Research On Electro-optic Properties And Femtosecond Laser Modification Of SiC Crystal

Silicon carbide (SiC) crystal, with unique characteristics of wide band gap(namely, high transparency from visible to near infrared region), high Young’s modulus,high hardness, and high optical damage threshold, is not only a promising candidateas semiconductor electronic material, but also applicable as high-performance opticalmaterial. Based on the excellent electrical effects and optical effects of SiC crystal, wehave explored the feasibility of6H-SiC electro-optic modulator, and further researchedelectro-optical properties of6H-SiC, which shows SiC crystal can be used to frabicatehigh temperature electro-optic modulator.In this thesis, electro-optical delays of6H-SiC crystal are analyzed on the basis ofrefractive index ellipsoid theory. During series of experiments, He-Ne laser (632.8nm)is employed to study the dependence of refractive index on the directions of lightpropagation and applied electric field, and then corresponding half-wave voltages andPockels electro-optic coefficients are calculated. Therefore, the database forelectro-optical parameters of6H-SiC are further enriched, which paues the way forfurther investigation in this field.We have studied the interaction mechanism of femtosecond laser and6H-SiC, andanalyzed the photoconductivity changes of SiC after its surface modification. It is foundexperimentally surface modification of6H-SiC by femtosecond laser will greatllyenhance the photoconduction at illumination of365nm arc lamp(namely, thephotocurrent is amplified of about ten times at the same appied dc voltage). Usingfemtosecond laser micromachining technology, high-quality gratings are form on thesurface and interior of6H-SiC crystal. Before and after annealing of6H-SiC crystal at1300°C, there are not significant differences on grating parameters. In other words,grating formed in6H-SiC is suitable for high temperature environment. It can be widelyapplied for optical processing, optical diffraction and optical sensor under theenvironment of high temperature.The sensing experiment has been done using the gratings, which form with theabove mentioned method. In the temperature range from room temperature to240°C, itis easily found that there is a good linear relationship between grating parameters andtemperature. This would not only offer an atternative way of high-temperaturetelemetering pickup, but also combine organically high temperature resistant properties and optical properties of SiC. At the same time it provides the possibility for opticalapplication of SiC in high-temperature environment.