Question

The band gap in silicon and germanium (in eV) respectively is:
A. 0.7, 1.1
B. 1.1, 0.7
C. 1.1, 0
D. 0.7, 0

Answer 1

Hint: Both Silicon and Germanium are semiconductors, hence they have energy band gaps. Silicon has a larger band gap than germanium. Bandgap of any material is never negative.

Complete step-by-step answer:
Let’s understand what band gap is.
Bandgap is the energy gap between the valence and the conduction band. In electronics based on the energy band gap we have 3 categories:

1) Conductors: Here the bandgap, which is the gap between the valence and the conduction bands, isn’t present at all. These 2 bands overlap, hence causing a free flow of electrons from the electron rich valence band to conduction band even at room temperature. This ease in the conduction ability leads us to calling these kinds of materials as conductors. Its examples are essentially all kinds of metals, which are excellent conductors.

2) Insulators: Here, the energy band gap between the valence and conduction bands is very large. This makes it impossible for electrons to flow from valence band to conduction band, which is necessary for conduction. Hence, these kinds of materials having very large energy band gaps are known as insulators. The examples for insulators include plastics, rubber, ceramics etc.

3) Semiconductors: Semiconductors have an intermediate energy band gap between insulators and conductors. The semiconductors can act as conductors upon application of external electric fields. If the applied external electric field is greater than the band gap of the material then, conduction will occur in the semiconductor.

Both Silicon and Germanium fall under the semiconductors category. Conventionally at room temperature, the energy bandgap for Silicon is 1.1 eV and that of Germanium is 0.7 eV.

Note: For semiconductors, the energy bandgap has temperature dependence. Hence, the band gap changes with corresponding change in the temperature. However, whenever we are asked about the conventional value, the bandgap value at room temperature is considered.