碳纳米墙-硅肖特基结的热载流子发射机理与光电响应特性研究

Due to the long lifetime and high temperature of hot carriers, graphene is a promising material to overcome the limitation of metal-based Schottky barrier devices, which are usually restrained by the low efficiency of hot-carrier emission, and then the detection of photons with energy lower than normal semiconductor could be more convenient. However, these photodetectors suffered from the low absorption rate of light due to the single-layer structure of graphene. In this project, based on the strong absorption in the infrared range and its in-situ growth property at silicon substrate, we proposed that, using graphene nanowalls (GNWs) as the electrode of Schottky barrier and absorption materials, a photodetector with high responsivity could be obtained. Through the research of phonon interaction in vertical and multilayer conditions, we will study the feasibility of hot-carrier theory for GNWs; based on surface charge transfer doping technique, the work-function as well as the barrier height will be adjusted for the hot-carrier emission; finally, GNWs-Si heterojunction will be formed with in-situ growth and micro-nano fabrication including electron-beam-lithography, and high responsivity will be verified in the mid-wave infrared range. The hot-carrier emission mechanism and methodology for high-quality photodetector studied in this project could provide new thought for the development of high-efficiency optoelectronic devices.

石墨烯具有热载流子温度高和热弛豫时间长的特点，可有效解决传统金属材料肖特基结热载流子发射效率低的难题，对发展新型红外探测器件具有重要意义。然而，石墨烯肖特基结的性能受限于其单原子层结构导致的低吸光率。碳纳米墙是纵向生长的石墨烯交叠形成的三维材料，保持了石墨烯的零带隙和层状结构特征。本项目提出利用碳纳米墙材料在红外波段的高吸收和原位生长工艺优势，研究碳纳米墙-硅肖特基结的热载流子发射机理及其红外光电响应特性。通过分析碳纳米墙的声子作用规律，研究其热载流子发射物理机制；利用表面电荷转移掺杂技术调控碳纳米墙的功函数，实现有利于热载流子高效发射的势垒高度；基于碳纳米墙原位生长工艺结合电子束直写等微纳加工技术，制备高理想因子的碳纳米墙-硅肖特基结，并在红外波段实现高响应度光电探测实验验证。本项目研究的碳纳米墙热载流子发射机制和高性能光电探测器件实现方法，将为红外高效光电转换器件的发展提供新思路。

碳纳米墙是纵向生长的石墨烯交叠形成的三维材料，不仅保持了石墨烯从可见光到太赫兹宽波段吸收的特性，还解决了石墨烯吸收弱的问题。本课题通过在硅上原位生长可控的石墨烯纳米墙，制备出高性能的石墨烯纳米墙/硅异质结光电探测器，首先研究了石墨烯纳米墙的光电性能和石墨烯纳米墙/硅异质结在可见光的光响应，再利用表面电荷转移掺杂技术调控碳纳米墙的功函数，研究石墨烯纳米墙/硅异质结的热载流子发射机理及其红外光电响应特性。主要的研究内容和结论包括：.（1）石墨烯纳米墙薄膜的制备与表征。利用射频等离子体增强化学气相沉积法制备了不同生长时间的石墨烯纳米墙薄膜，采用扫描电子显微镜、拉曼光谱、透射电镜、高分辨率-透射电镜对石墨烯纳米墙薄膜的表面形貌、结构进行了表征与分析。.（2）研究石墨烯纳米墙/硅异质结光电探测器的光电特性。利用在硅上原位生长石墨烯纳米墙制备出高质量界面的异质结光电探测器，测试了在可见光波段的光电响应，得到了0.52 A/W的响应度，开/关比高达2×107，时间响应为40 μs。器件还具有105 dB的高线性型动态范围，其3dB截止频率为8.5KHz，并实现了3.1fA Hz-1/2的超低噪声电流谱和5.88×1013 cm Hz1/2/W的比探测率。通过肖特基结模型拟合得到1.18的理想因子和0.69eV的势垒高度，从理论上分析了暗电流低的原因。.（3）研究石墨烯纳米墙/硅肖特基结的热载流子发射机理及其红外光电响应特性。通过用热退火硅上金膜的方式制备无规则的金纳米颗粒，利用表面电荷转移掺杂技术来调控碳纳米墙的功函数。通过对不同结构，不同金属颗粒和不同GNW生长时间的GNW/Si光电探测器光响应的分析，器件的响应度达到138mA/W，比探测率提高到了1.4×1010cm Hz1/2/W，开/关比高达104，时间响应为370μs。器件在3.5μm波段0V的响应度为0.44μA/W，.本课题研究的石墨烯纳米墙热载流子发射机制和高性能光电探测器件的实现方法，可为红外高效光电转换器件的发展提供新思路。