adjustable band gap, allows construction of. a) Ternary This coefficient κ is an optical property of the semiconductor material and is related to the index of refraction n, which merely determines how much light is absorbed by the material. Used in infrared detectors for thermal imaging. High stability, low drift, used for measurements. b) False c) GaSb According to our relation, the crystal momentum increases with energy; however, we know that absorption must depend on the density of electrons and holes in the material. The wavelength range of interest for Germanium is __________ The semiconductor material for which the lowest energy absorption takes place is? 1 above) is the energy required to cross the band gap and hf is the energy of the absorbed photon 1. _________________ materials are potentially superior to germanium. A substrate for high-efficiency. As the photon energy increases, not just the electrons already having energy close to that of the band gap can interact with the photon. Legal. Possible use in solar cells, but p-type doping difficult. To discuss the different types of absorption in semiconductors, let’s understand just a little bit about the dynamics of charge carriers, and the relationship between photon energies, the band gap in semiconductors, and momentum of charge carriers. The birefringence of the hexagonal material and the scattering from the columnar grain structure found in most nitride materials further complicates matters. Used in infrared detectors and thermal imagers, transistors, and magnetoresistors. Narrow-gap layered semiconductor. View Answer, 11. Brittle. That is, in such transparent materials, light production is not limited to just the surface. b) Silicon Ionic conductor, applications in fuel cells. For example, gallium arsenide (GaAs) has six times higher electron mobility than silicon, which allows faster operation; wider band gap, which allows operation of power devices at higher temperatures, and gives lower thermal noise to low power devices at room temperature; its direct band gap gives it more favorable optoelectronic properties than the indirect band gap of silicon; it can be alloyed to ternary and quaternary compositions, with adjustable band gap width, allowing light emission at chosen wavelengths, which makes possible matching to the wavelengths most efficiently transmitted through optical fibers. Superior electron velocity, used in high-power and high-frequency applications. Nanoscale 8.27 (2016): 13407-13413. The absorption coefficient is related to the wavelength of light and another quantity called the extinction coefficient, which is also related to the wavelength of light (the electromagnetic waves propagated from the sun). The momentum imparted on the crystal is small, but the quantity is squared for a greater effect. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Semiconductor materials have a sharp edge in their absorption coefficient, since light which has energy below the band gap does not have sufficient energy to excite an electron into the conduction band from the valence band. 2. 1 above) is the energy required to cross the band gap and hf is the energy of the absorbed photon 1. a) Direct absorption Can be doped with nitrogen. High electrical conductivity, low thermal conductivity. a) 0.8 to 1.6 μm Nickelous Oxide (NiO) Semiconductor IP address: 72.10.50.208, on 26 Nov 2020 at 20:34:35, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. Oxygen-deficient n-type semiconductor. a) GaAs Used in infrared detectors for 1–5 µm. Legal. If λ is in nm, multiply by 107 to get the absorption coefficient in the units of cm-1. Better mechanical and thermal properties than HgCdTe but more difficult to control the composition. The probe laser should emit a longer-wavelength radiation, so as not to experience self-absorption and not to be amplified in the material of the active region. The force on a charge carrier in a crystal is F = m*a, or the product of “effective mass” and acceleration. d) 1.09 μm Conversely, silicon is robust, cheap, and easy to process, whereas GaAs is brittle and expensive, and insulation layers can not be created by just growing an oxide layer; GaAs is therefore used only where silicon is not sufficient. Metalorganic vapour phase epitaxy (MOVPE) is the most popular deposition technology for the formation of compound semiconducting thin films for devices. Semiconductor materials have a clear advantage in their absorption coefficient, because light which has energy below the band gap doesn’t possess enough energy to excite an electron from the valence band into the conduction band. 2: The valence band and conduction band curves in a graph of energy vs. crystal momentum are aligned if the semiconductor has a direct band gap. It is known that the density of electrons increases (see Fermi Levels) downward in energy from the valence band edge, while the density of holes increases upward in energy from the conduction band edge. Good high temperature thermoelectric material. a) True Chichester: John Wiley & Sons Ltd., 1998. Strong, Used in infrared detectors and thermal imaging sensors, high quantum efficiency, low stability, require cooling, used in military long-range thermal imager systems. All Rights Reserved. Pure GaP emits green, nitrogen-doped GaP emits yellow-green, ZnO-doped GaP emits red. Materials with higher absorption coefficients more readily absorb photons, which excite electrons into the conduction band. b) Silicon In a material with a low absorption coefficient, light is only poorly absorbed, and if the material is thin enough, it will appear transparent to that wavelength. AlInSb-InSb-AlInSb structure used as, Photocatalytic. Absorption Related electrical process: electron - hole pair generation The photon with the energy exceeding the bandgap energy of semiconductor can be absorbed. Extensive use in sensitive cooled. Inefficient emission at 210 nm was achieved on AlN. Thin-film transistors are good examples: the mobility is affected by band tailing [2], although the band-tail-state effect on carrier transport is strongly material dependent [3]. Commonly used as substrate for epitaxial InGaAs. "Two-dimensional BX (X= P, As, Sb) semiconductors with mobilities approaching graphene." The absorption coefficient, α, in a variety of semiconductor materials at 300K as a function of the vacuum wavelength of light. So, what this tells us is that if we can get to the density of states, we're actually almost there, and we have a pretty good read on what we'd expect for the absorption coefficient. d) GaAsSb Have questions or comments? Used in some gamma-ray and x-ray detectors and imaging systems operating at room temperature. The data is graphed on a log scale. For photons which have an energy very close to that of the band gap, the absorption is relatively low since only those electrons directly at the valence band edge can interact with the photon to cause absorption. Englewood Cliffs: Prentice-Hall, Inc., 1982.Full book ordering information at www.pv.unsw.edu.au. The absorption of photons in a photodiode is dependent on __________ So, that's the absorption coefficient. a) 3.01 μm b) Band gap energy The absorption and extinction coefficients are related by the following equation1: where f is the frequency of the monochromatic light (related to the wavelength by λ=v/ƒ, where v is the velocity of the light wave), c is the speed of light, and π is a constant (≈ 3.14). Join our social networks below and stay updated with latest contests, videos, internships and jobs! Used for blue lasers and LEDs. c) GaSb D\![_øÉå. Efficient thermoelectric material near room temperature when alloyed with selenium or antimony. Source: “An Introduction to Solar Cell Technology”. c) Charge carrier at junction Used in infrared detectors, photodetectors, dynamic thin-film pressure sensors, and. These semiconductors typically form in periodic table groups 13–15 (old groups III–V), for example of elements from the Boron group (old group III, boron, aluminium, gallium, indium) and from group 15 (old group V, nitrogen, phosphorus, arsenic, antimony, bismuth). Source: , Adding the two previous equations together produces a very useful result for explaining absorption in a certain class of semiconductors. 1: The energy level difference, Eg, between the edges of the conduction and valence bands constitutes the minimum energy a electron requires from a photon to become conductive (a free charge carrier). c) 0.92 μm Semiconductor materials have a sharp edge in their absorption coefficient, since light which has energy below the band gap does not have sufficient energy to excite an electron into the conduction band from the valence band.

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