Question

What is the energy band gap of silicon and germanium respectively in eV?
(A). 1.1, 0.7
(B). 0.7, 1.1
(C). -0.7, -1.1
(D). -1.1, -0.7

Answer 1

- Hint: The region at which electrons are not occupying is known as energy band gap or forbidden band. Silicon and germanium are semiconductors.

Complete step-by-step solution -
Bandgap is the energy difference between the bottom of the conduction band and top of the valence band. It’s a space in which no electron states are occupying. Silicon and germanium are extensively used semiconductors. The energy band gaps of silicon and germanium are 1.1 eV and 0.7 eV respectively. Hence the correct option is (A).

Additional information:
Valence electrons in the outermost orbit decide the electrical characteristics of a material. Valence bands are the energy level which is closer to the nucleus. These bound electrons can excite to high energy levels when a suitable amount of energy is received. This is the concept of semiconductors. It will act like insulators at absolute temperature. When the temperature increases it will start conduction. Conduction band is the energy level occupied far away from the nucleus. Energy band is the criteria to characterise the materials into conductor, semi-conductor and insulators.
For direct band gap semiconductors, conduction band minimum and valence band maximum occur at the same value of momentum. Ex; GaAs, GaAsP. In these, electrons can directly emit photons.
For indirect bandgap semiconductors, conduction band minimum and valence band maximum occurs at different values of momentum. Ex; Si, Ge. In an indirect band gap, electrons must pass through the intermediate state and transfer momentum to the crystal lattice. Thus, it cannot emit photons.

Note: Silicon has more band gap than the germanium. Semiconductors used for solar cells require a bandgap of range from 1 eV to 1.7 eV. They will show maximum efficiency only at this range. That’s why silicon is mostly used for solar cell production than germanium. It is better to remember this to find the right answer.