Advanced epitaxy for the synthesis and integration of optically active Hexagonal SiGe crystal phases – Adhex-SiGe

The hexagonal 2H crystal phases of SixGe(1-x), with their direct band gap, are on the verge of revolutionizing the optoelectronic industry by providing the holy grail: an efficient light emitter compatible with the Silicon platform. Our previous studies have used phase transformation or core/shell nanowire synthesis, two fabrication processes which are limited to small volumes. For future integration, there is a need to grow such SixGe(1-x)-2H in a scalable way.

Adhex-SiGe aims at establishing a route to synthesize planar layers of SixGe(1-x)-2H. By mastering the epitaxy on adequate hexagonal substrates, one can overrule the stability of the cubic bulk material and obtain the SixGe(1-x)-2H phase. Based on the use of II-VI wurtzite substrates, our epitaxy approach is definitely new. We will study the crystal growth mechanisms and the defect formation in SixGe(1-x)-2H. Various approaches are considered to accommodate the lattice parameters between the substrate and the SixGe(1-x)-2H layer. This includes the recently reported process of remote epitaxy, based on the insertion of a graphene buffer layer. Its study with highly ionic II-VI materials is expected to validate or refute the process, and to give great insight into the mechanisms involved. A great advantage will be the possibility to peel off the grown layer in order to transfer it onto a Si-platform.

The synthesis of high quality planar SixGe(1-x)-2H layers will allow us to answer many open questions about the physical properties of these new materials: exact band structure, active doping, optical properties, etc. For SixGe(1-x)-2H with 0<x<0.4, the band gap is expected in the MIR region from 1.8 and 3.5 µm. The full success of ADHEX-SiGe would be demonstrating the transfer of the grown SixGe(1-x)-2H layer on Si platform for CMOS compatibility. This will open a large market for MIR laser applications.<br />The project benefits from the recognized and complementary expertise of the three partners (C2N, GEMAC, NPSC) in the epitaxy of relevant semiconductors and in a wide range of advanced material characterization tools (STEM-EDX, HR-XRD, SIMS, XPS/AES). The extension of a SEM-cathodoluminescence setup toward the infrared region will be available at the beginning of the project. This unique tool will be combined with photoluminescence for the analysis of emission properties as well as spectral signature of impurities and/or defects below the band-gap.