Photoconductivity detector

There are two classes of photoelectric detectors photoconduction detectors and photodiodes. 

Progress in this area has been considerable in recent years and hopefully some non precious metal catalyst will be used in fuel cells in the near future. On the other hand, the stability of metallophthalocyanines makes them appropriate for applications in various fields such as chemical catalysis (such as the MEROX process for the sweetening of oils), dye stuffs, coloring for plastics and metal surfaces, sensors, chromatographic detectors, photoconducting agents, and so on. These complexes are also used for photobiology and photodynamic cancer therapy, electrochemical... 

Hg Cd Te is an example of a ternary detector, in which the value of x controls the cutoff wavelength. Photoconductive detectors are generally simpler to couple to low noise amplifiers photodiodes generally have lower power consumption because these have no external bias, and better high frequency performance (15,16). 

Lead sulfide is used in photoconductive cells, infrared detectors, transistors, humidity sensors in rockets, catalysts for removing mercaptans from petroleum distillates, mirror coatings to limit reflectivity, high temperature solid-film lubricants, and in blue lead pigments (82). 

Fig. 9. Spectral sensitivity of detectors where the detector temperatures in K are in parentheses, and the dashed line represents the theoretical limit at 300 K for a 180° field of view, (a) Detectors from near uv to short wavelength infrared (b) lead salt family of detectors and platinum siUcide (c) detectors used for detection in the mid- and long wavelength infrared. The Hg CdTe, InSb, and PbSnTe operate intrinsically, the doped siUcon is photoconductive, and the GaAs/AlGaAs is a stmctured supedattice and (d) extrinsic germanium detectors showing the six most popular dopants.

The photoconductive detector is primarily used in the visible-infrared region rather than the ultraviolet—visible range. 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

The lead compounds PbS, PbSe, PbTe are narrow-gap semiconductors that have been widely investigated for infrared detectors, diode lasers, and thermo-photovoltaic energy converters. Their photoconductive effect has been utilized in photoelectric cells, e.g., PbS in photographic exposure meters. Integrated photonic devices have been fabricated by their heteroepitaxial growth on Si or III-V semiconductors. 

The most common approaches to sulfonylurea determinations involve high-performance liquid chromatography (HPLC). The earliest reported methods utilized normal-phase liquid chromatography (LC) with photoconductivity detection this type of detector demonstrated undesirably long equilibration times and is no longer... 

Quantum detectors are based on semiconductors. The absorption of a photon excites an electron from the valence band into the conduction band. This can be measured either through a change in resistance (photoconductive... 

Paul W. Kruse, Indium Antimonide Photoconductive and Photoelectromagnetic Detectors... 

H.S. Sommers, Jr., Macrowave-Based Photoconductive Detector Robert Sehr and Rainer Zuleeg, Imaging and Display... 

Peter R. Bratt, Impurity Germanium and Silicon Infrared Detectors E.H. Pulley, InSb Submillimeter Photoconductive Detectors... 

W.F.H. Micklethwaite, The Crystal Growth of Cadmium Mercury Telluride Paul E. Petersen, Auger Recombination in Mercury Cadmium Telluride R.M. Broudy and V.J. Mazurczyck, (HgCd)Te Photoconductive Detectors M.B. Reine, A.K. Sood, and T.J. Tredwell, Photovoltaic Infrared Detectors M.A. Kinch, Metal-Insulator-Semiconductor Infrared Detectors... 

The materials and design of the various photoelectric detectors available are such that the absorption of radiation results in the displacement of electrons and hence in the development of a potential difference between two electrodes. The main types of photoelectric detectors may be classified as either photovoltaic or photoconductive (Figure 2.24). 

Figure 2.24 Photoelectric detectors. Photovoltaic detectors measure the flow of electrons displaced by the absorption of radiation. Photoconductive detectors measure the changes in conductivity caused by the absorption of radiation.

Fignre 3.12 shows the operational scheme of a photoconduction detector. The incident light creates an electrical current and this is measured by a voltage signal, which is proportional to the light intensity. This proportional relation is provided by the fact that, in most photoconduction detectors, the density of carriers in the steady state is proportional to the number of absorbed photons per unit of time that is, proportional to the incident power. 

Figure 3.13 The spectral dependence of the specific detectivity for several photoconduction detectors. The values corresponding to a typical thermopile and to a typical piroelectric detector are also shown.

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