Photovoltaic detector

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.

Photovoltaic detector (detector with p-n junction, PV detector, photovoltaic) Photoexcitation creates an electron-hole pair to be separated at the p-n junction, thus generating photocurrent. In dependence on the structure type and the junction used it may belong to a number of the existing types with homojunction or heterojunction, p-i-n photodiode. Camel s diode (photodiode with modulated barrier), avalanche photodiode (APD), bipolar phototransistor (floating-base), etc. 

The noise is expressed as noise density in units of V/(Hz), or integrated over a frequency range and given as volts rms. Typically, photoconductors are characterized by a g-r noise plateau from 10 to 10 Hz. Photovoltaic detectors exhibit similar behavior, but the 1/f knee may be less than 100 Hz and the high frequency noise roU off is deterrnined by the p—n junction impedance—capacitance product or the amplifier (AMP) circuit when operated in a transimpedance mode. Bolometers exhibit an additional noise, associated with thermal conductance. 

Figure 15. Photovoltaic detector potential well. The example in this figure is the p-n junction of a n-channel CCD. The x-y-z axes match the orientation shown in Fig. 5. The charge generated in the 3-D volume of a pixel is swept toward a 2-D layer, which is the buried channel that is 0.25-0.5 pm from the front surface of the detector. The z-direction potential is created by the p-n junction combined with the voltages on the polysilicon wires deposited on the frontside of the CCD (not shown in this figure).

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. 

Fig. 3. Schematic diagram of the Northwestern apparatus for IR laser kinetic measurements in the gas phase. D, and D2 are InSb detectors with D2 being a high speed photovoltaic detector. M = Mirror, I = iris, C = chopper, BS = beam splitter, P = photolysis cell. [Reproduced with permission from Ouderkirk et al. (75).]...

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 detector in a spectrometer must produce a signal related to the intensity of the radiation falling on it. For instruments operating in the visible region a photovoltaic or barrier-layer cell is the simplest and cheapest available. Current produced when radiation falls on a layer of a semiconductor material, e.g. selenium, sandwiched between two metallic electrodes, is proportional to the power of the incident radiation and can be monitored by a galvanometer. Barrier layer cells are robust and are often used in portable instruments but they are not very sensitive and tend to be unstable during extended use. 

Hence, for an absorbance of 0.434, there is a minimum in the relative error of the measurement. Figure 9.4 (curve A) shows how the relative error varies with absorbance (d T= 1%) for a simple instrument incorporating a photovoltaic detector (p. 282). Measurements outside the range 0.2-... 

Constant instrumental error 1%. Curve A photovoltaic detector. Curve B photomultiplier detector. 

Photovoltaic (PV) cells, 23 32-53. See also Photovoltaic materials commercial history of, 23 49—51 conducting polymer applications, 7 541 polymethine dyes in, 20 516—517 selenium, 22 100, 103 spectrum and band gap of, 23 37-39 structure of, 22 220-221 third generation, 23 44 workings of, 23 32-37 Photovoltaic detectors, 19 133, 138 Photovoltaic detectors/arrays/focal planes, 19 163-164... 

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). 

Infrared spectrophotometers use photovoltaic-type detectors to measure the intensity of radiation... 

The infrared radiation caused by the heat of reaction of an enantioselective enzyme-catalyzed transformation can be detected by modern photovoltaic infrared (IT)-thermographic cameras equipped with focal-plane array detectors. Specifically, in the lipase-catalyzed enantioselective acylation of racemic 1-phenylethanol (20), the (K)- and (S)-substrates were allowed to react separately in the wells of microtiter plates, the (7 )-alcohol showing hot spots in the IR-thermographic images (113,114). Thus, enantioselective enzymes can be identified in kinetic resolution. However, quantification has not been achieved thus far by this method, which means that only those mutants can be identified which have E values larger than 100 (113-115). 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

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