Influence Of Stacking Fault On The Electronic And Optical Properties Of H-BN: First-principles Study

Hexagonal boron nitride (h-BN) has similar layered crystal structure to that of graphite, which attracts much attention due to its charming physical and chemical properties. For example, h-BN is stabile in the vacuum or oxygen environment under high temperature. It is an excellent solid lubricant and good thermal conductor due to its sliding inter-planar and great thermal conductivity. Because it is a wide band gap semiconductor, h-BN also can be used as an electrical insulator. Moreover, h-BN is widely used in the scope of medicine and aerospace engineering.Recently, the pure h-BN single crystal has been synthesized in experiments, and it shows a dominant luminescence peak around 215nm, which attracts great interests in optoelectronics due to its promising applications in the ultraviolet devices. Despite a large number of theoretical and experimental studies of the electronic properties of h-BN, the band properties, including the type of its band gap in nature, are still controversial at present. Experimental reports showed that h-BN is a direct band gap semiconductor. However, theoretical proved that it is an indirect band gap semiconductor. In view of such controversial situation, we systematically study the electric and optical property of h-BN with stacking fault using the first-principles plane-wave method within the density functional theory (DFT). The main results are as follows:1. We systematically studied the structure properties of five h-BN stacking (AA, AB, AD, AE, AF) and the formation energy of each stacking h-BN with different stacking fault. We find that the formation energy is very low ranging from -58~55 meV, which indicates that the stacking fault can be easily introduced into the material. Based on the results of formation energy, we can further conclude that the single crystal h-BN can hardly reserve a unique ideal stacking sequence. Its most favorable stacking sequence maybe disorder one.2. We compare the L-J attractive potential energy based the empirical parameters and total energy of the systems based on the PAW-LDA within the first-principles method. Both results give similar evolution trend. The consistency of both methods further prove the feasibility of the method we adopted.3. The influence of stacking fault on the electric and optical property of h-BN is systematically investigated. Here we introduce the kinetic energy which defined as the electron transition from the k-point of VBM to the k-point of CBM in the Brillouin zone to analyze the change of the type of band gap. We find that the AE-liked stacking sequence plays an important role in the band type conversion. When the AE-liked stacking fault introduced into h-BN the kinetic energy is significantly reduced. The materials tend to be quasi-direct band gap semiconductors. And we find that the influence of the AE-liked stacking fault on the electronic structures is insensitive to its concentration.4. The dielectric function of five typical stacking h-BN with stacking fault shows that the stacking fault can apparently influence the optical properties of h-BN. We find that the dielectric characteristic peaks change in the range of -313meV~179meV and the position of the band-edge optical absorption thresholds change in the range of -763meV~33meV.