OTHER DIODES

Another device, the PNPN trigger diode, has an extra junction and therefore is not symmetrical. More will be explained about this configuration in the next chapter, where threshold gate circuits are discussed. 

A useful avalanche diode that works in either direction is the varistor, sometimes called the metal oxide varistor, or MOV. It is not just a single crystal device as the previously described semiconductors are, but instead it is polycrystalline ceramic material, usually zinc oxide, with many small PN junctions at the grain boundaries. It is quite inexpensive and is very rugged, so it can be found as an important part inside most surge protector power strips for connecting multiple computer modems, printers, etc., to protect them against inductive kicks and even most spikes ( transients ) from lightning.  

A fuse, as most readers know, protects against too much current flow by melting and thus breaking contact to the power source. It must be replaced after doing its protective job, while a circuit breaker (see index) can be reset after it has been tripped (operated to break contact), without replacing it. Sometimes a circuit breaker is an electromagnetic relay, and sometimes an SCR or Triac. 

A temperature compensating diode has only two wires coming out of it, but it usually has a complex integrated circuit inside its container ( package ). Its properties self-adjust in a manner that compensates for changes in room 

A constant current diode (lower left of Fig. 14.11) also has two exterior wires but is more complex inside. It changes resistance according to the current passing through it, within reasonable limits, which tends to keep the current constant. (More in Chapter 18.) It is used to make sawtooth waves (see index) with straight ramps, instead of the otherwise exponential voltage buildups. 

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This technique can be applied at a range of gate biases and plotted as a function of channel charge density, gate voltage, or applied lateral electric field. Non-linear models have been proposed for the contact resistance as a function of the applied bias (see, for example, [ffS]), which generally assume a Schottky or other diode-like charge injection from the contact into the channel. The transfer line method can also be used to extract a purely empirical model. 

The speetrum of the emission from the APDs extends from 600 to 1,000 nm [299]. Therefore, decoupling often cannot be achieved by filters. The only way to get reasonable results is with a carefully designed optical system. Features to be strictly avoided are lenses focusing the emission of one diode into the other, and glass surfaces reflecting the emission into the other diode, as shown in Fig. 5.106. 

According to the structural FSM in Table 8.5, a faulty diode D4 also affects ARR residual r. However, the impact on is negligible (Fig. 8.44b). A residual fa 7 0 does not permit to conclude that diode D4 is faulty. It could also be the other diode Di in leg a that causes residual ra to produce values significantly different from zero. A fault in one of the two diodes in a leg of the rectifier can be detected but cannot be isolated with the given sensors. 

Shottky Diodes. All diodes require at least a small forward bias voltage in order to work. Shottky diodes are fabricated by using a metal-to-semiconductor junction rather than the traditional dual semiconductor p-n junction used with other diodes. Such a construction allows Shottky diodes to operate with extremely low forward bias. 

The supplanting of germanium-based semiconductor devices by shicon devices has almost eliminated the use of indium in the related ahoy junction (see Semiconductors). Indium, however, is finding increased use in III—V compound semiconductors such as indium phosphide [22398-80-7] for laser diodes used in fiber optic communication systems (see Electronic materials Fiber optics Light generation). Other important indium-containing semiconductors include indium arsenide [1303-11-3] indium antimonide [1312-41 -0] and copper—indium—diselenide [12018-95-0]. 

Lasers having wavelengths ranging from the deep uv to the near infrared have been used in Raman spectroscopy. In industrial laboratories, the most common laser is the Nd YAG operating at 1.06 pm. Increasingly, diode lasers or other lasers operating in the 750—785-nm region are encountered. These... 

Fig. 11. Schematic diagram of semiconductor diode laser where the junction is ca 1 ]lni. Other dimensions are <1 mm.

The relevance of photonics technology is best measured by its omnipresence. Semiconductor lasers, for example, are found in compact disk players, CD-ROM drives, and bar code scaimers, as well as in data communication systems such as telephone systems. Compound semiconductor-based LEDs utilized in multicolor displays, automobile indicators, and most recendy in traffic lights represent an even bigger market, with approximately 1 biUion in aimual sales. The trend to faster and smaller systems with lower power requirements and lower loss has led toward the development of optical communication and computing systems and thus rapid technological advancement in photonics systems is expected for the future. In this section, compound semiconductor photonics technology is reviewed with a focus on three primary photonic devices LEDs, laser diodes, and detectors. Overviews of other important compound semiconductor-based photonic devices can be found in References 75—78. 

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