| Since the emergence of graphene, it is proved that the two dimensional materials can be stably at room temperature, and the research on the two dimensional materials is rapidly expanding. Along with the research, it is found that stacking two kinds of 2D materials have some new characteristics, and because of the weak van der Edward force, it does not need to consider the limitations caused by the lattice mismatch, which greatly increases the research boom of two-dimensional materials, and has a bright future. In this paper, the simulation software studio material, we calculate the TMDs-Mo S2 heterojunction, Graphene-TMDs heterojunction model to study their internal structure?band structure?optical properties, etc.The results obtained are as follows:First, To investigate the new features of the WSe2/Mo S2 heterojunction, the lattice parameters, band structure, density of states, electron population and electron density difference of the heterojunction are calculated and analyzed, respectively, using the plane wave pseudopotential method based on the first-principles in this paper. The calculation results of the band structure and density of states show that the WSe2/Mo S2 heterojunction has a direct band structure and the band gap width is 0.441 e V which is less than that of WSe2 and Mo S2. The calculation results about electron population and electron density difference indicate that the WSe2 molecular layer is positively electrical and Mo S2 molecular layer is electronegative thus forming a built-in electric field of WSe2 layer to Mo S2 layer that will be helpful to the separation of electron-hole pairs. The analysis of the band structure and built-in electric field indicates that the WSe2/Mo S2 heterojunction is suitable for the fabrication of optoelectronic devices such as solar cell or optoelectronic detector, especially in the absorption and response to long-wave length photon.Second, the influence of three kind of the different stacking modes on the WSe2-MoS2 heterojunction is analyzed by the first principle of the plane wave pseudo potential method. The results of band structure calculation show that the three kinds of WSe2-Mo S2 have a direct band gap,and the band gaps are 0.442 e V, 0.859 e V, 0.522 e V. This means that the stacking of different ways can be used to control the proper band gap, so as to broaden the application range of this kind of heterojunction. Through the calculation of the formation energy, the three kinds of structures are all negative, and the difference is little,which showsthis three structures are easy to be formed. And when we would analyze the practical experiments, three kinds of structures should be considered together. Optical properties of the calculation results shows that, due to the difference band gap, structure two about absorption coefficient and conductivity in the middle and long wave range is better than structures one and three; The absorption edge generally shifts to left, which is in favor of heterojunction's absorption to the long wave infrared. The calculations of Mo Se2-Mo S2 heterojunction and WS2-Mo S2 heterojunction show that the two kinds of heterojunction are direct band gap and the band gap is 0.780 e V and 1.389 e V respectively. The comparison of the absorption spectra shows that the Mo Se2-Mo S2 has a strong absorption in the high frequency range and can be used to study the ultraviolet and deep ultraviolet detector.In the end, we calculate the Graphene-TMDs heterojunction,and find that the GrapheneMo S2 heterojunction stacked in second ways can open graphene's band gap. The main difference between the two structures lies in the fact that the S atom influence on the different degree of C atom hybridization. The formation energy of the calculation shows that the two kinds of structures are easy to form. Graphene-WS2 heterojunction in the two ways that graphene has a 17 me V and 49 me V band gap open, which means that stacking the graphene and WS2 can be used to control graphene's band gap, so as to expand the application space of graphene in the switching devices. The two stacking modes of graphene-WSe2 heterojunction are still zero band gap, and the gap is not open.The reasons of this difference lies in the conduction band bottom and valence band top have the same contribution of W and Mo atoms,and come from the different contributions of S atoms and Se atoms. Optical properties study found that those heterostructures broaden light absorption spectrum,better than the single material, and found graphene-Mo S2 heterojunction and the other two heterogeneous have a different absorption to high-frequency high-energy photon. By using these properties, the heterojunction is more favorable to the application of the photoelectron field. |
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