Intrinsic and extrinsic semiconductor materials

Semiconductor materials have a huge role in modern technology. The discovery of semiconductor materials has changed our daily life. Almost all electronic devices we use are made of the semiconductors. In this article, we are going to discuss the properties, examples of semiconductor material, intrinsic and extrinsic type of semiconductor material, n-type and p-type semiconductors etc.

Contents in this article:

  • What is a Semiconductor?
  • Examples of Semiconductors
  • Properties of semiconductors
  • Intrinsic Semiconductors
  • Extrinsic Semiconductors
  • Difference between intrinsic and extrinsic semiconductors
  • n type semiconductor
  • p type of semiconductor
  • Differences of n-type and p-type semiconductor
  • Applications of Semiconductor materials
  • Some questions and answers

What is a Semiconductor?

On the basis of the conductivity, there are four types of substances – Conductors, Insulators, Semiconductors and Superconductors. Semiconductors are the type of material having the conductivity greater than the insulators but less than that of the conductors.

Examples of semiconductor materials:

Silicon (Si), Germanium (Ge) are two most common semiconductors. Apart from these, there are some compound semiconductors like Gallium Arsenide (GaAs), Indium Phosphide (InP), Indium Arsenide (InAs) etc.

Properties of Semiconductors:

All the properties of a semiconductor are as the followings-

  1. Semiconductors have four valence electrons. They belong to Group-IV in periodic table. In a Semiconductor crystal each of the atoms forms four covalent bonds with four nearest neighboring atoms by sharing the valence electrons of opposite spin.
  2. At absolute zero temperature (0 K) semiconductors behave like perfect insulators. That means at absolute zero temperature semiconductors have almost zero conductivity.
  3. If we increase the temperature, Conductivity of semiconductors increases. Thus, the increase in temperature causes the decrease in resistance or resistivity of the semiconductors.
  4. Semiconductors have two types of carriers – electrons and holes. Holes are the positively charged carriers and actually are the absence of electrons.

Intrinsic semiconductor

One can define intrinsic semiconductor as a pure semiconductor i.e. the semiconductor without any impurity.

  1. Intrinsic semiconductors are the pure semiconductors. There is no doping in intrinsic semiconductors.
  2. The concentration of electrons and the concentration of holes are same in an intrinsic semiconductor.
  3. Conductivity of intrinsic semiconductor is lower than that of an extrinsic semiconductor.

Extrinsic semiconductor

One can produce extrinsic semiconductor by doping the intrinsic semiconductor with impure atoms. The process of mixing impure atoms in intrinsic semiconductor is known as doping. Extrinsic semiconductors have some specific properties as followings –

  1. Extrinsic semiconductors are impure semiconductors. This type of semiconductor is formed by doping impure atoms with pure or intrinsic semiconductor.
  2. Electron and hole concentration differ depending upon the nature of impure atoms.
  3. Conductivity of extrinsic semiconductors is much higher than that of intrinsic one.

Extrinsic semiconductor examples

Aluminum doped Silicon, Arsenic doped Silicon, Boron doped Silicon, Aluminum doped Germanium, Boron doped Germanium, etc. are the examples of extrinsic semiconductors.

Difference between intrinsic and extrinsic semiconductors

Intrinsic SemiconductorExtrinsic Semiconductor
1. Intrinsic semiconductors are the pure semiconductors.1. Extrinsic semiconductors are the doped impure semiconductors.
2. Electron concentration and hole concentration are equal.2. Electron concentration and hole concentration are not equal.
3. Conductivity of intrinsic semiconductor is relatively low.3. Conductivity of extrinsic semiconductor is higher than intrinsic one.
Difference between intrinsic and extrinsic semiconductors

n and p type of semiconductor

On the basis of doping impurities there are two types of Extrinsic Semiconductors – n-type and p-type extrinsic semiconductors.

n type of semiconductor

n-type semiconductor (or donor type semiconductor) can be formed by doping pentavalent atoms like Arsenic (As), Phosphorus (P), Antimony (Sb) etc. in an intrinsic semiconductor crystal.

Pentavalent atoms have four valence electrons. At the time of doping of semiconductor with pentavalent atoms, four valence electrons of each pentavalent atom form four covalent bonds with four valence electrons of four nearest neighboring silicon atoms. Now, there will be an extra unpaired electron (fifth electron) of pentavalent atom in the semiconductor crystal. This fifth electron helps to increase the concentration of electron in semiconductor crystal even at room temperature. The doping concentration is about one impurity atom per ten lakhs (106) semiconductor atoms. Therefore, electron concentration becomes very high and thus the conductivity of the crystal becomes very high, even at room temperature.

n-type semiconductor examples: Arsenic doped Silicon, Phosphorus doped Silicon, Arsenic doped Germanium, etc. are the examples of n-type semiconductors.

p type of semiconductor

p-type semiconductor (or acceptor type semiconductor) can be formed by doping trivalent atoms like Boron (B), Aluminum (Al), Gallium (Ga), Indium (I) etc. in an intrinsic semiconductor crystal.

