Light Sources For Silicon Photonics Research Articles

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.

Advances in silicon photonics with quantum dot lasers

More than forty years ago, in 1982, we proposed the concept of quantum dot lasers and at the same time theoretically predicted the temperature insensitivity of the threshold current. With advances in growth technology, the predicted characteristics were demonstrated in 2004, and high-temperature operation up to 220°C became possible in 2011. Currently, quantum dot lasers are positioned as a promising light source for silicon photonics, especially in terms of their ability to operate at high temperatures in co-packaged optical technology. In this talk, I will describe the historical development of quantum dot lasers and their integration into 5 mm square silicon-based transceiver chips, as well as the direct epitaxial growth of quantum lasers on silicon. The talk will also demonstrate the integration of quantum dot-based light sources, including single-photon sources, on silicon integrated circuits using transfer printing methods.

Sensitized electroluminescence from erbium doped silicon rich oxynitride light emitting devices

Erbium doped Si-related compound films, with the 1540 nm emission coinciding with the minimum loss window of optical telecommunication, are regarded as appealing platforms of light sources for silicon photonics. In many previous reports, however, the unipolar carrier injection in silicon oxide/nitride films leads to favorable impact excitation of Er rather than sensitization, requiring high onset voltage that is not compatible with Si microelectronics. Silicon rich oxynitride (SRON) with tunable bandgap enables equivalent bipolar injection, yet there are few reports about light emitting devices (LEDs) based on this material with Er doping. Here, sensitized electroluminescence (EL) from erbium doped SRON with an onset voltage as low as 5 V has been demonstrated. The sensitization mechanism is evaluated by correlating the evolution of charge transport in SRON films subjected to different thermal treatments with that of Er3+ EL. The EL can be attributed to bipolar Poole-Frenkel injection of carriers and subsequent capture by Si dangling bond related trap states, followed by energy transfer to Er3+ ions. These results indicate that SRON serves as a promising Er3+ host for complementary metal-oxide-semiconductor (CMOS) compatible light sources.

Theoretical Study on the Effects of Dislocations in Monolithic III-V Lasers on Silicon

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 μm quantum dot (QD) lasers grown on silicon. We identify two effects with particular importance for practical applications from studying the reduction of the local gain in carrier-depleted regions around dislocation locations and the resulting impact on threshold current increase and slope efficiency at high dislocation densities. 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.

Phosphorus-free 1.5 µm InAs quantum-dot microdisk lasers on metamorphic InGaAs/SOI platform.

III-V semiconductor lasers epitaxially grown on silicon, especially on a silicon-on-insulator (SOI) platform, have been considered one of the most promising approaches to realize an integrated light source for silicon photonics. Although notable achievements have been reported on InP-based 1.5 µm III-V semiconductor lasers directly grown on silicon substrates, phosphorus-free 1.5 µm InAs quantum dot (QD) lasers on both silicon and SOI platforms are still uncharted territory. In this work, we demonstrate, to the best of our knowledge, the first phosphorus-free InAs QD microdisk laser epitaxially grown on SOI substrate emitting at the telecommunications S-band by growing metamorphic InAs/InGaAs QDs on (111)-faceted SOI hollow structures. The lasing threshold power for a seven-layer InAs QD microdisk laser with a diameter of 4 µm is measured as 234 μW at 200 K. For comparison, identical microdisk lasers grown on GaAs substrate are also characterized. The results obtained pave the way for an on-chip 1.5 µm light source for long-haul telecommunications.

Enhanced Raman scattering of graphene using double resonance in silicon photonic crystal nanocavities

We demonstrate enhancements of Raman scattering from graphene on two-dimensional photonic crystals using double resonances, which originate from simultaneous enhancements by a localized guided mode and a cavity mode. By adjusting the photonic crystal cavity parameters, the double resonance can be tuned to the G′ Raman scattering. Excitation wavelength dependence measurements show a large Raman peak enhancement when the excitation and emission wavelengths meet the double resonance condition. Furthermore, spatial imaging measurements are performed to confirm that the enhancement is localized at the cavity, and we find that the enhanced Raman intensity is 60 times larger compared to the on-substrate Raman signal. The observed cavity enhancement of Raman scattering opens up new possibilities for the development of graphene-based light sources for silicon photonics.

