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Semiconductor Devices

According to the band theory of solids, semiconductors are defined as substances that have the forbidden energy gap in the region of 1.1 eV (electron-volt). They have conductivity value lying between that of an insulator and a conductor. This means they are neither good conductors nor good insulators. Semiconductors are widely used in manufacturing electronic devices.

Semiconductor devices are electronic devices that use the properties of a semiconductor in their operations. Semiconductor devices have replaced vacuum tubes in most of the devices. They give better performance than a vacuum tube. This is because semiconductor devices conduct electricity in a solid-state rather than a thermionic state, as is the case in a vacuum tube.

Semiconductors can be used to make single devices or integrated circuit (IC) chips. These chips could be made up of as many as a billion different interconnected devices. The chips are manufactured on a single semiconductor wafer, which is also called the substrate.

The performance of a semiconductor device can be improved by means of a process called doping. Doping refers to the introduction of certain impurities in a semiconductor. These impurities help in the generation of ‘holes’ in the semiconductor. Holes are vacancies in the valence band. Holes are responsible for the flow of electricity in a semiconductor. The conductivity of a semiconductor can be controlled by the introduction of an electric or magnetic field. This can also be achieved by exposing the semiconductor to light or heat. This helps in stabilizing the flow of current in a semiconductor.

You may also want to know if copper is a semiconductor or not. 

History

Semiconductors were used in the electronics field well before the invention of the transistor. They were then used as detectors in radios. In the early part of the twentieth century, Jagdish Chandra Bose invented a device called ‘Cat’s Whisker’. It was a kind of detector. The working of this device proved to be very problematic. The device worked by moving a small tungsten filament (called ‘Cat’s Whisker’) around the surface of galena or carborundum until the whisker picked up signals. Then after a few hours or a few days, the detector would lose the signal. Then the process would have to be repeated again. The device made by Bose is an early example of a Schottky diode.

When World War II began, the radar receivers were still using vacuum tubes. The war pushed the radar receivers to work with higher and higher frequencies. At that time, Cat’s Whisker was used again as a receiver and worked much better than the vacuum tubes. This led to renewed research in the field of semiconductors. Furthermore, led to the invention of the first diode.

A diode is a simple device made up of two semiconductors separated by a thin strip of a conductor. Semiconductors on both sides are doped. This allows for the current to pass only in one direction. This simple device has found many uses in electronics. The unidirectional nature of the current is due to the formation of a depletion region near the thin conductor strip.

Types of semiconductor devices

  • A diode is the simplest semiconductor device. It simply consists of two different types of semiconductors separated by a thin strip of a conductor. On one side is a p-type semiconductor; on the other side, an n-type semiconductor. This is called a p-n junction diode. At their junction, a depletion area is formed. This depletion area stops the current from flowing. To make electricity flow in the diode, the diode is put in a forward bias. Forward bias means the p part of the semiconductor is at a higher potential than the n part. This causes the depletion region to become small, and conduction can take place. It is called reverse bias when the n part is at a higher potential than the p part. In reverse bias, the depletion region becomes larger, and the conduction stops.

  • Diodes have several uses. Among many of their uses, they are used to convert small AC currents to DC currents.
     
    • A transistor is perhaps the most important semiconductor device ever invented. The first transistor was invented by John Bardeen, Walter Houser Brattain, and William Bradfield Shockley. They were awarded the 1956 Nobel prize for this invention. The word transistor is made up of the words ‘transconductance’ and ‘varistor’.

    • A transistor is formed from two p-n junctions. This can either be a p-n-p junction or an n-p-n junction. The middle region is very narrow. The other regions are called emitters and collectors. The passage of a small current through the base and emitter changes the device's property, and it can conduct current even in reverse bias. The base emitter current controls this current.
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