What is Semiconductors? Fundamentals of Semiconductors

What is a semiconductor?

The semiconductor has a huge impact on our everyday life. Semiconductors are used in a microprocessor, microcontroller and in almost every electronics equipment semiconductors are used. So it is very important to know the concept of the semiconductor.

A semiconductor is in between conductor and insulator, which means semiconductor is neither a good conductor nor an insulator. In semiconductor doping impurities are added. Silicon, germanium are examples of semiconductors. Semiconductors are used in the development of electronic chips, computing components, and devices. Silicon is widely used in semiconductor material development. So you can say that silicon is the heart of every electronic device.

Semiconductors are created after adding impurities in the element. 

Band Diagram Of Semiconductor

In Semiconductor there is small band gap smaller than the conductor so a flow of current is very less. There are free electrons in valence band when the temperature is increased free electrons of valence band moves toward conduction band and generate an electron-hole pair. So current is flow.

Types of semiconductor

1)Intrinsic semiconductor

2)Extrinsic Semiconductor 

What is Intrinsic Semiconductor?

The intrinsic semiconductor is pure semiconductor which means an intrinsic conductor doesn’t have any impurities. Each atom of silicon and germanium share electron with their neighbor. As shown in the above diagram sharing of the electron makes a covalent bond. when a covalent bond is broke electron and hole pair is generated. To remove the valence electrons from the outer shells require 1.1eV. When an electron is moved from one covalent bond to other covalent bond vacancy is created in a covalent bond. This vacancy is called the hole. A hole is filled by any other electron. Hole have positive charge carriers. The direction of holes is opposite to the direction of the electron. In this Intrinsic semiconductor holes and electrons are moved in a random direction but Number of electrons and holes are remaining same.

What is Extrinsic Semiconductor?

Extrinsic Semiconductors are not pure some impurities are added in the semiconductor is called as an extrinsic semiconductor. Depending on the Doping level Extrinsic Semiconductors are classified as:

1)N-Type Semiconductor

2)P-Type semiconductor

N-Type Semiconductor:-

When Pentavalent impurities are added in pure semiconductors then it is said to be an N-Type Semiconductors. Arsenic, Phosphors are an example of the pentavalent impurities. Pentavalent impurities have 5 valence electron. Pentavalent impurities are also known as donor impurities.

Let’s take one example suppose in silicon pentavalent impurity phosphors are added. Silicon atom has 4 valence electron on other side phosphors have 5 valence electron. So all 4 valence electrons of phosphors are made a pair with each 4 valence electrons of silicon and make a covalent bond. One electron of phosphors atom cannot able to make a covalent bond because silicon atom has only four valence electron. So this remaining electron of phosphors is free to move and not attached to the parent atom as shown in below figure.

Conduction in the N-type semiconductor.

As shown in below figure when a voltage is applied across the n-type semiconductor material. Free electrons are moved toward the positive terminal of the battery and holes are moves toward the negative terminal of the battery.

In the N-Type semiconductor, conduction takes place due to the large no of free electrons. In n-type semiconductor number of free electrons are more than the number of holes. So electrons are majority carrier and holes work as minority carrier. 

P-Type Semiconductor:-

When a trivalent impurity is added in the pure semiconductor then it is said to be a p-type semiconductor. All trivalent impurities are called as acceptor impurities. Gallium, boron, indium are an example of trivalent impurities.

Now let’s consider boron is added in silicon atom. Silicon has a 4 valence electron on other side boron have 3 valence electron. So each 3 valence electrons of boron make a covalent bond with the 3 silicon atoms. So in a fourth covalent bond, one valence electron of silicon is remaining, which results in a shortage of one electron. The missing electron is called a hole. This shows that each boron atom is Accept one electron from silicon atom to fill the hole which is called as acceptor impurities.

Conduction in P-Type Semiconductor

As shown in below figure when a voltage is applied across the p-type semiconductor holes in the valence band move towards the negative terminal of the battery. Free electrons are a move towards the positive terminal of the battery.

In the P-Type semiconductor, conduction takes place due to the large no of Holes. In P-type semiconductor number of holes are more than the number of free electrons. So holes are majority carrier and free electrons work as minority carrier.

Properties of Semiconductors
  • Electrical Conductivity
  • High no of Excited electrons
  • Vey High thermal conductivity
  • Light Emission
  • Heterojunctions
  • Efficient Thermal energy conversion 
  • Photo Conductivity