Photovoltaic detectors responsivity

A common additional requirement on a detector is to minimize its response time. The response time of a photovoltaic detector is often determined by its RC time constant [4.7]. Thus for a given RA, one wants to minimize the capacitance per unit area of the junction. 

The speed of response of a photovoltaic detector is often determined by its RC time constant, as noted in Subsection 4.2.1. TheRC time constant is given by the product of RA and (4.30) taking this product and substituting (4.39) for W we get... 

Thus the zinc blende structure semiconductors can be useful for intrinsic photoconductive detectors. Compounds such as InSb have been used as intrinsic photoconductors [4.20], as well as for photovoltaic detectors, but greater versatility of wavelength response is possible with the Hg j tCd Te alloy system. The Hgi j.Cd,Te alloys have received considerable development effort in recent years and are the most prominent intrinsic photoconductor materials they will be analyzed in this subsection. The development of Hg, Cd Te has concentrated almost entirely on n-type material since it provides high photoconductive gain however, p-type Hg, Cd,(Te crystals may be useful for intrinsic photoconductive detectors also [4.21]. 

The detector characteristic may very well be included in the filter design. For example, an indium arsenide photovoltaic detector, operating at 195 K, has a very sharp cut-off at 3.6 m. In combination with a thin germanium window, a well-defined 1.9-3.6 m response function is obtained. However, with a limited number of substances available for the design of filters based on intrinsic absorption and reflection phenomena other methods must be found to constmct filters where the transmission limits can be set by the scientific objectives and not so much by the absorption properties of available substances such methods are based on the interference principle, to be discussed in Section 5.6, but first we deal with prism spectrometers, gas filters, and pressure modulation. 

Shappir (1977) The Response of Small Photovoltaic Detectors to Uniform Radiation by J. 

GaN/AlGaN heterostructures for solar-blind detectors have been grown by both RMBE and PMBE. By tuning the AIGaN bandgap the cut-off wavelength has been varied from 360 to 310 nm in p-i-n photovoltaic devices [72,73], Very competitive data were achieved, regarding the responsivity of 0.15 A/W and external quantum efficiencies of over 50%. 

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,... 

Photovoltaic MCTIR detectors with response times on the order of five nanoseconds are now available. 

The type of detector used in an FT-IR spectrometer is highly dependent upon the bandwidth (i.e. the spectral frequencies), the modulation rate of the interferometer, and the intensity of the radiant flux. Several types of detectors are used in the infrared regions photoconductive, photovoltaic, bolometers, pyroelectric and Golay cells. A detailed discussion of detectors may be found elsewhere.12 In general, the photovoltaic and photoconductive detectors can be used in the near- and mid-infrared regions as rapid response, high sensitivity detectors. Usually the bandwidths are limited and will not cover the total ran passed by the beamsplitter. Examples of such detectors are given in Table I. As can be seen from the... 

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