离子束辅助下碳化硅基硅纳米晶薄膜低温生长及结构光电特性研究

With the properties of bandgap modulation with size, high absorption coefficient, high multiple-excition production yield, silicon nanocrystal thin films are promising in high-efficient photovoltaics and light emitting devices. The preparation of Si nanocrystals by heat-induced phase separation and crystallization process is operated under temperature higher than 1000 ℃, which severely restricts their application and integration. This project aims to fabricate Si nanocrystals embedded in SiC directly by ion beam assisted magnetron sputtering under low substrate temperature (T≤600 ℃). The processes of phase separation, Si nanocrystals nucleation and growth can be achieved during films deposition at low temperature. The effects of parameters of assisted ions, substrate temperature, substrate bias during magnetron sputtering on the films deposition process, structural (crystal size, density and defect), optical (absorption coefficient and band gap), electrical (carrier concentration and mobility), and charge transfer properties of Si nanocrystals in SiC matrix are investigated systematically. The formation mechanism, absorption, doping and charge transfer properties of the Si nanocrystals in SiC matrix prepared by ion-assisted sputtering will be clarified, the low-temperature preparation method of high-quality Si nanocrystals in SiC matrix will be established. This project will be helpful not only to the broadening of the applications of Si nanocrystals in optoelectronic devices, but also to the fabrication of other embedded nanocrystals systems at low temperature as well as their mechanism understanding.

硅纳米晶薄膜带隙连续可调、光吸收系数高、多激子产生效应强，在高效光伏和发光领域受到广泛关注。采用热致相分离晶化法制备硅纳米晶需历经高于1000 ℃的高温过程，这严重制约其器件集成与应用。本项目拟以碳化硅基硅纳米晶薄膜为研究对象，采用离子束辅助磁控溅射技术提高沉积过程中原子动能，从而在薄膜生长过程中较低温度下（T≤600 ℃）实现硅纳米晶的形核和生长；系统研究辅助离子束工作参数、磁控溅射衬底温度等条件对硅纳米晶薄膜的沉积过程、结构特性（晶粒尺寸、密度、缺陷）、光学特性(带隙、吸收系数)、电学特性（载流子浓度、迁移率）、载流子输运行为的影响规律，阐明离子束辅助下硅纳米晶薄膜的形成机制以及吸收、掺杂、电学输运特性，建立低温制备高质量硅纳米晶薄膜的技术路线。本项目的实施不仅有助于降低硅纳米晶薄膜的生长温度，拓展其应用范围，同时对于其它纳米晶体系的低温可控制备及其动力学规律研究也有重要的借鉴价值。

硅纳米晶薄膜带隙连续可调、光吸收系数高、多激子产生效应强，在高效光伏和发光领域受到广泛关注。采用热致相分离晶化法制备硅纳米晶需历经高于1000 ℃的高温过程，这严重制约其器件集成与应用。本项目采用离子辅助磁控溅射方法，通过辅助离子束的碰撞作用提高沉积原子动能，低温生长碳化硅基硅纳米晶薄膜。研究了辅助离子源类型、束流、能量对硅薄膜结构特性的影响。研究前驱体组分，后续退火温度、时间、气氛对碳化硅基硅纳米晶薄膜结构特性（晶化率、晶粒尺寸、密度），光学特性（光学带隙），电学特性（电导率、载流子浓度、迁移率、电导激活能）的影响规律。在800oC下得到晶粒尺寸5-10 nm的硅纳米晶薄膜。提出了碳化硅基硅纳米晶薄膜的形成机制，即调幅分解相分离结合形核-长大过程。阐明硼原子及磷原子在硅纳米晶薄膜内的掺杂行为。发现相比B掺杂，P掺杂硅纳米晶薄膜具有较高电导率及较低电导激活能，表明P原子掺杂效率更高。提出了碳化硅基硅纳米晶薄膜电导率快速增加的渗逾阈值为30-40%的晶体硅体积含量。本项目的实施不仅有助于降低硅纳米晶薄膜的生长温度，拓展其应用范围，同时对于其它纳米晶体系的低温可控制备及其动力学规律研究也有重要的借鉴价值。