Question

In semiconductors, the forbidden energy gap between valence band and conduction band is of the order of:
A) 1eV
B) 5eV
C) 1KeV
D) 1MeV

Answer 1

In semiconductors, the transition of electrons from valence band to conduction band take place in the visible range of the electromagnetic spectrum. The energy of the visible rays of the electromagnetic spectrum is in the range of 1eV to 3eV. Therefore, the value of the band gap in semiconductors is also in the range of 1eV to 3eV.

Formula used:
Energy and wavelength are related to each other by: $E = \dfrac{{1240}}{\lambda }$
where $E$ is the energy and $\lambda$ is the wavelength.

Complete step by step answer:
The properties of semiconductors lie between those of conductors and insulators. Therefore, they are known as semiconductors.
There are two bands in which electrons can exist. They are the conduction band and the valence band. The energy difference between these two is called the Energy band gap. Valence shells consist of filled electrons. The electrons can jump from valence band to conduction band when they are excited by absorbing some energy. Conduction band primarily consists of empty shells. The excited electrons are accommodated in the conduction band after absorbing energy.
This excitation of electrons results in transitions from valence band to conduction band. These transitions can occur by absorption of a photon of the same wavelength or energy as that of the band gap. These transitions can easily occur by the frequencies of the visible spectrum. So, the energy of the band gap is almost the same as the energy of visible radiation.
The range of visible frequency is 380 to 700 nanometers. The relation between wavelength and energy is given by $E = \dfrac{{1240}}{\lambda }$ where $E$ is the energy and $\lambda$ is the wavelength.
So, the energy range must be between 3eV to 1eV.

So, the correct answer is “Option A”.

Note:
Band Gap in semiconductors consists of two types. One is, Conventional band gap semiconductors: e.g.- Silicon has a band gap of 1.15eV. Second is, Wide band gap semiconductors: e.g.- Titanium DiOxide has a band gap of 3-3.2eV.
Conduction band primarily consists of empty shells. The excited electrons are accommodated in the conduction band after absorbing energy.