Au/TiO_(2)复合纳米结构增强热电子光电探测器宽谱响应性能

Enhancing broadband response of hot-electron photodetectors by Au/TiO_(2)composite nanostructure

宽谱响应光电探测器在图像传感和光通信等领域应用前景广阔。金属微纳结构通过激发表面等离激元共振效应可高效产生热载流子,将它们与宽带隙半导体构成异质结构,便可利用热载流子开发出低成本宽谱响应光电探测器。研究设计了一种基于Au/TiO_(2)复合纳米结构的热电子光电探测器。其中TiO_(2)层经退火后形成尺度约为百纳米的凹凸结构,Au纳米颗粒层与用作电极的保形Au膜共同组成了激发表面等离激元共振的纳米结构。由于Au/TiO_(2)复合纳米结构的协同作用,该器件在400~900 nm范围内具有宽谱光吸收性能,器件的平均光吸收效率为33.84%。在此基础上,该器件能够探测TiO_(2)本征吸收波段以外的入射光子。例如,在600 nm波长处,器件的响应率为9.67μA/W,线性动态范围为60 dB,器件的上升/下降响应速度分别为1.6 ms和1.5 ms。此外,利用有限元法进行了仿真计算,通过电场分布图验证了Au/TiO_(2)复合纳米结构中所激发的丰富表面等离激元共振效应是其实现宽谱高效探测的原因所在。

Objective Hot electron photodetectors(HEPDs)with wide spectrum responses are promising in the fields of image sensors and optical communications,etc.Metallic micro/nano-structures can efficiently generate hot carriers by exciting surface plasmons.It is helpful to realize low-cost and wide-spectrum response photodetectors when the heterostructures form by combining metallic micro/nano-structures with wide bandgap semiconductors.This approach can also be applied to improve the performance of HEPDs made of other semiconductors.This work contributes to the development of advanced plasmonic devices.Methods During the fabrication,the wet-cleaned FTO glass substrates were first subjected to the surface plasma treatment for increasing the work function of FTO substrates.Then,TiO_(2)and Au films were prepared by radio frequency(RF)and direct current(DC)magnetron sputtering,respectively.In detail,a TiO_(2)layer with a thickness of 20 nm was deposited onto the FTO substrate,followed by the deposition of an ultrathin Au film with its thickness varying from 2 nm to 8 nm.Then,the as-prepared multiplayer samples were annealed in air at 500℃.The annealing process could,simultaneously,transform the ultrathin Au film into a layer of Au NPs,and transform the amorphous TiO_(2)film into its polycrystalline anatase film structure with a rough profile.After that,another thin Au film was deposited onto the annealed samples by DC magnetron sputtering.Here,the thin Au film can act as the transparent electrode with its thickness fixed to 20 nm.Results and Discussions The proposed hybrid plasmonic nanostructure based HEPD has an architecture as shown in Figure 1.Here,the TiO 2 layer formed a concave-convex nanostructure with a scale of about 100 nm after annealing process,the nanostructure constructed by the Au nanoparticle layer and the conformal Au film used as electrode is for exciting surface plasmons.With the assistance of the Au/TiO_(2)composite nanostructure,the device has a wide spectrum absorption in the range of 400 nm to 900 nm,and the average absorption efficiency is 33.84%.Therefore,the proposed device can detect the incident photons outside the intrinsic absorption band of TiO 2.The responsivity and linear dynamic range of the device under the wavelength of 600 nm separately are 9.67μA/W and 60 dB(Fig.2).Besides,the corresponding rise/fall response speed are 1.6 ms and 1.5 ms respectively.(Fig.3).The finite element method is also used for simulation calculation,and the electric field distribution diagrams verify that the rich surface plasmon resonances excited in the Au/TiO_(2)composite nanostructure,which is the reason for realizing the wide spectrum and high efficiency detection(Fig.5).Conclusions In summary,we demonstrated a TiO_(2)-based HEPD by incorporating a hybrid plasmonic nanostructure made of Au NPs together with a conformal Au film.Different from other similar approaches that were designed for high-efficiency hydrogen generation in the photocatalysts,a hybrid plasma nanostructure was used in photodetectors for realizing wide spectrum response.With the structural diversity of the hybrid plasmonic nanostructure,different surface plasmon resonances were excited,so that the device can respond to incident photons in a broadband wavelength range,covering UV-visible-NIR.The method of constructing hybrid plasmonic nanostructures has a guidance in developing high-performance optoelectronic devices.