Laser Diode Principles: Stimulated Emission & Voltage

[Goodver]

As far as I understand, when forward biased voltage applied, electrons from N diffuse to P, then recombine. Since energy gap between conductive electron and hole is const => only certain wavelength photons is emitted.

In gaseous lasers for example you need to gain a populational inversion, which requires to have a certain energy levels, including one of them to be metastable.

How the stimulated emission works for laser diodes?

 

[UltrafastPED]

Here is a lecture/outline on that topic:

http://ocw.mit.edu/courses/electric...vices-spring-2003/lecture-notes/lecture20.pdf

 

[Cthugha]

By the way, the formal name for the semiconductor equivalent of population inversion which is discussed in the PDF linked by UltrafastPED is the Bernard-Duraffourg condition. If you need more details, that is the term to look for.