Development of Modulation p-Doped 1310 nm InAs/GaAs Quantum Dot Laser Materials and Ultrashort Cavity Fabry-Perot and Distributed-Feedback Laser Diodes

Multiple-layer InAs/GaAs quantum dot (QD) laser structures were etched to remove the p-side AlGaAs cladding layers to investigate the temperature-dependent photoluminescence (PL) characteristics. Four QD samples, including undoped as grown QDs, p-doped as grown QDs, undoped annealed QDs, and p-doped annealed QDs, were prepared by molecular beam epitaxy (MBE) and a postgrowth annealing process for comparison. Among them, modulation p-doped QD samples exhibit much less temperature-dependent characteristics of PL spectra and notable insensitivity to intermixing compared to undoped ones. This is attributed to the effects of modulation p-doping, which can inhibit holes' thermal broadening in their closely spaced energy levels and significantly suppress In/Ga interdiffusion between QDs and their surrounding matrix. These results provide greater freedom in the choice of MBE growth for high-quality active regions and claddings of QD laser diodes. The superior features of the modulation p-doped QD materials have been transferred naturally to the laser devices. The continuous-wave ground-state (GS) lasing has been realized in both p-doped QD Fabry-Perot (F-P) and laterally coupled distributed-feedback (LC-DFB) narrow ridge lasers with very short cavity length without facet coatings, in which a 1315 nm GS lasing has been found in a F-P laser with a 400 μm cavity length, while single longitudinal mode lasing with a very large tunable range of 140 nm and side mode suppression ratio of 51 dB is achieved in an LC-DFB laser. This work demonstrates great development potential of InAs/GaAs QD lasers for applications in high-speed fiber-optic communication.