Gain in ultra-low-threshold InAs/InGaAs quantum dot lasers

Semiconductor lasers are grown on a GaAs substrate by MBE containing self-assembled InAs quantum dots (QDs) in an InGaAs quantum well, the so-called dot-in-a-well (DWELL) structure. The QDs are /spl sim/15 nm in diameter in the basal plane and /spl sim/7 nm in height. Several wafers are investigated in detail. The in-plane dot density is either 2.5x10/sup 10/ or 7.5x10/sup 10/ cm/sup -2/. The ground-state emission wavelength is 1230-1250 nm at room temperature, and the spectral FWHM is from 40 to 75 nm. We obtained and analyzed the dependence of the gain on current density in ultra-low-threshold laser diodes with DWELL quantum-dot structures.