Discussion of the linewidth enhancement factor α 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 α 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 α increases with carrier density. Particularly, in SQW-SCH laser structures with thin quantum wells, α 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 α considerably. Furthermore, only a weak dependence of the α factor on the number of quantum wells is found in the case of MQW lasers. Finally, a comparison of α-simulations and measurements on SQW-GRINSCH and SQW-SCH BCRW laser structures shows a good agreement