Why Silicon Carbide Is the Material of Choice for Power Electronics and Aerospace Applications

Silicon carbide (SiC) is one of the world’s premier wide bandgap semiconductors, often chosen for use in power electronics and aerospace applications that demand robust performance. Thanks to its high breakdown voltage, insulating properties, and efficient thermal conductivity capabilities, SiC provides superior power management.

Impurities play an essential role in shaping the electrical and optical properties of SiC. First-principles formation-energy calculations provide key information regarding impurity attributes such as site preference, lattice distortion, solubility, etc.

Electrical Properties

Silicon carbide (SiC) is an advanced wide bandgap semiconductor material that has quickly become the backbone of power electronic devices. Thanks to its superior electron mobility and saturation electron velocity characteristics, SiC enables efficient operation at elevated voltages and temperatures far exceeding conventional silicon devices’ capabilities. As such, SiC makes for a great material choice when robust performance in harsh operational environments is required, such as electric vehicles (EVs), renewable energy systems, or aerospace electronics applications.

Doping 4H-SiC to tailor its electrical properties in order to achieve these applications requires altering its electrical properties using an process called doping. Doping is an integral step in producing Schottky barrier diodes (SBDs), which offer several advantages over conventional semiconductor devices, including ultrafast switching speed and low reverse leakage current. Unfortunately, due to being such an insulating material the doping process may become complicated.

A new study employing automated first-principles formation-energy calculations aims to alleviate the complexity associated with doping 4H-SiC. To this end, they created a database of formation-energy diagrams for impurity ions found in 2H and 3H polytypes of SiC; providing details regarding their site preferences, lattice distortion levels, solubility characteristics and charge transition levels – information which will aid designers of tailor-made doping schemes to optimize electrical properties of 4H-SiC.

Determining which SiC polytype best meets an application’s demands in terms of electrical, thermal, and mechanical performance depends on its individual demands for electrical, thermal, and mechanical performance. While 4H-SiC may be ideal for power devices, 6H-SiC excels when light emission and mechanical resilience are key criteria.

Crystal structures of each polytype differ slightly, yet their physical properties remain similar. Both polytypes share a hexagonal crystal structure; however, 4H-SiC features an ABCB stacking sequence compared to 6H-SiC’s ABABAB one, leading to variations in their symmetry and lattice constants that ultimately alter physical properties of both polytypes.

6H-SiC’s thermal conductivity differs slightly from 4H-SiC but still exceeds that of silicon, providing for superior heat dissipation – an essential feature in maintaining device stability and longevity in applications involving high operational stress. Furthermore, its inherent strength and hardness make this material ideal for radiation-hard electronics as its resilience plays a key role.

Thermal Properties

Silicon carbide (SiC) is a covalent semiconductor with an interlayered structure composed of carbon and silicon atoms. The lattice patterns vary among its polytypes 3C, 4H, and 6H to produce different physical and electrical properties.

The 6H-SiC polytype is an ideal material to fabricate optoelectronic devices, thanks to its large bandgap that makes light emitting devices such as blue LEDs and UV photodetectors possible. Furthermore, its robust mechanical properties such as fracture toughness and resistance to wear make it suitable for mechanical devices like cutting tools and turbine components.

4H-SiC is widely considered one of the ideal materials for high-power electronics and high-frequency power devices due to its wide bandgap, excellent breakdown voltage, low defect density, and superior thermal conductivity. Furthermore, its compatibility with other semiconductor materials such as Gallium Nitride (GaN) broadens its applications further.

Impurities play an essential role in shaping the electrical, optical, and mechanical properties of silicon carbide (SiC).1-5 A thorough knowledge of impurity characteristics such as site preference, lattice distortion, solubility, charge transition levels (CTLs), and site preference is necessary for designing devices with desired performance characteristics.

Utilizing first-principles formation-energy calculations, we have created an exhaustive database of SiC formation energies for various impurity species in 4H-SiC, offering valuable insight into the energetics behind impurities’ influence on its electrical properties.

This work offers a quantitative understanding of how impurity doping affects the electrical properties of 4H-SiC. More specifically, its calculation methodology offers a means to examine how dopant locations and concentration affect electronic band structures, phonon dispersion characteristics, defect density levels of SiC.

