protect the C/C composites from oxidation and ablation.

Photoelectric Properties of GaN Layers Grown by Plasma-Assisted Molecular-Beam Epitaxy on Si(111) Substrates and SiC/Si(111) Epitaxial Layers

The photoelectric properties of GaN/SiC/Si(111) and GaN/Si(111) heterostructures grown by plasma-assisted molecular-beam epitaxy under the same growth conditions on identical silicon substrates, but with different buffer layers, are experimentally investigated. The GaN/SiC/Si(111) structure is formed on a Si substrate with the SiC buffer layer grown by a new atom-substitution technique and the GaN/Si(111) structure, on a Si substrate subjected to pre-epitaxial plasma nitridation. The significant effect of carbon-vacancy clusters contained in the SiC layer on the growth of the GaN layer and its optical and photoelectric properties is found. It is experimentally established that the GaN/SiC/Si(111) heterostructure has a higher photosensitivity than the GaN/Si(111) heterostructure. In the GaN/SiC/Si(111) heterostructure, the coexistence of two oppositely directed p–n junctions is observed. One p–n junction forms at the SiC/Si interface and the other, at the GaN/SiC interface. It is shown that the occurrence of an electric barrier in the GaN/Si(111) heterostructure at the GaN/Si(111) heterointerface is caused by the formation of a thin silicon-nitride transition layer during pre-epitaxial plasma nitridation of the Si(111) substrate.

Эпитаксия слоев GaN(0001) или GaN(1011) на подложке Si(100)

AbstractTwo different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10 $$\bar {1}$$ 1) on a V -shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10 $$\bar {1}$$ 1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ω_θ ~ 45 arcmin, whereas for the semipolar GaN(10 $$\bar {1}$$ 1), these values are –0.29 GPa and ω_θ ~ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.

Фотоэлектрические свойства слоев GaN, выращенных методом молекулярно-лучевой эпитаксии с плазменной активацией на подложках Si(111) и эпитаксиальных слоях SiC на Si(111)

AbstractThe photoelectric properties of GaN/SiC/Si(111) and GaN/Si(111) heterostructures grown by plasma-assisted molecular-beam epitaxy under the same growth conditions on identical silicon substrates, but with different buffer layers, are experimentally investigated. The GaN/SiC/Si(111) structure is formed on a Si substrate with the SiC buffer layer grown by a new atom-substitution technique and the GaN/Si(111) structure, on a Si substrate subjected to pre-epitaxial plasma nitridation. The significant effect of carbon-vacancy clusters contained in the SiC layer on the growth of the GaN layer and its optical and photoelectric properties is found. It is experimentally established that the GaN/SiC/Si(111) heterostructure has a higher photosensitivity than the GaN/Si(111) heterostructure. In the GaN/SiC/Si(111) heterostructure, the coexistence of two oppositely directed p – n junctions is observed. One p – n junction forms at the SiC/Si interface and the other, at the GaN/SiC interface. It is shown that the occurrence of an electric barrier in the GaN/Si(111) heterostructure at the GaN/Si(111) heterointerface is caused by the formation of a thin silicon-nitride transition layer during pre-epitaxial plasma nitridation of the Si(111) substrate.

Cвойства полуполярного GaN, выращенного на подложке Si(100)

AbstractSemipolar GaN layers synthesized on a nanostructured Si(100) substrate are studied. It is shown that using a Si(100) nanoprofile combined with Si_ x N_ y nanostrips on top of nanostructures can yield, via metal-organic chemical-vapor deposition, GaN(10 $$\bar {1}$$ 2) layers. An additional SiC buffer layer makes it possible to obtain GaN(10 $$\bar {1}$$ 1) layers with a full-width at half-maximum of the diffraction-curve of ω_θ ≈ 35′ arcmin. It is found that the luminescence properties of the semipolar layers are mostly due to basal plane stacking faults BSF_ S -I_1, in contrast to polar layers in which these properties are mostly due to the recombination of excitons.

Nanostructured Bi Grown on Epitaxial Graphene/SiC.

Controllable growth of metal nanostructures on epitaxial graphene (EG) is particularly interesting and important for the applications in electric devices. Bi nanostructures on EG/SiC are fabricated through thermal decomposition of SiC and subsequent low-flux evaporation of Bi. The orientation, atomic structure, and thickness-dependent electronic states of Bi are investigated by scanning tunneling microscopy/spectroscopy. It is found that metallic Bi nanoflakes and nanorods prefer to grow on the SiC buffer layer region with higher diffusion barrier, but Bi nanoribbons are formed on regularly ordered EG. Although the thicker Bi nanoribbons of 11 monolayers on EG are still metallic, the thinner ones become semiconducting owing to the interfacial effect. This indicates that the electronic states and physical properties of Bi are substrate-dependent. The results are helpful for the design of Bi- and graphene-based electronic and spintronic devices.

