Diodes in forward-biased circuits emit electromagnetic radiation. Specifically,

Question

Diodes in forward-biased circuits emit electromagnetic radiation. Specifically, when an electron from the conduction band in the n-type semiconductor of the diode fills a hole in the valence band of the p-type semiconductor of the diode, it emits a photon whose energy is equal to the difference in energy between the two bands. The energy required for this emission is provided by whatever is driving the electric current in the circuit.

The accompanying photograph shows a circuit containing green light emitting diodes (LEDs). LEDs actually look a lot like computer chips, but they are enclosed in protective plastic lenses like the ones you see here so that they will project a bright light. Light emitting diodes are made from non-silicon semiconductors such as gallium, and the energy difference between their conduction and valence bands is such that the photons they emit have wavelengths in the visible light spectrum. LEDs are used for applications ranging from jumbo TV screens in sports stadiums to the digits of glow-in-the-dark clocks.

The LEDs in the photograph emit green light with a wavelength of 520 nm. What is the energy difference between their conduction and valence bands?

Explanation / Answer

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