Ground-state lasing at room temperature in long-wavelength InAs quantum-dot lasers on InP(311)B substrates

InAs quantum dots (QDs) with a high density of 9×1010 cm−2 are formed on InAlGaAs layer/InP (311)B substrates. Lasers having five-period stacked InAs QD layers are operated in the ground state (λ≈1.6 μm) at room temperature, and the maximal modal gain of the ground state is measured to be 20 cm−1. We obtained a threshold current density of 380 A/cm2 at room temperature, and observed the temperature-insensitive threshold current at temperatures from 77 to 220 K.