Question

What is the energy band gap of:
(i) silicon and (ii) germanium

Answer 1

Hint: Energy band gap is defined as the region between valence and conduction band in which electrons do not occupy any state or energy level. Energy band gap is also known as band gap or forbidden energy gap. It is the criteria to differentiate between conductors, semi-conductors and insulators. Energy band gap is very small for a semiconductor.

Complete answer:
Energy band gap is the energy difference between the top of the valence band and the bottom of the conduction band. In this region, no states are occupied by the electrons. Depending upon the size of the energy gap, conductors, semiconductors and metals are formed. Silicon and germanium are extensively used semiconductors.
(i) Energy band gap of silicon is 1.1 eV.
(ii) Energy band gap of germanium is 0.7 eV.

Additional Information:
The energy band gap of the semiconductor may be of two types. They are:
1) Direct band gap: For semiconductors with direct band gap, the maximum energy level of valence band and minimum energy level of conduction band occur at same momentum. Example: GaAs, GaAsP etc.
2) Indirect band gap: For semiconductors with indirect band gap, the maximum energy level of valence band and minimum energy level of the conduction band does not occur at the same momentum. Example: Si. Ge etc.

Note:
Students must remember that the energy band gap of a semiconductor decreases with the temperature of the semiconductor. In the case of semiconductors, this gap is very less. So, as we increase the temperature, the gap between the valence and conduction band gets smaller which reduces the forbidden energy gap. In case of conductors/ metals, conduction and valence band overlap. So, they might not have this gap. Insulators have a large energy gap.