AlGaN基量子阱的界面陡峭技术及其增强量子限制效应

AlGaN based Deep ultraviolet (DUV) device has shown its advantages over those shortcomings, e.g., limited output-powers, poor lifetimes and instability, of traditional devices and shown its potential applications in various optoelectronic fields. These applications appear in air, water and surface sterilization, disinfection and decontamination, water purification, gas sensing, and etc. These combined markets are worth in excess of several billion dollars, which provides strong motivation for researches in relevant areas. However, till now the emission efficiency of the AlGaN based DUV light emitting diodes (LEDs) still remains below 1%, far from satisfactory for application purpose. Among those handicaps, the interface abruptness has been one of the most crucial issues in the construction of multi quantum wells (MQWs) as active layers in optoelectronic devices, which is extremely critical in achieving stronger quantum confinement and consequently higher emission efficiency therein. The interfacial sharpness is highly associated with the crystal structure as well as the elemental inter-diffusion across the interface. In this project, we propose thorough investigations on the interface abruptness of the AlGaN based MQWs/superlattice and novel schemes attempting improvement of elemental sharpness at the interfacial layers. Metal-organic chemical vapor deposition (MOCVD) method will be employed for MQWs growth and DUV LED fabrication. Firstly, an accurate determination of the elemental inter-diffusion depth across the interface is to be carried out by using high resolution transmission electron microscopy (HRTEM), Auger electron microscopy (AES), and high resolution X-ray diffraction (HRXRD), based on which the mechanism of metal diffusion across the interface at high growth temperature (1070 ?C) will be clarified. Secondly, in order to improve the interface abruptness and to minimize the diffusion depth, special schemes such as intentional interruption during interfacial formation, blocking layer insertion, and low temperature interface technique, will be proposed and employed to the AlN/AlGaN superlattice. Hence, the enhancement of quantum confinement effect of abrupt quantum wells could be achieved improving light emission efficiency. Furthermore, first-principles calculations and quantum chemistry calculations are used to simulate the dynamics of metal atoms (Al and Ga) across the interface or into the surface in function of diffusion barrier and replacement energy. Together with experimental results, mechanism leading to AlGaN abrupt interfacial layers will be discussed and applied to the deposition techniques. New concepts and important principles is to be proposed for extending new research areas in wide bandgap semiconductors.

深紫外光电子器件已成为III族氮化物材料的科学和应用研究的新重点。但目前，AlGaN基深紫外LED的发光效率普遍还不到1%。其中的关键问题是如何增强有源层对载流子的量子限制效应，提高量子效率，而这就与量子阱界面的陡峭程度密切相关。本课题将通过研究高Al组份AlGaN生长动力学机理，探索量子阱界面元素互扩散问题及其控制技术，研究陡峭的界面形成的条件及其对材料光学性质的影响。采用MOCVD方法，在界面处理技术上，通过生长中断、低温插入层、扩散阻挡层等技术，提高界面的平整度和陡峭度，从而达到增强量子限制效应的目的。在表征技术上，采用HRTEM、HRXRD、AES等高分辨测试手段，深入研究量子阱界面处的扩散深度、界面陡峭度等性质，利用变温阴极荧光－STM复合系统，结合第一性原理模拟计算，研究量子阱微区的量子能级间跃迁对发光效率的影响。揭示新规律、提出新技术，为深紫外器件的发展提供科学数据和技术支持

深紫外光电子器件已成为III 族氮化物材料的科学和应用研究的新重点。但目前，AlGaN 基深紫外LED 的发光效率普遍还不到1%。其中的关键问题是如何增强有源层对载流子的量子限制效应，提高量子效率，而这就与量子阱界面的陡峭程度密切相关。本课题通过研究高Al 组份AlGaN 生长动力学机理，探索量子阱界面元素互扩散问题及其控制技术，发现了AlGaN/GaN量子阱的上下界面，出现明显不对称的Al 元素扩散深度现象；通过实验观测和第一性原理计算等方法，研究量子阱界面处的扩散深度、界面陡峭度与AlGaN的组分在界面的梯度有直接关系，从而阐明了陡峭的界面形成的必要条件条件；采用MOCVD 方法，在界面处理技术上，首次提出超薄的低Al组分AlGaN扩散阻挡对层的技术，不仅有效提高界面的平整度和陡峭度，克服了长期以来困扰人们的极性材料界面扩散和高温界面扩散的难题，实现了低于0.59 nm陡峭界面，从而达到增强量子限制效应的目的。此外，该重要思想和结果还应用到了GaN纳米柱阵列的生长中，提出将In 浸润层氮化为InN 壳层的技术，发现了N原子的反常隧穿现象，对纳米柱侧壁量子阱结构器件制造具有重要意义。该项目成果在国际前沿刊物上发表论文11篇；申请发明专利7项，其中1项关键专利已获得授权；国际氮化物半导体和纳米材料会议上进行邀请报告、口头报告7次；培养博士2名，硕士3名。