Photoelectronic Detection And Device Functional Integration Based On Two-dimensional PdSe₂ Semiconductor

With the rapid expansion of information technology,the development trend of functional integration of photodetectors is inevitable.Two-dimensional（2D）materials have brought new opportunities for the development of photodetectors due to their ultrathin structures,rich physical properties,and strong light-matter interactions.Among a wide range of 2D materials,the emerging 2D PdSe₂ semiconductor has the advantages of widely tunable bandgap（0～1.3 e V）,high carrier mobility(>1000 cm² V^-1 s^-1),strong anisotropy and tunable bipolarity,which not only provides a new dimension for the modulation of optoelectronic properties,but also create favorable conditions for the functional integration of optoelectronic devices.Therefore,the 2D PdSe₂ semiconductor shows great application prospects in the field of multifunctional photoelectric detection.Based on these,this thesis mainly focuses on the photoelectronic detection and device functional integration based on 2D PdSe₂ semiconductor.The main research contents and results are as follows:（1）Orientation-tunable polarized photoelectric detection of 2D PdSe₂ nanosheets.Polarized Raman spectroscopy and reflectance difference spectroscopy revealed the crystal orientation and strong optical anisotropy of PdSe₂ nanosheets.Angular-resolved electrical transport measurements revealed the strong electrical anisotropy of PdSe₂ nanosheets,and the anisotropic ratio of the electron mobility reached 8.9.In addition,PdSe₂ nanosheets also showed excellent polarized photodetection performance with the polarized photoresponse ratios up to 1.8 under 532 nm and 2.2 under 369 nm,and the polarization orientation of polarized photoresponse differed by 90°,realizing high-sensitivity and orientation-tunable polarized photoelectric detector.（2）Reconfigurable photovoltaic detection of 2D PdSe₂/MoTe₂ van der Waals（vd W）heterostructures.Under 980 nm illumination,the PdSe₂/MoTe₂ heterojunction realized self-driven photovoltaic detection under the built-in electric field,exhibiting an ultrafast response speed as low as 0.4μs and an on-off ratio as high as 10⁵.In addition,the reversible transition between type II and type III band alignment of the PdSe₂/MoTe₂heterojunction was also achieved by modulating the gate voltages with different polarities,making the device exhibited reconfigurable positive and negative photovoltaic characteristics.The positive and negative photovoltaic responsivity could reach 22 m A W^-1 and-34 m A W^-1,respectively,and the fill factor was as high as 58.4%.The reconfigurable photovoltaic properties were also suitable for a wide spectral range from365 nm to 980 nm,confirming that the 2D PdSe₂/MoTe₂ heterojunction could achieve high-performance and reconfigurable photovoltaic detection.（3）Sensor-computing integrated image sensing of 2D PdSe₂/MoTe₂ heterojunction devices.Based on the positive and negative photovoltaic effects,the PdSe₂/MoTe₂heterojunction devices not only showed linear light intensity dependence for both positive and negative photoresponses at different optical spectrum bands,but also exhibited linear gate-dependence for the broadband photoresponse.The positive and negative light responsivity with linear modulatment could correspond to the weight update in the convolution calculation process,so that the in-sensor convolution calculation could be implemented with PdSe₂/MoTe₂ heterojunction devices.Furthermore,the heterojunction devices could set different convolution kernels by updating the gate voltage to realize the filtering of remote sensing images,including image sharpening and edge enhancement.In addition,it could also achieve efficient recognition and classification functions for different types of letter images.After only three training cycles,the recognition accuracy reached～100%.It was confirmed that the 2D PdSe₂/MoTe₂ heterojunction could be further used as the prototype of sensor-computing integrated image sensor,which enabled simultaneous image sensing and convolution computing functions.