掺杂硅量子点薄膜的电荷输运研究

Colloidal silicon quantum dots (Si QDs) are expected to play an important role in the development of novel low-cost and environmentally friendly semiconductor devices based on solution processing and additive manufacturing given the abundance and non-toxicity of Si. It is generally accepted that doping is critical to the device applications of colloidal Si QDs. With the continuous progress of the doping of colloidal Si QDs it is imperative that the mechanisms of the charge transport of the films of doped Si QDs should be elucidated to lay a solid foundation for the use of colloidal Si QDs in devices. The current project will mainly rely on the temperature-dependent electrical characterization of thin-film transistors and scanning tunneling spectroscopy (STS). The effects of the dopant type and concentration on the carrier concentration, conductivity and mobility of doped Si-QD films will be investigated. The ionization of dopants, the energy barrier of charge transport and surface/interface-related localized states will be analyzed. The mechanisms of the charge transport of the films of doped Si QDs will be finally proposed. Models related to the charge transport mechanisms will be built. The success of the current project can not only guide the tuning of the charge transport of doped Si-QD films for device applications, but also set up an example for the study on the new physics of novel semiconductors based on the building blocks of QDs.

胶态硅量子点由于硅元素在地壳中仅次于氧元素的高含量和无毒性，有望在基于溶液加工和加法制造的低成本和环境友好的新型半导体器件发展过程中扮演重要角色。人们普遍认为，掺杂对胶态硅量子点的器件应用至关重要。随着近年来胶态硅量子点的掺杂研究不断取得进展，目前迫切需要弄清由胶态掺杂硅量子点形成的薄膜的电荷输运机制，为胶态掺杂硅量子点的器件应用奠定坚实的基础。本项目提出以变温薄膜晶体管测试和低温扫描隧道谱（STS）分析为主要研究手段，研究硅量子点的掺杂类型和浓度影响掺杂硅量子点薄膜的载流子浓度、电导率和迁移率的规律，分析掺杂硅量子点薄膜中杂质的电离、电荷输运势垒以及表面/界面引起的电子局域态，进而阐明掺杂硅量子点薄膜中电荷输运的机制并建立相应的模型。本项目的成功开展，不仅能指导面向器件应用的掺杂硅量子点薄膜的电荷输运性能的调控，而且能给以量子点为结构单元的新型半导体的物理机制研究提供示范。

随着近年来掺杂硅量子点的制备不断取得进展，人们越来越关注掺杂硅量子点在半导体器件中的应用。掺杂硅量子点的器件应用往往需要形成掺杂硅量子点的薄膜。对掺杂硅量子点薄膜的电荷输运机制的认识对于掺杂硅量子点器件的发展至关重要。本项目利用低温扫描隧道显微镜和扫描隧道谱，对单个掺杂硅量子点的金属性能带结构做出了直接的观察与测量。通过对比掺杂/未掺杂硅量子点的扫描隧道显微镜表征结果，证实了掺杂对硅量子点电子能带结构具有明显影响。我们在掺杂硅量子点的扫描隧道显微镜形貌上发现了电子驻波所引起的精细结构，利用傅里叶变化红外光谱、电子顺磁共振谱和理论计算，认为该精细结构来源于掺杂硅量子点的金属性和其表面隧穿透明的薄氧化层，排除了悬挂键引起的费米能级钉扎机制。另外，我们对掺硅量子点薄膜的晶体管性质进行了研究，利用变温电导和转移输出曲线等方法，发现硅量子点薄膜中电荷输运的机制为最近邻跳跃，激活能为86 meV，与此同时，掺杂硅量子点内部及表面的陷阱会俘获和释放载流子，进而引起电流迟滞。在研究掺杂硅量子点薄膜晶体管的光响应时，我们发现未氧化的掺杂硅量子点呈现正光响应，而表面有氧化层的掺杂硅量子点呈现负光响应，响应速度和衰减时间在秒量级。基于此，我们用掺杂量子点构建了一系列的光电神经突触器件，探索了其在类脑计算中的应用。