SiC Heterostructures Research Articles

Thermodynamics and electronic structure of adsorbed and intercalated plumbene in graphene/hexagonal SiC heterostructures

Graphene-covered hexagonal SiC substrates have been frequently discussed to be appropriate starting points for epitaxial overlayers of Xenes, such as plumbene, or even their deposition as intercalates between graphene and SiC. Here, we investigate, within density functional theory, the plumbene deposition for various layer orderings and substrate terminations. By means of total energy studies we demonstrate the favorization of the intercalation versus the epitaxy for both C-terminated and Si-terminated 4H-SiC substrates. These results are explained in terms of chemical bonding and by means of layer-resolved projected band structures. Our results are compared with available experimental findings.

SAW Filters on LiNbO3/SiC Heterostructure for 5G n77 and n78 Band Applications.

The 5G communication system has experienced a substantial expansion of the spectrum, which poses higher requirements to radio frequency (RF) filters in enhancing their operating frequencies and bandwidths. To this end, this work focused on solving the filtering scheme for challenging 5G n77 and n78 bands and successfully implemented the corresponding spurious-free surface acoustic wave (SAW) filters exploiting large-coupling shear horizontal (SH) modes based on X-cut LiNbO3 (LN)/silicon carbide (SiC) heterostructure. Here, we initially investigated the suppression methods for spurious modes theoretically and experimentally and summarized an effective normalized LN thickness ( [Formula: see text] range of 0.15-0.30 for mitigating Rayleigh modes and higher order modes, as well as tilted interdigital transducers (IDT) by about 24° for eliminating transverse modes. Resonators with wavelengths ( λ) from 0.95 to [Formula: see text] were also fabricated, showing a scalable resonance from 2.48 to 4.21 GHz without any in-band ripple. Two filters completely meeting 5G n77 and n78 full bands were finally constructed, showing center frequencies ( fc) of 3763 and 3560 MHz, 3-dB fractional bandwidths (FBW) of 24.8% and 15.6%, and out-of-band (OoB) rejections of 18.7 and 28.1 dB, respectively. This work reveals that X-LN/SiC heterostructure is a promising underpinning material for SAW filters in 5G commercial applications.

Structural characterization of epitaxial γ-Ta2N thin films and AlN/γ-Ta2N heterostructures on SiC substrates

Tantalum nitride (γ-Ta2N) thin films were grown by radiofrequency plasma molecular beam epitaxy (MBE) on 3 in. diameter 6H- or 4H-SiC substrates. Epitaxial characteristics of these MBE grown layers were determined using high resolution x-ray diffraction (HRXRD) and transmission electron microscopy (TEM) measurements. HRXRD, TEM, and XRD reciprocal space map measurements show that γ-Ta2N on SiC grows pseudomorphically and stabilizes to a nearly pure γ-Ta2N phase. Structural properties of these layers are uniform across the 3 in. wafer diameter. Measured a and c lattice parameter values of a 43 nm thick γ-Ta2N film on 6H-SiC are 3.079 and 4.898 Å, respectively, and the film has an in-plane tensile strain of 1.03%. MBE growth of AlN/ γ-Ta2N /SiC heterostructures has also been demonstrated. Measured lattice a and c constants of AlN on γ-Ta2N /SiC are 3.120 and 4.974 Å, respectively. TEM and XRD show that SiC substrate and γ-Ta2N films have parallel epitaxial relation.

Raman investigation of substrate-induced strain in epitaxially grown graphene on low/high miscut angled silicon carbide and its application perspectives

The remarkable properties of graphene/SiC heterostructures have demonstrated promise for use in future power electronics; however, the substrate-induced strain is detrimental to the optimal yield. Epitaxial graphene (EG) grown on nominally low miscut angled (0.05° off-axis) SiC (0001) intensely suffers from substrate-induced biaxial strain via a buffer layer. Buffer layer-free quasifreestanding graphene (QFSG) grown on high miscut angled (8° off-axis) vicinal SiC using the one-pot synthesis, as compared to EG/SiC (0001), exhibits contrasting Raman 2D-peak features. In this study, the substrate-induced strain exerted on graphene grown on both nominal and vicinal SiC was quantitatively investigated using Raman 2D mapping, and the unstrained feature of QFSG was demonstrated on vicinal SiC. Furthermore, metal-graphene-metal devices were fabricated and photocurrent enhancements of 430- and 150-fold were observed in QFSG/vicinal SiC devices, as compared to EG/SiC (0001), with and without gold nanoparticles, respectively. The significantly increased conductivity and photoresponse of the QFSG/vicinal SiC heterostructure, as compared to that of EG/SiC (0001), will increase the potential of gFOraphene/SiC heterostructures in practical SiC microelectronics applications.

