Fabrication And Strain Enhancement In Germanium Nano-belts On Insulator

Germanium on insulator (GOI) with high carrier mobility, large absorption coefficient in optical communication band and compatible with mature silicon microelectronic technology, is considered to be one of the promising materials for Si-based integration of efficient light source and the next generation of microelectronic devices. However, it is still a big challenge to reslize Si based Ge light-emitting device due to its nature of indirect band gap. Whether applied to Si based light-emitting device or improve the carrier mobility in semiconductor device, large strain in Ge material is expected. In this thesis, two methods of preparation of GOI nanobelts are designed to improve the strain. The main works are summarized as follows:1. Strain profiles in Ge nano-belts on insulator surrounded by Si3N4or SiO2were simulated by using the finited difference time domain (FDTD) method. The parameters of width, thickness of Ge nano-belts on insulator, which have great effects on strain profile, are optimized. A large uniaxial tensile strain of1.16%in50nm width and12nm thickness Ge nano-belts with the sidewalls protected by Si3N4is predicted with proper thermal treatments, which provides theoretical basis for fabrication of Ge nano-belts.2. Based on Ge condensation method and hololithography,500nm wide GOI nano-belts were prepared by using epitaxial Si/SiGe/Si structure on SOI substrate. It was found that the strain in GOI nano-belts was improved to0.62%after deposition of Si3N4layer and thermal annealing. The simulation results demonstrated that the thermal mismatch between Ge and the top-and buried SiO2layers are the main reasons to increase the strain in GOI nanobelts during thermal treatment process.3. A method to fabricate size-controlled and Ge component-contolled SiGe nano-belts was proposed and prepared. The effects of oxidation and annealing time on the size and Ge component of SiGe nano-belts have been analysed.100nm wide Ge nano-belts with large compressively strain of2%were prepared, by using secondary oxidation for the striped SiGe nano-belts. It was found that the strain partly released depending on the bulge islands and breakage of Ge nano-belts. The simulation results showed the primary factor leading to compressively strain is thermal shrinkage of Ge, which extruding to Ge nano-belts on radial direction and along nano-belts direction during cooling process.