Gain characteristics of quantum-dot injection lasers

The current dependence of the optical gain in lasers based on self-organized InGaAs quantum dots in a AlGaAs/GaAs matrix is investigated experimentally. A transition from lasing via the ground state of quantum dots to lasing via an excited state is observed. The saturated gain in the latter case is approximately four times greater than for the ground state. This result is attributable to the fourfold degeneracy of the excited level of quantum dots. The effect of the density of the quantum-dot array on the threshold characteristics is investigated. A lower-density array of dots is characterized by a lower threshold current density in the low-loss regime, because the transmission current is lower, while dense quantum-dot arrays characterized by a high saturated gain are preferable at high threshold gains. (C) 1999 American Institute of Physics. [S1063-7826(99)02309-1].