Etched-facets Mid-IR laser on on-axis Silicon substrate for photonic integrated circuits
Résumé
Silicon photonics has recently made great progress,particularlywiththe integration of passive devices such as (de)multiplexer or beam splitter among others. However, an efficient light source is still missing, because silicon has an indirect bandgap.Consequently, there is high interest for the integration of efficient III-V semiconductor laser sources compatible with the well-developed silicon platforms.This would open the way to compact, robust and affordable sensors based on silicon photonics integrated circuits (PICs). Although two approaches, bonding and direct epitaxy, are possible, direct epitaxy appears as the most promising approach for large scale integration.Therefore,this work is focused on the demonstration of mid-infrared Sb-based laser diodes (LDs) suitable for Si PICs for sensing applications.The actual integration of lasers on PICs first requires,on one hand,the epitaxy of high performance LDs on on-axis Si substrates and,on the other hand, the fabrication of a laser cavity without resorting to the cleavage stepused with discrete devices. In this communication we will focus on facet fabrication. We have developed a technology processto obtain good quality cleavage-free laser facets by using standard lithography and dry etching techniques. We first focus on GaSb-based laser diodes grown on GaSb substrates and emitting at 2.3 μm.We compare different geometries of the etched facets, T-shape and square shape,as well as shallow and deep ridge etching and we benchmark them with cleaved facets.The LD performances are very similar, which means that facet etching doesnot increase the optical losses. Then we transfer the optimized facet etching technological process to GaSb-based laser diodes grown on Silicon substrates. CW operation was achieved with similar threshold as discrete devices.1These results represent a step forward towards mid-infrared GaSb-based devices monolithically integrated on silicon for smart, compact and robust sensors on PICs