Research On Novel Two-dimensional Photoelectric Devices Modulated By Interface Effect

Since the emergence of graphene in 2004,two-dimensional(2D)materials have attracted extensive attention in the fields of science and engineering due to their potential applications in electronics,optoelectronics,valley electrons,spintronics,and catalysis,etc.These materials,including graphene,transition metal chalcogenides,black phosphorus(BP),etc.,have brought many breakthroughs in high-speed and wide-band photodetection in virtue of their layer-dependent band structure,and unique electronic and photoelectric properties.However,the ubiquitous shortcomings of low sensitivity and responsivity for the single 2D material,as well as the integration requirement to realize on-chip multi-functions,pose great challenges on developing 2D materials-based photodetector with high-performance and high-integration.Fortunately,the atomic thickness and dangling-bond-free on the surface make the structural integration and electronic modulation of 2D materials more easily.Specifically,it can be combined with any substrate by van der Waals forces without lattice matching,thus leading to more combination freedom,which would lay the foundations for electronic and optoelectronic devices designing with high performance and multi-function.On these basis,we have first explored some novel 2D optoelectronic materials,including narrow-gap semiconductor Cr2S3 and PdSe2,and conducted in-depth investigations on their physical properties correspondingly,and finally constructed interfacial charge-induced optoelectronic devices(Cr2Ge2Te6/SiO2 and BP/lead zirconate titanate(PZT))and interfacial band engineering optoelectronic devices(BiCuOSe/WSe2).Under different interfacial inducing mechanisms,these heterogenous devices have largely surpassed the corresponding single materials over the photoelectric performance and function.All in all,we have realized the detectable spectrum coverage expansion and sensitivity improvement in light detection,and obtaining a new mechanism-based optoelectronic storage device integrated with multi-function,and tunneling photodetector.The main research contents are as following:1.Synthesizing new semiconductors with narrow band gap and superior physical properties to expand the detectable light spectrum coverage.a)To solve the problems of difficult preparation,high cost and low integration for infrared detectors relying on traditional narrow band gap semiconductors,a controllable growth of ultrathin(with thickness down to unitcell of-1.85 nm)narrow-gap(-0.15 eV)semiconductor Cr2S3 is achieved using a low-cost and facile chemical vapor deposition method.The as-grown 2D Cr2S3 exhibits outstanding environmental stability with negligible degradation even after exposure in air for more than two months.The photodetector based on the 2D Cr2S3 exhibits a high responsivity(14.4 A W-1 at 520 nm,6.0 A W-1 at 808 nm,and 3.0 A W-1 at 1550 nm)and excellent detectivity(4.0 � 1010 Jones at 520 nm,1.7 � 1010 Jones at 808 nm,and 8.3 � 109 Jones at 1550 nm)under ambient conditions.b)2D PdSe2 can realize a transformation from semiconductor to metal by changing its thickness,and also shows high thermoelectric coefficient and carrier mobility,which makes it a potential light detection material.On these grounds,a metal-semiconductor-metal detector is constructed based on excellent characteristics of PdSe2.Under the potential-well effect induced by electromagnetic wave,PdSe2 terahertz device shows a response as high as 1.7 V W-1 at 366.12 GHz,and the terahertz response bandwidth even reaches-2.9 kHz,which extends the detectable wavelength to a large extent.2.Designing devices to achieve a significant improvement in the optical detecting performance of a single material,and the multi-functional integration through interfacial charge-induced mechanism.a)By constructing Cr2Ge2Te6/SiO2 device,Cr2Ge2Te6 photodetector shows an unusual negative photoconductivity(NPC)induced by silicon-based interfacial charge.Besides,this NPC can be adjusted by changing the incident light intensity.More importantly,the NPC behavior enables the Cr2Ge2Te6 ultrasensitive photoresponsivity,where the detection limitation of a weak light with an incident power intensity can reach as low as 0.04 pW and the corresponding responsivity can reach as high as 340 AW-1.b)A ferroelectric field effect transistor adopting BP/PZT heterostructures was developed.An unique polarization-dependent photoresponse is observed under effect of interfacial charge-mediated electric-field,resulting in both positive(PPC)and negative(NPC)photoconductivity in a single device element.This enables a nonvolatile photoelectric memory working in a novel "electrical writing-optical reading"processing mode.Furthermore,the device exhibits a reliable data retention(over 3.6� 103 s)and fatigue(exceeding 500 cycles)performance as well as extremely low energy consumption(driving voltage<10 mV).3.Fabricating multi-functional tunneling photodetector through interfacial band engineering.As a novel 2D material,BiCuOSe bearing self-doping effect always shows characteristics of heavily intrinsic p-type doping and high chemical stability,rendering it potential to be p-type channel material for tunneling devices.In this work,we have adopted low pressure chemical vapor deposition(LPCVD)method to synthesize 2D BiCuOSe film with thickness less than 10 nm and size larger than 80 ?m by controlling the growth condition to inhibit the phase separation.Through the exploration of transport characteristics and energy band structure,we found it's carrier concentration is as high as 1020 cm-3,with band gap about 0.45 eV and work function in range of 5.1-5.2 eV.The BiCuOSe/WSe2 heterojunction is further fabricated by manual dry transfer method,which shows a high rectification ratio more than 105and a high on/off ratio more than 104.Simultaneously,owing to the interfacial band engineering,a low voltage threshold swing tunnelling transistor(84 mV dec-1)with an excellent photovoltaic detection performance(-1 A W-1)is achieved.