Controllable growth of high-density tapered N-doped SiC nanowires arrays

Tapered nitrogen-doped SiC nanowires (N-doped SiCNWs) arrays were vertically grown on the carbon cloth utilizing Si, SiO2, C, and dicyandiamide powders as raw materials via a simple Fe(NO3)3 assisted chemical vapor deposition process. High-density tapered N-doped SiCNWs possessed homogeneous morphology. The diameter of the synthesized nanowire increased from ∼120 nm at the tail to ∼1.30 μm at the tip, while the length could be up to tens of micrometers. Moreover, the as-prepared N-doped SiCNWs were examined to be 2H/3C–SiC mixed crystals. The appearance of 2H crystal might be responsible for the high density defects in 3C–SiC. And since the interesting tapered shape was significantly affected by the catalyst droplet, the growth of N-doped SiCNWs may be governed by Fe-assisted VLS mechanism. In addition, the main emission peak of PL spectrum of N-doped SiCNWs was located at 474 nm, exhibiting a certain blue shift, which was mainly attributed to the special tapered shape, defects, 2H/3C–SiC heterostructure and the quantum confinement effect of the N-doped SiCNWs.

Graphene-based SiC Van der Waals heterostructures: nonequilibrium molecular dynamics simulation study.

The structural properties and thermal conductivity of graphene-based SiC heterostructures are investigated using the reverse nonequilibrium molecular dynamics. The C/SiC/C heterostructure has the greatest value of cohesive energy due to the effect of vdW interactions between layers. The surfaces of heterostructures begin to ripple as a direct consequence of the plane fluctuations observed around T = 400 K. The thermal conductivity at room temperature is determined. The length and the armchair and zigzag orientations increase the magnitude of κ which decreases with increasing temperature. This change is attributed to the phonon Umklapp scattering and phonon cross-plane couplings. The impact of point vacancy, bi-vacancy and edge vacancy in a concentration range up to 2% is also discussed. The localization of low-frequency phonons around the vacancy induces a decaying characteristic of thermal conductivity. The effect depends on the type of vacancy and is more pronounced in heterostructures with point vacancy. The present results make pristine and defective heterostructures promising materials for various thermoelectric applications with tunable functionalities.

Efficient thermal dissipation in wafer-scale heterogeneous integration of single-crystalline β-Ga2O3 thin film on SiC

The semiconductor, β-Ga2O3 is attractive for applications in high power electronic devices with low conduction loss due to its ultra-wide bandgap (∼4.9 eV) and large Baliga's figure of merit. However, the thermal conductivity of β-Ga2O3 is much lower than that of other wide/ultra-wide bandgap semiconductors, such as SiC and GaN, which results in the deterioration of β-Ga2O3-based device performance and reliability due to self-heating. To overcome this problem, a scalable thermal management strategy was proposed by heterogeneously integrating wafer-scale single-crystalline β-Ga2O3 thin films on a highly thermally conductive SiC substrate. Characterization of the transferred β-Ga2O3 thin film indicated a uniform thickness to within ±2.01%, a smooth surface with a roughness of 0.2 nm, and good crystalline quality with an X-ray rocking curves (XRC) full width at half maximum of 80 arcsec. Transient thermoreflectance measurements were employed to investigate the thermal properties. The thermal performance of the fabricated β-Ga2O3/SiC heterostructure was effectively improved in comparison with that of the β-Ga2O3 bulk wafer, and the effective thermal boundary resistance could be further reduced to 7.5 m2K/GW by a post-annealing process. Schottky barrier diodes (SBDs) were fabricated on both a β-Ga2O3/SiC heterostructured material and a β-Ga2O3 bulk wafer. Infrared thermal imaging revealed the temperature increase of the SBDs on β-Ga2O3/SiC to be one quarter that on the β-Ga2O3 bulk wafer with the same applied power, which suggests that the combination of the β-Ga2O3 thin film and SiC substrate with high thermal conductivity promotes heat dissipation in β-Ga2O3-based devices.

