Practice portal › Semiconductor Electronics › Optoelectronic Devices
Asked in GUJCET 2023 · LED
Idea: when an electron in an LED falls from the conduction band into a hole in the valence band it gives out a photon of energy close to the band gap, so E_g fixes the colour.
Visible light runs from about 700 nm at the deep red end to about 400 nm at the violet end.
Photon energy and wavelength are tied together by E(eV)≈(1240)/(λ(nm)).
The red end therefore needs E≈1240/700≈1.8 eV. A gap any smaller emits in the infrared, and the LED would not be visible at all.
So the minimum band gap for a visible LED is about 1.8 eV.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer