Question

What type of semiconductor is used in LED ?

• A. Intrinsic semiconductor
• B. Compound semiconductor
• C. Degenerated semiconductor
• D. Compensated semiconductor

Hint:

Silicon and Germanium are great for processors and standard diodes, but terrible for light! For LEDs, lasers, and optical devices, we always turn to direct-bandgap compound semiconductors like $\text{GaAs}$ or $\text{GaN}$.

Answer 1

The Correct Option is B

Concept: A Light Emitting Diode (LED) operates on the principle of radiative recombination, where injected electrons from the conduction band recombine with holes in the valence band across a semiconductor bandgap, releasing energy in the form of photons (light). Semiconductors can be broadly categorized into two structural band types:
• Direct Bandgap Semiconductors: The conduction band minimum and valence band maximum align at the exact same momentum vector value ($k=0$). Recombination occurs directly, converting nearly all energy into light.
• Indirect Bandgap Semiconductors: The band extrema do not align in momentum space. Recombination requires a momentum-balancing phonon, meaning energy is dissipated primarily as heat rather than light. Step-by-step Material Selection Logic:
• Elemental semiconductors like Silicon ($\text{Si}$) and Germanium ($\text{Ge}$) are indirect bandgap materials, making them highly inefficient for producing light.
• To obtain direct bandgaps with customizable wavelength outputs, we use compound semiconductors synthesized from combining elements across multiple groups (such as Group III and Group V elements).
• Common examples include Gallium Arsenide ($\text{GaAs}$), Gallium Phosphide ($\text{GaP}$), and Indium Gallium Nitride ($\text{InGaN}$). Since these are formed by blending multiple chemical elements, they are classified as compound semiconductors.