What Is Silicon Carbide Electrical Conductivity?

Silicon carbide (SiC) is an intermetallic solid that lies somewhere between metals (which conduct electricity) and insulators, with wide band gaps and high electron mobility, making it an attractive material choice for power electronics applications.

Silicon’s ability to resist chemical attack at high temperatures and its strength across a broad temperature range make it ideal for resistance heating elements in semiconductor furnaces and thermistors; however, unlike metals it does not conduct electricity as efficiently.

Conductivity

Silicon carbide (SiC) is an extremely hard, tough material with many unique properties that can be tailored for different applications. As an insulator at lower temperatures and conductor at higher ones, this makes SiC an excellent material choice for use in high temperature applications such as refractories and cutting tools as well as semiconductor manufacturing, aerospace components manufacturing and thermal management systems.

Silicon carbide’s strong, insoluble crystalline structure renders it highly resistant to corrosion and wear. With a Mohs scale hardness of 9, it ranks just one step below diamond in terms of hardness. Silicon carbide is widely used as an abrasive material as well as being one of the hardest synthetic materials; impact and heat resistance make it an essential raw material in producing steel, refractory ceramics and inorganic chemicals.

SiC is a gray to brown insoluble substance composed of four silicon and carbon tetrahedra bound together through covalent bonds, making an inorganic material with great durability, resistant to acids and alkalis attack and temperature up to 1600degC. SiC makes for an excellent material when grinding other carbides, ceramics or nonferrous metals that may be more fragile or soft than its hard surface material.

Porous SiC is highly dependent upon its chemical composition, processing conditions and microstructure; specifically its polytype, doping level, porosity and additive composition (metal nitrides and carbides). Furthermore, the sintering atmosphere has a profound impact on its electrical conductivity by changing crystalline phase structure as well as altering b-to-a transitions.

Recently, a research team investigated the influence of sintering atmosphere on the electrical conductivity of porous SiC with a Y2O3 + AlN composition. Their investigation determined that Ar sintering proved superior for lowering its conductivity when compared with vacuum sintering due to reduced b-to-a transformation rates and N doping of sintered material.

Seebeck coefficient of pure SiC is between -70 to -200 uV K-1, while commercial SiC source powder contains N impurities from air that cause it to conduct as an n-type conductor. However, its conductivity can be altered into p-type by adding 3-5% C additive.

Temperature

Temperature plays a pivotal role in silicon carbide’s electrical conductivity. At lower temperatures, silicon carbide behaves more like an insulator by resisting the flow of electricity; at higher temperatures however, its crystal structure allows phonons to move more freely allowing electricity to pass through more easily.

Silicon carbide can be modified to exhibit semiconducting properties through the careful addition of impurities or dopants, including aluminum, boron or gallium as dopants; doping with nitrogen or phosphorus will produce an N-type semiconductor.

Silicon carbide’s properties make it an invaluable material choice for high-powered devices and cutting-edge industrial applications. Furthermore, its resistance to chemical corrosion and wear make it a versatile material choice suitable for cutting-edge use.

Researchers aimed at better comprehending how temperature affects silicon carbide conductivity have studied various composites and fibers to gain more insight. For instance, they have compared electrical conductivity of SiC fibers produced through chemical vapor infiltration with those created via polymer-impregnation-pyrolysis (PIP). Their results demonstrated significant variations between thermal conductivities between PIP-SiC and CVI-SiC materials ranging from 20 to 1000 degC.

Researchers also analyzed the effect of carbon content on material conductivity. They observed that sintering samples in Ar was more successful at decreasing electrical resistivity due to reduced b-to-a phase transition and N-doping of samples than vacuum sintering.

Thermal conductivity was also improved with increasing amounts of carbon addition, possibly because excess carbon forms a solid solution in the SiC lattice that enables more free phonon flow. Furthermore, sintering may alter lattice parameters of SiC crystal and be one factor for why C-SiC and Si-SiC samples had higher Seebeck coefficients than their pure SiC counterparts.

Porosity

Silicon carbide is an extremely hard, chemical-resistant and thermal conductive material with excellent thermal conductivity properties that is used across industries – tribological, electrical, mechanical and nuclear alike. Due to its low friction rates and wear rates it allows operations with lower power (P) but higher velocity or rotational speed (V), which makes it especially useful in mechanical seal members which must withstand both compressive loads as well as high sliding velocities.

However, the intrinsic conductivity of n-type hexagonal silicon carbide is low; to increase it further and improve conductivity further, it must increase porosity through low-pressure liquid phase (LPP) techniques such as using 0.01 bar pressure at LPP to create pores in crystals – far cheaper than traditional methods such as hot isostatic pressing while producing higher quality porous silicon carbide products.

Silicon carbide’s porous structure permits electrons to pass freely through, thus decreasing its electrical resistance and increasing conductivity. This effect is achieved through energy levels formed near its band gap that can be altered using various additives such as C and N2 acceptors to reduce electrical resistivity while B and V donors increase it.

To achieve desired porosity, it is critical that sintering parameters be carefully managed. Furthermore, the process should take place under conditions which preserve microstructure integrity – for instance by adding polymer fugitives into raw batch. This allows us to control pore size, shape, quantity and control porosity during sintering; hence the term controlled Porosity Silicon Carbide or PCSSC.

One of the primary applications for porous SiC is mechanical seal members, which must withstand both high PV and sliding velocity conditions while also accommodating for temperature fluctuations. Such properties make porous SiC an invaluable component not only in mechanical seals, but in many other applications that demand low friction/wear rates – something not readily met until recently by commercially available materials; thanks to new technology however, a generation of PCSSC is now available that is suitable for wide variety of industrial applications.

Doping

Silicon carbide can be altered to produce different electrical properties by way of doping. Doping involves adding impurities into its crystal structure that create more free charge carriers (electrons or holes). Doping can increase or decrease electrical conductivity of silicon carbide; doping is widely practiced within the semiconductor industry as an efficient means to regulate material characteristics.

Doping silicon carbide involves introducing impurities with lower valence electron counts than SiC atoms into its crystal structure, creating an empty electron state in its band gap which can then be filled by thermally excited electrons from its valence band; this process produces what is known as an N-type semiconductor; to change this properties further a p-type semiconductor can be formed by substituting some SiC atoms with ones with more electron valence electrons such as Al, Be, Boro or Gallium atoms can produce similar effects; in turn this creates an N-type semiconductor can also result in doped semiconductor.

Most semiconductor devices combine N-type and p-type semiconductors in a PN junction and operate it under forward bias to increase electrical conductivity by inducing electron flow from one semiconductor into another via forward bias induced positive built-in potential of the p-type semiconductor to flow more freely into N-type semiconductor, increasing electrical conductivity.

Ohmic conduction occurs when electron energy is dissipated within a semiconductor material to generate heat, increasing electrical conductivity of its electrical conductivity and thus the temperature of a device can be altered by changing the voltage applied.

Electrical conductivity of porous silicon carbide depends on several variables such as doping concentration, temperature and electric field. A study on two kinds of porous silicon carbide showed that 4H-SiC had higher conductivity than 6H-SiC; additionally, dopants and porosity affect its conductivity significantly.

Porous silicon carbide is most often utilized in composites and fibers, while its most popular applications involve composites made with silica- and metal-containing matrices and carbon-rich fibers created through chemical vapor infiltration or polymer-impregnation-pyrolysis processes. Different companies sell different kinds of silicon carbide according to application and desired properties – for instance Matmatch has an extensive range of products from various silicon carbide manufacturers.