GeSn on Insulators (GeSnOI) Toward Mid-infrared Integrated Photonics

In recent years, Ge and Ge1-xSnx materials and devices have achieved rapid progress in integrated photonics. However, conventional heteroepitaxy of active photonic devices compromises the area on Si for CMOS electronics, limiting the scale of integration. Furthermore, it is not possible to grow GeSn epitaxially on amorphous and/or flexible substrates towards 3D photonic integration in mid infrared (MIR) regime. Here we present low-temperature crystallization of direct bandgap, high crystallinity Ge1-xSnx (0.08100x longer than the direct gap transition in Ge, confirming the indirect-to-direct band gap transition in GeSn at ~9 at. Sn composition. Moreover, a prototype p-GeSn/n-Si photodiode from a-GeSn crystallization achieves 100 mA/W responsivity at =2050 nm and T=300 K, approaching the level of some commercial PbS detectors. The device also demonstrates photovoltaic behavior and a low dark current density of 1 mA/cm2 at -1V reverse bias, comparable to epitaxial Ge/Si photodiodes. These results indicate that crystallization of GeSnOI offers a promising solution for active devices towards 3D MIR photonic integration and/or MIR photonics on flexible substrates.