Growth And Characterization Of Si-based Strain Relaxed SiGe Substrate And SiGe/Si Quantum Wells

In recent years,Si-based optoelectronics have made significant progress for Si-based optoelectronic devices have many advantages such as a low cost,compatible with micro-electronics technology and so on.It will become one of the most important technologies in the optical interconnection chip in future.To realize a single chip integration of Si-based optoelectronic devices,it is hoped to overcome the limitation of indirect band property of Si-based materials,and then an effective Si-based light source should be carried out.SiGe/Si quantum wells have many novel optical and electronic properties,which are promising to improve luminescence of Si-based materials by tailing band structures with quantum effect and strain effect via the virtual substrate technology.In this thesis,the Si-based strain relaxed SiGe substrates were prepared by inserting a low-temperature Ge layer in ultra-high vacuum chemical deposition (UHV/CVD).The SiGe/Si quantum wells were designed and fabricated on the strain relaxed SiGe buffers and the optical properties were anlysised.1.Strain relaxed SiGe substrates were prepared on silicon substrate by inserting a low-temperature Ge layer in UHV/CVD.The growth conditions of the buffer including LT Ge layer,LT SiGe layer and HT SiGe layer were systemically studied and optimized.By inserting a LT Ge layer at 330℃,thin strain realxed Si_0.73Ge_0.27 buffers with the dislocation density of 2×10⁵cm^-2,91%strained relaxation were obtained without cross-hatch misfit dislocation line on surface.The root-mean-square surface roughness was less than 1.8nm.2.The role of LT Ge layer in the mechanism of strain relaxation of Si-based SiGe buffer was analyzed.With inserting a LT Ge layer,the surface of the SiGe buffer layers become smooth with a reduced threading dislocation density.The island-like surface undulation of the LT Ge layer,acting as a soft substrate,could alleviate the cross-hatch misfit dislocation line on surface and promote the relaxation of strain in the buffer homogeneously. 3.Design and optimization of W type and N type SiGe/Si quantum wells structures were carried out.On the basis of calculating the wavefunction overlap of carriers in quantum wells,W type quantum wells are predicted to have a greater transition probability.The optical properties of the SiGe/Si quantum wells grown on the Si-based strain relaxed SiGe buffers were investigated.