4H Silicon Carbide – High-Power and High-Frequency Applications

Silicon carbide has many applications in high-power electronics and quantum technologies. Not only is it known for its excellent electrical properties, but also for its high thermal conductivity and chemical stability.

Wurtzite crystal structure features an irregular hexagonal close-packed arrangement composed of Si C double layers that stack in an ABCB sequence.

Wide Bandgap

Silicon Carbide (4h SiC) stands out as an exceptional semiconductor material due to its wide bandgap, outperforming most common electronics like silicon (Si). SiC’s large bandgap allows it to function at higher temperatures and voltages than many of its counterparts – an advantage especially beneficial in applications requiring high performance such as automotive electronics or for efficient heat dissipation such as aerospace applications.

SiC’s large bandgap makes it capable of withstanding high breakdown electric fields, making it ideal for power electronics such as switches, thyristors and MOSFETs. Furthermore, its low intrinsic carrier concentration and strong oxidation resistance help it withstand demanding environmental conditions including high temperatures and mechanical wear.

4h SiC’s large bandgap compares favorably with silicon’s 1.5eV gap, enabling it to feature much lower on-state resistance and electron mobility compared to silicon-based alternatives, making SiC an excellent candidate for power electronic device manufacturing at lower costs than silicon alternatives. This material’s high carrier mobility also means it can be used to develop more efficient power electronic devices at significantly reduced manufacturing costs than silicon alternatives.

4h SiC’s large bandgap makes it more appealing than other semiconductor materials such as GaN for growing compound semiconductors that can further improve its electrical properties, such as emitters. Furthermore, 4h SiC’s superior thermal conductivity enables it to disperse heat more effectively than other semiconductors and performs better under harsh environments where temperature fluctuations could damage other semiconductors.

SiC is well known for its physical and chemical properties; however, the science underlying its remarkable electrical transport properties is still being explored. This includes issues related to crystal-field splitting – which determines separation between lh and hh bands in a sample – under uniaxial strain, as well as how projection of C-p orbitals onto the valence band structure affects hole mobility.

Further, fully reversible elastic strains of up to 6.2% were observed in single-crystal [0001]-oriented 4h SiC crystals, providing the opportunity for strain modulation of its electrical properties through altering its ordering of the valence band top through compressional stress rather than deformation of orbitals themselves.

High Carrier Mobility

4h silicon carbide has an exceptional carrier mobility that makes it suitable for semiconductor applications that demand large current flows, including electronic devices that operate at high voltages and frequencies such as power switches found in electric vehicles (EV) or renewable energy converters. Furthermore, its thermal conductivity helps ensure effective heat dissipation in these devices.

Silicon carbide’s crystal structure can be divided into two polytypes, 6H and 4H. Each polytype differs in terms of their symmetry, lattice constant, and atomic arrangement which has an impactful influence on their properties and performance. 4H SiC stands out due to its higher thermal conductivity than 6H SiC while still offering great electrical and mechanical properties – an exceptional combination which has made 4H SiC an essential material in many semiconductor devices.

To accurately predict the electrical and optical properties of silicon carbide, a comprehensive understanding of its physical structure is required. This requires an appreciation for how atomic bonds interact with optical band structures that influence its electronic properties.

Researchers have conducted mode-level first principles calculations in order to gain a greater insight into what’s limiting carrier mobility in 4H silicon carbide, using mode-level first principles calculations. Their calculations have revealed that its low hole mobility is mostly caused by large effective masses for heavy and light holes near its Valence Band Maximum (VBM), as well as strong interband electron-phonon scattering mediated by low energy acoustic phonons.

Another factor limiting hole mobility of 4H SiC is its spin-orbit coupling. This effect has an adverse impact on valence bands near the VBM but relatively minimal effect in conduction bands. To address this restriction, researchers have devised techniques to modify atomic bonding in 4H SiC to lower spin-orbit coupling and thus increase hole mobility.

These modifications have proven to significantly enhance both in-plane and out-of-plane hole mobility of 4H SiC as well as its insulating properties, leading to new strategies for optimizing silicon carbide MOS transistor performance.

High Thermal Conductivity

Silicon carbide boasts high thermal conductivity, making it an excellent material choice for use in power electronic devices. Furthermore, its stability makes it resistant to thermal shocks and its low thermal expansion makes it chemically inert – all characteristics essential in such devices. There are various polytypes available with 4H silicon carbide being most popular for high power and frequency applications as well as being utilized by refractory ceramic manufacturers due to its outstanding mechanical properties.

Silicon carbide’s superior thermal conductivity is due to both its crystal structure and defect density within the material. 4H silicon carbide consists of stacking Si C double layers in either cubic (k) or hexagonal (h) arrangements; moreover, crystal size may be altered through doping with different impurities; thus leading to various forms of defects within its crystals.

Carbon vacancies are the dominant defect in 4H silicon carbide and are responsible for its wide band gap. Therefore, understanding their atomic and electronic structures is of utmost importance in using 4H silicon carbide successfully. Therefore, this study focused on characterizing its carbon vacancy defect with various experimental techniques.

An in-depth understanding of impurities and defects present in 4H silicon carbide is crucial to realizing its full potential in power electronics and quantum technologies. Herein, the authors provide an update of recent experimental and theoretical advances related to impurities and defects found in this material.

A specific polytype for a specific device depends on the needs of the semiconductor industry. Both 4H SiC and 6H SiC are excellent materials suitable for many semiconductor industry needs, yet have unique characteristics which differentiate them. Perhaps most notable between them is their crystal structures – 4H SiC has higher symmetry than 6H SiC which leads to different defect densities and crystal quality as well as higher thermal conductivity along the c-axis than in basal plane.

High Stability

4H silicon carbide’s remarkable stability results in excellent mechanical strength and resilience, making it an ideal material choice for cutting-edge electronic and mechanical applications such as power semiconductors for electric vehicles (EVs) and renewable energy systems, durable aerospace components and devices, and semiconductor power components requiring reliable performance under challenging conditions.

Silicon carbide is a covalent material composed of silicon and carbon atoms arranged in an ordered tetrahedral crystal structure. It comes in various polytypes with different arrangements of the atomic layers within the crystal lattice – hexagonal a-silicon carbide is often found, while cubic b-silicon carbide has both hexagonal and tetragonal structures.

Both polytypes feature excellent electrical and thermal properties; however, their respective atomic arrangements differ significantly, creating unique physical and chemical characteristics for each one. For instance, hexagonal a-silicon carbide features four silicon atoms bonded with four carbon atoms in a six bilayer-height step structure as depicted below.

In a-SiC, each bilayer is arranged at an approximate 30deg angle from adjacent layers, creating a structure with extremely long covalent bond lengths and high conductivity and resistance. Furthermore, its wide bandgap enables it to produce high-speed electrons for fast energy transfer.

As a shallow donor impurity, nitrogen doping enhances the electrical conductivity of SiC substrates by filling C lattice sites. However, to achieve maximum conductivity it must balance between crystal stability and doping concentration – too much doping may induce double Shockley stacking faults and result in 3C SiC multi type inclusion defects if too high a concentration exists.

Researchers have recently discovered that doping concentrations of 0.5 weight percentage can effectively mitigate surface steps growth and encourage formation of single crystal structures with continuous c-axis directions, by controlling seed crystal polarity and doping concentration during growth processes. Furthermore, cerium doping has also proven successful at stabilizing 4H SiC crystal forms by suppressing multitype inclusion defects.

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