Highly Reliable Low-Threshold InAs Quantum Dot Lasers on On-Axis (001) Si with 87% Injection Efficiency

Quantum dot lasers epitaxially grown on Si are promising for an efficient light source for silicon photonics. Recently, considerable progress has been made to migrate 1.3 μm quantum dot lasers from off-cut Si to on-axis (001) Si substrates. Here, we report significantly improved performance and reliability of quantum dot lasers enabled by a low threading dislocation density GaAs buffer layer. Continuous-wave threshold currents as low as 6.2 mA and output powers of 185 mW have been achieved at 20 °C. Reliability tests after 1500 h at 35 °C showed an extrapolated mean-time-to-failure of more than a million hours. Direct device transparency and amplified spontaneous emission measurements reveal an internal optical loss as low as 2.42 cm–1 and injection efficiency of 87%. This represents a significant stride toward efficient, scalable, and reliable III–V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with CMOS foundries.

Nonclassical light sources for silicon photonics

Quantum photonics has recently attracted a lot of attention for its disruptive potential in emerging technologies like quantum cryptography, quantum communication and quantum computing. Driven by the impressive development in nanofabrication technologies and nanoscale engineering, silicon photonics has rapidly become the platform of choice for on-chip integration of high performing photonic devices, now extending their functionalities towards quantum-based applications. Focusing on quantum Information Technology (qIT) as a key application area, we review recent progress in integrated silicon-based sources of nonclassical states of light. We assess the state of the art in this growing field and highlight the challenges that need to be overcome to make quantum photonics a reliable and widespread technology.

Wavelength division multiplexed light source monolithically integrated on a silicon photonics platform.

We demonstrate monolithic integration of a wavelength division multiplexed light source for silicon photonics by a cascade of erbium-doped aluminum oxide (Al2O3:Er3+) distributed feedback (DFB) lasers. Four DFB lasers with uniformly spaced emission wavelengths are cascaded in a series to simultaneously operate with no additional tuning required. A total output power of -10.9 dBm is obtained from the four DFBs with an average side mode suppression ratio of 38.1±2.5 dB. We characterize the temperature-dependent wavelength shift of the cascaded DFBs and observe a uniform dλ/dT of 0.02 nm/°C across all four lasers.

Design and analysis of a CMOS-compatible distributed Bragg reflector laser based on highly uniaxial tensile stressed germanium.

We design a CMOS-compatible Distributed Bragg Reflector (DBR) laser based on highly uniaxial tensile stressed germanium. Our design first incorporates three critical elements including high uniaxial tensile stress, low loss optical resonator and heterojunction for electrical injection. A threshold current density of 80 kA/cm2 and an internal quantum efficiency of 8.5% are estimated when the Shockley-Reed-Hall (SRH) lifetime is chosen to be 3 ns. Furthermore, the performance of the DBR laser can be enhanced by improving the crystal quality and carefully designing the p-n junction. The simulation results also indicate that the limitation of the improvement of threshold current density and internal quantum efficiency are 29 kA/cm2 and 19.6%, resulting from the Auger recombination. The influences of strain and n-type doping on the threshold current density and the internal quantum efficiency are discussed. The proposed DBR laser offers a new approach to realize on-chip light source for silicon photonics.

On-chip light sources for silicon photonics

Hybrid silicon lasers based on bonded III–V layers on silicon are currently the best contenders for on-chip lasers for silicon photonics. On-chip silicon light sources are highly desired for use as electrical-to-optical converters in silicon-based photonics. Zhiping Zhou and Bing Yin of Peking University in China and Jurgen Michel of Massachusetts Institute of Technology assess the three main contenders for such light sources: erbium-based light sources, germanium-on-silicon lasers and III-V-based silicon lasers. They consider operating wavelength, pumping conditions, power consumption, thermal stability and fabrication process. The scientists regard the power efficiencies of electrically pumped erbium-based lasers as being too low and the threshold currents of germanium lasers as being too high. They conclude that III–V quantum dot lasers monolithically grown on silicon show the most promise for realizing on-chip lasers.

Hybrid single quantum well InP/Si nanobeam lasers for silicon photonics

We report on a hybrid InP/Si photonic crystal nanobeam laser emitting at 1578 nm with a low threshold power of ~14.7 μW. Laser gain is provided from a single InAsP quantum well embedded in a 155 nm InP layer bonded on a standard silicon-on-insulator wafer. This miniaturized nanolaser, with an extremely small modal volume of 0.375(λ/n)(3), is a promising and efficient light source for silicon photonics.