Physics

Semiconductors

Definition of Semiconductors:

All the materials that act as electric conductors (such as copper, aluminum, etc.), as well as insulators (such as glass, plastic, etc.), are called semiconductors. In other words, the materials whose electric conductivity falls between a conductor and an insulator are called semiconductors, eg. silicon, germanium, arsenic, gallium, etc. Most semiconductors are crystals made of certain materials, most commonly silicon.

 Semiconductor:

Properties of Semiconductors:

Semiconductors resistivity falls as its temperature rises, due to which the resistance temperature coefficient of semiconductors is negative. The conductivity of semiconductors can be increased or decreased by adding a controlled amount of impurities. The process of mixing these impurities is called ‘doping’. Electronic devices (diodes, transistors, etc.) are made only by doping. Their conductivity can also be changed by an externally applied electric field or light.

Types of Semiconductors:

There are two main types of semiconductors;

1. Intrinsic (pure) Semiconductor:intrinsic Semiconductor:

Semiconductors without impurities are called intrinsic semiconductors. An intrinsic (pure) semiconductor, also called an undoped semiconductor or i-type semiconductor is a pure semiconductor without any significant dopant species present. Thus pure germanium and silicon are their own semiconductors in their natural state.

2. Extrinsic Semiconductor:

Extrinsic semiconductors have very low electrical conductivity. But if a very small amount of a substance having valency 5 or 3 is mixed as an impurity in pure germanium or silicon crystal, then the conductivity of the crystal increases significantly. Extrinsic semiconductors are doped with specific impurities. The impurity modifies the electrical properties of the semiconductor and makes it more suitable for electronic devices such as diodes and transistors.

There are two types of extrinsic semiconductors:

1) n-type Semiconductor:

When a pure semiconductor (Silicon or Germanium) is doped by pentavalent impurity (P, As, Sb, Bi) then it replaces one of the germanium atoms. Four out of the five valence electrons of the valence atom form covalent bonds with one valence electron each of the four germanium atoms located around them. The 5th valence electron dissociates from the atom of the precipitant and moves freely within the crystal. This free electron acts as a charge carrier. Thus adding adsorbent to pure germanium increases the number of free electrons i.e. increases the conductivity of the crystal.

Such types of semiconductors are called n-type semiconductors because the charge carriers (free electrons) in them are negative. The impurity atoms are called donor atoms because they provide conducting electrons to the crystal.

Extrinsic Semiconductor

p-type semiconductor

When a pure semiconductor (like germanium or silicon) is doped with a trivalent impurity (B, Al, In, Ga ) then, the three valence electrons of the impurity bond with three of the four valence electrons of the semiconductor. Whereas the fourth valence electron of germanium cannot form a bond. Therefore, a blank space is left on one side of the impurity atom in the crystal, which is called a hole. When an external electric field is applied an electron bound to the neighboring germanium atom comes into the coater, thereby vacating space in the neighboring atom to form the coater. Thus the coater moves from one place to another within the crystal in the opposite direction of the electric field. It is clear that the coater is equivalent to a positively charged particle that moves in the opposite direction with respect to the electron.

Such types of semiconductors are called p-type semiconductors because the charge carriers in it are positive. Improper atoms are called receptor atoms because they accept electrons from a pure semiconductor.

Uses of Semiconductors:

Semiconductors are used in the manufacturing of various kinds of electronic devices, including diodes, transistors, and integrated circuits. Such devices have found wide application because of their compactness, reliability, power efficiency, and low cost. Semiconductor devices can display a range of useful properties such as showing variable resistance, passing current more easily in one direction than the other, and reacting to light and heat.

Important Questions:

Question 1: What are semiconductors?

Answer :

All the materials whose electric conductivity falls between a conductor and an insulator are called semiconductors, eg. silicon, germanium, arsenic, gallium, etc. Most semiconductors are crystals made of certain materials, most commonly silicon.

Question 2: What are the main properties of semiconductors?

Answer:

a) Most semiconductors are crystals made of certain materials, most commonly silicon.

b) Semiconductors resistivity falls as its temperature rises, due to which the resistance temperature coefficient of semiconductors is negative.

c) The conductivity of semiconductors can be increased or decreased by adding a controlled amount of impurities.

d) Semiconductors conductivity can also be changed by an externally applied electric field or light.

Question 3: What are the main types of semiconductors?

Answer:

There are two main types of semiconductors?

  1. Intrinsic (pure) semiconductor
  2. Extrinsic (pure) semiconductor

Question 4: What is an intrinsic (pure) semiconductor?

Answer:

Semiconductors without impurities are called intrinsic (pure) semiconductors. An intrinsic semiconductor also called an undoped semiconductor or i-type semiconductor is a pure semiconductor without any significant dopant species present.

Question 5: What is an intrinsic (pure) semiconductor?

Answer:

Extrinsic semiconductors are doped with specific impurities. The impurity modifies the electrical properties of the semiconductor and makes it more suitable for electronic devices such as diodes and transistors.

Question 6: What is an n-type semiconductor?

Answer:

When a pure semiconductor (Silicon or Germanium) is doped by pentavalent impurity (P, As, Sb, Bi) then it replaces one of the germanium atoms. Four out of the five valence electrons of the valence atom form covalent bonds with one valence electron each of the four germanium atoms located around them. The 5th valence electron dissociates from the atom of the precipitant and moves freely within the crystal. This free electron acts as a charge carrier. Such types of semiconductors are called n-type semiconductors because the charge carriers (free electrons) in them are negative.

Question 7: What is a p-type semiconductor?

Answer:

When a pure semiconductor like; germanium is doped with a trivalent impurity (B, Al, In, Ga ) then, the three valence electrons of the impurity bond with three of the four valence electrons of the semiconductor.Whereas the fourth valence electron of germanium cannot form a bond and a blank space is left on one side of the impurity atom in the crystal, which is called a hole. On applying an electric force an electron bound to the neighboring germanium atom comes into the coater, thereby vacating space in the neighboring atom to form the coater. Thus the coater moves from one place to another within the crystal in the opposite direction of the electric field. Such types of semiconductors are called p-type semiconductors because the charge carriers in them are positive.

Question 8: What are the main uses of semiconductors?

Answer:

Semiconductors are used in the manufacturing of various kinds of electronic devices, including diodes, transistors, and integrated circuits. Such devices have found wide application because of their compactness, reliability, power efficiency, and low cost. Semiconductor devices can display a range of useful properties such as showing variable resistance, passing current more easily in one direction than the other, and reacting to light and heat.

Related Articles

Leave a Reply

Your email address will not be published.

Check Also
Close
Back to top button

Adblock Detected

Please consider supporting us by disabling your ad blocker