Silicon vacancy center in4H-SiC: Electronic structure and spin-photon interfaces

Fluorescent paramagnetic defects in solids have become attractive systems for quantum information processing in the recent years. One of the leading contenders is the negatively charged nitrogen-vacancy defect in diamond with visible emission but alternative solution in technologically mature host is an immediate quest for many applications in this field. It has been recently found that various polytypes of silicon carbide (SiC), that are standard semiconductors with wafer scale technology, can host nitrogen-vacancy defect (NV) that could be an alternative qubit candidate with emission in the near infrared region. However, it is much less known about this defect than its counterpart in diamond. The inequivalent sites within a polytype and the polytype variations offer a family of NV defects. However, there is an insufficient knowledge on the magneto-optical properties of these configurations. Here we carry out density functional theory calculations, in order to characterize the numerous forms of NV defects in the most common polytypes of SiC including 3C, 4H and 6H, and we also provide new experimental data in 4H SiC. Our calculations mediate the identification of individual NV qubits in SiC polytypes. In addition, we discuss the formation of NV defects in SiC with providing detailed ionization energies of NV defect in SiC which reveals the critical optical excitation energies for ionizing this qubits in SiC. Our calculations unravel the challenges to produce NV defects in SiC with a desirable spin bath.

Raman spectroscopy has been increasingly used, in recent years, to characterize irradiated materials, in particular silicon carbide. The interpretation of the spectra is nevertheless problematic. In this paper, we provide a first step toward a more quantitative interpretation, by providing first‐principles calculations of Raman intensities for various polytypes of silicon carbide (SiC) and for point defects in cubic SiC. We consider here, as benchmarks, the carbon antisite, CSi, and the doubly charged carbon vacancy/carbon antisite complex, VC. We show that some care is necessary to understand the contribution of point defects on the Raman spectrum of the material, due to supercell size effects.Calculated Raman spectra of cubic SiC with and without point defect, here a carbon antisite, CSi, in a 216‐atom supercell.

Microelectromechanical systems (MEMS) devices made of single crystalline silicon carbide (SiC) are attractive for applications in harsh environment, because SiC is chemically inert and semiconductor devices made of SiC can be operated at very high temperature. On the other hand, due to its chemical inertness, controllable etching of SiC has been difficult. Molten KOH etching has been widely used to detect crystalline defects in SiC as etch pit in crystal growth researchers. Some etch pits have hexagonal shape, indicating anisotropic etching nature. Therefore, molten KOH etching may have potential as a SiC MEMS fabrication process. In this study we have developed the anisotropic wet chemical etching of single crystalline hexagonal SiC using molten KOH for SiC bulk micromachining. 6H-SiC (0001)Si face and (000-1)C face substrates are used. Etching rates of (0001)Si and (000-1)C faces at 490 °C are evaluated to be 37 nm/min and 3.1 &#956;m/min, respectively, indicating that the (0001)Si face is etched almost 100 times slower than the (000-1)C face is. Cross sectional analysis of etched structure of (000-1)C face revealed that inclined crystal plane was formed as a sidewall with some undercut. To assess in-plane etching anisotropy, ring shape mesa structures are formed on SiC (0001)Si face by RIE and then etched by molten KOH. Ring shape changed into hexagonal shape, clearly indicating etching rate along <11-20> direction is larger than <1-100> direction in (0001)Si face.

This short review provides an overview of advancements in the characterization of defects in silicon carbide (SiC) wafers using polarized light observation. SiC, which has a wide bandgap and excellent thermal and electrical properties, is widely used in power devices. However, various defects such as threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD) can significantly affect device performance and reliability. Polarized light observation offers a nondestructive method for visualizing these defects and analyzing the stress fields induced within the SiC crystal structure. This paper summarizes recent developments in this technique, including the application of analyzer rotation to enhance the contrast in defect visualization. Furthermore, the development of automated systems for rapid wafer evaluation is discussed, highlighting the role of polarized light observation in improving quality control and production efficiency in SiC power device manufacturing.

Determination of neutron irradiation temperatures of SiC using electrical resistivity method

The controlled creation of defects in silicon carbide represents a major challenge. A well-known and efficient tool for defect creation in dielectric materials is the irradiation with swift (E(kin) ≥ 500 keV/amu) heavy ions, which deposit a significant amount of their kinetic energy into the electronic system. However, in the case of silicon carbide, a significant defect creation by individual ions could hitherto not be achieved. Here we present experimental evidence that silicon carbide surfaces can be modified by individual swift heavy ions with an energy well below the proposed threshold if the irradiation takes place under oblique angles. Depending on the angle of incidence, these grooves can span several hundreds of nanometres. We show that our experimental data are fully compatible with the assumption that each ion induces the sublimation of silicon atoms along its trajectory, resulting in narrow graphitic grooves in the silicon carbide matrix.

Silicon carbide (SiC) is a very promising platform for quantum information processing, as it can host room temperature solid state defect quantum bits. These room temperature quantum bits are realized by paramagnetic silicon vacancy and divacancy defects in SiC that are typically introduced by irradiation techniques. However, irradiation techniques often introduce unwanted defects near the target quantum bit defects that can be detrimental for the operation of quantum bits. Here, we demonstrate that by adding aluminum precursor to the silicon and carbon sources, quantum bit defects are created in the synthesis of SiC without any post treatments. We optimized the synthesis parameters to maximize the paramagnetic defect concentrations-including already established defect quantum bits-monitored by electron spin resonance spectroscopy.

