Silicon carbide (SiC) is an exceptional material with remarkable electrical and mechanical properties, making it especially suitable for applications that demand performance at elevated temperatures and voltages. SiC is particularly well suited to high-power and high-frequency applications where heat dissipation is essential.
Atmospheric microscopy (OM) and laser scanning confocal microscopy (LSCM) were employed to analyze etch-pit morphologies of an etched 4H-SiC epitaxial layer. To measure local leakage currents, tunneling atomic force microscopy (TUNA) measurements were conducted; these allowed us to determine what kind of dislocations may exist in our samples.
High thermal conductivity
SiC is known for its excellent thermal conductivity, enabling it to disperse heat more effectively, prolonging electronic devices’ performance and lifespan. Coupled with its high refractory temperature and rigidity, SiC makes an ideal material for applications that require resistance against heat while providing exceptional heat dissipation capabilities in environments with high operational stress such as space-grade sensor devices or radiation-hard electronics.
Silicon carbide’s atomic-level structure is essential to its properties. Multiple factors impact its thermal conductivity, such as lattice oxygen/nitrogen content, porosity, grain size distribution and phase transformation – but an in-depth understanding of their influence remains limited.
This study presents the first systematic measurement of anisotropic room-temperature thermal conductivity in 3C-SiC bulk crystals. The measured in-plane k values are over 50% higher than those reported for commercially available 6H-SiC and AlN crystals; and rank second highest among large crystals of any material. To conduct their measurements, authors utilized a BO-TDTR instrument with modulation frequency 1.9 MHz and 10x objective lens.
CVD SiC, also known as chemical vapor deposition-grown silicon carbide, is a face-centered cubic polycrystalline form of silicon carbide with wide bandgap and high breakdown voltage characteristics, making it an ideal material for power electronic devices that operate at higher temperatures and voltages. Furthermore, its exceptionally low thermal expansion coefficient and highly refractoriness make SiC ideal for various applications including telescope mirrors in astronomy telescopes.
High breakdown voltage
Silicon Carbide (SiC) offers numerous advantages for power device applications. Its wide bandgap allows devices to function at higher temperatures and voltages while its low defect density boosts performance – all making SiC an attractive replacement for Silicon (Si) power devices. Nevertheless, SiC’s unique material properties must be taken into account when designing and fabricating semiconductor devices that utilize SiC; for instance its crystal structure influences both performance and breakdown voltage; when designing these types of devices 4H-SiC and 6H-SiC vary in their atomic arrangements giving rise to differences in physical and electronic properties that must be considered when designing or fabricating them to ensure optimal use when designing them as replacements for silicon power devices.
Breakdown voltage in SiC bipolar power devices depends on two variables – its voltage blocking layer thickness and doping concentration. Thinner blocking layers result in lower resistance while more highly doped layers increase breakdown voltage. Littelfuse developed a space-modified Junction Termination Extension (JTE) structure with appropriate dimensions and doping concentration for improved SiC bipolar transistor performance.
To increase the breakdown voltage of a bipolar transistor, its JTE structure was passedivated with a layer of SiO2 deposited and annealed in NO. This enhanced surface recombination, and enabled 23kV maximum breakdown voltage – providing high power applications a bipolar transistor can now achieve.
Low resistivity
Silicon carbide is an extremely hard, chemically resistant material with superior thermal conductivity that finds wide use in electronics devices and light-emitting diodes (LEDs). While natural moissanite may occasionally occur in meteorites, corundum deposits, or kimberlites, most commercial silicon carbide sold worldwide is synthetic; its high hardness and temperature resistance make it an attractive material choice for telescope mirrors.
Silicon carbide comes in two main varieties, alpha and beta. The alpha form, with its Wurtzite crystal structure, is by far the more popular type; while zinc blende is less so. Prior to recently, beta was rarely utilized commercially for high temperature applications; now however it has become an attractive alternative.
4H SiC and 6H-SiC differ primarily in their crystal structures. Both polytypes possess hexagonal crystal structures; however, there may be subtle variations between their stacking sequence of their layers and this results in differing lattice constants and electrical properties between the two polytypes.
4H-SiC can further increase its low resistivity by decreasing defect density, either through decreasing impurity concentrations or low temperature growth techniques, or through optimizing etching process to minimize use of toxic HF reagents.
High thermal stability
Silicon carbide is a wide bandgap semiconductor material capable of withstanding high temperatures and voltages, thanks to its exceptional thermal stability. As a result, this material can withstand even demanding applications like power electronics. Furthermore, silicon carbide’s high electron mobility enables fast switching speeds that make it an excellent choice for power switches, diodes, and rectifiers.
Silicon Carbide can be found in several polytypes, each with unique characteristics. Of these types, 4H-SiC stands out due to its exceptional electrical and mechanical properties; among these variants it is considered one of the most advanced polytypes due to its hexagonal crystal lattice formation while 6H-SiC forms a cubic one.
Impurities present in 4H-SiC have an immense effect on its performance; yet their nature and impact remain poorly understood. To address this gap, first-principles formation-energy calculations were performed to develop an extensive database of impurity sites within 4H-SiC; this includes information such as lattice distortion, solubility levels, charge transition levels etc.
Secondary Ion Mass Spectrometry was used to analyze depth profiles of O, B, and N densities near Si substrate and growth face surfaces close to Si substrate and growth face for 4H-SiC samples, and revealed that most impurities caused lattice expansion while only B and N atoms led to lattice contraction of about 0.51%.
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