Study On Field-induced Second-order Nonlinear Optical Effects In Silicon And Germanium MOS Structures

Silicon and germanium MOS structures are basic structural units of silicon-based and germanium-based semiconductor devices,respectively.MOSEFT and CMOS are the basic device units in integrated circuits,whose gate regions are composed of typical MOS structures.The interface property in the MOS structure has a huge impact on the device performance,so it is important to analysis the interface property of MOS structures.In the past,the field-induced second harmonic generation effect from the surfaces and interfaces of silicon and germanium materials was intensively studied,and became an effective method to detect the surface and interface properties of silicon and germanium.But the field-induced Pockels effect and optical rectification effect of silicon and germanium MOS structure were seldom researched.Therefore,we will focus on this aspect and explore the feasibility of using the field-induced Pockels effect and optical rectification effect as a method to analysis interfaces and surfaces of silicon and germanium MOS structure in this thesis.The main research contents and results in this thesis are as follows:1.Based on the classical polarization theory,we interpreted the field-induced Pockels effect and optical rectification effect,and measured the Pockels effect and optical rectification effect from the interface and surface layers of Si（100）and Si（110）MOS structures.It is found that the Pockels signals and optical rectification signals from the SiO₂/Si interface layers are much stronger than the corresponding signals in the silicon surface layers without SiO₂ films.Raman spectroscopy results show that,because of SiO₂ films deposited on surfaces of Si（100）and Si（110）crystals,the Raman peaks have a blue-shift of 1.75 cm^-1,which proves that SiO₂ films cause compressive stress in silicon interface layers.The stress-induced second-order nonlinear polarizabilities of SiO₂/Si（100）and SiO₂/Si（110）interface layers were estimated to be about 13.8 pm/V and 11.6 pm/V,respectively.2.We also measured the field-induced Pockels effect and optical rectification effect in the interface layers of Ge（100）and Ge（110）MOS structures.The experimental results show that considerable Pockels signals and optical rectification signals exist in interface or surface layers of germanium crystals,and both Pockels signals and optical rectification signals in the SiO₂/Ge interface layers are stronger than the other side without SiO₂ films.Raman spectroscopy results show that the SiO₂films induce tensile strain in the interface layers of Ge（100）and make the Raman peak have a red-shift of 1.79 cm^-1.The stress-induced second-order nonlinear polarizability is about 271.5 pm/V.3.The distributions of the field induced optical rectification signals along the normal direction of the surface layers of Si（100）,Si（110）and Ge（100）MOS structures were measured.The overlap integral of the polarization field and optical field is used for simulating the experimental data.The electric-field-induced second-order nonlinear polarizabilities in the SiO₂/Si（100）interface layer and Si（100）surface layer were respectively estimated to be 13.67 pm/V and 13.4 pm/V,and those in SiO₂/Si（110）interface layer and Si（110）surface layer were respectively 16.02 pm/V and 11.05 pm/V.Since the field-induced optical rectification signal is closely related to the interface state,built-in electric field,strain field,width of space charge region of the MOS structure and the size of laser spot,the field-induced optical rectification effect can be used as an effect method to research the surface or interface property of materials with the inversion symmetry such as silicon and germanium.