semi conductor devices

Semiconductor Devices:-

Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices (vacuum tubes) in most applications.

There are two basic groups or classifications that can be used to define the different semiconductor types:

Intrinsic material: An intrinsic type of semiconductor material made to be very pure chemically. As a result it possesses a very low conductivity level having very few number of charge carriers, namely holes and electrons, which it possesses in equal quantities.

Extrinsic material: Extrinisc types of semiconductor are those where a small amount of impurity has been added to the basic intrinsic material. This ‘doping’ uses an element from a different periodic table group and in this way it will either have more or less electrons in the valence band than the semiconductor itself. This creates either an excess or shortage of electrons. In this way two types of semiconductor are available: Electrons are negatively charged carriers.

N-type: An N-type semiconductor material has an excess of electrons. In this way, free electrons are available within the lattices and their overall movement in one direction under the influence of a potential difference results in an electric current flow. This in an N-type semiconductor, the charge carriers are electrons.

P-type: In a P-type semiconductor material there is a shortage of electrons, i.e. there are ‘holes’ in the crystal lattice. Electrons may move from one empty position to another and in this case it can be considered that the holes are moving. This can happen under the influence of a potential difference and the holes can be seen to flow in one direction resulting in an electric current flow. It is actually harder for holes to move

than for free electrons to move and therefore the mobility of holes is less than that of free electrons. Holes are positively charged carriers.

Advantages of Semiconductor Devices

 As semiconductor devices have no filaments, hence no power is needed to heat them to cause the emission of electrons.

 Since no heating is required, semiconductor devices are set into operation as soon as the circuit is switched on.

 During operation, semiconductor devices do not produce any humming noise.

 Semiconductor devices require low voltage operation as compared to vacuum tubes.

 Owing to their small sizes, the circuits involving semiconductor devices are very compact.

 Semiconductor devices are shock proof.

 Semiconductor devices are cheaper as compared to vacuum tubes.

 Semiconductor devices have an almost unlimited life.

 As no vacuum has to be created in semiconductor devices, they have no vacuum deterioration trouble.

Disadvantages of Semiconductor Devices

 The noise level is higher in semiconductor devices as compared to that in the vacuum tubes.

 Ordinary semiconductor devices cannot handle as more power as ordinary vacuum tubes can do.

 In high frequency range, they have poor responder.

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