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

直径只有几纳米的硅纳米线在微电子晶体管技术的进一步发展中起着关键作用，而微电子晶体管技术对几乎所有的电子器件都是必不可少的。纳米线通过栅极全环绕场效应晶体管（GAA-FET）架构实现对源极-漏极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，所有这些都依赖于通过经典杂质掺杂（使用例如磷或硼）的导电性控制。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。这些问题包括例如掺杂剂的不期望的扩散、界面处掺杂剂的偏析或失活，介电和量子限制，抑制离子化的杂质，以及统计问题时，试图掺杂超小硅纳米体积与相同数量的一个定义数量的掺杂剂原子。在这个项目中，我们要追求一个理论概念，采用调制掺杂已知的III-V半导体为Si。调制掺杂意味着母掺杂剂原子通过将它们嵌入到具有较高带隙的相邻材料中而与待掺杂的体积空间分离。密度泛函理论（DFT）计算预测，SiO2中的铝（Al）原子在Si价带边缘以下具有未占据状态，其在电子捕获时在Si中产生空穴作为多数电荷载流子。因此，嵌入Si纳米结构的SiO2被掺杂，而自由多数电荷载流子有助于Si的导电性。与直接Si掺杂相关的所有问题都以这种方式规避。在广泛的前期工作中，我们证明了这种Al诱导的受主态的存在，并确定了几个基本性质。现在，我们想采用这个概念的Si纳米线，以证明通过调制受体掺杂的SiO2壳的导电性的大幅增加，并制造和表征功能纳米线晶体管测试设备。除了Al之外，DFT计算还提出了其他4种可能的元素，它们可能代表Si的SiO2调制受体。在该项目中，将详细研究这些元素，并开发将其应用于Si纳米线晶体管的工艺，以比较不同调制受体元素的掺杂特性。

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.