Visual Display Units (VDUs): Large arrays of characters can be built up using alphanumeric devices, already discussed, but the number of connections and the complexity of the drive-logic circuitry increase significantly, although large-scale integrated (LSI) circuits can be employed for this purpose. A versatile alternative to an array of individual devices is the CRT and …
Cold Cathode Display or Nixie Tube – Operation and Characteristics: These are the most well known type of alphanumeric displays. They operate on the basis of emission of light in a cold cathode gas filled tube under breakdown condition. These are also known as neon or gas-discharge displays. The Nixie tube is a numeric indicator …
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Heterojunction Lasers – Definition, Construction, Working, Advantages, Disadvantages and Applications: The device described in previous section was the first type employed in the early development of semiconductor lasers. It is known as an homojunction laser because it contains only one junction in a single type of material. Multiple layers have to be built-up in the …
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Light Emitting Materials: Since the eye is only sensitive to light of energy hf ≥ 1.8 eV (~ 0.7 μm), semiconductors of interest must have energy band gaps larger than this limit. The band gaps of different binary compound Light Emitting Materials semiconductors are illustrated in Fig. 25.4. A large variation exists in photon energy between …
IR Emitters or Infrared-emitting diodes: IR Emitters or Infrared-emitting diodes are solid-state gallium arsenide devices that emit a beam of radiant flux when forward biased. Fig. 25.53 depicts the basic construction of the device. When the junction is forward biased, electrons from the N-region will recombine with excess holes of the P-material in a specially …
Photoemissive cells or Tubes – Working Principle and Types: These Photoemissive cells or Tubes devices are basically of two types namely vacuum type and gas filled type. 1. Vacuum Type Photocell (or Phototube): This device essentially consists of a thin metal curved sheet with its concave surface coated with Photoemissive cells material forming the cathode and …
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Avalanche Photodiode – Definition, Basic Structure and Workings: The avalanche photodiode is similar to the P-N or PIN photodiode except that it is operated at high reverse-bias voltages so that impact ionization occurs, EHPs are created in the space charge region by photon absorption. Also additional EHPs are created by photon generated electrons and holes …
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Pin Photodiode – Definition, Working and Applications: The PIN photodiode is one of the most common photodetectors, since the depletion-region thickness (intrinsic layer) can be tailored to optimize the quantum efficiency and the frequency response. The Pin Photodiode is depicted in Fig. 25.26(a). It consists of a P region and an N region separated by …
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Light Dependent Resistors (LDRs) – Definition, Construction, Workings and Applications: Light dependent resistors (LDRs) are made from cadmium sulphide containing no or very few free electrons when not illuminated. Its resistance is then quite high. When it absorbs light, electrons are liberated and the conductivity of the material increases. Cadmium sulphide (CdS) is, therefore, a …
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Photodetectors – Definition and Applications: Photodetectors are the semiconductor devices that can detect optical signals through electronic processes. The extension of coherent and incoherent light sources into the far-infrared region on one hand and the ultraviolet (UV) region on the other has enhanced the requirement for high-speed, sensitive photodetectors. A general photodetector has basically three …