Photovoltaic detectors operation

Schottky barrier if > E, a layer of the semiconductor next to the surface is inverted in type, and there is then a p-n junction within the material. Let us estimate RA with these limitations for a Schottky barrier photovoltaic detector operating at T=77 K we obtain RA <470ohm-cm from (4.29). This estimate represents the upper limit of RA achievable with a Schottky barrier. We should keep this result in mind for comparison later with the RA values calculated for p-n junction photovoltaic detectors. [Pg.113]

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. [Pg.190]

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. [Pg.422]

From the exit slit, the beam is directed to either of two detectors by the movable mirror behind the exit slit. Typical detectors are InSb, a photovoltaic indium antimonide detector operated at 77 K, and He Ge, a photo-conductive mercury-doped germanium detector maintained at 15 K by a closed-cycle helium refrigerator... [Pg.158]

A short time later, Levin s group modified step-scan FT-IR spectrometer to operate with a mid-IR MCT FPA detector. Unlike most MCT detectors used in FT-IR spectrometers, which operate in the photoconductive (PC) mode, the pixels of MCT FPA detectors operate in the photovoltaic (PV) mode. As noted in Section 1.2.2, the cut-off wavenumber of narrow-band PC MCT detectors is about 750 cm" . The PV detector elements used in MCT FPA detectors have the same high sensitivity as narrow-band PC MCT detectors, but the cut-off wavenumber is higher, at about 850 cm" . [Pg.45]

Operating Temperature. The calculations in the previous sections assumed that only fluctuations in the rate of arrival of photons from the forward hemisphere were important. This is evidenced by the employment of M(v, 7 ), which applies to a hemisphere. If the sensitive element of the detector is at the same temperature as the background, it will receive radiation not only from the forward hemisphere but from the reverse as well. Even though the back side of the element is mounted on a substrate, radiation will enter either through or from the substrate. Whether or not this is important is determined by whether the detector responds only to radiation incident on the front surface. In most photovoltaic detectors the back surface is much farther from the junction than the sum of the optical absorption depth and the carrier diffusion length. Thus most photovoltaic detectors have a preferred surface, and the background limit does not depend upon the mode of operation. [Pg.54]

Combined Effects of Mode of Operation and Operating Temperature—The expressions for Df and D Ts) given in (2.78) and (2.81) apply directly to photovoltaic detectors, and to photoemissive detectors having opaque photocathodes. [Pg.54]

Related to the problem of detector operating temperature is that of its electrical power dissipation. A photoconductive detector must always carry a primary current / and therefore dissipate l R of electrical power, whereas a photovoltaic detector can be operated without a bias. The trend toward mechanical or electrical cooling, occurring for practical reasons, makes it necessary that a detector dissipate a minimum of electrical power and thereby heat itself as little as possible. [Pg.108]

All semiconductor detectors operate on the photo-conductive principle, namely the inner photoelectric effect. However, it is normal to use the term photo-conductive detector for those that rely on the incident photons to change the conductivity in the bulk of the photoconductive layer. When a p-n junction is present these are called junction detectors or photodiodes. Photodiodes are generally subdivided further into photovoltaic (i.e., operating without bias voltage) and photoconductive (i.e., operating with a bias voltage). The mode of operation usually depends on the requirements for the detector electronics. [Pg.3493]

This is actually the increase of the dark current due to illumination and is a dc value (valid for/= 0 Hz). Here rj denotes the quantum efficiency of the detector, < ) is the incident photon flux density, A is the detector active area. The factor T denotes the photoelectric gain or photogain (the ratio between the number of electrons flowing through the electric circuit and the number of absorbed photons). The fundamental equation of photoconductivity is also valid without changes for the short circuit current of a photovoltaic detector (photodiode operating in photo-conductive mode). In that mode of operation T = 1 in most of the cases. [Pg.12]

Chapter 4 discussed the general characteristics of photon detectors, provided some details for two classic detector types simple photoconductive (PC) and photovoltaic (PV) detectors, and described general detector operation. That information will suffice for many users of most IR detectors, but we need to at least acknowledge some of the many other photon detectors now available. [Pg.151]

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. [Pg.282]

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