标题: | 以第一原理与量子传输来计算植入特殊离子的镍锗化物与N型锗接面 First-principles and Quantum-transport Calculations of the Ion-implanted NiGe/n-type Ge Contact |
作者: | 李昆霖 Li, Kun-Lin 林炯源 Lin, Chiung-Yuan 电子工程学系 电子研究所 |
关键字: | 第一原理计算 密度泛函理论 非平衡格林函数 萧特基位障 量子传输 掺杂析离 锗;First-principles Density functional theory Nonequilibrium Green's function Schottky barrier height Quantum transport Dopant segregation Germanium |
公开日期: | 2015 |
摘要: | 现今技术的发展使得元件越做越小,而传统使用的矽基金氧半场效电晶体也逐渐接近其微缩极限。因此,寻找合适的替代材料便非常重要。其中,在元素周期表位于矽正下方的锗,由于拥有比矽更高的载子迁移率,而被认为可以取代矽作为新的通道材料。然而,在金属与 N 型锗接面中,由于锗在价电带附近有大量的介面态产生,造成非常强的费米能阶钉扎效应,使得电子萧特基位障不容易降低,亦使得特征接触阻抗无法降低。因此,如何减缓费米能阶钉札效应便成为首要目标。 在我们的研究中,将考虑植入不同特殊离子的镍锗化物与锗接面,计算其电子结构与量子传输,并且镍锗化物与锗的晶面方向分别选择(112)与(001)面,考虑不同的植入离子包含了硒、铝、锡、钪、钛、钒、硫、氯、铂等离子。计算结果可分为三个部分:第一个部份,经由密度泛函理论搭配局域密度近似法,讨论植入离子是否会析离于镍锗化物与锗接面的介面处;第二个部分,经由密度泛函理论搭配杂化泛函法,讨论植入离子在其稳定位,是否有降低电子萧特基位障的效果,我们从结果得知,硒、钒离子较有降低萧特基位障的效果,并分别降低 0.175、0.097 eV,且发现它们都会析离于介面并倾向聚集在半导体端,另外,实验方面也对硒离子作了量测与分析,并得到降低萧特基位障0.15 eV 左右的结果;第三个部分,经由密度泛函理论与非平衡格林函数理论搭配mBJ位能近似,讨论植入离子在其稳定位,是否可以降低特征接触阻抗,我们的结果也显示,对于硒、铝、锡等三种植入离子,硒、锡可以降低特征接触阻抗大约一个数量级左右。 从以上的结果来看,经由第一原理模拟计算可以使我们知道在原子尺度下,植入离子于介面的析离作用,以及植入离子对于萧特基位障与特征接触阻抗的改善效果。最后,我们也预期这些结果将对实际制程的研究方向有所帮助。 As the state-of-the-art semiconductor process techniques drive devices toward sub-10nm sizes, the traditional Si-based MOSFETs are approaching their scaling limit in near future. It is very important to find a suitable material to replace Si. The element right below Si in the periodic table, Ge, is considered a potential channel material due to its higher mobility. However, Ge suffers from its strong fermi level pinning effect because many interface states appear near its valence band. Consequently, the interfacial electronic structures exhibit a high value of Schottky barrier height, which results in an undesired specific contact resistance. Therefore, fermi level depinning is a critical step to make Ge become feasible in semiconductor devices. In our research, we calculate the electronic structures and quantum transport of the NiGe/Ge contact with various ions implanted. We choose the interface crystal orientations of NiGe and Ge to be (112) and (001), respectively. The implanted ions are Se, Al, Sn, Sc, Ti, V, S, Cl, and Pt. Our calculations can be divided into three parts. We first study, in atomic scale, how the implanted ions segregate at the interface using the local density approximation of density functional theory (DFT). Second, we calculate the Schottky barrier height under the influence of the implanted ions using the DFT’s HSE06 hybrid functional. Calculations show that Se and V ions, both most stably located at the Ge side of the interface, reduce the Schottky barrier height by 0.175 and 0.095 eV, respectively, where the former is consistent with the experiment. Finally, we calculate the specific contact resistance of the same contact by employing the nonequilibrium Green's function method with the DFT’s modified Becke-Johnson potential. Such quantum-transport calclations show that ion implantation could reduce the specific contact resistance, up to one order from our results. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT070150174 http://hdl.handle.net/11536/127786 |
显示于类别: | Thesis |