Semiconductor Devices and Circuits, Applications - Electrical C & V


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03 April 2020

Semiconductor Devices and Circuits, Applications

What is a semiconductor?

A Semiconductor is a substance whose electrical properties lie between Conductors and Insulators. Germanium and silicon are the most popular examples of these substances.
According to the energy band assumption, semiconductor materials at room temperature are those that:

Semiconductor Devices and Circuits, Applications

1. The conduction and connective bands are partially filled.

2. Those between which the Forbidden energy band is very narrow is about one electron volt, for example, it is 0.75 electron volts for germanium and about 1.12 electron volts for silicon.

Special properties of semiconductor

1. The electrical conductivity of semiconductors increases with increasing heat, which is why the resistance heat coefficient of semiconductors is negative.

2. Many other useful properties are also seen in semiconductors, such as the flow of current in one direction more easily than the other direction i.e. the differing conductivity in different directions.

3. In addition, the conductivity of semiconductors can be reduced or increased by adding controlled amounts of impurities.

4. The process of mixing these impurities is called doping. Electronic devices (diodes, transistors, etc.) are made by doping.

5. Their conductivity can also be changed by an electric field or light applied from outside.

Type of semiconductor

There are two types of semiconductors -

1. Intrinsic Semiconductor

A semiconductor in which no impurities or impurities are found is called a Intrinsic semiconductor. Thus pure germanium and silicon are natural semiconductors in their natural state.

2. Extrinsic Semiconductor

The electrical conductivity of individual semiconductors is very low. But if a small amount of a substance with a valency of 5 or 3 is mixed as an impurity in pure germanium or silicon crystal, the conductivity of the crystal increases considerably.

The process of mixing is called doping. Such impure semiconductors are called external semiconductors.

There are two types of Extrinsic semiconductors -

1. n-type semiconductor (n-type semiconductor)

Semiconductor Devices and Circuits, Applications
N-type Semiconductor

When a germanium or silicon crystal with five valence atoms is added, it removes one atom of germanium and replaces it.

Out of the five valence electrons of the non-atom, 4 electrons form covalent bonds with one valence electron each of the four atoms of germanium. The 5th valence electron separates from the atom of the impervious and begins to move freely within the crystal.

It acts as an electron and charge carrier. Thus by adding impurities to pure germanium, the number of free electrons increases i.e. the conductivity of the crystal increases.

This type of impure germanium crystal is called n-type semiconductor because the charge carriers (free electrons) in it are negative. The non-atom atoms are called donor atoms, atoms because they provide the driving electrons to the crystal.

2. p-type semiconductor 

Semiconductor Devices and Circuits, Applications
P-Type Semiconductor
If a valence atom with three valencies is added to a germanium or silicon crystal, it also replaces a germanium atom. Its three valence electrons form covalent bonds with one valence electron each of the three nearest germanium atoms.

While the fourth valence of germanium is unable to form an electron bond. Therefore, there is a blank space on one side of the non-atom in the crystal, which is called Hole.

Applying an external electrical field brings an electron bound to the neighboring germanium atom into the coater, leaving a space in the neighboring atom to form the coater.

Thus the coater starts moving from one place to another in the opposite direction of the electric field within the crystal. Clearly, the coater is like a positively charged particle which moves in the opposite direction relative to the electron.

Germanium crystals found in this type of non-residue are called p-type semiconductors because the charge carriers are positive. Inelastic atoms are called receptor atoms because they take electrons from pure semiconductors.

Examples of semiconductor devices

1. p-n junction diode

The p-n connector diode is a basic semiconductor device. It is a semiconductor crystal with an excess of acceptor effluent in one region and an excess of donor impurities in another region. These regions are called p-regions and n-regions respectively and the boundary between these regions is called p-n pact.

2. Light Emitting Diodes: LED 

There is a device that converts the electrical energy of a biasing battery into radiation energy. It is a p-n pact that is more adulterated than normal p-n treaties.

It is also used for making burglar alarms, for entering information into optical computer memory, displaying the numerical display of computers and calculators, and remote control of television.

3. Photo Diode

It is a device used in the detection of optical signals. The photo diode is a p-n joint made of a photosensitive semiconductor based on the effect of incident light on the joint.

This diode is used to read light-operated keys, computer, etc.

4. Transistor

It is an electronic key device made of p and n type semiconductors that is used in place of a triode valve. Transistors are used in many ways.

It is used as amplifier, switch, voltage regulator (regulator), signal modulator (signal modulator), oscillator etc.

Advantages of semiconductor devices

1. Since semiconductor devices have no filament, no power is required to heat them due to the emission of electrons.

2. Since no heating is required, semiconductor devices begin to operate immediately when the circuit is switched on.

3. Semiconductor devices require lower voltage operation than vacuum tubes.

4. Semiconductor devices are cheaper than vacuum tubes. Semiconductor devices have an almost unlimited life.

Disadvantages of semiconductor devices:

1. Noise levels are higher in semiconductor devices than vacuum tubes.

2. Ordinary semiconductor devices cannot bear more power than vacuum tubes.


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