Extremely low room-temperature threshold current density diode lasers using InAs dots in In0.15Ga0.85As quantum well

Introduction: 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 density of states [1]. In particular, efforts have been made in the past few years to reduce the threshold current density of quantum dot lasers on GaAs substrates [2, 3]. A recently developed approach is to put the InAs dots in a strained In0.2Ga0.8As quantum well [3, 4]. This ‘dot in a well’ (DWELL) design not only improves carrier capture by the dots, but also increases the density of quantum dots (to 7 × 1010cm–2) over growth on GaAs directly. Consequently, 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 [5], quantum well transitions were not observed in previous work [3] or in this study. In this Letter, we present further improvements that have been made by putting a single layer of InAs quantum dots into a strained In0.15Ga0.85As quantum well. An extremely low threshold current density of 26A cm–2 has been achieved for a 7.8mm cavity length, cleaved facet laser. Other operating characteristics of these DWELL lasers are described.