Theoretical Prediction On The Electronic Properties Modulation And New Phase Exploration Of 2D Group ? Monochalcogenides

The rise of phosphorene,a two-dimensional?2D?semiconductor material,has led to the development of its isoelectronic group ? monochalcogenides MXs?GeS,GeSe,SnS and SnSe?.MXs with corrugated honeycomb structure not only have much higher chemical stability than phosphorene,but also inherit and develop many excellent properties of phosphorene,which can be widely used in the fields of photoelectric converter,photoelectric detector,lithium electrics,thermoelectrics and piezoelectrics.However,systematic theoretical work for these MXs is relatively less.In particular,the electronic properties modulation through construction of heterostructure and prediction of new phase need to be further explored.Based on the density functional theory?DFT?,this thesis focuses on the influence of strain on the electronic properties of GeS/SnS in-plane heterojunction,the novel regulation methods for the interfacial properties of blue-phosphorene-phase GeSe/graphene van der Waals heterojunction.In addition,a new phase of MXs with saddle-shaped-like structure was predicted and its electronic properties were discussed.The main contents of this thesis are organized as follows:In the first chapter,the research progress of 2D nanomaterials and 2D group ? monochalcogenides as well as the research significance and content of this thesis are summarized.In the second chapter,DFT is summarized and VASP,CALYPSO softwares are briefly introduced.In the third chapter,GeS and SnS monolayers were used to construct the in-plane heterojunction along the direction of the armchair,and the electronic properties as well as the influence of uniaxial strain on the electronic properties were studied.Results show that with the increase of tensile strain along the zigzag direction,band gap shows a very interesting change:it linearly increases in the beginning until 2.4%strain,then remains nearly constant until 5.7%,and finally linearly decreases within the tensile limit.Meanwhile,the electronic properties successively change from quasi-type II alignment to direct band gap to type II alignment with complete carrier separation.By calculating the effective mass and mobility of the carrier,it is proved that the electrons and holes are separated significantly with the increase of strain,and the electron mobility of the heterojunction in the direction of armchair under the strain of 7%is as high as 11220cm²v^-1s^-1.In the fourth chapter,graphene and blue-phosphorene-phase GeSe with a built-in dipole were selected as metal electrode and channel material,respectively,for the construction of van der Waals heterojunction.The regulation of interface dipole on schottky barrier height?SBH?was systematically investigated.The results show that SBH can be controlled by applying external vertical pressure?adjusting the spacing between layers?.Moreover,creative using the built-in dipole of GeSe itself,interface property can be modified by changing the stacking mode,accompanied by the mutual transformation between p-type and n-type schottky contact,and even the transformation to ohmic contact.The principle of its regulation method is similar to that of applying electric field.In the fifth chapter,based on the Particle-swarm optimization method,a stable t-SnSe state with saddle-shaped-like configuration was found.According to the isoelectronic substitution rule,SnS monolayer in this phase was also found to be stable.The band gaps of SnSe and SnS were calculated to be 1.56 and 1.63 eV,respectively.The calculated carrier mobility showed that the hole mobility of SnSe and SnS reached 642-672 cm²v^-1s^-1and 934-999 cm²v^-1s^-1,respectively.The sixth chapter summarizes the research work of this thesis and prospects the future research.