4H-SiC Research Articles

TCAD simulation on an UACCUFET inserted with 3C/4H–SiC hetero-crystalline junctions for accumulation-channel and fly-back

Due to high channel mobility, SiC accumulation-channel field-effect transistors (ACCUFETs) exhibit important research and application values in high-frequency and large-power fields, but still encounter poor reverse recovery, etc. An enhancement-mode U-shaped gate ACCUFET integrated with 3C/4H–SiC hetero-crystalline junctions (HCJs) and semi-super-junction (SSJ) is constructed, where a (n−)4H–SiC-layer in (n)3C–SiC/(n−)4H–SiC HCJ is adopted to form accumulation-channel for conduction due to field-effect, another HCJ composed of (n)3C–SiC and (n)4H–SiC drift region is employed for fly-back under low cut-in voltage (VF) to shorten reverse recovery time (trr). Additionally, a SSJ is used to raise the breakdown voltage (VB). The device structure and performance are optimized by the Silvaco TCAD, which illustrates the values of VB and static figure of merit (FOMHM) are increased by 15.6 % and 5.6 % respectively compared to those of the counterpart with Schottky barrier diode. This paper can provide new ideas for devising high-performance ACCUFETs.

Generating stacking faults in 4H–SiC junction transistor by indentation and forward biasing

Stacking faults in silicon carbide have been widely studied due to their negative impact on the application of silicon carbide in the power electronics industry. In this work, with the assistance of forward biasing, we observe several triangular shaped structures emerging near the indenter imprint in two separate 4H–SiC bipolar junction transistor samples that were deformed by nanoindentation. Based on the study of electroluminescence spectra on one of the samples, the emission peak at 420 nm indicates the formation of single Shockley stacking faults inside deformed transistors. We conclude that the use of indentation can provide a method to study recombination induced stacking faults in silicon carbide junction devices by intentionally introducing dislocations at selected areas of interest.

Self-activated epitaxial growth of ScN films from molecular nitrogen at low temperatures

Unlike naturally occurring oxide crystals such as ruby and gemstones, there are no naturally occurring nitride crystals because the triple bond of the nitrogen molecule is one of the strongest bonds in nature. Here, we report that when the transition metal scandium is subjected to molecular nitrogen, it self-catalyzes to break the nitrogen triple bond to form highly crystalline layers of ScN, a semiconductor. This reaction proceeds even at room temperature. Self-activated ScN films have a twin cubic crystal structure, atomic layering, and electronic and optical properties comparable to plasma-based methods. We extend our research to showcase Sc’s scavenging effect and demonstrate self-activated ScN growth under various growth conditions and on technologically significant substrates, such as 6H–SiC, AlN, and GaN. Ab initio calculations elucidate an energetically efficient pathway for the self-activated growth of crystalline ScN films from molecular N2. The findings open a new pathway to ultralow-energy synthesis of crystalline nitride semiconductor layers and beyond.

Novel 4H–SiC MESFET with high ability in gate capacitances control for high frequency applications

The ability to control the gate capacitances is crucial for high-frequency applications, as it affects the device's frequency characteristics, gain and power handling capabilities. We present a 4H–SiC metal-semiconductor field-effect transistor (MESFET) with high gate capacitance control ability for high-frequency applications. The proposed structure (GCC-MESFET) consists of a step gate and a SiC well for adjusting the channel depletion layer and modifying the channel charges. Therefore, the gate capacitances will be controlled (GCC-MESFET). The proposed structure significantly improves the cut-off frequency (fT) and maximum oscillation frequency (fmax). The fT has increased from 23.5 GHz to 33 GHz and the fmax from 50.1 GHz to 54.4 GHz in the proposed structure compared to a conventional structure (C-MESFET). The results show that the DC maximum output power density (Pmax), DC transconductance (gm), cut-off frequency (fT) and maximum oscillation frequency (fmax) of GCC-MESFET improve in comparison with a conventional structure (C-MESFET). It is necessary to mention that the drain current and the breakdown voltage of the proposed structure increase by 48 % and 20 % respectively, compared with the C-MESFET structure due to modifying the channel charges and adjusting the electric field. So, the proposed structure can be used for high current, high voltage, high-power and high frequency applications.

