Construction of semiconductor laser

In the last article, I have explained the basics of semiconductor. Today I will explain the construction of a semiconductor laser.

Example of semiconductor laser: One of the examples of semiconductor lasers is gallium arsenide (GaAs). It is heavily doped semiconductor. Its n-region is formed by heavily doping with tellurium in a concentration of 3 x 1018 to 5 x 1018 atoms/cm3 while its p-region is formed by doping with zinc in concentration around 1019 atoms/cm3.


Active medium:

The active medium in GaAs is GaAS. But it is also commonly said that depletion region is the active medium in semiconductor laser. The thickness of the depletion layer is usually very small (0.1 μm).

Pumping Source: Forward biasing is used as pumping source. The p-n junction is made forward biased that is p side is connected to positive terminal of the battery and n side to negative. Under the influence of forward biased electric field, conduction electrons will be injected from n side into junction area, while holes will enter will enter the junction from the p side. Thus, there will again be recombination of holes and electrons in depletion region and thus depletion region becomes thinner.

Optical resonator system: The two faces of semiconductor which are perpendicular to junction plane make a resonant cavity. The top and bottom faces of diode, which are parallel to junction plane are metallised so as to make external connections. The front and back faces are roughned to suppress the oscillations in unwanted direction.

Note: In next article, I will explain the working. Till then, try to make the construction diagram. In case of any problem in this article or any other physics article, post in the comment section.

Reference: This article is referred from my authored book “optics and lasers” having ISBN 978-81-272-2948-2

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