First-principle Study On Transport Prorperties Of Two-Dimensional Semiconductor Materials

Based on the deformation potential theory, this paper takes the scatterings of acoustic phonons, optical phonons and piezoelectric effect（1H structure） into consideration in order to establish a rather accurate model of the carrier mobility of two-dimensional（2D） single-layered materials. On the basis of the model, the calculations of the carrier mobilty of 14 kinds of transition metal dichalcogenides（TMD） are performed. By comparing the calculation results with the experimental ones, this paper validates the method of calculating the mobility of 2D single-layered TMD materials by employing the deformation potential（acoustic phonon deformation potential, optical phonons deformation potential, piezoelectric effect deformation potential） to approximate the electron-phonon scattering matrix.The calculation results show that WS2 has both the highest electron mobility of 1739 cm²V^-1s^-1, and the highest hole mobility of 2604 cm²V^-1s^-1 among the 5 1H-structured materials. While in the 1T-structured materials, the highest electron mobility of 4037 cm²V^-1s^-1 is found in PtSe2, with the highest hole mobility of 1959 cm²V^-1s^-1 in HfS2. On the other hand, WS2 is a direct bandgap semiconductor with the direct bandgap 1.99 eV, while PtSe2 and HfS2 are both indirect bandgap semiconductors of which the indirect bandgaps are 1.69 eV and 1.05 eV, respectively. On account of the two prerequisites（ proper bandgap and high carrier mobility） to be an ideal semiconductor, WS2 and PtSe2 may be the suitable candidates of n-type 2D semiconductors, and WS2 and HfSe2 may have the potential to be good p-type 2D semiconductors. However, the rest 11 materials can not perform well as 2D semiconductors.The method in this paper could be extended to be applied to all the 2D materials. Compared with the method of Kaasbjerg and Kim, in which the electron-phonon interaction matrix is directly calculated, the method proposed in this paper, including only several simple calculations（band structure calculation, phonon-dispersion calculation）, reduces the calculation resource and calculation time at a large scale, which suits the need of quick search for materials with special properties in the vivid material world.In addition, this paper also carries out the detailed study on the role played by van der Waals in PtSe2-like materials with long-range interaction between layers when changing from single layer to bulk materials. Compared with the researches of Z. Zhu and S. Bhattacharyya, this paper has drawn such a conclusion that when the transition from single layer to bulk materials takes place, van der Waals pushes the charge on the inter-layer non-metal atom to transfer to the metal atom, making the in-plane crystal constant increase and the out-plane crystal constant decrease, leading to the reducing of the minimum of conducting band and the rising of the maximum of valence band, resulting in the narrowing of bandgap, as a consequence of which the semiconductor-semimetal transition shows up.