What are Semiconductors and their types

In this article, we are going to focus on the very basic constituents of electronics – Semiconductors.

Unlike general electric circuits, in electronics we need controlled flow of electrons, i.e. controlled flow of current through the electronic circuits. So, here we cannot use metals like copper, aluminium, and silver. What we rather use are semiconductors. Let’s try to understand what these materials are.

Table of Contents

• What is a Semiconductor?
• Types of Semiconductors
• Types of External semiconductors
• What is a p-n Junction Diode?

What is a Semiconductor?

The name is self-explanatory. Semiconductor are those materials whose electrical conductivity at room temperature lies in between that of insulator and conductor.

We generally use three elements as semiconductors (in their crystalline form):

• Silicon (Si)
• Germanium (Ge)
• Grey tin (Sn)

Types of Semiconductors

There are basically two types of semiconductors:

• Intrinsic semiconductor: Semiconductor in extremely pure form.

• Extrinsic semiconductor or Doped semiconductor: As the name suggests, these are the impure form of semiconductors, which are obtained by doping the intrinsic semiconductor with measured small amount of chemical impurity.

But why do we need to make Extrinsic semiconductors?

That’s because Intrinsic semiconductors have a major drawback - The conductivity of an intrinsic semiconductor depends on its temperature. But in case of almost all semiconductors, their conductivity is very low at room temperature. This means that we cannot use them in most of our electronic devices, which more often than not work at room temperature.

For them to become better conductors at room temperature, we need to mix in some impurities in them.

So, what elements can work as these impurities?

The impurities may be:

• Trivalent element impurity, e.g. indium, boron, gallium or aluminum etc
• Pentavalent element impurity, e.g. phosphorous, arsenic, antimony, etc.

So, the semiconductors we often see in our electronic devices are extrinsic semiconductors. Let’s learn a bit more about them.

Types of External semiconductors

External semiconductors are basically of two types. It depends on the kind of impurities mixed in them.

• n-type semiconductor: It is an extrinsic semiconductor wherein electrons are the majority charge carriers, and holes are minority charge carriers. It is made by adding pentavalent element impurities in Ge and Si.
  

• p-type semiconductor: It is an extrinsic semiconductor wherein holes/voids are the majority charge carriers, and electrons are minority charge carriers. It is made by adding trivalent element impurities in Ge and Si.
  

We use n and p type semiconductors to form diodes. Let’s learn about them.

What is a p-n Junction Diode?

A p-n junction is formed when p-type and a n-type semiconductors are connected. A device containing such a junction is called p-n junction diode.

There’s a region between p-n junction wherein there are no charge carriers. This region is called Depletion Layer.

There’s a potential difference across this depletion layer, which acts as a barrier. The value of this potential difference depends on the type of semiconductor used, e.g. it’s 0.3 V for Ge and 0.7 V for Si.

Solar Cell

We all know what a Solar Cell is – it converts solar energy into electrical energy, using the phenomenon of photo voltaic effect. But do you know that a solar cell also uses a p-n junction. So basically, it’s also a semi-conductor device.