| Carrier mobility and energy gap are key parameters to dominate a semiconductor material, which play an important role in practical applications of electronic devices. The former determines the power dissipation and switching speed, while the latter is a necessary condition to respond the external field. Thus, it is an intensive issue to obtain a good semiconductor material, which should simultaneously possesses a high carrier mobility and a proper band gap. Just recently, phosphorene, an atomic monolayer of black phosphorus, has attracted much research interest as it meets the above two criteria. The carrier mobility of phosphorene is theoretically predicted to be as high as 103-104 cm2V-1s-1, which is comparable to graphene. More importantly, phosphorene has a direct band gap of around 1 eV at crystal momentum Γ, providing the possibility of device manipulation.Motivated by the above mentions, in this thesis, we study how to modulate the band gap of phosphorene, aiming to extend its perspective applications, more detailed as follows. First, based on the quantum confinement effect and the edge states, we studied the band gap of phosphorene nanoribbons as a function of ribbons’ width. Second, particular elements, such as boron, carbon, and sulfur are doped in phosphorene nanoribbons. The results show that the impurity states are thus introduced, changing the electronic properties of phosphorene nanoribbons. Finally, we also investigated the heterostructure of phosphorene and silicone, and found that the silicene has a big effect on the band gap of phosphorene.It is well known that phosphorene has a negative Poisson’s ratio, which can be applied in some special areas, such as national defense, medical, anti-seismic and aviation, etc. In order to expand this unusual feature to other two-dimensional materials, we studied the mechanical properties of phosphorene-like arsenene. The results show that arsenene has a larger Poisson’s ratio than that of phosphorene, which should be a focus of future researches. All above researches are carried out based on the first-principles calculations in the framework of density functional theory. The main conclusions are summarized as follows.1. The electronic structures of zigzag phosphorene nanoribbons largely depend on the width, and the band gap increases with decreasing the ribbon’s width. When the width changes from N = 20 to N = 4, the corresponding band gap increases from 1.0 eV to 2.2 eV. By contrary, the band gap of armchair phosphorene nanoribbons is not sensitive to the ribbons’ width, which oscillates around at 1 eV.2. In the case of boron and carbon doped in the zigzag phosphorene nanoribbons, the introduced impurity states appear above the Fermi level of phosphorene nanoribbons as the system loses the electron in such doping. The obtained band gaps are in the range of 1.27-1.87 eV for B-doped and 0.67-2.08 eV for C-doped phosphorene nanoribbons, respectively. When phosphorene is doped with sulfur, some extra electrons are introduced. Thus, the band gaps change from 0.57 eV to 2.20 eV, which are dependent on the doped sites.3. For the heterostructure of phosphorene and silicone, sp3 hybridization occurs between the phosphorus and silicon atoms at the interface, inducing interlayer covalent bonds. As a result, this heterostructure is changed to a narrow band gap(0.12 eV) semiconductor. Generally, the stark effect of electric field in a heterostructure is stronger than that in the single atomic layer. We applied a vertical electric field to adjust the band gap of phosphorene/silicone heterostructure and found that the electric field has an obvious influence on the band gap of this system.4. When the stress applied at the zigzag direction of arsenene, a negative Poisson’s ratio will appear in the perpendicular direction of arsenene surface, and the value is about-0.09 which is three times that reported in phosphorene. The physical nature of arsenene’s negative Poisson’s ratio is the interaction between the two vertical hinges. Further, we also studied the stacking effect for the negative Poisson’s ratio of arsenic. We found that the negative Poisson’s ratio of arsenic increased with the increasing number of layers, when the layer number of arsenic reach four the negative Poisson’s ratio tends to saturation which is the value of the bulk. |
