Detector active area

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. 

In the case when the surface of the detector receiving the incident optical flux is not equal to the detector active area, i.e., when some kind of concentrator is used to collect radiation from a larger area and direct it to the active area, a factor of optical concentration [8] may be formally introduced into the expression for the specific detectivity. This factor is equal to the square root of the ratio between the optical and active ( electrical ) detector area. 

We denote as optical or equilibrium methods all various procedures that increase the number of photons of the useful signal within the detector active area. This means that they improve the performance of photonic MWIR or LWIR detectors without causing a nonequilibrium between charge carriers and the semiconductor crystal lattice. 

The cadmium molar fraction of the photodetector was x = 0.165, which is the optimum for the operation at 300 K. The detector-active area was assumed to be 1 mm X 1 mm, one of the standard dimensions for uncooled HgCdTe photoconductors for the detection of CO2 laser radiation. The bias voltage was 1.5 V, and the detector resistance 50 Q.. 

The whole concept of extraction photodiodes poses a practical problem, since the requirement exists that the active region thickness must be smaller than the diffusion length. Such a requirement poses design restrictions regarding the absorption path and the total detector active area. One of the approaches utilized to solve the above problem was not to use a single detector but rather a densely packed matrix of separate elements with lateral contacts on a joint substrate and with a joint exclusion junction (Fig. 3.28a) [376]. 

The detector setup consists of four 256 x 256 pixel amorphous silicon technology sensor flat panels with 0.75 x 0.75 mm pixel size, having an active area of 192 x 192 mm [5j. These sensors are radiation sensitive up to 25 MeV and therefor well suited for detecting the LINAC radiation. The four devices are mounted onto a steel Irame each having the distance of one active area size from the other. With two vertical and two horizontal movements of the frame it is possible to scan a total area of about 0.8 x 0.8 m with 1024 x 1024 pixel during four independent measurements. 

The NEP may be written in terms of the detector element active area, the number of detector pixels elements cormected for additive output the electronic noise bandwidth B and the detector element detectivity, D. Typically = 1, but may be increased for improved sensitivity with an attendant loss in resolution. 

Ap = the detector element (pixel) active area, typically 1.5 E-5 cm ... 

Eig. 18. Microbolometer (a) array portion showing pixels on a 50-pm pitch. Each pixel is coimected to a readout amplifier in the supporting siUcon IC chip, (b) Detector having a 35 x 40 pm active area. The serpentine arms give excellent thermal isolation and the low mass results in a 10-ms response time, ideal... 

A light beam of 21 mW reaches a photoconduchon detector with a 1 mm thick active area. The absorption coefficient at 965 nm (the incident wavelength) is 23 cm Calcnlate the nnmber of carriers created per unit hme if the quantum efficiency of the process is 0.13. 

All infrared spectra were recorded with an IR-PLAN microscope (IR-PLAN is a registered trade mark of Spectra Tech, Inc.) integrated to a Perkin-Elmer Model 1800 Fourier transform infrared (FT-IR) spectrophotometer. The spectrophotometer consisted of a proprietary heated wire source operated at 1050°C, a germanium overcoated potassium bromide beamsplitter, and a narrow-band mercury-cadmium-telluride (HgCdTe) detector. The detector was dedicated to the microscope and had an active area of 250 x 250 pm. The entire optical path of the system microscope was purged with dry nitrogen. 

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