Abstract
The tremendous demand for low-cost, low-consumption and high-capacity optical transmitters in data centers challenges the current InP-photonics platform. The use of silicon (Si) photonics platform to fabricate photonic integrated circuits (PICs) is a promising approach for low-cost large-scale fabrication considering the CMOS-technology maturity and scalability. However, Si itself cannot provide an efficient emitting light source due to its indirect bandgap. Therefore, the integration of III-V semiconductors on Si wafers allows us to benefit from the III-V emitting properties combined with benefits offered by the Si photonics platform. Direct epitaxy of InP-based materials on 300 mm Si wafers is the most promising approach to reduce the costs. However, the differences between InP and Si in terms of lattice mismatch, thermal coefficients and polarity inducing defects are challenging issues to overcome. III-V/Si hetero-integration platform by wafer-bonding is the most mature integration scheme. However, no additional epitaxial regrowth steps are implemented after the bonding step. Considering the much larger epitaxial toolkit available in the conventional monolithic InP platform, where several epitaxial steps are often implemented, this represents a significant limitation. In this paper, we review an advanced integration scheme of AlGaInAs-based laser sources on Si wafers by bonding a thin InP seed on which further regrowth steps are implemented. A 3 µm-thick AlGaInAs-based MutiQuantum Wells (MQW) laser structure was grown onto on InP-SiO2/Si (InPoSi) wafer and compared to the same structure grown on InP wafer as a reference. The 400 ppm thermal strain on the structure grown on InPoSi, induced by the difference of coefficient of thermal expansion between InP and Si, was assessed at growth temperature. We also showed that this structure demonstrates laser performance similar to the ones obtained for the same structure grown on InP. Therefore, no material degradation was observed in spite of the thermal strain. Then, we developed the Selective Area Growth (SAG) technique to grow multi-wavelength laser sources from a single growth step on InPoSi. A 155 nm-wide spectral range from 1515 nm to 1670 nm was achieved. Furthermore, an AlGaInAs MQW-based laser source was successfully grown on InP-SOI wafers and efficiently coupled to Si-photonic DBR cavities. Altogether, the regrowth on InP-SOI wafers holds great promises to combine the best from the III-V monolithic platform combined with the possibilities offered by the Si photonics circuitry via efficient light-coupling.
Highlights
Data traffic exponential growth has pushed forward the demand for high speed, high performance, energy-efficient and cost-effective data transmission [1]
Alternatives based on strained Ge, Ge-Sn materials grown on Si wafers have permitted band-gap engineering and even laser demonstration [4], but performance is still far behind the one that can be obtained in the III-V conventional approach
9 of 17 epto a more traditional approach based on discrete DFB lasers fabricated from different itaxial growths further integrated on a SOI wafer by means of die-bonding [41], Selective Area Growth (SAG) technique allows us to obtain the entire set of emission wavelength from a single growth step
Summary
Data traffic exponential growth has pushed forward the demand for high speed, high performance, energy-efficient and cost-effective data transmission [1]. HP group have reported pulsed and CW laser demonstrations up to 20 ◦ C based on the regrowth of a 2.5 μm-thick GaInAsP-MQW laser coupled to a Si-waveguide [31] Their approach involves InP-Si bonding using Vertical Outgassing Channels (VOCs) buried under the III-V stack to absorb the generated gas produced at the bonding interface [10]. These VOCs have to be opened up by etching the III-V stack in order to be compatible with MOVPE annealing temperature [32], which induces alignment constraints and more complexity to the fabrication process In this context, we developed a novel integration scheme based on InP-seed-bonding and regrowth using an oxide layer at the bonding interface thick enough to act as a hydrogen reservoir [33].
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