Nb掺杂浓度对单层MoS_2电子能带结构的影响

Effect of Nb Doping Concentration on the Electronic Band Structure of Single Layer MoS_2

运用密度泛函理论的第一性原理方法,研究了本征和不同浓度Nb掺杂单层MoS_2的晶体几何结构、能带结构、态密度、电荷局域密度函数以及形成能。计算结果发现,本征单层MoS_2为直接带隙,禁带宽度为1.67 e V。随着Nb掺杂浓度的增加,单层MoS_2价带顶会越过费米能级向高能区方向移动,导带底则向低能区方向移动,致使其禁带宽度大幅度减小。当掺杂浓度为8.33%时,其禁带宽度减小至1.30 e V。带隙值的大幅减小,电子从价带激发到导带变得更容易,应用在以晶体管为代表的逻辑器件等领域,将使其电流开关比、导电性等电学性能得到显著提升。此外,掺杂前后成键类型均是离子键与共价键的混合键,形成能较低,说明掺杂体系的热力学稳定性良好,易于实现。研究结果为单层MoS_2在半导体器件的实际应用提供了理论指导。

Using the first principle method of density functional theory, The crystal structure, band structure, density of States, charge density function and formation energy of intrinsic and Nb doped monolayer MoS2 were studied. The results show that the intrinsic monolayer MoS2 has a direct band gap characteristic with band gap energy of 1.67 eV. With the increase of Nb doping concentration, single MoS2 valence band edge cross the Fermi level shifts to the high energy direction, while the conduction band bottom to low energy direction, resulting in great reduction of the band gap. When the doping concentration is 8.33~, the band gap decreases to 1.30 eV. With the decreasing of band gap value, electron excitation from valence band to conduction band becomes easier. For the application in transistor logic devices and other fields, the current on-off ratio, conductivity and other electrical properties will be significantly improved. In addition, the bond types before and after doping are both the mixture of ionic bond and covalent bond with a small formation energy, which shows that the doping system has good thermodynamic stability and is easily realized. The results provide theoretical guidance for the practical application of single layer MoS2 in semiconductor devices.