1.32-μm InAs/InGaAs/GaAs quantum-dot lasers operating at room temperature with low-threshold current density

We report on the growth and characterization of low threshold 1.32-μm quantum dots (QDs) laser diodes. The quantum dot active region was optimised to get the highest photoluminescence emission and the lowest Full Width at Half Maximum (FWHM). From samples containing multilayer QDs and using the Limited-Area Photoluminescence (LAPL) technique we have shown that the gain of an N-layer structure is higher than N times that of a single layer. This enhancement is attributed to the increase of the quantum dot density in the upper layers and also to the use of the high growth temperature spacer layer. Broad area laser diodes were processed from the grown samples containing three layers of InAs QDs grown directly on GaAs and capped with 4-nm-thick In _xGa_1-xAs layer. Than measurements were performed at room temperature under pulsed excitation. The laser diodes operate at room temperature and emit between 1.29 and 1.32-μm which is beyond the strategic telecommunication wavelength. The characteristic temperature is around 80 K and very stable in the hole range of the operating temperature (from 0 to 90°C). The internal quantum efficiency is 53 % and the modal gain per QD layer was estimated to be ∼ 6 cm^-1. For an infinite cavity length a threshold current density of 8 A/cm² per QD layer was obtained. From the calculation of the optical confinement of QDs, we have estimated a material gain of 1979 cm^-1.