Growth and characterization of low pressure chemical vapor deposited Si on Si-face 4H–SiC

Si/4H–SiC heterostructures are synthesized with low pressure chemical vapor deposition at temperatures ranging from 700 to 1080 °C. Microstructural investigations comprise scanning and transmission electron microscopy, as well as X-ray diffractometry analyses. The Si<111> and Si<110> growth orientations are found to be the most dominant, with a strong influence from the deposition temperature. Almost only Si<110> oriented and closed Si films are found at a deposition temperature of 900 °C. At the latter deposition temperature and above, the Si growth is heteroepitaxial. Heterojunction diodes by p+ and n+ doping of the Si top layer are fabricated and characterized. Strong Fermi level pinning is found to be responsible for deposition temperature dependent Schottky barrier heights.

Electronic and optoelectronic properties of van der Waals heterostructure based on graphene-like GaN, blue phosphorene, SiC, and ZnO: A first principles study

The combination of two-dimensional materials in the form of van der Waals heterostructures has been proved to be an effective approach for designing electronic and optoelectronic devices. In this work, we investigate the electronic, optical, and photocatalytic properties of vdW heterostructures based on BlueP, SiC, ZnO, and g-GaN using density functional theory. We find that all the g-GaN based vdW heterostructures are energetically and thermally stable at room temperature. The g-GaN–BlueP and g-GaN–SiC heterostructures show indirect bandgaps with the type-II and type-I band alignments, respectively, whereas the g-GaN–ZnO heterostructure shows a direct bandgap with type-II band alignment. Furthermore, the absorption coefficient is also calculated to understand the optical behavior of these hetrostructures. Our results demonstrate that the lowest energy transitions are dominated by excitons, and the blue shift is also observed in these hetrostructures. The g-GaN–BlueP, g-GaN–SiC, and g-GaN–ZnO vdW heterostructures possess outstanding optical absorption in the visible light. The g-GaN–P shows the highest absorption intensity of 105cm−1, which is larger than that of g-GaN–SiC and g-GaN–ZnO vdW heterostructures by three times. These findings demonstrate that these vdW heterostructures are promising candidates for water splitting in the visible light region. Moreover, the heterostructures also show good response to the photocatalytic properties at pH=0 and pH=7.

Electronic and photocatalytic properties of two-dimensional boron phosphide/SiC van der Waals heterostructure with direct type-II band alignment: a first principles study.

Designing van der Waals (vdW) heterostructures of two-dimensional materials is an efficient way to realize amazing properties as well as opening opportunities for applications in solar energy conversion and nanoelectronic and optoelectronic devices. In this work, we investigate the electronic, optical, and photocatalytic properties of a boron phosphide–SiC (BP–SiC) vdW heterostructure using first-principles calculations. The relaxed configuration is obtained from the binding energies, inter-layer distance, and thermal stability. We show that the BP–SiC vdW heterostructure has a direct band gap with type-II band alignment, which separates the free electrons and holes at the interface. Furthermore, the calculated absorption spectra demonstrate that the optical properties of the BP–SiC heterostructure are enhanced compared with those of the constituent monolayers. The intensity of optical absorption can reach up to about 105 cm−1. The band edges of the BP–SiC heterostructure are located at energetically favourable positions, indicating that the BP–SiC heterostructure is able to split water under working conditions of pH = 0–3. Our theoretical results provide not only a fascinating insight into the essential properties of the BP–SiC vdW heterostructure, but also helpful information for the experimental design of new vdW heterostructures.

The Effect of Technological Factors on the Characteristics of Ohmic Contacts of the Power AlGaN/GaN/SiC-HEMT

The effect of the microrelief, dislocation structure, and other defects of epitaxial layers in the source and drain regions of a Nitride High Electron Mobility Transistor (НЕМТ) on the parameters of the formed ohmic contacts is discussed. The investigations are carried out directly on the chips of power microwave transistors manufactured on the GaN/AlGaN/GaN/SiC heterostructures. The ohmic fired contacts are formed with the use of Ti–Al–Mo–Au and Ti–Al–Ni–Au compositions. The microrelief of the surface on the interface of the fired contact/AlGaN and the defects formed on it is investigated in order to estimate the structural features of the contact areas. It is found that the resistance of the source and drain regions are determined to a considerable extent by the microstructure of the surface on the boundary. The formation of the conductive layer in AlGaN under an ohmic fired contact is shown by the experiments. The possibility of the formation of a new type of structural defect with a high aspect ratio in the contact and active areas of the devices at the formation of ohmic fired contacts is demonstrated. It is shown that the existence of high densities of such defects results in an increase of the leakage currents of the devices.

Low-dimensional heterostructures obtaining from an intelligent material and carbon material on a silicon

The results of the study of the technological regimes of the formation of a microcantilever beam of layered heterostructures based on the integration of smart material and silicon carbide are presented. Layers of silicon dioxide (SiO2), silicon nitride, silicon carbide, and platinum (lower electrode) are successfully formed on a silicon substrate. The results of an experimental study of the Pt / PZT / Pt / SiC heterostructures parameters confirmed the technological compatibility of the layers and the promise of using these structures in sensors of dynamic deformation when creating new generation sensors, including those operating in heavy rocket conditions of space technology.

Influence of technological factors on the characteristics of ohmic contacts of powerful AlGaN/GaN/SiC HEMT

Abstract. In this paper are considers the effect of the microrelief, dislocation structure and other defects of the epitaxial layers of the source and drain regions of the nitride HEMT transistors on the parameters of the formed ohmic contacts. The studies were carried out directly on high−power microwave transistors made of GaN/AlGaN/GaN/SiC heterostructures. Ohmic burning contacts were formed using the compositions Ti—Al—Mo—Au and Ti—Al—Ni—Au. To estimation the structural features of the contact areas, the surface microrelief at the interface of the burned contact/AlGaN and the defects formed on its surface was studied. It is shown that the resistance of the source and drain regions is largely determined by the surface microstructure at the boundary. Experimentally shown is the formation of a conducting layer in AlGaN under the ohmic contacts. The possibility of the formation of a new type of structural defects with a high aspect ratio in the contact and active areas of the devices during the formation of ohmic burned contacts is demonstrated. It is shown that the appearance of high densities of such defects leads to an increase of the device leakage currents.

Stability of SiC and SiN interfaces in titanium carbide and nitride based heterostructures

First-principles molecular dynamics simulations of the stability of the NaCl-type (B1) SiC and SiN interfaces in TiX/one multilayer SiY (X,Y=C,N) heterostructures were carried out as functions of temperature. It was previously shown that the SiX interfaces in the heterostructures based on transition metal compounds could be dynamically unstable owing to the elongated interfacial Si-X bonds compared to the Si-X bonds in the B1-SiX phases in equilibrium. However, this criterion is not satisfied for some SiX(111) interfaces. The aim of this work is to study the temperature-induced changes in the structure of the heterostructures under consideration and to clarify a possible origin of instability of the interfaces in them. It is shown that, at finite temperatures, the interfacial layer in the TiN(001)/SiC heterostructure transforms into the zinc blende-type (B3) SiC-like layer, whereas the interfaces in other (001) heterostructures transform into amorphous-like interfacial layers. The TiC(111)/SiC and TiN(111)/SiN heterostructures are stable up to 1400 K. The TiN(111)/B3-like SiC and TiC(111)/B3-like SiN systems form during static relaxation of the initial heterostructures. The phase transformations of the interfaces are explained in terms of dynamical and elastic stability criteria. In contrast to the (111) interfacial layers, all the B1-(001) interfaces are found to be dynamically unstable. The formation of the B3-(111) interfaces occurs due to the elastic instability of the corresponding B1-(111) interface.