Fabrication of grooves on 4H–SiC using femtosecond laser vector beam

Femtosecond lasers are widely acknowledged for their capability to groove and generate laser-induced periodic surface structures (LIPSS) on various materials. LIPSS structures include LSFL (low spatial frequency LIPSS) and HSFL (high spatial frequency LIPSS). In this study, a segmented waveplate (SWP) was used to transform a linearly polarized femtosecond laser Gaussian beam with a wavelength of 515 nm into a vector beam with a donut-shaped energy peak distribution and polarization of azimuthal and radial. Grooving was conducted on three different SiC surface conditions: polished and pre-processed (LSFL and HSFL), using linear, azimuthal, and radial polarization. This study investigated the differences in microstructure morphology and compared the ablation depths of the grooves. It was found that grooving on pre-processed LSFL 4H–SiC surfaces resulted in grooves with higher ablation depths than those produced on polished surfaces. Additionally, using azimuthal polarization on the HSFL surface could create fine HSFL structures (with a period of approximately 100 nm) between the initial periodic structures (with a period of approximately 250 nm) formed during the pre-processing.

Ordinary and Extraordinary Permittivities of 4H SiC at Different Millimeter-Wave Frequencies, Temperatures, and Humidities

Ordinary and Extraordinary Permittivities of 4H SiC at Different Millimeter-Wave Frequencies, Temperatures, and Humidities

Nonlinear piezoresistive effect of 4H–SiC for applications of high temperature pressure sensors

Nonlinear piezoresistive effect of 4H–SiC for applications of high temperature pressure sensors

Spectroscopic ellipsometry investigation of a 6H–SiC single crystal plate for potential use in graphene optoelectronic devices

At room temperature, the spectroscopic ellipsometry SE parameters Epsi (ψ) and Delta (Δ) for 6H–SiC crystal substrate were measured in the wavelength range 350–1700 nm at four different angles of incidence, 60°, 65°, 70°, and 75°. An SE model was developed to extract optical consents of 6H–SiC crystal substrate from the experimentally measured SE parameters. In the wavelength range 350–1700 nm, the refractive index of the 6H–SiC crystal substrate was extracted and fitted to two terms of the Sellmeier dispersion function. In the wide spectral range (350–1700 nm), the Wemple-DiDomenico (WDD) dispersion model shows how the real refractive index changes with wavelength. The analysis of refractive index dispersion of the 6H–SiC crystal substrate using Sellmeier dispersion function and WDD optical model allows to extract oscillator strength Nfij, average oscillator energy Eo, dispersion energy of the single oscillator Ed, lattice oscillator strength El, Abbe dispersion number, energy gap Eg, density of valence electrons nv, refractive index at infinite wavelength n∞, lattice dielectric constant εL, the ratio of free carrier density to free carrier effective mass (N/m∗), and plasma frequency ωp. For the 6H–SiC crystal substrate, in the desired spectral range (240–1700 nm), it does not have any depolarization effect on the reflected polarized light.

Effect of Fe-Co catalysis on the temperature field distribution during the growth of 3C-SiC fibers synthesised by microwave heating

Microwave heating produce local hot spots on materials, which result in uneven heating and other issues. Regulate the microwave temperature field using different catalyst combinations such as Fe (NO3)3·9H2O and Co (NO3)2·6H2O. The electromagnetic and temperature field distributions of 3C–SiC fibers and the molecular dynamics of the SiC interfacial growth process and interfacial oxidation reaction during microwave heating in the presence of a catalyst were simulated and calculated respectively. The results show that the combination of Fe and Co at 9 wt% catalyst concentration can effectively improve the electromagnetic loss capability of SiC fibers. The Fe and Co bimetallic catalysed synthesis of 3C–SiC fibers follows a vapor–liquid–solid growth mechanism. The Fe–Si and Fe–Co–Si alloy phases can induce 3C–SiC growth along (111) crystal faces. The simultaneous exothermic reactions provide a highly catalytically active growth environment that facilitates the enhancement of microwave temperature field uniformity. This phenomenon facilitated the synthesis of 3C–SiC fibers.