Trivalent atoms have three valence electrons. At the time of doping trivalent atoms in pure semiconductor (like Si), three valence electrons of trivalent atom form three covalent bonds with three valence electrons of three nearest neighboring silicon atoms. Now, there is an absence of electron in trivalent atom to form the fourth covalent bond with the electron of its fourth neighboring silicon atom. So, there will be an extra hole (absence of electron) in the semiconductor crystal. This hole will increase the concentration of positive charge in the crystal. Therefore, large number of impure trivalent atoms will give large number of extra holes in the crystal to increase the hole concentration to a high value. In this way we can get high conductivity of semiconductor by doping trivalent impurity atoms in it, even at room temperature.

p-type semiconductor examples: Aluminum doped silicon, Boron doped silicon, Aluminum doped germanium, etc. are the examples of p-type semiconductors.

Difference between n type and p type semiconductors

  n-type semiconductor  p-type semiconductor
1. To get n-type semiconductor we need to dope Pentavalent atoms in intrinsic Semiconductor.
2. Majority Carriers in n-type semiconductor are negatively charged electrons.
3. Minority carriers in n-type semiconductor are holes.
4. n-types are also called donor type semiconductors.  
1. To get p-type semiconductor we need to dope Trivalent atoms in Intrinsic Semiconductor.
2. Majority carriers in p-type semiconductor are positively charged Holes.
3. Minority carriers in p-type semiconductor are electrons.
4. P-types are also called acceptor type semiconductors.
Difference between n-type and p-type semiconductors

Applications of semiconductor material

In modern days, semiconductor materials have huge applications. Modern technology is based on semiconductors. Semiconductor materials have the uses in all the electronic devices like Mobiles, Computers, LED TVs, Solar Panels, electronic watches, self-controlled cars, 3D painting machines etc. Semiconductor materials are also used in control system to control Robots, Trains etc.

What is a hole? How does it form?

Holes are the absence of electrons. If there is any absence of electron in a place, a hole arises at that place. So, holes are positively charged particles.

If we heat a semiconductor crystal, two electrons in a covalent bond become free. If one of these electrons reaches to conduction band from the valence band by getting the required energy, an absence of electron or Hole appears in valence band. Thus, in the position of covalent Bond ‘electron-hole pair’ appears.

Both of the free electron in conduction band and the hole in valence band conducts current.

Why the Conductivity of semiconductors increases with increase in temperature?

If we increase the temperature of a semiconductor, free electrons and holes are produced by breaking the covalent bonds. Both of the free electrons in conduction band and holes in valence band carry current. Thus, the conductivity of semiconductors increases with the increase in temperature.

Are the n-type and p-type semiconductors positively and negatively charged?

No, n-type semiconductor and p-type semiconductors are not positively and negatively charged respectively. It is true that n-type semiconductor has electron concentration greater than hole concentration, but total number of electrons and protons in the crystal are equal. In n-type semiconductors we have free electrons, but it does not mean that n-type is negatively charged. Similarly, for p-type semiconductor hole concentration is greater than electron concentration, but total number of electrons and protons are equal in the entire crystal.

How the holes move in valence band to carry current?

Holes are the absence of electrons. When a vacant appears at some point, a hole appears at that point . Now, an electron comes from neighboring bond to fill that vacant. As the neighboring electron comes to fill that vacant, it creates the vacant or hole in that neighboring bond. Then it looks like the hole moves from first bond to its neighboring bond. This is a continuous process i.e. the same phenomena occur for other bonds too in a chain way. So, holes are not moving, electrons are moving one place to another to fill the vacant and looks like the holes are moving.

“At very high temperature Extrinsic Semiconductor behaves like an Intrinsic Semiconductor”- Explain it.

In n-type semiconductor, electron concentration is larger than the hole concentration. Again, in p-type semiconductor, hole concentration is larger than the electron concentration. Now, if we increase the temperature of the semiconductor, then one electron and one hole appears by breaking each covalent bond. At very high temperature, a large amount of covalent bonds get broken and the appeared electron and hole numbers becomes so large that the difference between the electron and hole concentration becomes negligible. Thus, at very high temperature the concentration of electrons and holes becomes nearly equal. Hence we can call the extrinsic semiconductor an intrinsic one at the high temperature.

This is all from this article on the intrinsic and extrinsic semiconductor material. If you have any doubt or query on this topic feel free to ask me in the comment section.

Thank you!

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