Silicon-based All-dielectric Metasurface And Devices With Embeded Ge Quantum Dots

In the past few decades,electromagnetic metamaterials and metasurfaces have received wide attention in the whole world due to their unique electromagnetic properties.Different from the existing media in nature,metamaterials and metasurfaces can almost arbitrarily control the phase,polarization,and amplitude of the light field by flexible structure design and periodic arrangement.Especially,with simple fabrication process and high integration degree,the development of metasurfaces has shown the tendency to replace the traditional optical devices in some region.After years of development,the working wavelength of the metasurfaces has been shifted to the near-infrared and visible light range,and the constitute materials have been changed from noble metal to transparent dielectric medium,the basics of dielectric metasurfaces is the Mie resonance of the dielectric particles.In terms of functionality,dielectric metasurfaces can be divided into two categories: the first one is the gradient metasurface which can control the wavefront of light wave,such as surper lens;and the other is the resonant-type metasurface which enhances the resonance of optical field,this kind of metasurfaces can enhance the light-matter interaction through the resonant mode with high quality factor and strong near field enhancement.The focus of this thesis is the resonant-type dielectric metasurfaces.We designd different kinds of polarization-dependent and polarization-independent dielectric metasuface devices,and successfully fabricated the device on silicon-based material platform.The details of research are as follows:(1)Through the in-depth study of the Fano resonance in dielectric metasurfaces,the generation mechanism of the Fano resonance in dielectric disk arrays and the limitations of the resonance quality factor are analyzed.We proposed a method to balance the reversed electric dipole resonances by introducing a ring-shape defect,to realize a more fully destructive interference and higher quality factor.At the same time,the realization of high quality factor only destroys the local symmetry of the structure,the device still retains the complete symmetry in plane and belongs to polarization-independent structure.In addition,the slot effect brought by the ring-shape defect further enhances the local field enhancement at the resonant wavelength of the dielectric metasuface,which is conducive to enhancing the light-matter interaction.(2)A high-quality factor metasurface based on asymmetric microdisk structure is proposed.By analyzing the bright-dark mode coupling process and the generation mechanism of the trapped mode,we found that the dark mode is the limiting case of the trapped mode.The traditional bright-dark mode interaction is an indirect process to excite a high-quality factor resonant mode,which requires the structural asymmetry between bright and dark modes.If we regard the bright-dark model as a whole,this method can be seen as a way to couple the field from dark mode to the far field by breaking the structural symmetry.Therefore,it is only necessary to simply destroy the symmetry of the dark mode so that its resonance mode can be leaked to the far field,without the need of the bright mode.This new design idea allows us to flexibly design the high-quality factor dielectric metasurface.The simplest structure we proposed is to break the symmetry of a perfect disk array,the unit cell is equivalent to a semi-disk and a semi-elliptical disk spliced together,leaving a smooth sidewall.(3)We explored the full set of fabrication techniques for the silicon-based dielelctric metasurfaces.Through many experiments we concluded that the proximity effect and the stitching problems are the most critical issues faced in the fabrication of large-area dielelctric metasurface devices,especially the proximity effect in continuous large-area exposure.It can not be eliminated even with the use of professional proximity correction software,leading to the difficulty of obtaining dielectric metasurface devices with high uniformity using columnar structure.The most effective solution is to reduce the influence of the proximity effects by changing the design of the structure.Instead of the continuous large-area exposures,the separate small-area exposures are in favor,which means to replace the columnar structure with a hole-type structure.(4)A dielectric metasurface basd on asymmetric hole structure was designed and successfully fabricated.The spatial light test system confirmed its agreement with the simulation results.For the first time we combined the dielectric metasurface with the active light-emitting material.A dielectric metasurface is fabricated on the Ge quantum dot epitaxial wafer,a photoluminescence enhancement of more than 1000 times was observed using low temperature photoluminescence measurement.The highest quality factor of the emission peak is 1011,and the performance of device has reached the international advanced level.We have also explored the polarization characteristics of the dielelctric metasurface emission peaks and the effect of the pump spot size on device performance.The experiment results are consistent with the theoretical expectations.Furthermore,we compared the results of the passive spatial light test and the active photoluminescence light emission test,and for the first time the correspondence between the strongest light emission point and the Fano resonance peak has been confirmed,filling the gap in this research field.