Interface Control And Optoelectronic Properties Of MoS₂-MOSFET

At present,silicon-based integrated circuits have entered the sub-nanometer technology node,and the process size is gradually approaching the physical limit of silicon materials.The process yield and device reliability are more difficult to control and the cost of integrated circuit process development is also rising exponentially.Therefore,it is urgent to find new semiconductor materials to promote the development of the integrated circuit manufacturing industry.Since the discovery of graphene in 2004,two-dimensional materials have become a feasible technical solution in the international semiconductor technology roadmap due to their atomic-level material thickness and good interface morphology.Among them,molybdenum disulfide has a bandgap width of 1.2 e V～1.8 e V,and the theoretical phonon-limited room temperature mobility can reach 410 cm²/V s.Its excellent material properties make it possible to replace silicon materials in the post-Moore era.However,due to the incomplete experimental and theoretical research on molybdenum disulfide,there is still a big gap between the performance of the actually prepared molybdenum disulfide transistor device and the advanced silicon-based device.Aiming at the problems of low mobility and high contact resistance in current molybdenum disulfide transistors,this paper focuses on improving the performance and stability of molybdenum disulfide thin film transistors from two aspects:high k dielectric integration and metal-semiconductor contact engineering optimization.In addition,in view of the problems of large dark current and poor rectification characteristics of the current two-dimensional material vertical heterojunction photodiode,this paper designs a self-powered molybdenum disulfide photodiode through van der Waals heterogeneous integration based on energy band engineering.The specific research content and innovation points of this paper are as follows:1.In view of the outstanding problems of molybdenum disulfide transistors with traditional Si/SiO₂ substrate structure,such as high operating voltage,large power consumption,and obvious hysteresis effect,this paper proposes to integrate lanthanide oxide high-k dielectric to improve the performance of molybdenum disulfide transistor devices.First,a lanthanide oxide film with a high dielectric constant was prepared through ALD technology,and a post-deposition annealing process was used to further improve the dielectric properties and interface characteristics of the lanthanide oxide.The mobility and current-on-off ratio of the molybdenum disulfide transistor are significantly improved by integrating the lanthanide oxides high k dielectric.Under the optimal annealing condition of550°C,the current-on-off ratio I_on/I_offof the molybdenum disulfide transistor is 10⁷,and the field-effect mobilityμis 60 cm²/V·s,the minimum subthreshold swing SS is 77.5 m V/dec and the interface state density D_it is 1.8×10¹² e V^-1·cm^-2.Secondly,in order to understand the physical mechanism that limits molybdenum disulfide transistors,this paper studies in detail the effects of scattering mechanisms and interface charge trapping mechanisms on the performance of molybdenum disulfide devices,providing theoretical guidance for further optimizing device performance.2.Due to its strong gate control capability,two-dimensional floating gate memory can effectively resist the non-ideal effects caused by device size reduction.Not only that,its high sensitivity to the amount of floating gate charge makes the realization of multi-level storage technology possible.However,the current two-dimensional floating gate memory needs to be further improved in terms of storage characteristics,programming speed and durability.The choice of charge trapping layer and channel material combination directly affects the floating gate storage performance.Based on the above-mentioned lanthanide oxide preparation process,this paper innovatively proposes the use of a floating gate structure of La Al O₃/GO/La Al O₃ for charge storage.The prepared molybdenum disulfide floating gate transistor obtained a storage window of 6.7 V in the voltage range of±8 V.The electron and hole densities stored on the floating gate were～1.8×10¹³ cm^-2 and～1.2×10¹³ cm^-2,respectively.And the device has millisecond programming speeds and good data storage cycles.3.Study on the metal-semiconductor contact characteristics of molybdenum disulfide field effect transistor.The fermi level pinning effect caused by the metal-induced gap state between the metal electrode and molybdenum disulfide limits the formation of ohmic contacts.At present,molybdenum disulfide transistors have the problems of high contact resistance and poor driving ability.This paper proposes a charge-transfer-based source-drain doping technique to improve the metal-semiconductor contact characteristics of MoS₂transistors.The graphene quantum dot/molybdenum disulfide heterojunction was prepared by the suspension coating method,and the corresponding material characterization and electrical transport properties were studied.The study found that there is electron transfer between graphene quantum dots and molybdenum disulfide.After pretreatment of graphene quantum dots,the effective Schottky barrier height of MoS₂ FET is reduced from 103 me V to 41 me V,and the contact resistance is also reduced from 24.8 kΩ·μm^-1 to 2.4 kΩ·μm^-1.Moreover,the contact strategy has good air stability,and the threshold voltage and on-state current of the device have only slight changes after 3 months.In addition,this paper studies the influence of contact characteristics on the photoelectric characteristics of MoS₂ FETs.The reduction of contact resistance can effectively improve the photoresponsivity of molybdenum disulfide transistors,but it will affect the fall time of the device.This work provides a preliminary understanding of the physical mechanism by which contact resistance affects the photoelectric properties of molybdenum disulfide transistors.4.Molybdenum disulfide-based self-powered photodetectors and surface enhancement effects.In view of the problems of large dark current and poor rectification characteristics of the current two-dimensional van der Waals heterojunction diode.In this paper,WSe₂/MoS₂ van der Waals heterojunction with type II energy band structure is used as the channel material.The Fermi level barrier between the two materials can reach 300 me V,and an asymmetric electrode structure is used to further increase the barrier height between the electrodes.The prepared WSe₂/MoS₂ van der Waals heterojunction diode has an extremely low device dark current(the dark current is lower than 10^-12 A at zero bias),and the device rectification ratio reaches 2×10⁴.This value can be compared with the current commercial silicon germanium rectifier diodes.The saturated open-circuit voltage of 0.3 V under illumination makes the device have stable photoresponse characteristics under zero bias state.In addition,this paper studies the absorption enhancement effect of surface plasmons on the light field of two-dimensional materials.The metal plasmon substrate can effectively enhance the Raman scattering signal of two-dimensional materials.The zero-bias photoresponsivity of the WSe₂/MoS₂ van der Waals heterojunction device after plasmon enhancement is increased by about an order of magnitude,reaching 1.2 A/W.