【作者】 肖美霞；

【导师】 赵明；

【作者基本信息】 吉林大学 ， 材料学， 2011， 博士

【摘要】 近年来,核壳纳米线作为非常重要的一维异质纳米结构材料,吸引了人们的广泛关注。半导体异质结构纳米线呈现出独特的电学、光学、和力学等性能,在基础科学和纳米技术应用方面有着重要的研究价值。GaN和InN分别具有宽能隙和窄能隙,是非常重要的半导体材料。通过控制不同的生长条件,纳米线可以具有不同生长方向（[0001]、[10（1|-）0]、[11（2|-）0]）,并具有不同的横截面形状（六边形横截面、三角形横截面）。GaN和InN纳米线在光生伏打器件、光催化剂、自旋电子器件、发光二极管等方面有着广泛的应用前景。在超大规模集成电路中,Cu互连线因其具有高电导率和优良抗电迁移能力逐步取代了Al互连线和Al（Cu）互连线。Cu互连线是非常重要的电子部件,对超大规模集成电路的发展起着决定性的作用。伴随着集成电路小型化的进一步发展,器件尺寸将会降低到22 nm,甚至14 nm以下。此时,超细的Cu互连线的电迁移稳定性将会面临着巨大的挑战。Cu互连线与低k电介质材料或者是与它相关连接的阻挡层形成的界面会成为电迁移效应的路径,这主要是因为界面处的结合强度比较弱。因此,人们急需寻找能够有效改善Cu互连线的电迁移稳定性的新材料。在小型化纳米器件的应用中,纳米器件的尺寸越来越小,其性能对原子结构的变化也越来越敏感,因而在原子水平上电子态的分析是非常重要的。特别是当原子结构直径小于5 nm时,实验研究将变得比较困难。随着计算机模拟技术的发展,第一原理模拟计算在这一尺度范围越来越具有优势,因其可以有效深入探讨原子结构和电子结构对于纳米材料性能的影响。表面修饰、界面、掺杂、电场、应变场等单种外界条件,或者是多种外界条件对纳米器件性能的调节效果是显著。GaN/InN核壳纳米线通过表面修饰以及应变场使其具有优异的电学和光学等性能,在新能源领域中的光生伏打器件应用上具有巨大的应用潜力。另外,Cu互连线可以通过界面掺杂的作用使其具有优异的界面环境,增强界面的结合强度,使其在电场的条件下能够具有较好的电迁移稳定性能。这为集成电路的进一步小型化发展提供了重要的设计思路。本论文采用基于密度泛函理论的第一原理模拟方法,研究了表面修饰和应变场对GaN/InN核壳纳米线的电学和光学性能的影响,和界面掺杂对Cu互连线的电迁移稳定性能的改善。本论文主要研究成果可分如下三部分内容:首先,研究了表面修饰对沿[0001]生长方向、不同直径、横截面为六边形和三角形的GaN/InN核壳纳米线的原子结构、和电学、光学性能的影响。结果表明,由于量子禁闭效应和内应变的作用,对于表面氢化的GaN/InN核壳纳米线,当GaN核的半径固定不变,伴随着InN壳的厚度增加,能隙将会减小;当InN壳的厚度固定不变,伴随着GaN核的半径增加,能隙也将会减小。当GaN/InN核壳纳米线的表面修饰采用H和F原子时,调整H和F原子的吸附位置以及F与H原子比,将会进一步调整其能隙。值得注意的是,表面修饰可以有效的实现电子空穴的分离。这个结果阐释表面修饰可以使核壳纳米线从类型-Ⅰ带偏移转变为类型-Ⅱ带偏移,从而在新能源领域的应用中开辟了一条新的途径。其次,研究了沿[0001]生长方向、不同直径、横截面为六边形和三角形的GaN/InN核壳纳米线在应变场作用下其原子结构、和电学、光学性能的变化。GaN核和InN壳之间存在的内应变导致氢化核壳纳米线中GaN核的能隙与同等尺寸的纯的GaN纳米线的能隙不同。当对氢化GaN/InN核壳纳米线施加外轴向应变场时,伴随着外拉应变增加时,能隙将会降低;伴随着外压应变增加时,能隙将会增加。同时,增加外拉应变将会促使电子空穴的分离程度明显增强。研究结果表明,内应变和外应变能够有效的调节核壳纳米线的电学和光学性能,这提供了一种适应性很强的方法来满足实际应用中对GaN/InN核壳纳米线性能的需求。第三,研究了α-Al₂O₃薄膜和在它与Cu薄膜形成的界面处掺杂的Al原子对Cu薄膜在电场情况下的原子结构的影响。研究发现当电场强度达到0.040 au （1 au = 51.4 V/（?））时,纯Cu薄膜的原子结构发生非常大的变化,与之相比,在Cu（Al）/α-Al₂O₃界面处掺杂Al原子的Cu（Al）薄膜,在电场强度为0.040 au,甚至是较强的电场强度下,其原子结构变化很小。这主要是因为界面处存在的Cu?O共价离子键和Al?O离子键能够有效的改善Cu薄膜的稳定性。这为Cu互连线在超大规模集成电路中的应用提供了一条解决Cu互连线的电迁移稳定性问题的便捷途径。更多还原

