High-performance III-V quantum-dot lasers monolithically grown on Si substrates have been demonstrated as a promising solution to realise Si-based laser sources with very low threshold current density, high output power and long lifetime, even with relatively high density of defects due to the material dissimilarities between III-Vs and Si. On the other hand, although conventional III-V quantum-well lasers grown on Si have been demonstrated after great efforts worldwide for more than 40 years, their practicality is still a great challenge because of their very high threshold current density and very short lifetime. However, the physical mechanisms behind the superior performance of silicon-based III-V quantum-dot lasers remain unclear. In this paper, we directly compare the performance of a quantum-well and a quantum-dot laser monolithically grown on on-axis Si (001) substrates, both experimentally and theoretically, under the impact of the same density of threading dislocations. A quantum-dot laser grown on a Si substrate with a high operating temperature (105 °C) has been demonstrated with a low threshold current density of 173 A/cm 2 and a high single facet output power >100 mW at room temperature, while there is no lasing operation for the quantum-well device at room temperature even at high injection levels. By using a rate equation travelling-wave model, the quantum-dot laser's superior performance compared with its quantum well-based counterpart on Si is theoretically explained in terms of the unique properties of quantum dots, i.e., efficient carrier capture and high thermal energy barriers preventing the carriers from migrating into defect states.

We report the first demonstration of gain-switched optical pulses generated by continuous-wave 1.3 μm InAs/GaAs quantum dot (QD) broad-area lasers directly grown on silicon (Si). The shortest observed pulses have typical durations between 175 ps and 200 ps with peak output powers of up to 66 mW. By varying the drive current pulse width and amplitude systematically, we find that the peak optical power is maximized through sufficiently long high-amplitude drive pulses, whereas shorter drive pulses with high amplitudes yield the narrowest achievable pulses. A three-level rate equation travelling wave model is used for the simulation of our results in order to gain a first insight into the underlying physics and the laser parameters responsible for the observed behavior. The simulations indicate that limited gain from the InAs quantum dots and a very high gain compression factor are the main factors contributing to the increased pulse width. As the optical spectra of the tested broad-area QD laser give clear evidence of multi-transverse mode operation, the laser's dynamic response could be additionally limited due to transversal variations of the gain, carrier density, and photon density over the 50 μm wide laser waveguide.

In this work, we present an approach to modelling III-V lasers on silicon based on a travelling-wave rate equation model with sub-micrometer resolution. By allowing spatially resolved inclusion of individual dislocations along the laser cavity, our simulation results offer new insights into the physical mechanisms behind the characteristics of 980 nm In(Ga)As/GaAs quantum well (QW) and 1.3 m quantum dot (QD) lasers grown on silicon. By studying the reduction of the local gain in carrierdepleted regions around dislocation locations and the resulting impact on threshold current increase and slope efficiency at high dislocation densities, we identify two effects with particular importance for practical applications. First, a large minority carrier diffusion length is a key parameter inhibiting laser operation by enabling carrier migration into dislocations over larger areas, and secondly, increased gain in dislocation-free regions compensating for gain dips around dislocations may contribute to gain compression effects observed in directly modulated silicon-based QD lasers. We believe that this work is an important contribution in creating a better understanding of the processes limiting the capabilities of III-V lasers on silicon in order to explore suitable materials and designs for monolithic light sources for silicon photonics.

In this paper, we present measurements and simulations of the small-signal modulation response of monolithic continuous-wave 1.3 m InAs/GaAs quantum dot (QD) narrow ridge-waveguide lasers on a silicon substrate. The 2.5 mm-long lasers investigated demonstrate 3dB modulation bandwidths of 1.6 GHz, D-factors of 0.3 GHz/mA 1/2 , modulation current efficiencies of 0.4 GHz/mA 1/2 , and K-factors of 2.4 ns and 3.7 ns. Since the devices under test are not designed for high-speed operation due to their long length and hence long photon lifetime, the modulation response curves are used as a fitting template for numerical simulations with spatiotemporal resolution to gain insight into the underlying laser physics. The obtained parameter set is used to unveil the true potential of the laser material in an optimized device geometry by modeling the small-signal response at different cavity lengths, mirror reflectivities, and for different numbers of QD layers. The simulations predict a maximum 3dB modulation bandwidth of 5 GHz to 7 GHz for a 0.75 mm-long cavity with 99 % and 60 % high-reflection coatings and ten QD layers. Modeling the impact of dislocations on the dynamic performance qualitatively reveals that enhanced non-radiative recombination in the wetting layer leaves the modulation bandwidth of QD lasers on silicon almost unaffected, while dislocation-induced optical loss does not pose a problem, as long as sufficient gain is provided by the QD active region.

Small-signal experiments with a 2.5 mm-long quantum dot narrow ridge-waveguide laser on silicon show a modulation bandwidth of 1.6 GHz. For the first time, we report key high-speed parameters such as the differential gain and the gain compression factor.