Investigation On The 2D Heterostructures?BP/g-GaN And Bi₂Te₃/Graphene?:The Potential Photocatalysis And Thermoelectric Property

With the successful exfoliation of graphene,two-dimensional materials have attracted wide attention.So far,at least dozens of two-dimensional materials with completely different properties have been discovered,including insulators,semiconductors and metals.Two-dimensional materials have been utilized widely.Like heterojunctions in three-dimensional structures,two-dimensional materials can be stacked like a LEGO toy.Amazing physical properties could be obtained when two-dimensional materials with different properties are stacked together.Thermoelectric materials based on Seebeck effect and Peltier effect can realize the conversion between thermal energy and electric energy.Thermoelectric devices made from thermoelectric materials have important application in refrigeration and waste-heat recycling.Thermoelectric devices have been widely studied because of the simple structure,no noise,portable characteristics and other advantages.The figure of merit ZT,a dimensionless value,is a parameter to measure and evaluate the performance of thermoelectric materials.ZT value is mainly corresponded to the Seebeck coefficient,electrical conductivity and thermal conductivity of the material.To improve the ZT value,it necessary to optimize the transport coefficients such as the higher Seebeck coefficient,the higher conductivity and the lower thermal conductivity.The Seebeck parameter can be increased significantly by using low-dimensional materials,and the thermal conductivity could be greatly reduced by using nano-enhanced phonon scattering.In this paper,the electronic structures and thermoelectric properties of heterojunctions in two-dimensional materials have been studied by first principles calculation.The specific work is as follows:(1)First-principle calculations based on density functional theory are carried out to explore the interface properties of the blue phosphorene/GaN van der Waals heterostructures.The edge positions for valence and conduction band of blue phosphorene and GaN nanosheets change with the Fermi energy level and form the type-II heterostructure.The internal electric field facilitates the separation of electron-hole pairs and restrained the carrier recombination in the blue phosphorene/ GaN interfaces.(2)The structural and electronic properties of a monolayer-and bilayer blue phosphorene/graphene-like GaN van der Waals heterostructures are studied by using first-principle calculations,respectively.The results show that the monolayer-blue phosphorene/graphene-like GaN heterostructure is an indirect band gap semiconductor with intrinsic type-II band alignment.More importantly,the external electric field tunes bandgap of monolayer-blue phosphorene/graphene-like GaN and bilayer-blue phosphorene/graphene-like GaN,and the relationship between bandgap and external electric field indicates a Stark effect.The semiconductor-to-metal transition are observed in the presence of a strong electric field.(3)The electronic and thermoelectric properties of Bi2Te3 and 1-3layer Graphene heterostructures are analyzed by using first-principles calculations and semiclassical Boltzmann transport theory.The power factor of Bi2Te3/graphene heterostructures is improved effectively with the quantum size effect.And the effect for number of layers dependence and stacking configurations for thermoelectric heterojunctions have been studied.