What are Holes?

Hint: There are two types of charge carriers in a semiconductor. A negative charge i.e electron and a positive charge i.e. hole. At a low temperature, the valence band of a pure semiconductor remains saturated and the conduction band remains completely empty. When the semiconductor gets a high temperature the concept of the occurring of the holes is generated. This concept has to be known for the given question. The number of electrons and holes are equal in a pure semiconductor.

Complete answer:
The substance in which the space between the valence band and conduction band is less than a conductor but greater than an insulator is called the semiconductor. Therefore, the electron of the valence band can reach the conduction band. The valence band of a semiconductor remains saturated and the conduction band remains empty at low temperature. At higher temperatures, when the electron reaches from the valence band to the conduction band there in the place of the electron the emptiness occurs. This absence of electrons is known as the holes.
Clearly, how much electron goes from the valence band that amount of holes are generated. That means the number of electrons and holes are equal.
In the crystal medium, the direction of motion of the holes is exactly opposite to that of electrons.
It is to be reminded that the hole is not a real particle. It is just a concept of the absence of an electron. Its charge is positive.

Note: The pure semiconductor is doped with a special type of substance to increase its conduction power. This type of semiconductor is called Impure or Extrinsic semiconductor. These semiconductors are of two types: n-type and p-type.
In an n-type semiconductor, the major carrier is negatively charged electron and the minor carrier is the positively charged hole.
In a p-type semiconductor, the major carrier is the positively charged hole and the minor carrier is the negatively charged electron.