The Study Of Photodetectors Based On Two-dimensional Materials And Their Heterostructures

Since the discovery of graphene over a decade ago,many other two dimensional(2D)materials,such as transition metal dichalcogenides(TMDs)and black phosphorus(b-P),have been discovered.Those 2D materials have attracted many research interests due to their unique physical properties.Graphene has been widely studied as a photodetector material due to the gaplesss band structure,high light absorption,linear dispersion relation,and high mobility.Due to these excellent properties,graphene has shown great potential applications for logic circuits,optical communication,broadband photodetection and high speed devices.The newly discovered black phosphorus and black arsenic phosphorus are direct band gap semiconductors.They are good candidates for mid-infrared(MIR)photodetecting.Besides,black phosphorus is a p-type semiconductor with high hole mobility.At present,as the most intensively-studied 2D materials,transition metal dichalcogenides exhibit many excellent performances in photodetection due to their strong light material interaction.The boron nitride(BN)with a large band gap?6 eV,is an insulator with good dielectric properties.With continuous studies on 2D materials,more and more new layered materials with unique properties could be discovered.Here,we investigated few 2D van der Waals heterostructure-based photodetectors.By designing and fabricating 2D van der Waals heterostructures,high sensitivity and high photoresponsivity photodetectors are obtained.Mid-infrared(MIR)range photodetecting has been proven to be crucial for applications on missile guidance and tracing the target in military field.At present,the widely-used infrared photodetectors usually work at low temperature.Liquid nitrogen is needed for cooling.Due to complex facilities and high cost,they are not suitable for facilely and widely using.Thus,to develop portable room temperature mid-infrared photodetectors is extremely urgent.Here we also explored the synthesis of new narrow gap layered materials such as PtSe2,and black arsenic phosphorus.In chapter three,we designed a broadband p-g-n photodetector.The large work function metals palladium and gold were used as contact to achieve p-type doping in WSe2.Due to strong Fermi level pinning,MoS2 remains n-type semiconductor.The gapless graphene layer works as an effective broadband absorption material.A broadband photoresponse from 400 nm to 2400 nm,high photoresponsivity 4250 AW-1 and high specific detectivity?1015 Jones were demonstrated at room temperature.In chapter four,we investigated the mid-infrared photodetecting using the narrow band gap and high mobility black arsenic phosphorus(b-As0.83P0.17)and b-As0.83P0.17-MoS2 heterostructures.We measured the photoresponse from 0.4?m to 8.05?m.Beside,we further studied the b-As0.83P0.17-MoS2 heterostructure photodetectors.The built-in electric field effectively suppressed the dark current and depressed the noise power.The specific detectivity of b-As0.83P0.17 FET photodetectors is higher than 108 Jones in the full range of 0.4?m to 8.05?m at room temperature.The specific detectivity for b-As0.83P0.17-MoS2 heterostructure devices is higher than 4.9×109 in the full range of 0.4 pm to 4.3?m at room temperature,which is two orders of magnitude higher than that of PbSe at the same condition.In chapter five,we explored the synthesis of new TMDs materials.This chapter includes three parts:the first part is the synthesis of p-doped WSe2by Ta doping;the second part is chemical vapor transition synthesis of WSe2 nano-wire;the third part is exploration of the narrow band layered materials such as CVD growth PtSe2.We realized the Ta doped p-type WSe2 by CVT method,which has been widely used in crystal growth.The vertical MoS2-Ta0.01W0.99Se2 heterostructure and WSe2-Ta0.01W0.99Se2 homojunction were assembled by try transfer technique.The performance of the MoS2-Ta0.01W0.99Se2 p-n junction with an ideality factor of?1 and a rectification ratio of?105 was demonstrated.Next,collaborating with other group members,we investigated the photoresponse of devices based on few-layer ReS2 and WSe2-grapene heterostructure.The high photoresponsivity and weak light detecting were demonstrated in ReS2/BN photodetectors.The high photovoltaic responsivity was also achieved on WSe2-grapene heterostructure-hased photodetectors.In the last chapter,we summarized our research,discussed the current trend of the field and listed possible plans for future investigations.