Research On The Physical Properties Of Fully Hydrogenated Boron Nitride Films

Since graphene was discovered experimentally in2004, atomic-layer-based materials havebecome a focus of interest in science and technology. These (quasi) two-dimensional (2D) materialsshow some new phenomena, such as quantum Hall effect and quantum topological characters in roomtemperature. Graphene is of great potential in the applications of the next-generation electrontransport devices for its high carrier mobility. However, its metallicity restricts the application in logicelectronic devices. In addition to graphene, boron nitride (BN) single layer film is later discovered2Dmaterial. BN monolayer is an insulator, which also limits its application in electron transport devices,such as field effect transistor. It is significant to make the graphene or BN layers transform intosemiconductor in terms of tuning up the energy band.In this thesis, we systematically studied the structural and electronic properties using thefirst-principles calculations based on density functional theory (DFT), and mainly focused on thechange of electronic structure under externally applied vertical electric field. It is found that boronnitride films will corrugate after the hydrogen atoms are adsorbed on its surfaces, and the bond typewill be changed into sp3bonds. Multi-layer boron nitride films have a variety of configurations butthe way of stacking is not important for the structure stability. The most stable structure is the bondtype of B-N between the layers. The band gap of a BN single layer is4.57eV. With the number oflayers increased, the gap reduces gradually and closes when n=4. Applying external electric field, thegaps of all of the fully hydrogenated multilayer boron nitride nearly linearly increase with the increaseof the field. The electric field engineering effect is more and more obvious with the increasing of thenumber of layers. The material is a direct semiconductor in a large range, which may have thepotential applications in electronics and optoelectronics.We further explored tight-binding (TB) method to study the above phenomenon. With referenceto the initial values in the related literature, the parameters are fitted with the ab initio results. Wecalculated the band structure, the spatial distribution of the electronic states，and the gap withvariation of the number of layers and external electrical field. The variation tendency of the results isin agreement with the first principle ones, which proves the feasibility of this TB scheme.