When the bandgap of the material used to construct an LED increases, which of the following statement(s) is/are correct?

Question

BlackTom AI · Accepted Answer

When the bandgap of the LED material changes, it directly affects the electrical and optical properties of the device, so we evaluate each statement in light of this relationship.
Option 1: 'the turn-on voltage of the LED increases' — This is correct. The turn-on or forward voltage is closely related to the energy gap that must be overcome to inject carriers across the p-n junction and initiate radiative recombination. A larger bandgap means more energy per electron is required, which generally translates to a higher forward voltage (approximately Eg/q for the ideal diode), so increasing Eg pushes the turn-on voltage upward.
Option 2: 'the turn-on voltage of the LED decreases' — This is incorrect. Reducing the turn-on voltage would imply needing less energy to initiate conduction, which contradicts the physics of a larger bandgap requiring more energy. Therefore this statement does not hold when Eg increases.
Option 3: 'the wavelength of the emitted light increases' — This is incorrect. The photon energy emitted in radiative recombination is roughly equal to the bandgap (in direct-bandgap semiconductors). Since Eg increases, the photon energy increases, which would correspond to a shorter wavelength, not a longer one. Thus this option misstates the optical consequence.
Option 4: 'the wavelength of the emitter light decreases' — This is correct. As Eg grows, the emitted photon energy increases and the corresponding wavelength λ = hc/Eg decreases. Therefore, a larger bandgap yields a shorter-wavelength (bluer) emission.

When the bandgap of the material used to construct an LED increases, which of the following statement(s) is/are correct?多项选择题

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