1.25 /spl mu/m low threshold current density dots-in-a-well (DWELL) lasers

It has been predicted that the threshold current density of quantum dot lasers should be lower than that of quantum well lasers due to the reduction of the density of states. In particular, efforts have been made in the past few years to reduce the threshold current density of quantum dot lasers on GaAs substrates. A recently developed approach is to put the InAs dots in a strained In/sub 0.2/Ga/sub 0.8/As quantum well. This "dots in a well" (DWELL) design not only improves carrier capture by the dots, but also increases the density of quantum dots over growth on GaAs directly. Consequently, ground state lasing from a single layer of dots is possible at reasonable cavity lengths. While competition with radiative quantum well transitions was suggested as a concern, quantum well transitions were not observed in previous work or in this study. Further improvements have been made by putting a single layer of InAs quantum dots into a strained In/sub 0.15/Ga/sub 0.85/As quantum well. An extremely low threshold current density of 26 Acm/sup -2/ has been achieved for a 7.8 mm cavity length, cleaved facet laser.