Phototransistor

Photodetectors operate by carrier transport across a semiconductor junction. A wide variety of these photodiodes are available, such as Schottky diodes, phototransistors, and avalanche photodetectors. Typical photodetector materials are gallium arsenic phosphide and gallium phosphide, which are produced by MOCVD or MBE. 

Photodiodes are the modem analogues to photocells. They increase their electrical resistance under light impact which, as part of an electric circuit, can be measured easily. Many current instruments display diode arrays instead of a single diode. Tens of photodiodes are arranged in a tight area. They are exposed to the sample bound spectrum where they respond to the color that corresponds to their positions in the diode array. A rapid, periodically performed electrical interrogation of all diodes (sequence periodicity in the order of milliseconds) reveals a quasi-stationary stable spectrogram. More sophisticated than photodiodes are phototransistors. They amplify internally the photoelectric effect, but the sensitivity of a photomultiplier cannot be achieved. 

Wavelength Optical Communication Systems J. C. Campbell, Phototransistors for Lightwave Communications... 

Hamilton, M. Martin, S. Kanicki, J. 2004. Thin-film organic polymer phototransistors. IEEE Trans. Electron Dev. 51 855-877. 

A phototransistor or photodiode may also be used to detect visible fight. Both devices have p-n junctions. In the photodiode the photon ejects an electron from the p semiconductor to the n semiconductor. The electron cannot cross back across the p-n junction and must travel through the circuitry, an ammeter to return to the p material. In a phototransistor, usually an npn type, the base (p-type semiconductor) is enlarged and photosensitive. Photons dislodge electrons that act as if a potential was applied to the base. This results in an amplified flow of electrons proportional to the number of photons striking the base (Fig. 5.11). 

The availability of integrated circuits paved the way for the next generation ofX-ray inspection system. These units featured a side-shooting fan beam of X-rays incident on an extended array of scintillators optically coupled to photodiodes or phototransistors. The resulting low-level electric currents were then amphfied, integrated, and electronically sampled and digitized. Such systems were under development by ScanRay and Picker in 1977. By 1979, Picker was marketing... 

FIGURE 4.5 Sea turtle orientation, (a) Bird eye s view of apparatus to test whether sea turtles discriminate sea water samples from different locations. Sea water flows from water inlet toward the standpipe (arrows). The turtle is placed near the standpipe. Phototransistors record when the animals move into different compartments. The water washes of sand come from Padre Island (P) and Galveston (G), and unscented water in two compartments serves as control (C). (b) Turtles spent more time in water extract of sand from Padre Island than in that from Galveston. (From Grassman etal., 1984.)... 

S. R. Forrest, Sensitivity of Avalanche Photodetector Receivers for High-Bit-Rate Long-Wavelength Optical Communication Systems J. C. Campbell, Phototransistors for Lightwave Communications... 

Selecki and Wasiak [54] have developed a modification of this technique which they named capillary method. Under the influence of a reduced pressure the foam moves continuously through a capillary tube with a known internal radius rin. The foam in the capillary is transformed into bubbles with extended cylindrical shape. By a lamp and two phototransistors the rate of film movement vy is measured, thus enabling to determine the equivalent diameter of each bubble... 

Some radiation detectors, i.e., photoemissive detectors (vacuum phototubes or photomultipliers) or semiconductor detectors (photodiodes or phototransistors) directly produce an electrical signal by quantum effects. Their output is strongly dependent on the wavelength of the detected radiation. Thermal detectors, i.e., thermocouples and thermopiles, bolometers, pyroelectric detectors, or pneumatic and photoacoustic detectors record a temperature increase through radiation and convert this into an electrical signal. This is proportional to the flux of the absorbed radiant power, independent of the wavelength. 

Bll. Boumans, P. W. J. M., and Brouwer, G., Studies of photodiodes and phototransistors as detection devices in multichannel emission spectrometry. Int. Colloq. Spectrosc., 16th, Heidelberg 1, 226-231 (1971). 

One additional type of peripheral—the light pen—can also be connected to this port. (On those models with more than one joystick port, the light pen can be connected only to port 1.) The pen contains a phototransistor that switches when it detects the electron beam of the video display sweeping past. A line is connected from the phototransistor through the port to the chip that generates the video signal (the VIC chip in the VIC, the VIC-H chip in the 64 and 128, and the TED chip in the Plus/4 and 16). 

For the measurement of density and viscosity using the falling body method, some effects, influencing the precision of the measured quantities, should be taken into account. First it is the dimension and the mass of the measuring body, eventually its shape. At the possible lowest off-balance of 10 mg, when the beam of the balance optical system still passes the distance between the two phototransistors, the effect of the moment of... 

Vo-Dinh T, Alaiie IP, Isola N et al (1999) DNA biochip using a phototransistor integrated circuit. Anal Chem 71 358-363... 

From the above discussion, it is evident that BR is a bifunctional electronic material [64] it is sensitive to light as well as to ions such as H+, Cl, and Ca. In the motion detector developed by Miyasaka etal, BR is configured as a photon sensor. In the cyclic-GMP cascade, a photon, via its action on rhodopsin, triggers the hydrolysis of cyclic-GMP, and thus in turn regulates the release of energy stored as a Na+ gradient. The hypothetical trigger mechanism based on the surface potential thus works like a field effect transistor (FET), or more precisely, a phototransistor. 

A reversible optical waveguide sensor for ammonia vapor was introduced more recently [137], consisting of a small capillary glass tube fltted with a LED and a phototransistor detector to form a multiple reflecting optical device. When the capillary was coated with a thin solid film composed of a pH-sensitive oxazine dye, the instrument was capable of reversibly sensing ammonia. Vapor concentrations from 100 to below 60 ppm were easily and reproducibly detected. A preliminary qualitative kinetic model was proposed to describe the vapor-film interactions. 

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