Energy Conduction band Filled states Band Emitted gap AEhund photon Empty states Filed Valence band states FIGURE P29.70 Energy-level diagram of an LED.
Light-emitting diodes, known by the acronym LED, produce the familiar green and red indicator lights used in a wide variety of consumer electronics. LEDs are semiconductor devices in which the electrons can exist only in certain energy levels. Much like molecules, the energy levels are packed together close enough to form what appears to be a continuous band of possible energies. Energy supplied to an LED in a circuit excites electrons from a valence band into a
The same kind of semiconducting material used to make an LED can also be used to convert absorbed light into electric energy, essentially operating as an LED in reverse. In this case, the absorption of a photon causes an electron transition from a filled state in the valence band to an unfilled state in the conduction band. If ΔEband = 1.4 eV, what is the minimum wavelength of
A. 140 nm B. 890 nm
C. 1400 nm D. 8900 nm
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