This study represents a major step toward creating a more complete thermodynamic model of ion-cutting SiC. Achieving such a goal will enable more precise and accurate predictions of damage caused by irradiation, as well as more informed experimental design and interpretation of results. Furthermore, such predictive models could then be applied to other WBG materials to ensure safe use within technological applications.

Mechanical Properties

SiC’s high mechanical properties enable it to be applied across a broad spectrum of applications, from power electronics and sensors that reliably perform under extreme conditions to its use as an excellent thermal conductivity material. SiC makes an ideal material for high-frequency power devices due to its wide bandgap, high breakdown voltage and low defect density as well as its excellent thermal conductivity properties that quickly dissipate electricity while its resistance to acids and alkalis makes it suitable for harsh environments.

4H-SiC stands out among polytypes of silicon carbide as it features an especially large elastic modulus, meaning that it can withstand significant stress without succumbing to strain. This property makes 4H-SiC an excellent material choice for high temperature power electronics and components as well as automotive applications, in addition to offering excellent fracture resistance and temperature stability for industrial equipment and aircraft engines.

4H-SiC’s impressive mechanical properties enable it to be utilized in numerous precision and ultraprecision machining applications, including chemical and mechanical methods of grinding. Chemical methods involve etching the wafer surface before cleaning with acetone before mechanical grinding begins; mechanical grinding uses a diamond-resin-bonded wheel.

To explore the mechanical behaviour of single-crystal 4H-SiC, various varied-load nanoscratch tests were systematically conducted using a nanoindenter system fitted with a Berkovich indenter. Results demonstrated that material removal characteristics and crack formation vary with respect to different planes, indenter directions, and normal loading rates.

An experiment was performed using a p-type SiC wafer with an epitaxial layer consisting of 375nm grown on an n-type substrate of 1018 cm-3 volume density, using various experimental conditions and loading rates to analyze scratch groove morphology under SEM and FIB observation. Edge forward direction proved more suitable than face or side face forward directions because it initiated the ductile removal phase earlier, thus expanding the range of ductility, increasing machineability for 4H-SiC single crystal.

Chemical Properties

Silicon Carbide (SiC) is a compound semiconductor material composed of silicon and carbon, offering excellent thermal, mechanical, electrical properties to replace silicon in high performance semiconductor devices. Notably, SiC provides advantages not available with silicon, such as 10x stronger breakdown electric field strength and wider band gaps than its competitor material.

SiC exists as various polymorphic crystalline structures known as polytypes, each possessing its own set of physical characteristics. 4H-SiC is one of the more frequently encountered forms, featuring hexagonal crystal structure similar to Wurtzite that forms at temperatures above 1700 degC and often preferred for power devices as its energy band gap and breakdown voltage allow efficient device operation.

4H-SiC stands out from other polytypes of SiC in that its high concentration of nitrogen atoms makes it suitable for producing n-type semiconductor devices. A variety of doping techniques can be applied to 4H-SiC to induce doping, such as ion beam implantation, low temperature ion implantation and hot electron beam ion implantation – with most doping being achieved through implantation in the n-type region.

Due to its stability at high temperatures, 4H-SiC is a fantastic material for producing high-temperature electronics and sensors. This includes applications like RF amplifiers for cell phone base stations, radar systems and high temperature thermocouples; additionally its high thermal conductivity and breakdown voltage make it suitable for production of automotive electronics.

4H-SiC makes an ideal substrate for blue and ultraviolet light-emitting diodes (LEDs). Its wide bandgap enables it to produce LEDs with low current density and high saturation velocity, and even high-powered versions that can be installed into cars, wind turbines or power supplies.

Impurity-induced lattice distortion in 4H-SiC can be illustrated using the figure below. Sky blue, dark blue and green bars represent charge transition levels where impurities occupy Si, C or interstitial sites respectively. Ge is one of the few non-electrically active p-type impurities which can be introduced without increasing lattice expansion; Al and group VA impurities, on the other hand, have amphoteric properties which could cause contraction instead.

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