Study Of Electro-Optical Effects And Optical Rectification In Silicon And Germanium

Both Silicon(Si)and germanium(Ge)are the first generation semiconductor materials,and have important applications in fields of microelectronics and optoelectronics.Especially,Si has drawn extensive concern in fields of integrated optics and optoelectronics,due to the cost effectiveness,the mature process,the convenience of integration,and the transparency at the communication wavelength of 1.3 ?m and 1.55 ?m.In recent years,Ge-based optoelectronic devices,which have the potential to extend the current communication wavelength to the mid-IR,have attracted attention as well,since Ge has good compatibility with the Si CMOS technology and is of good transparency in the mid-IR.Therefore,in this dissertation,the primary work focuses on the study of the PE and OR in Si and Ge surface layers.Moreover,as generalized electro-optical effects,the Franz-Keldysh(FK)effect and free carriers dispersion effect in Ge are investigated as well.These researches will provide experimental and theoretical basis for the applications of Si and Ge in fields of optoelectronics and nonlinear optics.The main research contents and results are as follows:(1)Based on the classical nonlinear polarization theory,theoretical analysis of the electric-field-induced(EFI)PE and OR was carried out.The Pockels signals and OR signals in Si(001)and Si(110)surface layers were measured.The Pockels signals changed linearly with the applied voltage,and are much larger than the Kerr signals.OR signals showed a cosine dependence on the azimuth of the linearly polarized light with a period of ?.These experimental results were in good agreement with the theoretical expectation.According to the fitted functions of the variation of OR with respect to the azimuth of the linearly polarized light,ratios of the effective second-order nonlinear susceptibilities in Si(001)and Si(110)surface layers were calculated.(2)The distribution of OR signals along the normal direction of the surface in Si(001)and Si(110)surface layers were studied.It is proved that the strength of OR signals is closely related to the surface properties of Si.A theoretical model for the relation of OR with the built-in electric field and the optical field was established.The distribution of OR signals was explained using the overlap integral of the built-in electric field and the optical field of the Gauss beam.The simulation results according to the theoretical model agreed well with the experimental data,which proved the feasibility to study the Si surface properties,such as the distribution of the built-in electric field and width of the SCR,using OR and the PE.In addition,the nonlinearities in Si(001)and Si(110)surface layers were compared.(3)EFI OR in Ge(001)and Ge(110)surface layers was researched for the first time.The relation between OR signals in Ge crystals and the azimuth of the linearly polarized light was measured,as well as the distribution of OR signals along the normal direction of the surfaces.The experimental results of the distribution of OR signals can be explained using the theoretical model metioned in(2).It proves that the method of using OR to study the properties of surface layers is also applicable to other materials with inversion symmetry.In addition,a primary study of the EFI PE and EFI OR in Ge(111)surface layers was carried out.(4)As generalized electro-optical effects,the FK effect and free carrier dispersion effect in Ge were researched.For different wavelengths,theoretical formulas about the dependence of the change of absorption coefficients and the change of refractive index on the electric field intensity and carrier concentrations were summarized.The results indicate that the change of the carrier concentration can give rise to a significant change of refractive index of Ge.Therefore,the free carrier dispersion effect is a potential mechamism for Ge-based modulators.