Hot Carrier Relaxation and Spectral Hole Burning in Quantum Wire and Quantum Well Laser Structures
The differential gain in quantum wires can be considerably greater than in quantum wells since the peak in the density of states at the band edge provides a much higher gain per injected carrier. In semiconductor lasers, however, the carriers are injected not at the band edge, but from the barriers at higher energies. If the carriers are continuously taken out by radiative recombination at the lasing wavelength, the rate at which they are replenished must balance the recombination rate. Otherwise, the occupation probability at the lasing wavelength is reduced with a concomitant drop in the gain. Also, when the laser is modulated, the carriers must be able to reach the band edge states in a time sufficient for an optical response characteristic of high injection. Therefore, carrier thermalization is of paramount importance in laser structures.
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