The dv/dt switching limitations of power semiconductor devices are evaluated in a boost (PFC) power converter using circuit simulations. State-of-the-art commercial silicon CoolMOS devices, commercial Silicon Carbide (SiC) Junction Barrier Schottky (JBS) diodes, and emerging Gallium Nitride (GaN) lateral power transistors are considered. It is shown that although SiC and GaN power devices have low stored charge and small capacitances, they experience high switching dv/dt stresses which may pose serious switching limitations especially in high-frequency power converters. This problem is likely to be further exacerbated by the presence of a high density of crystal defects in SiC and GaN materials which will manifest in the form of poor field-reliability. Specific guidelines for device selection are recommended in order to optimize both performance and field-reliability.

Silicon carbide (SiC) emerges as a promising wide-bandgap semiconductor featuring high breakdown field and outstanding thermal conductivity, making it promising for high-power application. Although extensive efforts have been devoted to understanding and controlling dislocations in SiC, the fundamental relationship between dislocations and thermal transport remains insufficiently understood. The major challenge lies in the giant supercell size required for reliable dislocation modelling. Here, we employ machine-learning molecular dynamic with neuroevolution potential (NEP) designed for modeling extended defects in SiC to overcome the computational challenge for phonon-dislocation interaction. Using this approach, we calculated the thermal conductivity over a range of temperatures and dislocation densities for typical dislocation types in SiC. The phonon-edge-dislocation scattering was found to be nonlinearly dependent on the dislocation density, which was attributed to the long-ranged dislocation-induced normal strain field. Spectral heat-current analysis further reveals that dislocations primarily scatter long-wavelength acoustic phonons below 20 THz. This work provides microscopic and quantitative perspective into the phonon-dislocation scattering mechanisms.

Interatomic potentials play a crucial role in the molecular dynamics (MD) simulation of silicon carbide (SiC). However, the ability of interatomic potentials to accurately describe certain physical properties of SiC has yet to be confirmed, particularly for hexagonal SiC. In this study, the mechanical, thermal, and defect properties of four SiC structures (3C-, 2H-, 4H-, and 6H-SiC) have been calculated with multiple interatomic potentials using the MD method, and then compared with the results obtained from density functional theory and experiments to assess the descriptive capabilities of these interatomic potentials. The results indicate that the T05 potential is suitable for describing the elastic constant and modulus of SiC. Thermal calculations show that the Vashishta, environment-dependent interatomic potential (EDIP), and modified embedded atom method (MEAM) potentials effectively describe the vibrational properties of SiC, and the T90 potential provides a better description of the thermal conductivity of SiC. The EDIP potential has a significant advantage in describing point defect formation energy in hexagonal SiC, and the GW potential is suitable for describing vacancy migration in hexagonal SiC. Furthermore, the T90 and T94 potentials can effectively predict the surface energies of the three low-index surfaces of 3C-SiC, and the Vashishta potential exhibits excellent capabilities in describing stacking fault properties in SiC. This work will be helpful for selecting a potential for SiC simulations.

On the interpretation of confocal spectral depth profiling of color center and carrier concentration by photoluminescence and Raman of implanted 4H–SiC

We investigate the core-level X-ray photoelectron spectroscopy (XPS) spectra of various defects containing boron in silicon carbide (SiC) using a first principles calculation with careful evaluation of the local potential boundary condition. It is found that a 512-atom cubic supercell for 3C-SiC and a 576-atom hexagonal supercell for 4H-SiC are required for convergence of the XPS binding energy to within 0.1 eV. The XPS binding energies of SiC have considerable site dependence owing to the electronegativity difference between Si and C. The difference of XPS binding energies between the Si and C substitutional sites is 3.4 eV.

Modifications in structural, optical and electrical properties of epitaxial graphene on SiC due to 100 MeV silver ion irradiation

The effect of the electron-irradiation temperature on radiation-defect formation in silicon carbide is studied for the first time. Commercial high-voltage 4H-SiC Schottky diodes are studied. Irradiation is carried out by electrons with an energy of 0.9 MeV at temperatures of 20°C and 200°C. The spectra of radiation-induced defects are measured using nonstationary capacitance spectroscopy. It is established that with an increase in the temperature of irradiated silicon carbide, not only the number of introduced radiation defects decreases, but also their spectrum changes. If cold irradiation leads to the formation of six deep traps, then hot irradiation leads to the formation of only three traps: Z1/Z2 (0.68 eV), EH5 (1.08 eV), and EH6/EH7 (1.58 eV). During hot irradiation the number of induced radiation defects also sharply decreases, which leads to a decrease in the rate of removal of charge carriers (compensation of semiconductor conductivity) by almost four times: from 0.25 to 0.065 cm–1. It is noted that nonlinear effects in radiation-defect formation are observed in silicon carbide. At a fixed dose of irradiation of silicon carbide by electrons, the number of introduced radiation defects depends on the electron-flux density (dose-accumulation time).

This chapter contains sections titled: Introduction Experimental Procedure Results Summary Acknowledgements