二维材料层堆叠异质结的第一性原理研究

发布时间：2018-05-03 12:01

本文选题：第一性原理 + 异质结　；参考：《西安电子科技大学》2015年硕士论文

【摘要】：自从石墨烯出现以后证明二维材料可以在常温下稳定存在,二维材料的研究迅速扩展开来。随着研究的不断深入,人们发现堆叠两种二维材料形成异质结可以呈现出一些新颖的特性,而且由于二维材料层间是靠微弱的范德华力结合而成,不需要考虑如体材料异质结一样因为晶格不匹配造成的限制,这样大大促进了二维材料异质结的研究。本文借助模拟软件Material Studio,对TMDs-MoS_2异质结和Graphene-TMDs异质结两类异质结进行模拟计算,研究其内部结构、能带结构、光学性质等,所取得的研究成果如下:1.首先对WSe_2-MoS_2异质结的超胞的晶格参数、能带结构、态密度、电子布局和差分电荷密度。能带结构和态密度的计算结果显示,WSe_2-MoS_2异质结具有直接带隙能带结构,禁带宽度为0.441eV。其值均小于WSe_2和MoS_2的禁带宽度,意味着若将该结构用于太阳电池或光电探测器,可以增强相关器件对长波长光子的吸收与响应。电子布局和差分电荷密度的计算结果表明,异质结构成后可使WSe_2分子层荷正电,MoS_2分子层荷负电,由此形成由WSe_2层指向MoS_2层的内建电场,该内建电场的形成有助于实现光生电子-空穴对的分离。计算结果分析说明WSe_2-MoS_2异质结非常适合被用来制作需要对长波长光子吸收与响应的太阳电池和光电探测器等光电子器件。2.分析了三种不同堆叠方式对WSe_2-MoS_2异质结的影响。能带结构计算结果显示,三种WSe_2-MoS_2异质结都具有直接带隙能带结构,禁带宽度分别为0.441eV、0.859eV、0.522eV。这就意味着通过不同方式的堆叠,可以用来调控该类异质结合适的禁带宽度,从而拓宽此类异质结的应用范围。通过形成能的计算表明,三种结构形成能都为负值,而且相差很小,说明三种结构都容易形成,在分析实际实验时,必须同时考虑三种结构共同存在的情况。光学性质的计算结果可知,由于禁带宽度的差别结构2的吸收系数、光电导在中长波范围内比结构1和结构3都要好;吸收边普遍左移,这有利于异质结对红外波段的长波的吸收。对MoSe_2-MoS_2异质结和WS_2-MoS_2异质结的计算显示,两种异质结都为直接带隙,禁带宽带分别为0.780eV和1.389eV。吸收谱的比较发现MoSe_2-MoS_2异质结在高频范围内有着很强的吸收,可以应用到对紫外、深紫外探测器的研究。3.最后,我们对Graphene-TMDs异质结进行计算研究,发现graphene-MoS_2异质结按照第二种方式堆叠能打开石墨烯能隙,两种结构主要差别在于S原子对石墨烯层中C原子杂化的程度的情况不同。形成能的计算显示两种结构都较容易形成。Graphene-WS_2异质结的两种方式使得石墨烯有着17meV和49meV带隙的打开,这就意味着可以通过利用石墨烯与WS_2的堆叠来控制石墨烯的能带,从而有利于石墨烯的开关器件中的应用。Graphene-WSe_2异质结的两种堆叠方式都为零带隙,并没有使得石墨烯能隙的打开。造成这种差别的原因在于导带低和价带顶Mo原子和W原子贡献相同,主要差别来自S原子和Se原子的不同贡献。光学性质研究发现,此类异质结拓宽了单一材料对光的吸收频谱,而且发现Graphene-MoS_2异质结与另两种异质结对高频高能光子的吸收范围有所不同。这样通过利用这些特性使得此类异质结更加有利于应用到光电子领域。
[Abstract]:Since the appearance of graphene has proved that the two-dimensional material can be stable at normal temperature, the study of two-dimensional materials has expanded rapidly. With the development of the research, it is found that stacking of two kinds of two-dimensional materials can present some novel properties, and the two dimension material is combined with weak van Edward force. It does not need to consider the restriction caused by the lattice mismatch, such as the bulk material heterojunction, which greatly promotes the study of the two-dimensional heterojunction. In this paper, the simulation software Material Studio is used to simulate two types of heterojunction, TMDs-MoS_2 heterojunction and Graphene-TMDs heterojunction, to study the internal structure, band structure and optics. The results obtained are as follows: 1. first, the lattice parameters of the supercell of the WSe_2-MoS_2 heterojunction, the band structure, the state density, the electron distribution and the differential charge density. The results of the band structure and the density of states show that the WSe_2-MoS_2 heterojunction has a direct band gap structure and the band gap of 0.441eV. is less than WSe_2 and Mo. The band gap of S_2 means that if the structure is used in solar cells or photodetectors, the absorption and response of the related devices to Nagawa Nagahikaruko can be enhanced. The results of the electronic layout and differential charge density show that the WSe_2 molecular layer can be charged positively and the MoS_2 molecular layer is charged, thus forming the WSe_2 layer to Mo. The internal electric field of the S_2 layer, the formation of the built electric field helps to realize the separation of the photoelectron hole pair. The calculation results show that the WSe_2-MoS_2 heterojunction is very suitable for making.2. analysis of three different stacking modes for the photoelectron devices, such as the solar cells and photodetectors, which need to absorb and respond to the WSe_2-. The effect of MoS_2 heterostructure. The results of band structure calculation show that the three WSe_2-MoS_2 heterostructures have direct band gap band structure, and the band gap is 0.441eV, 0.859eV, 0.522eV., which means that the different ways of stacking can be used to regulate the appropriate band gap of this kind of heterojunction, thus widening the application model of such heterojunction. The calculation of the formation energy shows that the formation energy of the three structures is negative, and the difference is very small, indicating that the three structures are easy to form. In the analysis of the actual experiment, the common existence of the three structures must be considered simultaneously. The long wave range is better than the structure 1 and the structure 3; the absorption edge is generally left shift, which is beneficial to the absorption of the long wave in the infrared band of the heterojunction. For the MoSe_2-MoS_2 heterojunction and the WS_2-MoS_2 heterojunction, the two heterostructures are all direct bandgap, and the band gap is compared to the 0.780eV and 1.389eV. absorption spectra, respectively. The junction has very strong absorption in the high frequency range, and can be applied to the study of UV, deep ultraviolet detector.3.. We have calculated the Graphene-TMDs heterojunction. It is found that the graphene-MoS_2 heterojunction can open the energy gap of the graphene by stacking in second ways. The main difference of the two structure is that the S atom has the C atom in the graphene layer. The formation energy is different. The calculation of the formation energy shows that the two structures are easier to form two ways of.Graphene-WS_2 heterojunction, which makes the 17meV and 49meV band gap open, which means that the energy band of graphene can be controlled by using the stacking of graphene and WS_2, thus it is beneficial to the switching devices of graphene. The two stacking methods used in the.Graphene-WSe_2 heterojunction are zero band gaps, and the energy gap is not opened. The reason for this difference is that the lead band is low and the valence band top Mo and W atoms contribute the same, the main difference is from the different contributions of the S atom and the Se atom. The absorption spectrum of light by a single material and the difference between the absorption range of the Graphene-MoS_2 heterojunction and the other two heterostructures for high frequency and high energy photons are found. By using these properties, this kind of heterojunction will be more beneficial to the application of the photoelectron field.

【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB30

【参考文献】