Epitaxial Growth Of Germanium Film On Silicon With MBE Process And Its RHEED Analysis

Epitaxial growth of Ge or GeSi on Si is increasingly attractive for the high carrier mobility and small derect energy band gap of Ge,which could be used to improve the performance of traditional devices.The emphasis of growing pure Ge on Si substrates is the control of the release of the strain in the heterostructure due to the 4.2%lattice misfit between Ge and Si.This thesis work mainly involves the deposition issues using the Moculer Beam Epitaxial equipment,and seeking for the techniques for the fabrication of high quality Si and Ge epitaxial films on Si.Atomic Force Microscopy,Etch Pits Density test,Raman Spectropy and so on are used to illustrate the characterizations of eptaxial films,while it is still difficult to in-situ monitor and detect of the deposition of films and micro-structures.In this work, we also study the way to in situ monitor the epitaxial fabrications using Reflection High Energy Electron Diffraction(RHEED).RHEED patterns from the epitaxial growth of Si—Ge crystal are interpreted basing on the kinetically diffractive theory of crystal.The transmission pattern is studied and interpreted,which relates to the rough surface after crystal growth.The RHEED patterns of polycrystalline rings and twin crystal and their evolvements are analyzed with considering the respective epitaxial growth conditions.This work has studied the epitaxial growth machanism,to fabricate high quality Ge epitaxial films on Silicon(001) substrates,with new structures of films designed and experimental parameters optimized.We have studied the effect of intermediate layer and low temperature Ge buffer layer,and proposed muti-buffer layers' structure for epitaxial growth of high quality Ge thin films on Si(001) substrates considering our MBE equipment's condition.The muti-buffer layers,including low temperature Ge seed layer,SiGe alloy intermediate layer under different temperatures,serve as defect gathering and annihilating sites to reduce the dislocation density in the top layers.The result reveals that the total thickness of the whole structure is less than 400 nm,with a low threading dislocation density of less than 5×10⁵ cm^-2 in the top layer and a root mean square surface roughness of 1.5nm.All our work is for the following study on devices applications.