基于氮化铝/石墨烯复合材料系统的高性能深紫外线探测器的研究

Ultraviolet photodetection (UP) devices are widely required in many aspects of modern society. But the traditional UP technologies severely suffer from their innate drawbacks in materials or structures. Aluminium nitride (AlN) crystal, a harsh-environment-stable semiconductor with a wide energy bandgap up to 6.1eV, is a perfect candidate for solar-blind (<280nm) deep ultraviolet photodetection applications. Nevertheless, the application of AlN in UP is hindered by its poor electrical properties, such as its low carrier mobility. To address this issue, this project proposes to use an AlN/grahene hybrid system instead of sole AlN crystal to fabricate UP devices. Graphene is a two dimensional material with super high carrier mobility and outstanding mechanical properties. Herein, graphene is supposed to play the role of carrier conductor and AlN crystals work as light absorber. In the photodetection process, AlN crystals absorb deep ultraviolet photons and generate carriers. These carriers should be injected into graphene and extracted from electrodes, generating photocurrent. Our previous research has proven the feasibility of this concept to bypass the low carrier mobility problem in light absorbing materials (AlN crystal in this project) by creating hybrid structures with high carrier mobility materials, thus realize high performance photodetection devices. Our preliminary investigation proves that the carrier injection from AlN to graphene is dynamically allowed. Here, we design several possible device configurations to attain optimum UP performance. With this concept, we expect a highly performing deep ultraviolet (<205nm) photodetection device with a record photoresponsivity beyond 2×103A/W. Moreover, we will deliberately study the generation, transport and transit processes of photo-induced carriers in the hybrid material system. The understanding of this physical mechanism will be of great significance for further research into ultraviolet optoelectronics application of AlN crystals.

深紫外探测技术在现代社会有着广泛的应用，但现有的紫外探测器产品有着各自的缺陷。氮化铝(AlN)晶体以其超宽的直接能带带隙(6.1eV)和稳定的材料性质，成为深紫外(<205 nm)光电探测器的理想材料。然而其低下的载流子迁移率，严重地阻碍AlN在紫外探测领域的应用。申请者在之前的工作中，通过将载流子从光敏材料导入具有高迁移率的材料中进行传导，实现了光电探测效率的大幅提高。有鉴于此，本项目计划以AlN晶体为深紫外光敏材料，利用其宽能带带隙特性，同时，以石墨烯为载流子传导材料，利用其超高载流子迁移率，构建基于AlN/石墨烯复合材料的高性能深紫外光电探测器，力图实现在该光波段大于2000 A/W的创记录的光电响应度。在此基础上，通过对该复合材料系统在紫外辐射下光生载流子的产生、传输与输运过程的研究与理解，为进一步拓展AlN晶体在紫外光电器件领域的应用做实验和理论积累。

本项目主要研究了石墨烯与氮化铝单晶在光电晶体管中的应用。首先就氮化铝单晶的物性特征与光电特性开展了工作。使用PVT方法生长出毫米级大尺寸的AlN单晶，对AlN单晶的结构与发光性能进行了表征，结果显示除了该AlN单晶的发光光谱除了包括在210nm的带边发光，还有300-1000nm的宽光谱发光。通过对AlN晶体的结构与成分分析，这些发光被归结为带间杂质能级发光。进一步的通过光谱分析定位了杂质能级的能带位置。利用AlN单晶作为发光芯片制备了基于单一材料的显色指数大于90的白光光源。显示出该材料在宽光谱白光发光方面具有较好的应用潜力。此外，本项目还使用AlN单晶制备了双极型光电探测器。由于AlN单晶的超宽能带带隙，使其有较大的能带空间容纳较多的中间能级。因此该光电探测器件表现出深紫外-可见-近红外区域的宽光谱光电响应。其光电探测度在360nm的近紫外区域达3.7 A/W。在此基础上结合单层石墨烯材料，制备了基于AlN/石墨烯复合材料体系的光电晶体管探测器，利用石墨烯的超高载流子迁移率，实现了较大的内增益，光电探测度在261nm的深紫外区域达5300 A/W。通过本项目的研究，说明AlN晶体具有良好的光电性能，在发光与光电探测领域都有着巨大的应用潜力。.此外，为进一步提高光电晶体管的性能，制备了基于石墨烯的复合材料系统的光电探测器，通过引入金纳米颗粒，利用金纳米颗粒的表面等离子光场增强效应，实现了探测器光电性能的两倍的提升，并且提高了光电响应速度。该研究具有广泛适用性，对提高光电探测器的性能具有指导性意义。