Advances on III-V on Silicon DBR and DFB Lasers for WDM Optical Interconnects and Associated Heterogeneous Integration 200mm-Wafer-Scale Technology

In the absence of practically efficient lasers achievable directly in Silicon or other group IV materials, Si-photonic transmitter sources must be made by "Hybrid integration" of III-V chips or "Heterogeneous integration" with III-V gain materials. "Hybrid integration" technologies consist in integrating processed (and finished) chips in a photonic microsystem. One commercial solution (from LUXTERA) makes use of a InP-bulk- processed laser-chip [3]. The laser chip is attached to the PIC, and its light is coupled into the PIC- waveguide by means of a lens, followed by an optical isolator, and a mirror for directing the light to a surface grating coupler in the Si-PIC. Other approaches (from KOTURA/ORACLE) consist in but-coupling a III-V- semiconductor reflective-SOA to the PIC-3μm- thick-Si-waveguide that comprises a Bragg-mirror for defining the laser cavity [4]. This forms an external-cavity DBR laser, with reported Waveguide-Coupled Wall-Plug-Efficiencies (WC-WPE) for the uncooled lasers of up to 9.5% at powers of 6 mW. In spite of the good demonstrated performances, this solution requires an accurate alignment between the R-SOA and the Si-PIC, limiting the capability for a low cost fabrication. As a more economical route that we opted for, "Heterogeneous integration" technologies were proposed [5], [6] together with new laser architectures. An InP-wafer having the III-V-gain- layers grown on top is bonded with loose alignment requirements (~50μm), the III-V gain-layers facing down to the bottom Silicon-On- Insulator (SOI) wafer on which silicon waveguides are pre- processed. In a more economical route, the InP-substrate having the laser III-V-gain- layers on top is first diced, and the dies are bonded where needed. Then the InP-substrate is removed, and the laser process is continued on the remaining III-V gain epi-layers, in a regular wafer level process flow. Putting the expensive III-V-gain material only where needed saves on cost. In addition- to lower cost, photonic integration promises improved reliability and performances and reduced footprints over discrete components systems. This paper will report on our recent advances on both, 1) the developed III-V on Silicon lasers (DBR and DFB types) built up from heterogeneous integration, and, 2) the development of the integration technology for processing the lasers on 200mm-wafers, with industrial CMOS tools at very low cost.