【Abstract】 Recently, as important one-dimension heterostructure nanostructures, core/shell nanowires （CSNWs） have attracted broad interest. Semiconductor heterostructure NWs exhibit unique electronic, optical, and mechanical properties. Thus, there are of importance in fundamental science and nanotechnology application. GaN and InN with wide and narrow band gaps are the most important semiconductor materials. Different growth directions （[0001], [10（1|-）0], and [11（2|-）0]） and different across shapes （hexagonal and triangular shapes） of NWs can be synthesized by controlling different growth conditions. It has been reported that GaN and InN NWs have great application prospects and can be widely used in photovoltaic devices, photocatalyst, spintronic devices, light emitting diode, etc.In ultra-large scale integration （ULSI）, Cu interconnection replaces Al and Al（Cu）, because of its high conductivity, and good electromigration （EM） resistance. Cu interconnection is one of the most essential concerns and determines the further development of ULSI. Upon miniaturization of ULSI with the feature sizes reduced to 22 or 14 nm, further thinning of Cu interconnection leads to more serious EM. The Cu/low-k dielectrics or Cu/barrier layers interfaces are main EM paths, due to the weak bonding strength at the interfaces. Thus, a vital issue addressed has arisen to seek a material that can effectively improve the EM reliability of Cu interconnection.In nanodevices with the miniaturization, the size becomes smaller and smaller. The performances of many nanoscale devices are sensitive to the variation of local atomic configurations, leading to that electronic state analysis at the scale of individual atoms becomes more and more important. In particular, when the diameter of NWs is less than 5 nm, it becomes a great challenge for studying in experimental studies. Thanks to the development of computer techniques, the first?principles calculations become much more powerful, and are beneficial to study the detail effects of the atomic and electronic structures on the properties of NWs. The surface modifications, interfaces, doping, electric field, strain field, ect, are essential to the properties of nanodevices. Especially, the coexistence of the external circumstance has significant effect on the performance of nanodevices. It is promising for GaN/InN CSNWs in the application as photovoltaic devices because of the unique electronic and optical properties of GaN/InN CSNWs induced by surface modifications and strain field. In addition, the good doping at the interfaces can enhance the interfacial stability and bonding strength of Cu interconnection, which effectively improves the EM reliability under electric field. The results provide a new way of designing the miniaturization of ULSI. In this thesis, using the first-principles calculations based on density-functional theory, we investigate the effects of the surface modifications and strain fields on the electronic and optical properties of GaN/InN CSNWs, and the effects of the doping at the interfaces on the EM realiablity of Cu interconnection.The main results obtained in the thesis are divided into three parts as following:Firstly, we investigate the effects of surface modifications on atomic structures, electronic and optical properties of triangular and hexagonal GaN/InN CSNWs along [0001] derection. The results show that the band gaps Eg decrease, as the thicknesses of InN shell （ radii of GaN core） increase in hydrogenated GaN/InN CSNWs with fixed radii of GaN core （thicknesses of InN shell）, due to the effects of quantum confinement and intrinsic strain. Furthermore, our calculations demonstrate that surface modifications with H and F atoms substantially modulate the band gaps dependent on the adsoprtion sites and the F/H ratio. It is worthy noting that surface modifications induce the separation of electrons and holes. The results elucidate that surface modifications change electronic structures of CSNWs with a transition from type-Ⅰband alignment to quasi-type-Ⅱ, which open a new way in the field of renewable energy applications.Secondly, we investigate the influence of the intrinsic and external uniaxial strains on the atomic structures, electronic and optical properties of GaN/InN CSNWs with hexagonal and triangular shapes along [0001] direction. It is found that the band gap of the GaN core in hydrogenated CSNW differs from that of the pure GaN NW due to the intrinsic strainεi between GaN core and InN shell. Under the external uniaxial strainεe on GaN/InN CSNWs, the direct band gap decreases （increases） with increasing the external tensile （compressive） strain. The efficient dissociation of electrons and holes excitons is enhanced by the external tensile strain. The results demonstrate thatεi andεe substantially influence electronic and optical properties of CSNWs, which probably reach the requirement of GaN/InN CSNWs applied in practic devices.Thirdly, the effects ofα-Al₂O₃ films and the Al atoms doped at theα-Al₂O₃/Cu interfaces on atomic structures of Cu（Al） films are investigated under external electric fields F. The Cu films with large deformation indicate that EM of Cu slabs occurs as F reaches 0.040 au （1 au = 51.4 V/（?））, in contrast, the Cu（Al） films coated byα-Al₂O₃ films slightly change and are more stable under the same and larger F. The main reason is that Cu?O covalent-ionic and Al?O ionic bonds exist at the interfaces, indicating that the stronger bonding strength effectively improves the reliability of Cu atoms. These results provide a solution of enhancing the EM reliability of Cu interconnection in ULSI.更多还原