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Semiconductor Physics & Diodes (Electrical Engineering) Solved Questions & Notes (2026) - Apex Rankers

Engineering & Technology > Electrical Engineering > Semiconductor Physics & Diodes

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Q. 1 Electronics Engineering
Difficulty: Medium (1 Mark)
Light Emitting Diodes (LEDs) are fabricated from direct bandgap compound semiconductors (such as GaAs, GaN, InGaN) rather than indirect bandgap semiconductors like Silicon because:
A
In direct bandgap materials, electrons recombine directly across the bandgap releasing energy predominantly as photons (light) without requiring lattice phonon momentum assistance
✓ Correct
B
Silicon is opaque to electricity
C
Direct bandgap materials have zero thermal resistance
D
Silicon cannot be doped P-type
💡 Step-by-Step Explanation & Concept Rationale
In direct bandgap semiconductors, the conduction band minimum and valence band maximum align at the same crystal momentum (k = 0). Radiative electron-hole recombination is direct and highly efficient, producing photons: lambda = h * c / Eg. In Silicon (indirect bandgap), recombination requires a phonon (lattice vibration), dissipating energy as heat.
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