Project 3.4

The project aims at realising innovative lasers in the important 2-2.5 μm wavelength range. This project shares many common challenges with ESR1.3 and the two students will work together to address the physical challenges before diverging to work on the particular issues with each wavelength range. In particular, the laser diodes developed by ESR3.4 will be fabricated in the GaSb technology which differs from the InP telecom technology investigated by ESR1.3. GaSb-based laser diodes are able to cover the wavelength range from 1.5 to 3.3 μm, and are particularly efficient in the 2-2.5 μm range. An innovative aspect of this project is that the gain sections will be epitaxially grown on Si substrates which will allow to fabricate the cavity and waveguide directly in the Si-based platform. This transfers the complex processing from the III-V material to the well mastered Si technology. The realisation of a hybrid epitaxial laser on Si will be a scientific first, regardless of the laser technology. A number of challenges have been identified. The epitaxial growth of III-V on Si is plagued by a high defect density which will have to be minimized. The growth on a structured Si template will add complexity to the task, and the growth conditions are expected to be significantly shifted away from those of growing on a plain wafer. The coupling scheme between the III-V gain zone and the Si-based waveguides will have to be clarified (butt-like coupling, evanescent coupling,..). The gain zone and Si-based waveguide will have to be co-designed to solve this issue. In particular, the design of the coupling will be carried out by means of several methods that also include the Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Rigorous Coupled Wave Analysis (RCWA) method and Transfer Matrix Method (TMM) implemented by commercial (VPI and others) and home-made codes. The process flow for both the gain zone structuring and cavity and waveguide fabrication will have to be defined to preserve the integrity of both III-V and Si-based materials.

The ESR will be involved in the cavity and waveguide design, in the growth by molecular-beam epitaxy of the gain zone and in the final device fabrication.