Study On Enhancing Optical Absorption And Infrared Detection Performance Of Two-dimensional Materials Based On Artificial Micro- And Nano-structures

Since the first discovery of graphene,its excellent electrical and optical properties have attracted extensive attention.Graphene has attracted much attention in the field of photoelectric detection due to its wide band absorption and high carrier mobility.With the development of material preparation technology,compared with two-dimensional graphene,new two-dimensional materials with various characteristics have emerged.Due to the quantum confinement of the longitudinal scale,they show many excellent optoelectronic properties that traditional semiconductors do not have,which greatly attracts the interest of optoelectronic devices based on two-dimensional materials.However,the optical path at the atomic layer level limits the optical absorption of two-dimensional materials,which is the key factor for the low responsivity of intrinsic two-dimensional materials optoelectronic devices.In recent years,it has become a new trend to improve the performance of two-dimensional materials optoelectronic devices by controlling the interaction between light and matter through micro-nano photonic structures,so as to enhance the absorption of two-dimensional materials.In this paper,we mainly focus on the research of using micro-and nano-structures to control the optical coupling of two-dimensional materials so as to enhance the optical absorption and photoresponse.The physical mechanism of the optical absorption and photoresponse enhancement of two-dimensional materials devices with integrated micro-and nano-optical coupling structures is analyzed theoretically and experimentally.The internal mechanism of the enhanced interaction between the light and two-dimensional materials is revealed,and the self-driven photoresponse enhancement of devices is realized.Perfect light absorption with high intensity and high bandwidth of two-dimensional materials is realized.The main innovative results are as follows:1.The hybrid structure of graphene and plasmonic micro-and nano-cavities is established.The electromagnetic parameters of the material are obtained through the experimental data.Based on the finite element method,the incident light is fully coupled into the hybrid structure.The strong local light field makes the graphene absorption significantly improved.The numerical results show that the absorptivity of graphene increases to 23% at the resonance wavelength,and the maximum electric field of the local mode is more than 35 times that of the incident light.Compared with the traditional sub wavelength grating,the local field of the hybrid structure is increased by more than 8 times.2.In order to realize the self-driven photoresponse of metal-graphene-metal FET like infrared detector,we propose to use asymmetric integrated plasmonic micro-and nano-cavities to break the symmetry of local field enhancement,which makes the graphene optical coupling present asymmetric distribution.At the end electrode fused with the coupling antennas,the photoresponse at one electrode of the integrated plasmonic micro-and nano-cavity is significantly improved due to the enhancement of the local light field and the increase of the junction area between graphene and metal.At the other end electrode which lacks coupling antenna but still has bottom dielectric layer and metal plane,the light absorption near the junction of metal and graphene is suppressed because graphene is inhibited by the metal plate near the bottom.Finally,the photoresponse contrast of graphene contact junction at both electrode is up to 105 times.This kind of ultra-high contrast is far more than the previous research results at home and abroad.Based on the ultra-high contrast of this asymmetric photoresponse,we have achieved a significant net self-driven photoresponse under the condition of infrared flooding and almost zero bias.Compared with the general coupled grating integrated graphene device,the infrared photoresponse of the graphene device integrated with plasmonic micro-and nano-cavities is improved by more than one order of magnitude.3.By controlling the width of the top metal microstructure strip and changing the cavity length,the peak detection wavelength of graphene infrared detector integrated with plasmonic micro-and nano-cavities is tuned.The experimental results show that the peak photoresponse of the hybrid structure device is red shifted from 1.3 ?m to 1.65 ?m by changing the width of the metal strip,and the bandwidth of the photoresponse resonance peak is about 200~300 nm.In addition,the response time of the device is less than a few microseconds,and the polarization extinction ratio is up to 30.The light response mechanism is attributed to photothermoelectric effect.4.The matching between the polarization direction of the local field and the anisotropic optical absorption of the two-dimensional materials plays an important role in the optical coupling of the two-dimensional materials.Based on the matching control between the polarization direction of the local field and the main absorption direction of the two-dimensional materials and the critical coupling control of the system,the optical absorptivity of the two-dimensional materials is greatly improved,and the optical absorption loss of the metal coupled structure is suppressed.Concerning a popular light coupling structure,i.e.the MIM structure,it is demonstrated to have two forms: magnetic resonator form with the light mode mainly polarized out-of-plane and metasurface Salisbury screen form with the light mode mainly polarized in-plane.When the MIM structure in the metasurface Salisbury screen form is integrated with graphene,the local field polarization direction is mainly parallel to the graphene plane(that is,along the main absorption direction of graphene).The peak absorptance of graphene is pushed to nearly 100% in the THz regime and 90% in the mid-infrared regime.Compared with the magnetic resonator form whose local field polarization direction is perpendicular to the graphene plane(that is,perpendicular to the main absorption direction of graphene),the metasurface Salisbury screen form increases the absorptance enhancement of graphene by 1.6 to 4.2 times,enlarges the bandwidth of the resonant absorption enhancement by 3.6 to 6.4 times,and reduces the metal loss by 7.4 to 24 times.Concerning monolayer black phosphorus(BP),the MIM structure in the metasurface Salisbury screen form enhances the absorptance of BP at the wavelength of 3.5 ?m from 0.44% to 31%,which is 5.4 times higher than that induced by the magnetic resonator form.In addition,the bandwidth is also 1.8 times larger.Moreover,the metasurface Salisbury screen form enhances the averaged absorptance of monolayer Mo S2 in the visible-near infrared range(415 nm to 800 nm)from 7.3% to 68.1%,which is 4.4 times higher than that induced by the magnetic resonator form.The improvement beyond critical coupling is attributed to the in-plane polarized light field that helps the 2D material overwhelm the metal in the light absorption competition.