Virtual Labs

1. In a direct bandgap semiconductor, photon emission is more efficient because:

a: Electron momentum changes significantly Explanation

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b: No phonon assistance is needed for recombination Explanation

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c: Absorption coefficient is independent of energy Explanation

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d: Bandgap energy is zero Explanation

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2. Which phenomenon is responsible for the delayed light emission in phosphorescence?

a: Fast radiative recombination Explanation

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b: Trapping of carriers in metastable states Explanation

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c: Direct transition across the bandgap Explanation

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d: Spontaneous stimulated emission Explanation

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3. Which property determines whether a semiconductor is suitable for LED applications?

a: Indirect bandgap and high resistivity Explanation

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b: Direct bandgap and high radiative efficiency Explanation

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c: Low mobility of charge carriers Explanation

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d: Very wide bandgap Explanation

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4. If the absorption coefficient α of a material sharply increases when the incident photon energy exceeds Eg, this indicates:

a: The material has a direct bandgap Explanation

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b: The material has an indirect bandgap Explanation

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c: Photon energy is less than the Fermi energy Explanation

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d: Carrier mobility is constant Explanation

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5. Fluorescence differs from stimulated emission because:

a: Fluorescence is instantaneous and incoherent Explanation

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b: Fluorescence requires population inversion Explanation

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c: Stimulated emission emits random photons Explanation

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d: Stimulated emission occurs without energy input Explanation

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6. The peak wavelength (λ) emitted by a semiconductor LED is primarily determined by:

a: Carrier mobility Explanation

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b: Doping concentration Explanation

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c: Bandgap energy Eg Explanation

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d: Lattice constant Explanation

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7. A semiconductor has Eg = 1.8 eV. Calculate the wavelength of the emitted photons during spontaneous emission.

a: 689 nm Explanation

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b: 550 nm Explanation

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c: 1032 nm Explanation

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d: 450 nm Explanation

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8. In a laser diode, population inversion is necessary because:

a: It minimizes non-radiative recombination Explanation

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b: It ensures stimulated emission dominates over absorption Explanation

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c: It lowers the threshold current for LEDs Explanation

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d: It increases phonon scattering Explanation

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9. For a semiconductor with an indirect bandgap, efficient photon emission requires:

a: Only electron-hole recombination Explanation

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b: Phonon participation to conserve momentum Explanation

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c: High doping concentration Explanation

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d: Complete absence of defects Explanation

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Photon Semiconductor Interactions