The small and large signal responses of InP-based 1.55 μm high-speed quantum dot (QD) lasers with and without tunnel-injection (TI) quantum well (QW) and/or p-type doping in the active region (incorporating nominally identical QDs) were designed, manufactured and compared. The structures were grown by a molecular beam epitaxy system equipped with group-V valved cracker cells. In all cases, the active region consisted of six QD or TI-QD structures, which were embedded in InAlGaAs barriers lattice matched to InP. The InGaAs TI-QWs were separated by a thin InAlGaAs tunnel barrier from the InAs QDs. The laser structures were processed into ridge waveguide lasers and analyzed. The results show, that the bandwidth and maximum data rates were reduced by incorporation of TI-QWs. P-doping resulted in slightly worse performance of the simple QD laser, but in an improvement of the TI QD laser. Furthermore, the large signal response of the tunneling injection QD laser is one of the first reports of digital modulation of such a laser. An optimization of the doping profile is promising to further improve the laser performance over the undoped counterparts.
A comparison between QD lasers with and without tunnel-injection QW designs was performed. In both cases, six layers of a QD or TI-QD design were grown by molecular beam epitaxy equipped with group-V valved cracker cells. The InAs QDs are embedded in InAlGaAs barriers lattice matched to InP. The TI-QW consists of InGaAs separated by a thin InAlGaAs tunnel barrier. The lasers were processed into broad area and ridge waveguide lasers. Both laser designs exhibited high modal gain values in the range of 10-15 cm−1 per dot layer. The static and dynamic device properties of the different QD laser designs were measured and compared against each other.