InP-based quantum dot lasers emitting at 1.3 µm

In this paper, we report on InP-based quantum dot (QD) lasers with InAs QDs emitting at the telecom O-band. A molecular beam epitaxy (MBE) based novel growth technique was implemented by using strained islands allowing the formation of smaller QDs by still keeping a high QD density. The laser structure is lattice matched to InP except for the active region. The active layer consists of a few monolayers (ML) thick InAs QDs which were grown on a thin GaAs nucleation layer, which enables tuning the size of the QDs. The impact of different nucleation layer structures and of the InAs growth rate on the QD formation process was investigated, with results indicating that the surface roughness of the nucleation layer and the availability of nucleation sites strongly influence adatom diffusion and the resulting QD size and uniformity. Broad area lasers were processed and exhibited a high modal gain of 78 cm−1 for 6 QD layers and an internal quantum efficiency of 0.68 for the laser treated with rapid thermal annealing (RTA) at 680 °C. A further improvement in laser performance was obtained at an elevated annealing temperature of 766 °C.