Application of neutron transmutation technology to control the physical properties of nanoparticles at the atomic scale

Purposeful control of the physical properties of materials at the nanoscale is significant throughout the application. The most effective way for this is to change or replace the lattice atoms that make up the nanomaterial. In nanomaterials, the efficiency of the doping process will be high if individual lattice atoms are replaced at the atomic level without affecting neighbouring atoms. Here we show that, with the application of neutron transmutation technology (NTT), it is possible to perform targeted changes in nanoparticles (NPs) at the atomic scale. Similar experiments were carried out on different classes of NPs to explore the possible manipulation of the properties of nanomaterials using neutrons. During the experiments, nanocrystalline 3C–SiC, BN, B4C, Si and amorphous Si3N4 and SiO2 particles were modified by NTT. The possibility of nuclear reactions and neutron transmutation (NT) were investigated on the individual atoms, which are formed nanoparticles. As a result of NT, the changes in the physical properties of the listed NPs were explained by various spectroscopic approaches. Simultaneously, additional neutron effects, defects and structural changes on the surface of NPs were studied with microscopic imaging.

A Study of Process Interruptions during Pre- and Post-Buffer Layer Epitaxial Growth for Defect Reduction in 4H SiC

We perform epilayer growth where the process is interrupted (in situ) during post and pre buffer layer growth at a reduced temperature. Process interrupted during post buffer layer growth demonstrates significant reduction in basal plane dislocation (BPD) at a lower temperature. SIMS study demonstrates that etching takes place during the interruption time. We believe surface treatment of the buffer layer at different etching conditions during the interruption plays a major role in BPD reduction. However, the in-situ interruption, taking place prior to the buffer layer (i.e., on the substrate), does not contribute to the reduction in BPD in epilayer. We believe that the surface effect of interruption related etching on substrate during pre-buffer layer interruption, is not efficient enough to reduce BPD due to the higher doping and higher BPD associated with the substrate. Furthermore, we demonstrate that post buffer layer growth interruption contributes to the reduction in stacking faults in the epilayers. We also attribute this reduction of SF due to the surface etching prior to the drift layer growth.

Optical Ionization of Qubits and their Silent Charge States

Color centers in the technologically mature material silicon carbide are candidates for the implementation of quantum applications. Chargestate control and electrical read-out of qubits includes spin-to-charge conversion via optical excitation and subsequent ionization. In this work we address the dominant photoionization mechanism and the photophysical properties of the ionized silicon vacancy in 4H SiC using ab initio theory. We find that its nominally dark chargestates are infrared emitters.

Prediction of Contact Resistance of 4H–SiC by Machine Learning Using Optical Microscope Images after Laser Doping

In this study, machine learning (ML) was employed to predict the electrical properties of finished devices, specifically focusing on the state of the contacts at the electrodes. The predictions are based on optical microscope images of the surface conditions, which were captured immediately following the laser doping of nitrogen atoms into 4H-SiC. The laser doping process involved varying the laser fluence from 0.4 to 4.0 J/cm2 and using number of laser irradiation to 5, 10, 20, and 100 shots. The ML prediction was carried out in two steps. In STEP1, we classified the contact status into three types.: 1) Schottky junctions (insufficient doping), 2) Ohmic contact (good contact), and 3) Not ohmic (damage caused by laser irradiation). In STEP2, contact resistance prediction (numerical regression) was performed using the dataset predicted as an ohmic contact. As a result, we found that the three classifications in STEP1 could be predicted with a high accuracy of over 88%. Furthermore, the contact resistance prediction in STEP2 could be made with an accuracy (RMSPE: root mean square percent error) of 27.2%. Visualizing the prediction basis of numerical regression using modulus-reweighted grad-regression activation mapping (MoRAM) revealed that the ML model focused on the inside of the laser-irradiated area in the optical microscope image. The results of the scanning electron microscopy observation of the laser-irradiated area showed that ablation and residuals were generated during laser doping in that area. Consequently, it was concluded that our ML model predicted the contact resistance of the finished device taking into consideration these surface conditions. Even highly-skilled laser doping technicians have difficulty predicting the resistance values arising from the ablation and residue conditions. Based on above results, we conclude that our ML model is capable of predicting the electrical characteristics of a finished device, a task that is often considered challenging for humans.

