We report on the first electrically pumped continuous-wave (cw) InAs/GaAs quantum dot (QD) lasers monolithically grown on on-axis Si (001) substrates without any intermediate buffer layers. A 400 nm antiphase boundary (APB) free epitaxial GaAs film with a small root-mean-square (RMS) surface roughness of 0.86 nm was first deposited on a 300 mm standard industry-compatible on-axis Si (001) substrate by metal-organic chemical vapor deposition (MOCVD). The QD laser structure was then grown on this APB-free GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE). Room-temperature cw lasing at ~1.3 µm has been achieved with a threshold current density of 425 A/cm² and single facet output power of 43 mW. Under pulsed operation, lasing operation up to 102 °C has been realized, with a threshold current density of 250 A/cm² and single facet output power exceeding 130 mW at room temperature.

III-V semiconductors monolithically grown on Si substrates are expected to be an ideal solution to integrate highly-efficient light-emitting devices on a Si platform. However, the lattice mismatch between III-V and Si generates a high density of threading dislocations at the interface between III-V and Si. Some of these threading dislocations will propagate into the III-V active region and lead to device degradation. By introducing defect filter layers (DFLs), the density of threading dislocations propagating into the III-V layers can be significantly reduced. In this paper, we present an investigation on the development of InGaAs/GaAs strained-layer superlattices as DFLs for 1.3 μm InAs/GaAs quantum-dot lasers monolithically grown on a Si substrate. We compare two broad-area InAs/GaAs quantum-dot lasers with non-optimized and optimized InGaAs/GaAs DFLs. The laser device with optimal DFLs has a lower room-temperature threshold current density of 99 A/cm 2 and higher maximum operation temperature of 88 °C, compared with 174 A/cm 2 and 68 °C for the reference laser.

Electrically-pumped lasers directly grown on silicon are key devices interfacing silicon microelectronics and photonics. We report here, for the first time, an electrically-pumped, room-temperature, continuous-wave (CW) and single-mode distributed feedback (DFB) laser array fabricated in InAs/GaAs quantum-dot (QD) gain material epitaxially grown on silicon. CW threshold currents as low as 12 mA and single-mode side mode suppression ratios (SMSRs) as high as 50 dB have been achieved from individual devices in the array. The laser array, compatible with state-of-the-art coarse wavelength division multiplexing (CWDM) systems, has a well-aligned channel spacing of 20±0.2 nm and exhibits a record wavelength coverage range of 100 nm, the full span of the O-band. These results indicate that, for the first time, the performance of lasers epitaxially grown on silicon is elevated to a point approaching real-world CWDM applications, demonstrating the great potential of this technology.

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.

The monolithic growth of III-V semiconductor lasers on Si remains the 'holy grail' for full-scale deployment of Si photonics with reduced cost and added flexibility. Further, semiconductor lasers with active regions made from quantum dots (QDs) have shown superior device performance over conventional quantum well (QW) counterparts and offer new functionalities. There are other advantages of QDs for monolithic III-V-on-Si integration over QWs, such as QD devices being less sensitive to defects. It is, therefore, not surprising that the past decade has seen rapid progress in research on monolithic III-V QD lasers on Si, with a view to leveraging the benefits of QD gain region technology while benefitting from the economics of scale enabled by monolithic growth. This review has a special focus on O-band III-V QD lasers monolithically grown on Si for Si photonic optical interconnects, including Fabry-Perot lasers, distributed-feedback laser array, and micro-lasers. The successes and challenges for developing monolithic III-V lasers on Si are discussed.