Field-Effect Charge Coupled Device And Hot Electron Transistor Based On The 2D/3D Heterostructures

As the manufacturing process of integrated circuits continues to advance,the current prceess node has reached 7 nm,and the pace of Moore's Law gradually slows down.In addition to the dramatic increase in the cost of lithography,the "small-size effect" of MOSFETs(such as the"short-channel effect")also needs to be taken seriously.The academics and industry are thus developing two-dimensional(2D)materials to overcome the shortcomings of current semiconductor processes.Typical 2D materials include graphene,black phosphorus,transition metal dichalcogenide,hexagonal boron nitride.Due to the atomic-level thickness,2D materials can have very strong field effects,so that they can suppress "short-channel effects" and achieve extremely short gate-length FETs.In addition to electronic applications,2D materials are also widely used in optical communications or sensing.Photodetectors made of 2D materials or 2D/3D heterostructures exhibit excellent performance.2D materials have high transparency,high conductivity,strong field effect,different bandgaps,and new physical mechanisms,which can greatly improve the quantum efficiency,gain,and spectral response of photodetectors.This article mainly focuses on the application of 2D/3D heterojunction transistors in electrical and optoelectronic applications.The content and results are as follows:(1)We conducted theoretical research on the contact of 2D/3D systems,and developed a general theory applicable to N-layer systems.This analytical method considers the limited quantum capacitance of 2D materials,and can self-consistently calculate the charge transfer and band diagram of the N-layer system.We obtained the analytical formula for the graphene/silicon Schottky barrier,and studied its Schottky limit and the Bardeen limit.Based on the study,we proposed another type of Si-Schottky-gated graphene FET(SSG-GFET)and verified it experimentally.(2)We studied the graphene/silicon optoelectronic device,and found the photocurrent contribution and light-induced negative differential resistance effect(L-NDR).To study the origin,we proposed a novel graphene/silicon gate-controlled diode.Combining COMSOL simulations,we found that the two L-NDRs are due to the gate-voltage-dependent surface recombination under the oxide layer and the carrier confinement effect.We achieved a peak-to-valley ratio(PVR)of more than 30.(3)We proposed a charge-coupled device based on graphene field effect(FE-CCD),and fabricated its arrays,and;thieved high-quality imaging.The FE-CCD utilizes the photo-carrier integration effect in the deeply depleted potential wells,as in the traditional CCDs.However,different from the traditional CCD,the FE-CCD does not require the serial charge transfer between the wells,and the charges can be directly read out through the field effect of graphene.Meanwhile,we have extended the spectral response from the ultraviolet(300 nm)to the short-wavelength infrared(1870 nm).We also used van der Waals(vdW)heterojunction as the pixel to suppress power consumption to 1 nW.Finally,we demonstrated the real-time charge transfer between two FE-CCD pixels through the graphene readout.(4)We studied novel hot electron transistors(HET)based on 2D materials,providing the basis for a broadband hot-electron photodetector and high-speed analog/digital devices.The most important parameter in HETs is the common base collection efficiency.Specifically,we first studied the point-contact graphene-base HETs,and successfully demonstrated the hot electron collection.To achieve more stable hot electron collection,we proposed a real-space-transfer transistor(RSTT)based on graphene/silicon.The RSTT directly heats the electrons through bias,and those hot electrons can overcome the Schottky barriers.Finally,we used vdW stacking method to fabricate pure 2D HETs,and achieved a hot electron collection efficiency of 99.95%and output current density of 233 A/cm2.