Concept:Bandgap engineering uses compound semiconductor alloys where varying the composition fraction \( x \) alters the lattice parameters and energy bandgap \( E_g(x) \), tuning the emitted photon wavelength \( \lambda = h c / E_g \).
Formula:$$E_g(x) = x \cdot E_{g,1} + (1 - x) \cdot E_{g,2} - b \cdot x (1 - x) \implies \lambda_{\text{peak}} = \frac{h c}{E_g(x)}$$
Solution:- By varying the Indium fraction \( x \) in \( \text{In}_x \text{Ga}_{1-x} \text{N} \), the bandgap can be tuned from \( 0.7\text{ eV} \) (pure InN) up to \( 3.4\text{ eV} \) (pure GaN).
- This allows fabricating LEDs across the entire visible spectrum (red, amber, green, blue, and violet) using the same alloy family.
Why other options are incorrect:- Option A: Plastic lens thickness does not alter photon emission bandgap physics.
- Option B: Terminal lead length has no effect on emission wavelength.
- Option D: Reverse breakdown does not produce efficient electroluminescence.
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