Concept:External quantum efficiency (\( \eta_{\text{ext}} \)) measures how effectively an LED converts injected electrons into emitted photons that escape the semiconductor package.
Formula:$$\eta_{\text{ext}} = \frac{\text{Photons Emitted Externally / second}}{\text{Electrons Injected / second}} = \frac{P_{\text{optical}} / (h f)}{I_F / q} = \eta_{\text{int}} \cdot \eta_{\text{extraction}}$$
Solution:- Internal quantum efficiency (\( \eta_{\text{int}} \)) is the fraction of injected electron-hole pairs that recombine radiatively.
- External quantum efficiency (\( \eta_{\text{ext}} \)) accounts for optical extraction losses, measuring the fraction of injected electrons that result in photons escaping into free space.
Why other options are incorrect:- Option A: This describes power efficiency or thermal dissipation ratio, not quantum efficiency.
- Option B: Carrier-to-dopant ratio relates to ionization fraction, not optical conversion.
- Option C: Current ratios relate to rectification asymmetry, not photon emission.
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