P-i-n photodiodes

High-energy radation can be imaged with a-Si H, either directly or via a converter [3], A thick film is required for direct detection, due to the weak interaction of the radiation with the material. A converter usually is a phosphor, which emits in the visible, and thin a-Si H films are needed. X-rays with an energy up to 100 keV eject the electrons from the inner atomic core levels to high levels in the conduction band. The emitted electrons create electron-hole pairs due to ionization. These pairs can be detected in the same way as in p-i-n photodiodes. 

In one of the most common types of photodiodes used for time-resolved work, the p-i-n photodiode (see Figure 12.24), the depletion layer thickness (i for intrinsic) is fabricated to obtain this optimum performance. Manufacturers usually give full specification sheets detailing, active area, time/frequency response, responsivity amps/watt (AAV) at a given wavelength, dark current, depletion layer capacitance, and bias volts such that with minimal external electronics devices can be made operative. 

Photodetector — Device used to detect photons. After a long period having only thermal photodetectors, quantum photodetectors based on photocurrent were developed and are used quite widely in applications such as photographic meters, flame detectors and lighting control. In the late 1950s the p-i-n photodiode, simply referred to as photodiode, was developed and now is one of the most common photodiodes. There are several types of photodetectors, the most adequate depending on the specific application, like photoconductors, p-i-n photodiodes, Schottky-barrier photodiodes, charge-coupled... 

The above discussion has been confined to the photovoltaic effect arising at a p—n junction in a semiconductor due to photoexcitation of carriers on either side of the junction. Among the related areas of interest are a) avalanche photodiodes, b) p—i—n photodiodes, c) Schottky barrier photodiodes, d) heterojunction photodiodes, and e) bulk photovoltaic effect Each of these will be discussed briefly. 

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. 

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