Silicon Carbide Index of Refraction

Silicon carbide is a superior wide bandgap semiconductor with outstanding physical and chemical properties, including yellow to greenish-blue to bluish-black crystals with iridescence.

Refractive index measurements on epitaxially grown cubic SiC have been carefully made using variable-angle spectroscopic ellipsometry, showing both ordinary and extraordinary refractive indices increase with temperature.

The index of refraction

Index of Refraction is a dimensionless number which describes how light passes through it, for example glass has an index of Refraction of 1.5 while lead crystal has one at 1.77 and diamond at 2.42. Generally speaking, higher the index of Refraction for any material, the more sparkly its appearance is likely to be.

Silicon carbide possesses an exceptional index of refraction that rivals sapphire and ruby, and two times higher than quartz. This makes it a suitable material for manufacturing high-performance optical components like waveguides. However, its index of refraction may change depending on its depositing temperature or substrate material deposited upon. In addition, impurities or defects within its film may influence its properties.

SiC films of high-quality can be grown on various substrates, including silicon (Si), tungsten carbide (WC) and titanium dioxide (TiO2). However, it is crucial that we understand how each substrate affects the optical properties of SiC films produced on them.

Optic parameters of SiC thin films depend on their thickness; to measure these optical parameters accurately, measurements from an ellipsometry analysis must be fitted into simple dielectric functions using formulae for fitting them to measurement data from simple dielectric functions. When dealing with SiC, index of refraction and birefringence measurements at multiple wavelengths provide more precise results.

Information collected can then be used to build a model of the optical properties of SiC-on-SiC structures, with results being compared against observations of astronomical extinction spectra for comparison purposes and validation of theories; further experimental work may also be necessary in order to refine such theories further.

Tunable index of refraction for silicon carbide films is an integral element for developing chip-scale photonic devices. Its value depends on the ratio between silicon and carbon concentration in the film; and can differ depending on alpha or beta polymorphs of silicon carbide, or even depending on thickness.

Extinction Coefficients

Silicon carbide is a cubic material with high optical transmission and low dispersions, boasting excellent optical transmission properties and exceptional bridging capability, due to its large band gap energy. Due to low dispersion levels, silicon carbide makes an attractive material choice for applications requiring accurate modeling of radiation properties – such as porous media heat exchangers. Furthermore, its extinction coefficient provides useful calculations of radiative thermal conductivity.

Silicon carbide’s optical properties are determined by its crystalline structure and doping levels, with its normal refractive index being 2.6584 for the 111 crystal plane and 3.0823 for 100 crystal plane. Indices vary with wavelength; thus index of refraction proportional to frequency while also contributing to frequency dependent extinction coefficient.

Silicon carbide stands out among optical surfaces materials because of its excellent bridging capacity, low thermal expansion and rigidity properties, making it the ideal material for optical surfaces such as telescope mirrors. Silicon carbide also finds application in light emitting diodes (LEDs) and detectors used by electronic devices.

Silicon carbide comes in various forms, but alpha is the most prevalent variety. It features a hexagonal crystal structure similar to that of wurtzite and can form at temperatures above 1700 degC. Another polymorph is beta which features zinc blende crystal structure similar to diamond formation at lower temperatures.

Laboratory extinction spectra of alpha silicon carbide grains have been measured, which correspond closely with astronomical observations. Unfortunately, however, these measurements alone cannot provide enough information for accurate interpretation of 11.5 mm feature profiles on C-stars as radiative transfer models require knowledge of complex index of circumstellar material across electromagnetic spectrum. To address this problem and satisfy radiative transfer models’ requirement of knowledge about complex index of circumstellar material across electromagnetic spectrum, these authors present a complete dielectric function computed from Kramers-Kronig analysis which confirms that feature present by these extinction spectra is indeed alpha-SiC-related.

Optical Properties

Silicon carbide’s optical properties are determined by its atomic structure; specifically by the presence of two specific point defects: aluminum impurities on silicon sublattice AlSi and nitrogen impurities on carbon sublattice NC. These point defects, in turn, help define its optical characteristics. Alpha silicon carbide’s low thermal expansion, high hardness and rigidity make it an attractive material choice for astronomical telescope mirrors. Laboratory extinction spectra are available that accurately reflect what can be observed through observations in space. Laboratory spectra alone are insufficient to fully characterize the optical properties of materials across all electromagnetic frequencies. This paper presents a complete synthetic dielectric function for this material derived through Kramers-Kronig analysis of existing data and experimental extinction spectra. This function serves as the input to radiative transfer models that characterize space dust environments.

SiC thin film samples with various thicknesses were manufactured using plasma-enhanced chemical vapor deposition (PECVD). Their structure and morphology were examined through various means such as x-ray reflectivity, powder x-ray diffraction, scanning electron microscopy and atomic force microscopy; their optical constants (real/imaginary parts of complex dielectric function and refractive index), optical constant bandgap determination were all performed via spectroscopic ellipsometry.

Studies demonstrate that the index of refraction of SiC decreases as its thickness increases, as predicted. Both real and imaginary parts of its complex dielectric function, as well as absorption coefficients, depend on both wavelength of incident radiation and polarization direction; these findings confirm predictions that its layered structure has a positive influence on optical constants that enhance transmittance across an expanded electromagnetic spectrum.

Silicon carbide’s toxic effects stem largely from its strong interaction with oxygen and water molecules, leading to overexposure of hydrogen chloride gas that can lead to respiratory distress, bronchoconstriction and fluid accumulation in the lungs as well as abdominal cramps, nausea and vomiting. Furthermore, exposure to its vapors could alter the course of inhalation tuberculosis leading to extensive fibrosis and progressive disease progression.

Materials

The refractive index measures the ability of materials to bend light waves. Each material has different indices: water has an index of refraction of 1.5; lead crystal has a higher one; diamond has one over 2.42 which explains their gorgeous appearance when exposed directly to sunlight. Silicon carbide has an index of refraction of 2.5 which makes it an excellent hard and wear-resistant material with great electrical properties that makes thin films from it possible, used in electronics including LEDs and early radio detectors as well as electroluminescence with an efficiency of 10-2 at 5600 A (Engineering Property Data).

Silicon carbide’s high thermal conductivity and rigidity make it one of the premier materials for use in telescope mirrors, including Herschel and Gaia space observatories, where multiple large telescopes boast silicon carbide mirrors. Furthermore, its low thermal expansion coefficient makes it an excellent choice for spacecraft subsystems.

Contrary to silicon’s susceptibility to air oxidation at higher temperatures, silicon carbide is highly resistant. Furthermore, it’s the hardest of all the silicates. Most often found as polycrystalline material but single crystals may also be formed using Lely process with sublimed silica powder; cubic silicon carbide may also be grown through chemical vapor deposition with higher growth temperatures required.

Reaction-bonded silicon carbide is impermeable to oxygen, making it a cost-effective choice for applications requiring corrosion resistance at elevated temperatures.

CVD silicon carbide fibers are created by layering carbon-rich core material with carbon mantles and can be reinforced using various materials, including tungsten. Their room temperature strength averages 4GPa; their longitudinal and radial strengths vary, with longitudinal strength typically being greater. Over time however, these fibers become weaker, likely due to interfacial reactions between their core/mantle tungsten components as well as grain growth in their silicon carbide core material.