Very low room-temperature 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 in 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_0.2Ga_0.8As quantum well. This “dots in a well” (DWELL) design not only improves carrier capture by the dots, but also keeps the density of quantum dots high (up to 7×10¹⁰ cm^-2). 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. In this work, comparisons have been made by putting a single layer of InAs quantum dots into three different quantum wells, In_0.10Ga_0.9As, In_0.15Ga_0.85As, and In_0.2Ga_0.8 As. Very low threshold current densities of 40, 26, and 31 A cm ^-2 have been achieved with InAs dots in the three systems for the 7.8 mm cavity length, cleaved facet lasers