Modulation-Acceptor Doping of SiO2 as Novel Doping Method for Silicon Nanowires (MADSiNano)

直径很小的硅(Si)纳米线在微电子晶体管技术的进一步发展中发挥着关键作用，而微电子晶体管技术几乎对所有电子设备都是必不可少的。纳米线通过栅极场效应晶体管(GAA-FET)架构实现对源漏电流的最大栅极控制。对于纳米线晶体管的电子功能化，有几个概念可用(p/n结、隧道FET、无结晶体管)。然而，它们都依赖于经典的杂质掺杂(如磷或硼)的电导率控制。在纳米尺度上，可靠和有效的掺杂受到许多物理和技术问题的阻碍。这些问题包括：杂质的不希望的扩散，界面杂质的分离或失活，抑制杂质电离的介电和量子限制，以及当试图用相同数量的掺杂原子掺杂超小的硅纳米体积时的统计问题。在这个项目中，我们想要追求一个理论概念，对硅采用从III-V半导体中已知的调制掺杂。调制掺杂意味着母体掺杂原子通过将它们嵌入到具有较高带隙的相邻材料中而与要掺杂的体积在空间上分离。密度泛函理论(DFT)计算表明，在SiO_2中，Al原子在Si价带边缘以下有一个空态，捕获电子后在Si中形成一个空穴作为主要的电荷载流子。因此，嵌入了硅纳米结构的二氧化硅被掺杂，而自由多数载流子对硅的导电性有贡献。所有与直接掺硅相关的问题都可以通过这种方式绕过。在大量的前期工作中，我们证明了Al诱导受主态的存在，并确定了几个基本性质。现在，我们希望将这一概念应用于硅纳米线，以证明通过对SiO_2壳层的调制受主掺杂来大幅提高电导率，并制备和表征功能纳米线晶体管测试器件。除了Al，DFT计算还提出了其他4种可能的元素，它们可能代表了Si的SiO_2调制受体。在该项目中，将详细研究这些元素，并开发工艺将它们实施到硅纳米线晶体管中，以便能够比较不同调制接受者元素的掺杂性质。

Silicon (Si) nanowires with few nanometers in diameter play a key role in the further development of the microelectronic transistor technology, which is essential for virtually all electronic devices. Nanowires enable maximum gate control over the source-drain current via the gate-all-around field effect transistor (GAA-FET) architecture. For the electronic functionalization of nanowire transistors several concepts are available (p/n-junctions, tunnel-FETs, junctionless transistors). However, all them rely on the conductivity control by classical impurity doping (using e.g. phosphorus or boron). On the nanoscale, reliable and efficient doping is impeded by a multitude of physical and technological problems. These problems include e.g. the undesired diffusion of dopants, segregation or deactivation of dopants at interfaces, dielectric and quantum confinement that inhibit the ionization of an impurity as well as statistical problems when attempting to dope ultrasmall Si nanovolumes with an identical amount of a defined number of dopant atoms.In this project we want to pursue a theoretical concept to adopt modulation doping known from III-V semiconductors for Si. Modulation doping means that the parent dopant atoms are spatially separated from the volume that is to be doped by embedding them into an adjacent material with a higher bandgap. Density functional theory (DFT) calculations predicted that aluminum (Al) atoms in SiO2 have an unoccupied state below the Si valence band edge, which upon electron capture creates a hole in the Si as majority charge carrier. Thereby, the SiO2 embedding a Si nanostructure is doped, whereas the free majority charge carriers contribute to the conductivity of the Si. All the problems associated to direct Si doping are circumvented in that way. In extensive preliminary work we proved the existence of this Al-induced acceptor state and determined several fundamental properties. Now, we want to adopt this concept to Si nanowires to demonstrate a massive increase of the conductivity via modulation acceptor doping of the SiO2 shell and to fabricate and characterize functional nanowire transistor test devices. In addition to Al, DFT calculations suggest 4 other possible elements, which might represent SiO2 modulation acceptors for Si. In the project, these elements will be investigated in detail and processes will be developed to implement them into Si nanowire transistors to enable a comparison of the doping properties of the different modulation acceptor elements.