DISCUSSION OF THE LINEWIDTH ENHANCEMENT FACTOR-ALPHA OF GAAS/GAALAS QUANTUM-WELL LASERS

The fundamental contributions of optical interband transitions and the plasma effect of free carriers to the linewidth enhancement factor alpha of Ga(Al)As quantum well lasers has been discussed with respect to the dependence on the main laser structure parameters: confinement profile, number of quantum wells and well width. The results show clearly that alpha increases with carrier density. Particularly, in SQW-SCH laser structures with thin quantum wells, alpha is enlarged drastically by the plasma effect due to the necessary high threshold carrier densities. Both, the use of a GRINSCH structure or a MQW laser design reduce the free carrier component of alpha considerably. Furthermore, only a weak dependence of the alpha factor on the number of quantum wells is found in the case of MQW lasers. Finally, a comparison of alpha-simulations and measurements on SQW-GRINSCH and 3QW-SCH BCRW laser structures shows a good agreement.