What is Semiconductor?

We know that substances that conduct electricity are called conductors (such as copper and gold), and those that do not conduct electricity are called insulators (such as wood and glass). But there are some substances whose electrical conductivity falls between the conductors and insulators they are called semiconductors.

These types of substances are found in Group-14 of the Periodic Table. Elements like Germanium(Ge), Silicon(Si), and Gallium Arsenide(GaAs) are examples of semiconductors. Silicon is mostly used in the electronic circuit for fabrication and gallium arsenide is used in LEDs, solar cells, laser diodes, etc.

At absolute zero temperature (0K), there are no free electrons in the pure semiconductors. As a result, they act as a bad conductor of electricity at this temperature. In this state, each atom is strongly bound in its covalent bond with the surrounding atom. So there are no free electrons in the semiconductor at low temperature.

But when the temperature rises and the semiconductor is heated to room temperature, the thermal excitation breaks the covalent bonds of several atoms. As a result, a number of electrons are released from the bond and move freely in the crystal. In this condition the electrical conductivity of the semiconductor increases.

The higher the temperature of the semiconductor, the more covalent bonds are broken and free electrons are formed. As a result, the electrical conductivity of the semiconductor increases with increasing temperature. That is, the resistance of the semiconductor decreases with increasing temperature.

The electrical conductivity of the semiconductor is significantly increased when a very small amount of suitable impurities is mixed with the semiconductor in a special way. The process of mixing these impurities with semiconductors is called doping.

Know more about the Band Theory of Semiconductors, and Charge Carriers in Semiconductors (such as holes, and electrons).

Types of semiconductors

There are two types of semiconductors: Pure or Intrinsic Semiconductors and Impure or Extrinsic Semiconductors.

Pure or Intrinsic Semiconductors

Definition: Semiconductor obtained in a pure state is called Pure or Intrinsic Semiconductors. In this type of semiconductor, the number of free electrons and holes is equal and the movement of these free electrons and holes in opposite directions creates an electric current.

At absolute zero temperature, such semiconductors have no free electrons, their conductivity is zero at that temperature and they act as ideal insulators. The number of free electrons in such semiconductors is very low. So the electricity generated in this semiconductor is not usable.

For example, the magnitude of current flowing through pure germanium (Ge) crystals is less than a few microamperes(10-6A). In the case of pure silicon, the magnitude of this electric current is much lower, approximately a few nano amperes(10-9A).

Impure or Extrinsic Semiconductors

Definition: The electrical conductivity of pure semiconductors is multiplied, by systematically adding very small amounts of special impurities. The new type of semiconductor that is formed as a result of mixing special impurities is called Impure or Extrinsic Semiconductors.

The process by which impurities are mixed is called doping. There are different ways of doping like Diffusion, Ion implantation, etc. However, the electrical conductivity of impure semiconductors is higher than that of pure semiconductors. Few milliampere currents(10-3A) can easily pass through the impure semiconductor.

Depending on the type of impurities, there are two types of Impure or Extrinsic Semiconductors: N-Type Semiconductors and P-Type Semiconductors. Know more ...

Applications of semiconductors

We cannot think of the world without electronic devices (such as mobile phones, laptops, refrigerators, etc.). In all these devices we use semiconductor components (such as diodes, transistors, MOSFETs, ICs, etc.) which are made of semiconductor materials.

Microcontrollers/Microprocessors are such systems that revolutionized the world. These systems used nano transistors ( semiconductor components ) that act as smart switches in the systems.

There are many diodes made of semiconductor material that consume light energy to produce an electric current. For example Photodiodes (solar cells ).

There are many diodes made of semiconductor material that consumes electric current and emit light. For example LEDs.

So, semiconductors play a very important role in our daily life.