Question

The type of semiconductor bandgap essential for materials used in light-emitting diodes is:

• A. Insulator
• B. Indirect bandgap
• C. Direct bandgap
• D. Zero bandgap

Hint:

For glowing gadgets like LEDs, think “direct bandgap” — electrons jump straight down and light comes out!

Answer 1

The Correct Option is C

Light-emitting diodes (LEDs) function by converting electrical energy into light via a process called electroluminescence. When electrons recombine with holes in a semiconductor, energy is released — and this energy can be emitted as light if certain conditions are met.
In semiconductors with a direct bandgap, the minimum of the conduction band and the maximum of the valence band occur at the same momentum (k-vector). This allows an electron to directly fall into a hole without needing a change in momentum — making photon emission efficient and spontaneous.
In contrast, indirect bandgap materials like silicon require the assistance of a phonon to conserve momentum during recombination, making them inefficient for light emission.
Why the other options are incorrect:

• (A) Insulator: Has a very large bandgap and does not allow significant carrier flow or recombination.
• (B) Indirect bandgap: Poor radiative efficiency, unsuitable for LEDs.
• (D) Zero bandgap: Characteristic of materials like graphene, not suitable for diode-based light emission.

Thus, for LED applications, materials must have a direct bandgap to efficiently emit light.