【作者】 张倩；

【导师】 夏从新；

【作者基本信息】 河南师范大学 ， 材料科学与工程， 2019， 硕士

【摘要】 2004年,二维石墨烯被成功制备,因其高的载流子迁移率,良好的导电性和反常量子霍尔效应等优异性能,促使人们探索其它类石墨烯二维材料。二维材料种类繁多,大致可分为金属、半导体、绝缘体等,例如,氮化硼、过渡金属硫化物、黑磷等涵盖了元素周期表中大多数元素的化合物,从而形成了丰富的光、电、磁等物理化学性质,意味着它们在光电子、自旋等新型电子器件领域有较大的应用前景。此外,二维材料相邻层之间依靠范德华力结合,通过组装不同类型的二维层状材料以构建范德瓦尔斯异质结可以有效地调节二维材料的性能,例如,二硫化钼与g-C₃N₄构建异质结不仅可以克服二硫化钼易光腐蚀的缺点还可以提高材料的光吸收系数,从而扩宽其应用领域。本文我们基于密度泛函理论,详细研究了以SnS₂为基的几种二维范德瓦尔斯异质结,主要包括SnS₂/n-BN多层异质结、GeSe/SnS₂（SnSe₂）p-n结和SnS₂/polyphenylene异质结,通过对其光电性质的研究和外界因素的影响,探索出了更多新的超出相应单组分的潜在应用前景。主要研究结果如下:（1）对于SnS₂/n-BN多层异质结,我们的计算结果表明异质结体系始终维持直接带隙,类型II能带排列,导带底和价带顶分别由SnS₂和BN贡献,从而实现了较高的载流子分离效率,n表示BN层数;此外,我们研究了BN层数和外电场对异质结电学性质的调控,结果表明随着BN层数的增加,异质结的带隙和功函数逐渐降低并趋于稳定值;通过施加外电场,不同层数BN异质结体系都可以从直接带隙转变为间接带隙类型,能带排列也可以在类型II与类型I之间转变。（2）对于GeSe/SnS₂（SnSe₂）p-n结,我们的计算结果表明GeSe/SnS₂（SnSe₂）p-n结显示类型III能带排列,特殊的电子结构促使了载流子可以通过隧穿窗口从GeSe层转移到SnS₂（SnSe₂）层,从而大大提高载流子隧穿效率,此种隧穿方式称为带带隧穿机制;此外,施加外电场可以有效调控异质结电学性质,例如,负电场可以维持异质结类型III能带排列并增大隧穿窗口,提高载流子隧穿效率;而正电场可以将类型III能带排列转变为类型II或类型I能带排列,这对GeSe/SnS₂（SnSe₂）异质结在隧穿场效应晶体管领域的应用具有指导性意义。（3）对于SnS₂/polyphenylene异质结,我们的计算结果表明其具有类型II能带排列,能够实现较高的载流子分离率,且异质结在可见光和紫外区域具有较高的吸收峰;此外,Bader电荷分析表明,通过施加应变可以有效调控SnS₂与polyphenylene之间的相互作用,从而能够有效调控异质结的电学性质;外电场不仅可以有效地调控异质结带隙,还可以将类型II异质结转变为类型I或类型III能带排列,这些理论预测结果揭示了二维SnS₂/polyphenylene异质结在新型纳米光电器件领域具有较大的应用前景。更多还原

【Abstract】 Since the successful synthesis of graphene in 2004,more and more attention has been paid to explore other graphene-like materials due to the excellent properties of graphene,such as high carrier mobility,good conductivity and quantum hall effect at room temperature.There are many kinds of two-dimensional（2D）materials,which can be divided into metals,semiconductors,insulators.For example,boron nitride（BN）,transition-metal dichalcogenides（TMD）,black phosphorus（BP）and other compounds cover most of the elements in the periodic table,and thus exhibit unique optical,electronic and magnetic properties,indicating that they can be applied in the fields of optoelectronics,spinelectronics and so on.Moreover,constructing the van der Waals heterostructures（vdWHs）can effectively modulate the properties of 2D materials and broaden their applications fields.For example,the MoS₂/g-C₃N₄ heterostructure can overcome the corrosion resistance of MoS₂ and improve the light absorption coefficient.In this thesis,we study a series of SnS₂-based heterostructures,including SnS₂/n-BN multilayer heterostruture,GeSe/SnS₂（SnSe₂）p-n junctions and SnS₂/polyphenylene heterostruture based on density functional theory.The main results are as follows:Firstly,our theoretical results predicate that the SnS₂/n-BN multilayer heterostructure possess type-II band alignment with direct band gap.Moreover,the results show that the band gap and work function decrease with the increase of the layer BN for the SnS₂/n-BN multilayer heterostructure;In addition,the the SnS₂/n-BN multilayer heterostructure can be transformed from the type-II band alignment to the type-I band alignment under the external electric field,and the direct band gap also can be tuned to indirect band gap effectively.Secondly,we predict that the GeSe/SnS2（SnSe2）p-n junction exhibits the type-III band alignment with band to band tunneling mechanism（BTBT）.Moreover,when applying the negative external electric field,the p-n junction can retain the type-III band alignment and enlarge the tunneling window.However,the positive electric field can transfer the GeSe/SnS₂（SnSe₂）p-n junction from the type-III to the type-II or type-I band alignment.Our findings indicate that the GeSe/SnS2（SnSe2）p-n junction has potential applications in tunneling field effect transistors.Finally,the SnS₂/polyphenylene heterostructure exhibits the type-II band alignment,and possesses high absorption coefficient in the visible and ultraviolet region.In addition,the electronic properties for the SnS₂/polyphenylene heterostructure is sensitive to the interlayer distance.The external electric field not only can transform the type-II band alignment to the type-I or type-III band alignment,but also tune the band gap effectively.Our results offer useful information for the SnS₂/polyphenylene heterostructure has potential applications in nano-optoelectronic devices fields.更多还原