Research On The Micro-structural Regulation And Electrical Performance Of Two-dimensional Wafer-scale Graphene/Hexagonal Boron Nitride Heterostructures

With the development of science and technology towards high degrees of informatization and intellectualization,more requirements are put forward including high performance,low power consumption,miniaturization,and integration in diverse fields of application.The current technology has been difficult to meet the needs of the development of electronic devices.The emergence of new materials may bring outstanding breakthroughs to the current electronic industry.Graphene has not only ultra-high carrier mobility,but also excellent light transmittance,stable mechanical properties,and unique quantum mechanical properties,which is expected to provide a new way to achieve high-performance and highly integrated electronic devices.In order to promote the practical applications of graphene,it is necessary to scale it up to the wafer level while retaining its intrinsic advantage of ultra-high mobility.Besides,electromagnetic shielding films play a key role in applications such as civil precision instruments,medical protection,military electronic shelter,satellite radar,and so on.Graphene shielding material not only has a strong shielding effect but also has the advantages of optical transparency and flexibility,which is of great significance for high-end electromagnetic shielding applications.The structure of graphene/hexagonal boron nitride heterojunctions can combine the high electrical conductivity of graphene and the outstanding dielectric property of hexagonal boron nitride.Currently reported graphene/hexagonal boron nitride heterojunction structures are generally limited by small size,poor homogeneity,obvious doping phenomenon,and thickness uncontrollability.Poor crystal quality reduces the conductivity of graphene in a large area.Based on this,the growth mechanism and microscopic process of hexagonal boron nitride and graphene were studied in this paper.The effects of growth temperature,atmosphere,medium,and other parameters on the morphology and structure of the products were investigated,and large-area and uniform graphene/hexagonal boron nitride wafers with pure interfaces were obtained,which promoted its applications in the fields of microelectronics and electromagnetic shielding compatibility.Two-dimensional hexagonal boron nitride single crystal and continuous thin films were successfully grown on Cu-Ni alloy by chemical vapor deposition.The differences in solubility of boron atoms and nitrogen atoms were utilized to balance the chemical potential of hexagonal boron nitride elements during the growth process,so as to regulate the final morphology of crystal nuclei.At the same time,the nucleation density of hexagonal boron nitride is reduced and the grain size is increased.The ultra-violate photoelectron detector based on hexagonal boron nitride single crystal shows a very low dark current of 0.9 p A and strong photo-response up to 5.45 m AW^-1.The response time was 376 ms and 198 ms,respectively.This chapter provides a route for the controllable synthesis of two-dimensional hexagonal boron nitride and promotes its application in metal protection and ultraviolet detection.It provides a basis for the growth of graphene/hexagonal boron nitride heterojunction.Large area uniform graphene/hexagonal boron nitride vertical heterojunction was prepared by metal-assisted diffusion growth method.Here,copper-nickel alloy acts as both the catalyst substrate of hexagonal boron nitride and the mass transfer medium of carbon atoms to promote the formation of graphene.The results show that due to the high carbon solubility and diffusivity of the copper-nickel alloy,carbon atoms tend to appear uniformly at the alloy interface.Therefore,this efficient and mild method can be used to form uniform graphene films at relatively low reaction temperatures without causing element doping or miscibility.The high homogeneity of the vertical heterostructure is maintained even when further scaled up to 4.5 cm in size.A physical model of the diffusion process was established to accurately control the number of graphene layers via controlling the alloy content and diffusion time.Field-effect transistors were constructed based on the hexagonal boron nitride/graphene vertical heterostructure,and the carrier mobility is about 1 560cm²V^-1s^-1 at room temperature,and the Dirac point is distributed around 25 V,which has a significant effect of inhibiting the hysteresis effect.The atomic-level analog circuits of inverters and amplifiers are prepared,which provide a basis for their further application in the field of integrated circuits.Using single crystal graphene as an epitaxial template,the horizontal and vertical heterojunction structures of single crystal graphene/hexagonal boron nitride were obtained by van der Waals epitaxial growth method.The growth process of hexagonal boron nitride thin films epitaxial with graphene hexagon as template was systematically studied.It was found that the pre-grown graphene single crystal could guide the reaction sequence of nitrogen and boron active species in different stages of gas source during the growth and construction of heterojunction structure.In addition,the transverse size of the pre-grown graphene crystals is no longer limited,and their ultra-high single crystal mass remains intact during the epitaxial growth of hexagonal boron nitride.Based on the method of this experiment,a 2-inch graphene single crystal/hexagonal boron nitride heterojunction structure was obtained.The vertical heterojunction structure shows excellent electron transport performance at room temperature and atmospheric pressure,with carrier mobility of about 10⁴ cm²V^-1s^-1 at room temperature.The switching ratio of heterojunction transistors is improved by multi-gate electrostatic field regulation,and good filtering performance is demonstrated.Finally,the high quality and large size graphene single crystal film is used as the electromagnetic shielding film,and its electromagnetic shielding efficiency is twice that of polycrystalline graphite.The normalized electromagnetic shielding efficiency of graphene single crystal films is as high as 5.5×10⁷ d B·cm²·g^-1,which is the highest record of electromagnetic shielding materials reported at present.The importance of graphene crystal quality to electromagnetic shielding performance is revealed.The sandwich structure composed of graphene single crystal and magnesium fluoride has an electromagnetic shielding efficiency of 8.10 d B and an infrared transmittance of 91.5%at 5 000 nm.The electromagnetic shielding efficiency of graphene electromagnetic shielding films remains almost unchanged even in the state of bending.Flexible electromagnetic shielding film based on graphene single crystal can effectively block wireless network signals.It can reduce the power density of electromagnetic radiation generated by mobile phones from 7.648μW/cm² to 0.822μW/cm²,providing a guarantee for human health and safety.The resonant cavity composite structure was constructed by combining the high absorption loss of graphene with the conductive film of silver nanowires with strong reflection property,introducing a transparent medium,and combining the hexagonal boron nitride film with excellent protective performance.The electromagnetic shielding efficiency of the electromagnetic shielding composite structure based on the three-resonant cavity structure can be further improved to 28.76d B,and 99.9%of the incident electromagnetic wave can be shielded.The transmittance of visible light is 80.6%,which fully meets the requirements of commercial applications.The work of this paper provides a preparation method of graphene/hexagonal boron nitride hetero-crystalline circles,optimizes the growth process of chemical vapor deposition,and enriches the mechanism and model of heterojunction growth.The practical application of graphene/hexagonal boron nitride heterojunction in the field of microelectronics and electromagnetic shielding compatibility is extended.