A novel 4H–SiC thermal neutron detector based on a metal-oxide-semiconductor structure

Energy resolution and leakage current are two key parameters for semiconductor neutron detectors. Metal-Oxide-Semiconductor (MOS) detectors introduce an additional oxide layer compared to Schottky Barrier Diodes (SBDs) detectors in order to reduce leakage current. However, this also leads to a degradation in energy resolution due to the introduction of an additional dead layer. Therefore, optimizing the thickness of the oxide layer is important for MOS detectors. In this study, a 4H–SiC-based MOS thermal neutron detector was designed with comprehensive consideration of the oxide layer. Subsequently, a prototype of the detector was fabricated and tested. The prototype of the MOS detector achieved an nA-level leakage current under a reverse bias of −200 V. Additionally, it demonstrated good energy resolution performance in a moderated D-T neutron source test. The MOS detector was able to clearly distinguish between the two reaction channels of 10B converter events, which is consistent with the theoretical branching ratio. This work highlights the potential application of 4H–SiC-based MOS detectors for thermal neutron detection.

Discrimination of dislocation in highly doped n-type 4H–SiC by combining electrochemical reaction and molten alkali etching

This work proposes an effective etching method for highly doped n-type 4H–SiC by combining electrochemical reactions and molten alkali etching. By employing our developed method, threading mixed dislocation (TMDs) and threading screw dislocations (TSDs) can be distinctly visualized as hexagonal etching pits of varying sizes. The slightly smaller threading edge dislocations (TEDs) appear as roughly circular etching pits, while basal plane dislocations (BPDs) are revealed as characteristic seashell-shaped pits. Additionally, we provide a reaction equation that elucidates the mechanism of the electrochemical etching process, thus sparking a new investigation into the discrimination of dislocations under molten alkali conditions. By applying a positive voltage to the wafer, we ensure a continuous supply of holes crucial for the reaction, thereby maintaining both the etching rate and the selectivity towards defects. This approach not only enhances the efficiency of the etching process but also provides a more accurate and reliable method for characterizing and understanding the dislocation properties of highly doped n-type 4H–SiC wafers.

Investigation of the tribological behaviors for 4H–SiC substrate under different lubrication conditions

Lubrication conditions are an important factor affecting both the machining efficiency and quality of 4H–SiC. To investigate the tribological behaviors under different lubrication conditions, a series of scratching experiments are conducted under different loads and environments. The X-ray photoelectron spectroscopy (XPS) surveys and atomistic simulations are used to explain the different tribological behaviors. Both experimental and simulation results show that liquid lubrication can significantly reduce the coefficient of friction (COF) and minimize structural damage. Compared to pure water, the H2O2 solution is more conducive to the oxidation of SiC atoms and the modification of tribological behaviors. However, the difference in tribological behaviors between H2O2 solution and pure water diminishes as the load increases. The XPS surveys show that the liquids lead to higher-order oxidized species of SiC atoms, such as Si4C4-xO2 and Si-Ox-Cy, which are also observed in the simulation results. It is shown that the oxidized species can reduce the direct bonding between SiC and diamond indenter, which is an important reason for the lower COFs in the liquids. Since the liquids can reduce the direct bonding and mechanical interaction between 4H–SiC and diamond, the material removal rate is much lower under lubrication conditions.

Surface morphology of 3C–SiC layers grown on 4H–SiC substrates using TCS as silicon precursor

The hetero-epitaxial growth of 3C–SiC layers on on-axis 4H–SiC substrates has been demonstrated in a hot-wall CVD reactor using trichlorosilane and ethylene as precursors. The additional chlorine is supplied by hydrogen chloride for variation of Cl/Si ratio. The influence of temperature, C/Si ratio and Cl/Si ratio process parameters on the morphology is studied. Double-position-boundaries free 3C–SiC epitaxial layers have been successfully grown at the optimized condition, which is at a temperature of 1340 °C, with C/Si = 0.6 and Cl/Si = 6 using a carbon-rich pretreatment. Low temperature near bandgap photoluminescence shows a good optical property of the obtained 3C–SiC epitaxial layers. Compared to the standard chemistry, a higher growth rate of 12 μm/h could be achieved by utilizing the chlorinated precursors. This study provides a feasible way to grow double-position-boundaries free 3C–SiC epitaxial layers using TCS as silicon precursor.

