Absorption, Gain, and Threshold in InP/AlGaInP Quantum Dot Laser Diodes

We study self-assembled InP quantum dot (QD) laser structures grown at two temperatures (690^°C and 730 ^°C) each with three different quantities of deposited quantum dot material (2, 2.5, and 3 mono-layers). The absorption spectra of these structures show features associated with the QD distributions and the magnitude of the absorption increases for samples where more material is deposited and for lower growth temperature. The 690^°C growth temperature structures exhibit nonradiative recombination and internal optical mode loss that increase with the quantity of material deposited; we suggest that the laser performance is limited by the presence of defects. The higher growth temperature samples have lower threshold current density and are limited by gain saturation. For these samples and for 2-mm long lasers with uncoated facets, the threshold current density is as low as 150 A cm^-2, emitting in the wavelength range around 730 nm.