GaN外延片直接CVD生长免转移石墨烯及其在LED中的电极和散热应用

Gallium nitride (GaN) light emitting diodes are important short wavelength optoelectronic devices. Indium tin oxide (ITO) transparent electrodes are one of the key parts. However, due to the lack of indium, ITO becomes more and more expensive. Large-area high-quality graphene produced by chemical vapor deposition (CVD) becomes the ideal substitute for ITO, and can solve the issue that ITO is only transparent for visible light. Recently, international reports on the application of CVD graphene in GaN optoelectronic devices have increased dramatically. The bottleneck for industrialization lies in that the graphene has to be separated from metal catalyst and transferred to GaN, which is poorly controllable and has holes and wrinkles. This project studies the direct CVD of noncatalytic graphene on GaN and avoids the transfer. It includes 5 work packages: growth conditions and mechanism, in situ doping, graphene-GaN ohmic contact, device fabrication and optoelectronic characterization, and heat spreading study. Ammonia protection and other key techniques ensure that the GaN surface and internal structures are intact. It addresses the fundamental problem of growing graphene directly on III-V semiconductors. The as-synthesized graphene has high transparency and conductivity, can be steadily and efficiently controlled by in situ doping in terms of carrier densities and work function. There are clean interface and good electrical contact between graphene and GaN. Parameters such as the final lighting efficiency and working voltage surpass that for the-state-of-the-art devices of the same category. The breakthrough of this project is strategically important for China to secure its key role in the world graphene science and technology. It is also useful for the research involving other substrates and other types of optoelectronic devices.

GaN发光管是重要短波段光电器件。氧化铟锡(ITO)透明电极是关键部件，但铟极度稀缺使成本激增。化学气相沉积(CVD) 石墨烯面积大、质量高，是ITO 理想替代品，解决了其只对可见光透明的问题，且可用作热扩散层降低结温。最近各国CVD石墨烯在GaN 光电器件应用的报道激增。产业化瓶颈在于，须将石墨烯从金属催化剂剥离转移至GaN，可控性差，产生孔洞、褶皱。本项目研究非催化直接在GaN发光管上生长石墨烯以回避转移，包括生长条件与模型、原位掺杂、石墨烯氮化镓欧姆接触、器件制备和光电测试、石墨烯散热5个任务包。氨保护等关键技术确保氮化镓表里无损。解决三五族材料上长石墨烯的理论。石墨烯透明、导电导热均好，可用原位掺杂稳定高效地调控空穴浓度与功函数，与GaN界面洁净且电学接触好。发光效率、工作电压等指标全面超越现有同类器件。项目对我国抢占石墨烯科技全球制高点有战略意义，对其他衬底光电器件也有借鉴意义。

GaN发光二极管（LED）是重要的光电器件，在半导体固态照明、下一代信息显示技术中有核心作用，是当今电子产业的基本元件之一。氧化铟锡(ITO)透明电极是它的关键部件，但铟是我国战略资源，极度稀缺。化学气相沉积(CVD)石墨烯面积大、质量高，是ITO的理想替代品，且解决了其只对可见光透明的问题，还可用作热扩散层降低器件的结温。最近这成为各国竞争的热点之一。但是，其产业化瓶颈在于，必须将石墨烯从金属催化剂剥离转移至GaN，可控性差，产生孔洞、褶皱，且与GaN电学接触差。本项目研究直接在GaN外延晶圆上生长石墨烯以规避转移，具体内容包括材料生长、器件制备、表征测试、物理分析等。经过项目的攻关，提出了直接生长基本模型，并对氮化镓衬底上生长的特殊性进行了系统总结，试验了多种技术方案，最终从方阻、透明度、电学接触多方面确定了钴薄膜辅助催化等离子体增强化学气相沉积（PECVD）的路线。对所直接生长的石墨烯做了表征，在二吋晶圆GaN LED材料上制备了器件阵列，实现发光，重复性比转移石墨烯器件有根本性提高，且实现了散热功能。石墨烯生长温度仅有600摄氏度，氮化镓晶圆无损，LED开启电压3.8 V，在7.1 V电压下电流可高达100 mA，而未采用石墨烯的对比器件在同样电压下电流仅20 mA。在主流SCI期刊上发表了25篇论文，获授权专利5项，培养了6名博士生，项目的主要任务已完成或超额完成。项目对我国抢占二维材料-GaN科技全球制高点有重要战略意义，对其他衬底的光电器件也有借鉴意义。