CW Lasing at 1.35 $\mu$m From Ten InAs–Sb : GaAs Quantum-Dot Layers Grown by Metal–Organic Chemical Vapor Deposition

We report the fabrication of GaAs-based quantum-dot (QD) lasers grown by metal-organic chemical vapor deposition (MOCVD) above 1.3 m. We fabricated a laser diode with ten stacked InAs-Sb:GaAs(100) QD layers, grown by antimony-surfactant-mediated growth. Ground-state lasing was obtained under continuous-wave operation at room temperature at 1.35 mum, with a maximum ground state modal gain of 19.3 cm^-1. These values are the highest values reported for MOCVD-grown GaAs-based QD laser.

Because of their theoretically predicted properties, such as low threshold current density or high temperature stability [1], self-assembled InAs–GaAs quantum dots (QDs) are attractive candidates for emitters at the telecommunication wavelength of 1.3 . Lasing at 1.3 has been extensively reported for InAs–GaAs QDs grown by molecular beam epitaxy (MBE) [2], [3]. Because of advantages such as high throughput and lower maintenance costs, metal–organic chemical vapor deposition (MOCVD) would help QD lasers find commercialization. However, until very recently, there had been no report of lasing at, or above, 1.3 from InAs–GaAs QDs grown by MOCVD. This was mainly due to the difficulty of growing high-density QDs with sufficient gain from the ground state (GS) transition, and to the high temperature required for the growth of the AlGaAs upper cladding layer (UCL), that induced a strong emission blueshift. Recently, we showed that the antimony-mediated growth of InAs–Sb : GaAs QDs could break these deadlocks [4]–[6]. We demonstrated for the first time ground-state lasing above 1.3 (1.34 ) from MOCVD-grown GaAs-based QD lasers [6]. Despite this significant progress, the modal gain of 12.5 , obtained from five stacked QD layers [6], should be increased. Values of 30–40 are required in order to achieve 10-Gb/s data modulation [7]. Operation at 10 Gb/s has been reported for MBE-grown QD lasers [8], [9], corresponding to a gain of 35 . One way of increasing the modal gain is to increase the number of stacked QD layers. However, strain accumulation can become detrimental with stacking, and can cause severe degradation of the structure, such as threading dislocations, onset of undulations in the upper part of the QD active region, as well as a decrease of the QD density in the upper layers. In the present letter, we show that the antimony-mediated growth of InAs QDs is very effective in stacking a high number of QD layers. We report the fabrication of a MOCVD-grown QD laser structure with ten-stacked InAs–Sb : GaAs QD layers. GS lasing at 1.35 was obtained, with a maximum modal gain of 19.3 , which is the highest value reported by MOCVD.