Research On Longwave Infrared Absorber Structures Based On Local Field Enhancement

Traditional electromagnetic absorbers have disadvantages such as large volume and low absorbance;so,they are subject to many restrictions.Metamaterial absorbers have the advantages of small structure size,simplicity in fabrication,and high degree of integration.Therefore,the reaserch of metamaterials have attracted great interest in recent years.By designing appropriate parameters of the metamaterial absorption structure,perfect absorption can be achieved at the microwave,infrared,and even visible light.In this thesis,three metamaterial absorption structures are designed,and their absorption characteristics are studied by finite difference time domain method.The structure can achieve a high degree of light localization to realize the absorption enhancement in the longwave infrared band,and have a potential application prospect in the field of photoelectric detection.The main contents are as follows:(1)Based on the Fano resonance theory,a silicon-based absorber in micro-hole array structure is designed,which can confine the incident light field to the inside of the silicon and significantly enhance the interaction between the light and silicon.At the same time,with the help of the optical loss introduced by the P-type heavy doping of silicon material,the absoption of the system is significantly improved,and it is expected to be used for silicon-based hot carrier detector.The numerical simulation results show that the peak absorption of the system reaches 95.3%.(2)Combined with Fano resonance,a metamaterial structure with enhanced longwave infrared absorption of graphene is proposed.Graphene is a two-dimensional material with a single atomic layer thickness,and has an ultra-high carrier mobility,which is conducive to the integration of long-wave infrared detectors and the improvement of the responsivity of the device.At the same time,the introduced fano resonance can confine the incident light inside the structure to enhance the interaction between light and graphene,and overcome the problems of graphene's low absorptivity(?2.3%)and the wavelength selectivity.The numerical simulation results show that the peak absorption of graphene reaches 36%.(3)A graphene absorption enhancement structure based on surface phonon polariton is designed,in which the absorption of graphene is mainly contributed by the interband transition.It is expected to be used for photonic long-wave infrared detection.With the help of the additional wave vector provided by the top metal grating,the vertically incident transverse magnetic wave can excite the surface phonon polariton mode at the interface of aluminum nitride and gallium nitride,confining the light near the graphene to a large extent,and significantly increasing the absorption of graphene.The results show that the peak absorption is 46%.