# Why do semiconductor lasers become weaker after extended use (not due to battery)?

Why do semiconductor lasers become less bright as they are used for longer periods of time (assuming their battery is full)? Does it have something to do with the PN junction reaching some kind of equilibrium and becoming less effective? Does the laser induce some kind of temperature change reducing the efficiency of the semiconductor? Please explain!

• A list of faliure modes of LEDs is available on Wikipedia. Semiconductor lasers are basically LEDs with cavities, so these failure modes are also relevant for them (although some laser-specific failure modes may also exist). – Ruslan Mar 16 at 17:14
• Could it have something to do with population inversion? The electrons need to get excited back to the conduction band because they are dropping down to the valence band at a faster rate than they are being promoted? – Failure123 Mar 16 at 18:26

• Yep, temperature destroys very thin N-P layer. N-P layer becomes thickier and its $E=U/d$ will fall. With falling $E$, laser degrades. – sanaris Mar 16 at 18:17