LOW-THRESHOLD INJECTION-LASERS BASED ON VERTICALLY COUPLED QUANTUM DOTS

We have fabricated and studied injection lasers based on vertically co upled quantum dots (VECODs). VECODs are self-organized during successi ve deposition of several sheets of(In,Ga)As quantum dots separated by thin GaAs spacers. VECODs are introduced in the active region of a GaA s-AlGaAs GRIN SCH lasers. Increasing the number of periods (N) in the VECOD leads to a remarkable decrease in threshold current density( sim ilar to 100 A/cm(2) at 300 K for N = 10). Lasing proceeds via the grou nd state of the quantum dots (QD) up to room temperature. Placing the QD array into an external AlGaAs-GaAs quantum well allows us to extend the range of thermal stability of threshold current density (T-0 = 35 0 K) up to room temperature. Using (In,Ga)As-(Al,Ga)As VECODs in combi nation with high temperature growth of emitter and waveguide layers re sults in further reduction of threshold current density (60-80 A/cm(2) , 300 K;) and increase in internal quantum efficiency (70%). Room temp erature continuous wave operation (light output 160 mW per mirror) and lasing via the states of QDs up to I = (6-7) I-th have been demonstra ted.