Quantum-dot lasers

The reduction of the active region of semiconductor lasers to quasi-zero dimensions has different effects on static and dynamic laser parameters as already discussed in the last two decades. Most prominent effects due to thermodynamics of low dimensional electron-hole plasmas are the threshold reduction and improved temperature stability of lasers with low dimensional active regions. Based on the changed density of states also some interesting device properties with respect to modulation response and beam quality of a laser are expected but not yet reached. This obvious discrepancy between theoretical expectations and experimental results must be related to additional effects such as carrier transport and relaxation. After a brief review of nano-fabrication aspects of dot lasers by self assembled methods as well as by lithography based implantation and etching methods, also laser device properties based on thermodynamics in low dimensional systems will be discussed. Strong emphasis will be put on carrier dynamics (transport, recombination, and relaxation). On the footing of a rate equation approach we discuss the static and dynamic properties of quantum dot lasers as a function of the dot array filling factor. Also some applications and device properties will be discussed. Based on periodic dot arrays, gain coupled dot distributed feedback (DFB) lasers can be realized which result in an improved side mode suppression ratio of the laser emission. From modulation experiments, extremely low dynamic chirp of dot lasers can be observed making quantum dot lasers promising candidates for high speed communication in the long wavelength range, if modulation response limitations can be solved.