Si-Based Ge and GeSn Material Epitaxy and Thermal Stability Characterization

Abstract

_In the past decade, Si photonics has become one of the hottest research topics in the world since it holds great promise for maintaining the performance roadmap known as Moore’s law. The application of silicon photonics technologies to requires the development of high quality Si-based materials for photonics devices monolithically integrated to a Si platform. Germanium (Ge), due to its large absorption coefficient at near-infrared frequencies, and its lower cost and compatibility of parallel processing with silicon compared to III-V semiconductors, is perceived as the best candidate for on-chip photodetectors. Meanwhile, Ge is a pseudo-direct bandgap material because its direct Γ-valley CB is just 136.5 meV above the lowest L-valley CB at room temperature . This energy difference can be effectively reduced by incorporating Sn, another group-IV element, into Ge to modulate the band structure. GeSn alloy has been proven to be another promising material for the Si-based laser and PDs covering all telecommunication windows. In this presentation, Ge 、GeSn and GeSn/Ge MQW have been grown on Si, Ge/Si and Ge. The crystallinity and growth quality of the Ge and GeSn films were investigated through material characterization methods including x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy. In order to grow GeSn on Si and Ge subtrate,the growth is performed at low temperature, but the devices fabrication process will be carried out at high temperature, so the stability study is important. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is also examined. the results show that GeSn alloy have good thermal stability at 500℃if Sn contents are as low as ~3%. The stability of the GeSn/Ge MQW structure is temperature-dependentand and the temperature over 400℃ should be avoided to guarantee the structural integrity of the MQWs.