InAs detector

On the high-pressure device, the infrared measurements are performed using a Bruker Tensor 37 FTIR spectrometer. The IR configuration includes a NIR source, the Tensor 37 interferometer with a CaF2 beam splitter and a thermoelectrically-cooled InAs detector. The UV Visible measurements are made using a Varian Cary 300 spectrometer equipped with 600 pm core diameter optical fibres. 

The prototype instrument was based upon a spinning circular variable wavelength filter (CVF) and utilized a low-noise InAs detector. A CVE is a time-dependent wavelength selector that passes a narrow spectral band. The spectral region of the band depends on the angular position of the filter. 

The following general observations apply to both kinds of problems. The scale of operations is fixed by the necessity of comparing adjacent sections of tissue only microns in width, which makes it advisable to use the photographic plate as detector, in order that the necessary measurements of x-ray intensity can be made on greatly enlarged areas. Inas-... 

While most other techniques use a limited amount of detectors (e.g., silica for visible, photomultipliers for UV) and MIR has a small number, NIR uses many types of semiconductors for detectors. The original PbS detectors are still one of the largest used in NIR, however, indium gallium arsenide (InGaAs), indium arsenide (InAs), indium antimonide (InSb), and lead selenide (PbSe) are among the semiconductor combinations used, both cooled and ambient. 

Typical materials used in NIR photoconductive detectors are PbS, PbSe, InSb and InAs (lead sulphide, lead selenide, indium antimonide and indium arsenide). 

Fig. 7.15 Detectivities D of some photoconductive and pyroelectric detector materials curve 1, PbS curve 2, InAs curve 3, HgCdTe curve 4, PbSe curve 5, InSb curve 6, L-alanine-doped TGS curve 7, LiTa03 curve 8, PZ curve 9, PVDF. (Curves 1-5 measured at 200 K curves 6-9 measured at 300 K.)...

The use of cobalt radiation treatments for cancerous tumors was described in Example 26-3. Several other nuclides are used as radioactive tracers in medicine. Radioisotopes of an element have the same chemical properties as stable isotopes of the same element, so they can be used to label the presence of an element in compounds. A radiation detector can be used to follow the path of the element throughout the body. Modern computer-based techniques allow construction of an image of the area of the body where the radioisotope is concentrated. Salt solutions containing "iNa can be injected into the bloodstream to follow the flow of blood and locate obstructions in the circulatory system. Thallium-201 tends to concentrate in healthy heart tissue, whereas technetium-99 concentrates in abnormal heart tissue. The two can be used together to survey damage from heart disease. 

The antimonides are important for several emitter and detector applications, although high speed devices also have been demonstrated for these material systems. A variety of substrates such as GaAs, InP, GaSb and InAs are available. By varying the composition, the near-IR to mid-IR wavelengths can be covered. Through the use of strained layer quantum well structures, the far IR becomes accessible. 

This graph summarizes the wavelength response of some semiconductors used as detectors for infrared radiation. The quantity D (X) is the signal to noise ratio for an incident radiant power density of 1 W/cm and a bandwidth of 1 Hz (60° field of view). The Ge, InAs, and InSb detectors are photovoltaics, while the HgCdTe series are photoconductive devices. The cutoff wavelength of the latter can be varied by adjusting the relative amounts of Hg, Cd,... 

The Nernst effect in suitable semiconductors (InSb-NiSb mixed crystals, Paul and Weiss [3.64] CdjAsj-InAs, Goldsmid et al. [3.65] Bi-Sb, Washwellet al. [3.66]) has also been studied. This has produced a fairly fast rather insensitive detector which could perhaps be developed further. 

The materials in this class which are used in infrared photon detectors include the compounds InSb and InAs and the alloy system Hg,, Cd,jTe. The Hgj Cd Te alloys are the most important of these materials for detectors, and their properties shall be reviewed here. But InSb and InAs are analogous to those Hgi j Cd, Te alloys which have comparable energy gaps. Since the most recent comprehensive review of Hgj, Cd,jTe was published several years ago [4.40], we shall take this opportunity to update it, although still emphasizing the properties needed in this chapter. 

Most spectrometers use tungsten-halogen lamps with quartz windows. Cells for absorption measurements are usually quartz or fused silica transparent up to about 3000 nm. Cell lengths vary from 0,1 to 10 cm. Detectors range from PbS and PbSe photoconductors to InSb and InAs photodiodes. Array detectors, such as InGaAs detectors, have also become available for the region. Several commercial UV-visible spectrophotometers are designed to operate from 180 to 2500 nm and can thus be used to obtain NIR spectra. 

B. Infrared photon detectors (semiconductors such as InAs, InSb, PbS, and PbSe)... 

Figure 6.2. Plots of D (specific detectivity see Chapter 7) as a function of wavelength for several photodetectors made by one manufacturer. The detectors marked J15D12, J15D16, and J15D22 are MCT detectors. The last two digits refer to the cutoff wavelength, so these detectors are narrowband, midband, and wideband MCT detectors. If the product code includes the letters TE, the detectors are thermoelectrically cooled otherwise, they are cooled with LN2. Other detectors whose performance is shown on this plot include PbS, PbSe, InSb, InAs, InGaAs, and Ge. (Courtesy of Judson Technologies.)...

Schuster et al. (2012) Numerical Simulation of InAs nBn Back-Illuminated Detectors by J. Schuster, C. A. Keasler, M. Reine, and E. Bellotti, J. Elect. Mater. http //link.springer.eom/article/10.1007%2Fsll664-012-2168-5 page-l... 

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