Ask A Scientist© Physics Archive

name         Wentao J.
status       student
age          20s

Question -   In semiconductor devices such as a laser diodes, how can
the semiconductor's bandgap influence the wavelength of the laser emitted?
Why it is said that the larger the bandgap the bluer the laser?

The bandgap affects the energy loss of the electron emitting the light.  A
larger bandgap means the electron releases a more energetic photon of light.
Higher frequency/shorter wavelength photons of light are higher energy
photons.  Energy of a photon is proportional to its frequency.
Kenneth Mellendorf
=========================================================
The bandgap is the amount of energy required to raise a valence band electron
into the conduction band.  Conversely, it is the minimum amount of energy
released when an electron moves directly from the conduction band to the 
valence
band.  In lasers it is the minimum energy in the photon produced.  Thus the
larger the bandgap, the more energy in the photons emitted.  Since there is an
inverse relationship between energy and wavelength this means a smaller
(shorter) wavelength which shifts the emission spectrum towards the blue.

Greg Bradburn
=========================================================