Influence of annealing treatment on performance of 4H–SiC SBD irradiated by heavy ions under room temperature and low temperature

The influence of the annealing treatment on the performance of commercial 4H–SiC Schottky barrier diodes (SBDs) subjected to heavy ion irradiation under room temperature (RT) and low temperature (LT) are presented. Experimental results confirm that annealing treatment effectively eliminates defects and interface states caused by heavy ion irradiation, particularly for 4H–SiC SBD under LT irradiation. Increasing the annealing temperature leads to the slight improvement in forward current, leakage current and breakdown voltage. However, the annealing process may result in the formation of Ti and Si compounds at the interface between the Schottky metal and SiC, as well as a significant number of vacancies. Combined with Technology Computer Aided Design (TCAD) simulations, it is concluded that the interface trap charge concentrations exceeding 1 × 1012 cm−2 significantly impact the breakdown characteristics of 4H–SiC SBDs.

A P+ pocket doped 4H–SiC Schottky barrier FET as highly sensitive label-free biosensor

In this paper, a 4H–SiC Schottky barrier field-effect transistor with a P+ doping Pocket based on dielectric modulation effect for label-free detection of biomolecules has been proposed. Upon optimization of the length and position of P+ doping pocket, the sensitivity of the biosensor achieves the maximum when it is located within the channel 1 nm away from the Schottky contact with a length of 5 nm. Simulations have been performed for different dielectric constants and biomolecules with different charge densities by Sentaurus TCAD. The results show that the new structure has an on-current sensitivity of 1.03 × 108, a maximum transconductance sensitivity of 6.24 × 107, a threshold voltage sensitivity of 65 mV, and an Ion/Ioff ratio sensitivity of 1.8 × 104 for neutral biomolecules with K = 12. In addition, the fill factor of the cavity and linearity of the proposed structure are considered in this paper. Further, the on-current sensitivity of our proposed structure is gauged against state of the art, which demonstrate a high sensitivity of our proposed biosensors. The smaller size and prominent sensitivity characteristics of the biosensor proposed in this paper have made it widely used in the field of biomedical detection that requires high integration and efficient detection.

Modeling of Physical-Chemical and Electronic Properties of Lithium-Containing 4H—SiC and Binary Phases of the Si—C–Li System

In the equilibrium model of the solid surface–adatom system, including a three-dimensional interfacial surface, changes in surface properties are considered, taking into account the chemical potential due to the action of surface tension. The relationship between chemical potential and electrochemical potential of the ith component in an electrochemical cell is analyzed. Using the density functional theory (DFT), the adsorption, electronic, and thermodynamic properties of 2 × 2 × 1 and 3 × 3 × 1 supercells of crystalline compounds AmBn, (, where n and m are stoichiometric coefficients) of the boundary binary systems of the ternary phase diagram of Si–C–Li are studied. The stability of phases AmBn and property calculations are carried out with the exchange-correlation functional within the framework of the generalized gradient approximation (GGA PBE). The parameters of the crystal structures of the compounds AmBn, the adsorption energy of the lithium adatom on a 4H–SiC substrate, the electronic structure, and the thermodynamic properties of supercells are calculated. The thermodynamically stable configurations of the 4H–SiC–Liads supercells having different locations Liads are determined. The DFT GGA PBE calculations of the enthalpy of formation of compounds AmBn are carried out in the ternary Si–C–Li system. Taking into account the changes in the Gibbs free energy in the solid-phase exchange reactions between binary compounds, equilibrium sections (connodes) in the concentration triangle of the Si–C–Li phase diagram are established. An isothermal section of the Si–C–Li phase diagram at 298 K is constructed. The patterns of diffusion processes that are related to the movement of particles on the surface layer of the 6H–SiC sample are analyzed. The activation energy of lithium diffusion in 6H–SiC is calculated from the Arrhenius type relation in two temperature ranges (769–973 K) and (1873–2673 K).