How indirect band semiconductors are used in lasers ?

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Discussion Overview

The discussion centers on the use of indirect bandgap semiconductors in lasers, exploring the mechanisms of photon emission, the role of stimulated emission versus stimulated Raman scattering, and the challenges associated with achieving lasing in such materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the ability of indirect bandgap semiconductors to emit photons during transitions, suggesting that energy is primarily released as heat to the lattice.
  • Another participant counters that indirect bandgap semiconductors do emit photons, but also involve phonon interactions during transitions.
  • A participant notes that interest in indirect bandgap lasing is largely due to applications in optical processing with silicon, highlighting that most silicon lasers rely on stimulated Raman scattering rather than stimulated emission.
  • There is mention of a method to achieve direct stimulated emission in silicon by heavily pumping the material, which could lead to lasing despite being inefficient and potentially damaging to the silicon.
  • A request for further elaboration on Raman scattering is made, indicating interest in understanding this process better.

Areas of Agreement / Disagreement

Participants express differing views on the photon emission capabilities of indirect bandgap semiconductors, with some asserting that they do emit photons while others maintain that heat dissipation is the primary outcome. The discussion remains unresolved regarding the efficiency and practicality of lasing in these materials.

Contextual Notes

There are unresolved aspects regarding the efficiency of lasing mechanisms in indirect bandgap semiconductors and the specific conditions under which photon emission occurs. The discussion also highlights the dependence on the definitions of lasing and the processes involved.

Who May Find This Useful

This discussion may be of interest to researchers and students in the fields of semiconductor physics, optical engineering, and materials science, particularly those exploring laser technologies and optical processing applications.

luvagnihotri
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Hi,
I would like to know how we can use indirect band semiconductors in lasers. Such type of semiconductors do not emit photons when transition takes place. Energy is given up as heat to the lattice.

Regards,
 
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First of all, indirect band gap semiconductors certainly do emit photons when a transition occurs --- they emit/absorb photons and phonons simultaneously. Second, a material that does not produce photons would be pretty damn useless as a laser or a light-emitting anything!
 
As far as I know most of the interest in indirect bandgap lasing comes from people, who are interested in optical processing using silicon because silicon is an indirect bandgap material. As genneth already said, photon emission indeed happens at a transition. It is just not the only process.

Most lasers in silicon are not based on stimulated emission, but on stimulated Raman scattering if I remember correctly, so you need a pump laser in most cases anyway.

Another funny method I recently saw to achieve direct stimulated emission consists of pumping silicon so hard that the whole conduction band - even the states far from the band minimum - is filled with electrons. At some point even the point of the direct transition to the valence band will be filled, so that inversion can be present and lasing can be achieved. However this process is extremely inefficient and you need to pump so hard that two photon absorption losses can become critical and you are always close to destroy your piece of silicon due to the high power you fire at it. But in principle it works - or as my boss once said: If you pump it hard enough, you can achieve lasing in a slice of bread as well. ;)
 
Cthugha said:
Most lasers in silicon are not based on stimulated emission, but on stimulated Raman scattering if I remember correctly, so you need a pump laser in most cases anyway.

Good question and answers. While you are at it, could you elaborate more on Raman scattering ?
 

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