Research progress of Si-based germanium materials and devices

Si-based germanium is considered to be a promising platform for the integration of electronic and photonic devices due to its high carrier mobility, good optical properties, and compatibility with Si CMOS technology. However, some great challenges have to be confronted, such as: (1) the nature of indirect band gap of Ge; (2) the epitaxy of dislocation-free Ge layers on Si substrate; and (3) the immature technology for Ge devices. The aim of this paper is to give a review of the recent progress made in the field of epitaxy and optical properties of Ge heterostructures on Si substrate, as well as some key technologies on Ge devices. High crystal quality Ge epilayers, as well as Ge/SiGe multiple quantum wells with high Ge content, were successfully grown on Si substrate with a low-temperature Ge buffer layer. A local Ge condensation technique was proposed to prepare germanium-on-insulator (GOI) materials with high tensile strain for enhanced Ge direct band photoluminescence. The advances in formation of Ge n+p shallow junctions and the modulation of Schottky barrier height of metal/Ge contacts were a significant progress in Ge technology. Finally, the progress of Si-based Ge light emitters, photodetectors, and MOSFETs was briefly introduced. These results show that Si-based Ge heterostructure materials are promising for use in the next-generation of integrated circuits and optoelectronic circuits.