The growth of 3C-SiC on Si substrate using a SiCN buffer layer

Cubic silicon carbide (3C-SiC) has been grown on Si (111) substrate by chemical vapor deposition. The crystal quality of SiC with the SiCN buffer layer is obviously improved comparing with that grown on the SiC buffer layer. The SiCN film, composed of elemental Si and SiC1-xNx alloy, is formed by the constant-source diffusion of the C and N atoms into the Si substrate. During the 3C-SiC high temperature growth, this in-situ formed SiCN film evolves into a double sub-layered SiCN buffer, including the SiC1-xNx alloy and the SiCN composite sub-layers. The SiC1-xNx alloy layer (x from 0 to 0.09) results from the limited-source diffusion of N from the in-situ formed SiCN film to the subsequently deposited SiC. The SiCN composite layer, composed of elemental Si and SiC1-xNx alloy (x from 0.09 to 0.06), is caused by the constant-source diffusion of C from the SiC towards the substrate, as well as the outgoing diffusion of N in the in-situ formed SiCN film. The SiCN buffer layer can effectively accommodate the lattice mismatch between SiC and Si substrate.

Electrical Characteristics of Solder-Free SiC Die/Metal Foil/AlN Plate Junctions Fabricated Using Surface Activated Bonding

In conventional power device modules, Si-based dies are attached to metal layers on ceramic plates by using solders. Given that power devices made of widegap materials such as SiC and GaN are going to be launched into market, packaging technologies that exploit their superiority are strongly sought for. Solder-free modules, i.e., modules with dies directly bonded to metal layers on ceramic plates are likely to be ideal since fracture in the solder layer is one of the essential factors that limit the thermal tolerance of conventional power modules. In this work, we fabricated an SiC die/metal/ceramic plate junction by using surface activated bonding (SAB) and examined its current-voltage (I-V) characteristics at elevated temperatures. As ceramics AlN was used since the thermal expansion coefficient of AlN is close to that of SiC. The metal layer on AlN plate was made of an Al foil.We prepared a 635-μm-thick AlN ceramic plate and a 30-μm-thick Al foil. The average roughness (Ra) of the surface in AlN plate was ∼0.5 μm. Ra of the Al foil was 0.06 and 0.19 μm in its mirror and matte surfaces, respectively. The matte surface of Al foil was directly bonded to the AlN plate through a surface activation process using an Ar fast atom beam. In a preparatory study we fabricated an AlN/Al foil/AlN junction by bonding AlN plates to the both sides of an Al foil. We observed the cross section of AlN/Al foil/AlN junction by using scanning electron microscopy. We found that the AlN plate and Al foil were bonded to each other without gaps at the both AlN/Al interfaces although Ra of AlN plates and Al foils was much larger than typical Ra of semiconductor substrates that were bonded using SAB (≤~1 nm). We prepared an SiC epi substrate by growing an n+-SiC buffer layer and an n--SiC epi layer on an n+-4H-SiC (0001) substrate. We formed an ohmic contact on the backside of the epi substrate by evaporating an Al/Ni/Au and annealing at 1000 °C. Then we made a 300-μm-ϕ Ni/Au Schottky contact on the top by evaporation and lift-off. An Al layer was evaporated on the top of ohmic contact so that an SiC Schottky diode die was fabricated. Then the Al surface of ohmic contact of SiC die was bonded to the mirror surface of Al foil on AlN plate using SAB. Note that no intermediate layers such as solder were inserted at bonding interfaces.We measured the I-V characteristics between the Schottky contact of SiC die and the surface of Al foil at temperatures between room temperature and 300 °C. A reverse-bias current was ~10-7 A/cm2 at a reverse-bias voltage up to 6 V for temperatures lower than 250 °C. A larger reverse-bias current (~10-6 A/cm2) was observed in measurement at 300 °C. In the forward characteristics, lower turn-on voltages and larger series resistances were observed for higher temperatures. It is notable that these features are typically observed for Schottky diodes. In addition, no change was observed in appearance of the SiC die/Al foil/AlN junction even after the measurement at 300 ℃. Although the bonding strength in Al foil/AlN interfaces is still unclarified, these results suggest that SAB technologies could be useful for realizing solder-free modules of power devices.Acknowledgment—The Al foil employed in the work was supplied from Toyo Aluminium K.K. Figure 1

MBE Growth and Optical Properties of GaN, InN, and A3 B5 Nanowires on SiC/Si(111) Hybrid Substrate

The possibility of GaN, InN, and A3B5 nanowires MBE growth on a silicon substrate with a nanoscale SiC buffer layer has been demonstrated. Optical studies indicated a higher structural quality GaN NWs compared with the best structures of GaN NWs without silicon carbide buffer layer. The diameter of A3B5 NWs is smaller than diameter of similar NWs which were grown on a silicon substrate, because of higher lattice mismatch. In particular, InAs NWs diameter was evaluated as little as 10 nm, one of the smallest ever demonstrated for this NWs system.