Research On GeSn Near-and Mid-infrared Photodetectors Based On Surface Plasmon Absorption Enhancement

As one of the key core components in the field of optoelectronic technology,infrared photodetectors are widely used in military and civil fields,such as astronomy,missile tracking,free-space communications,safe surveillance,and solar cells inspection.At present,the commercial near and mid infrared photodetectors are mainly II-VI and III-V material,which are expensive and difficult to promote on a large scale.In recent years,silicon-based group IV GeSn material with adjustable bandgap has become the hot spot of silicon-based infrared detection technology due to its compatibility with standard complementary metal oxide semiconductor(CMOS)process and its potential performance advantages in infrared detection.However the problems of reported GeSn photodetector such as insufficient responsivity and poor signal-to-noise ratio are still outstanding.In order to meet the increasing demand for photodetector performance indicators,in this work some specially designed optical resonator and plasmon metal nanostructures are used to enhance the optical absorption without increasing the thickness of the absorption layer,so that the external quantum efficiency and the responsivity of the device can be significantly improved.Specific research results include the following aspects:Based on the mechanism of surface plasmon enhanced optical absorption,a polarization insensitive GeSn near and mid infrared photodetector is designed in this thesis.The structure model based on metal elliptic cylinder array is established.The influence of geometric parameters of elliptic cylinder array on the optical absorption spectrum of the device is studied by using finite difference time domain(FDTD)method.The optimal structure and parameters of the device with resonant wavelength near 2000 nm communication band are obtained.On this basis,by adjusting the key structural parameters of the metal elliptic cylinder array,the resonant wavelength is further extended to around 2400 nm.The optical absorption of the two optimized structures at 2000 nm and 2400 nm is increased by 8 and 50 times,respectively,compared with the GeSn planar structure.Two kinds of polarization sensitive GeSn near and mid infrared photodetectors are designed to satisfy the requirements of polarization sensitivity for polarization detection and spectral resolution applications.The structure model based on nanowire array is established,and the influence of geometric parameters of nanowire array structure on its optical absorption performance is studied.The optimized structure parameters of nanowire array with absorption close to 100% at 1550 nm and 2000 nm communication band are obtained.The cut-off response wavelength of the detector is extended effectively,and the absorption efficiency of the device is more than 90% at 2500 nm.The absorption extinction ratio under the illumination of incident light with different polarization angles reaches 9.In order to further explore the enhancement mechanism of introducing optical resonator and plasmon metal nanostructure into photodetector,a polarization sensitive dual mechanism enhanced photodetector composite structure is designed.The vertical cavity structure and plasmon metal grating structure are studied respectively.The influence of geometric parameters on the absorption spectrum of the structure is analyzed.On this basis,the two structures are optimized and combined and two kinds of composite structures with the strongest light absorption at 2000 nm and 2500 nm are obtained.The simulation results show that the optical absorption rate of the optimized composite structure increases 17% and 45%at 2000 nm,and the optical absorption rate of the composite structure after optimization at2500 nm increases 6% and 31% respectively,compared with the single plasmon grating structure and vertical cavity structure.In addition,the maximum absorption extinction ratio of 31 is achieved under the illumination of incident light with different polarization angles,which indicates that the structure has good polarization selectivity.In conclusion,the plasmon metal nanostructures designed in this thesis can not only significantly improve the optical absorption performance of photodetectors in the near and mid infrared band,but also meet the requirements of different applications on the polarization sensitivity of photodetectors,which is significant for the realization of high performance surface plasmon absorption enhanced GeSn near and mid infrared photodetectors.