本文選題：第一性原理 + 異質結　； 參考：《西安電子科技大學》2015年碩士論文

【摘要】：自從石墨烯出現以后證明二維材料可以在常溫下穩定存在,二維材料的研究迅速擴展開來。隨著研究的不斷深入,人們發現堆疊兩種二維材料形成異質結可以呈現出一些新穎的特性,而且由于二維材料層間是靠微弱的范德華力結合而成,不需要考慮如體材料異質結一樣因為晶格不匹配造成的限制,這樣大大促進了二維材料異質結的研究。本文借助模擬軟件Material Studio,對TMDs-MoS_2異質結和Graphene-TMDs異質結兩類異質結進行模擬計算,研究其內部結構、能帶結構、光學性質等,所取得的研究成果如下:1.首先對WSe_2-MoS_2異質結的超胞的晶格參數、能帶結構、態密度、電子布局和差分電荷密度。能帶結構和態密度的計算結果顯示,WSe_2-MoS_2異質結具有直接帶隙能帶結構,禁帶寬度為0.441eV。其值均小于WSe_2和MoS_2的禁帶寬度,意味著若將該結構用于太陽電池或光電探測器,可以增強相關器件對長波長光子的吸收與響應。電子布局和差分電荷密度的計算結果表明,異質結構成后可使WSe_2分子層荷正電,MoS_2分子層荷負電,由此形成由WSe_2層指向MoS_2層的內建電場,該內建電場的形成有助于實現光生電子-空穴對的分離。計算結果分析說明WSe_2-MoS_2異質結非常適合被用來制作需要對長波長光子吸收與響應的太陽電池和光電探測器等光電子器件。2.分析了三種不同堆疊方式對WSe_2-MoS_2異質結的影響。能帶結構計算結果顯示,三種WSe_2-MoS_2異質結都具有直接帶隙能帶結構,禁帶寬度分別為0.441eV、0.859eV、0.522eV。這就意味著通過不同方式的堆疊,可以用來調控該類異質結合適的禁帶寬度,從而拓寬此類異質結的應用范圍。通過形成能的計算表明,三種結構形成能都為負值,而且相差很小,說明三種結構都容易形成,在分析實際實驗時,必須同時考慮三種結構共同存在的情況。光學性質的計算結果可知,由于禁帶寬度的差別結構2的吸收系數、光電導在中長波范圍內比結構1和結構3都要好;吸收邊普遍左移,這有利于異質結對紅外波段的長波的吸收。對MoSe_2-MoS_2異質結和WS_2-MoS_2異質結的計算顯示,兩種異質結都為直接帶隙,禁帶寬帶分別為0.780eV和1.389eV。吸收譜的比較發現MoSe_2-MoS_2異質結在高頻范圍內有著很強的吸收,可以應用到對紫外、深紫外探測器的研究。3.最后,我們對Graphene-TMDs異質結進行計算研究,發現graphene-MoS_2異質結按照第二種方式堆疊能打開石墨烯能隙,兩種結構主要差別在于S原子對石墨烯層中C原子雜化的程度的情況不同。形成能的計算顯示兩種結構都較容易形成。Graphene-WS_2異質結的兩種方式使得石墨烯有著17meV和49meV帶隙的打開,這就意味著可以通過利用石墨烯與WS_2的堆疊來控制石墨烯的能帶,從而有利于石墨烯的開關器件中的應用。Graphene-WSe_2異質結的兩種堆疊方式都為零帶隙,并沒有使得石墨烯能隙的打開。造成這種差別的原因在于導帶低和價帶頂Mo原子和W原子貢獻相同,主要差別來自S原子和Se原子的不同貢獻。光學性質研究發現,此類異質結拓寬了單一材料對光的吸收頻譜,而且發現Graphene-MoS_2異質結與另兩種異質結對高頻高能光子的吸收范圍有所不同。這樣通過利用這些特性使得此類異質結更加有利于應用到光電子領域。
[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.

【學位授予單位】：西安電子科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB30

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本文編號：1838407