Исследование влияния структурных дефектов на спектры фотолюминесценции в n-3C-SiC

AbstractPhotoluminescence (PL) spectra have been studied in 3 C -SiC/4 H -SiC heterostructures and 3 C ‑SiC single crystals. It was shown that epitaxial 3 C -SiC layers grown on 4 H -SiC substrates have a markedly poorer crystal perfection than do 3 C -SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3 C -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 3 C -SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

Interfacial electronic states and self-formed p–n junctions in hydrogenated MoS2/SiC heterostructure

It is difficult to generate p–n junctions in atomically thin transition metal dichalcogenides (TMDs) because of the great challenge of selective doping.

Study of In-Plane Orientation of Epitaxial Si Films Grown on 6H-SiC(0001)

The Si/SiC heterojunctions were prepared on 6H-SiC(0001) by low-pressure chemical vapour deposition at 900°C. X-ray diffraction was employed to investigate the in-plane orientation of Si/SiC heterojunctions. A FCC-on-HCP parallel epitaxy was achieved for the Si(111)/SiC(0001) heterostructure with a growth temperature of 900°C and the in-plane orientation relationship was [01-1]Si//[11-20]6H-SiC. Based on the in-plane orientation characterizations, the lattice-structure model of the Si/6H-SiC heterostructure was constructed. It is shown that when the in-plane orientation was (111)[01-1]Si//(0001)[11-20]6H-SiC, the Si/6H-SiC interface had a 4:5 Si-to-SiC matching mode with a residual lattice-mismatch of 0.26%, and the misfit dislocation density at the Si/SiC interface was calculated as 0.487×1014cm-2.

Epitaxial growth of Si/SiC heterostructures with different preferred orientations on 6H-SiC(0001) by LPCVD

The in-plane orientations of Si/SiC heterojunctions on 6H-SiC(0001) were investigated by high-resolution X-ray diffraction. An Si(111)/SiC(0001) heterostructure with an in-plane orientation of Si[01−1]//SiC[110] is achieved at 900 °C, the Si/6H-SiC interface has a 4 : 5 Si-to-SiC matching mode with a residual lattice mismatch of 0.26%, and the edge dislocation density at the Si/SiC interface is calculated to be 4.87 × 1013 cm−2. As the growth temperature is increased to 1050 °C, the [110] preferential growth with an in-plane orientation of Si[−110]//SiC[0−10] is observed, along Si[001]SiC[210] orientations, the Si-to-SiC mode changes to approximately 1 : 2 and the residual mismatch is 1.84%. The edge dislocation density increases to 1.22 × 1014 cm−2 correspondingly.

Five channel WDM communication using a single a:SiC-H double pin photo device

Amorphous SiC heterostructures built as a double pin device has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. Illuminating the device with several single wavelength data channels in the visible spectrum allows for Wavelength Division Multiplexing (WDM) digital communication. Using fixed ultra-violet illumination at the front or back surfaces enables the recovery of the multiplexed channels. Five channels, each using a single wavelength which is modulated by a Manchester coded signal at 12,000bps, form a frame with 1024 bits with a preamble for signal intensity and synchronisation purposes. Results show that the clustering of the received signal enables the successful recovery of the five channel data using the front and back illumination of the surfaces of the double pin photo device.

Atomic-scale characterization of Si(110)/6H-SiC(0001) heterostructure by HRTEM

The atomic structure of Si(110)/SiC(0001) heterojunctions prepared on 6H-SiC(0001) was characterized by transmission electron microscopy and X-ray diffraction. An FCC-on-HCP parallel epitaxy is achieved for the Si(110)/SiC(0001) heterostructure with a growth temperature of 1050°C and the in-plane orientation relationship is Si[1-10]//6H-SiC[11-20]. The pure edge misfit dislocations with a Burgers vector of 13<11-20>SiC parallel to the interface are observed to accommodate the extreme lattice mismatch. Along the in-plane orientation Si[1-10]SiC[11-20], the Si/6H-SiC interface has a 4:5 Si-to-SiC matching mode with a residual lattice-mismatch of 0.26%. The misfit dislocation density at the Si/SiC interface is calculated as 1.217×1014cm−2.