Si衬底上GaN纳米柱基外延材料的制备及相关机理研究

Currently, the material system of light-emitting diodes (LEDs) is mostly based on GaN multi-layers grown on sapphire substrates. However, due to its relatively high cost and small size of sapphire substrate, the development of high-efficiency LEDs is facing the bottleneck. As comparison, Si can be available in much larger size at lower cost, and therefore is of great potential as substrate for LEDs. Nevertheless, there exist large mismatches in both lattice parameter and thermal expansion coefficient between Si and GaN, which makes it very difficult to grow high-quality and crack-free GaN epitaxial layers on Si substrates. .In order to solve these problems, this project will try to grow GaN nanowire-based LED epitaxial materials on Si substrates. By combining together various methods for growth of GaN nanowires on Si, including catalyst-assisted growth and selected-zone growth, along with different epitaxial techniques, such as pulsed laser deposition, molecular beam epitaxy, and metal-organic chemical vapor deposition, we will take advantages of these technologies to obtain high-quality GaN nanowires on Si. Furthermore, the epitaxial growth methodology, efficient doping and optimization of multiple quantum wells for GaN nanowires on Si substrates will be carefully investigated. Some key scientific issues, including the growth kinetics, the control of defects, the doping and the carrier recombination mechanisms of growth of GaN nanowires on Si, will also be studied in depth. In addition, we will adopt simulation tools such as TracePro and APSYS to simulate the growth process and LED epitaxial structures, respectively. These theoretical results can be used to guide the growth and the optimization of GaN nanowire-based LED epitaxial structures on Si, and ultimately help us achieve high-quality GaN nanowire-based LED epitaxial materials on Si substrates.

目前，LED大都是基于蓝宝石衬底上外延生长的多层GaN材料体系构建而成，其发展受到蓝宝石衬底价格昂贵及大尺寸衬底难以获得等缺点的限制。相比而言，Si衬底具有成本低、易获得大尺寸等优势。然而，Si与GaN外延之间存在大的晶格失配及热失配。这使得在Si衬底上外延高质量、无裂纹的GaN薄膜变得十分困难。.为解决上述难题，本项目将在Si衬底上生长GaN纳米柱结构LED外延材料。项目将克服目前的催化剂法及选区生长法制备GaN纳米柱的不足，综合利用上述各种生长方法的优点，采用多种生长方法及相应外延技术相结合的途径，取长补短，对Si衬底上GaN纳米柱的外延生长、高效掺杂、量子阱制作进行研究，并对其生长动力学及缺陷控制、外延掺杂机理、载流子复合机理等关键问题进行深入探讨；同时，采用TracePro、APSYS等软件模拟并结合生长实验，优化器件结构，力图得到Si衬底上的高效的纳米柱基LED外延材料

目前，LED大都是基于蓝宝石衬底上外延生长的多层GaN材料体系构建而成，其发展受到蓝宝石衬底价格昂贵及大尺寸衬底难以获得等缺点的限制。相比而言，Si衬底具有成本低、易获得大尺寸等优势。然而，Si与GaN外延之间存在大的晶格失配及热失配。这使得在Si衬底上外延高质量、无裂纹的GaN薄膜变得十分困难。. 为此，本项目重点研究了在硅衬底上制备基于GaN纳米柱的外延材料及其相关机理的研究，并进行了系统和关键技术研究。主要研究内容和结果如下：.（1）研究了GaN纳米柱在Si衬底上的生长以及各种生长条件对GaN纳米柱结构的影响。通过研究不同的衬底温度，V/III元素比，退火温度，退火气氛和其他参数，获得了掺杂浓度为10^18cm^-3的N型（In）GaN纳米柱。结果，我们提出了一种掺入In原子以促进生长的方法，并获得了形态可控且均一性高的（In）GaN纳米柱阵列结构。.（2）建立了Si衬底上（In）GaN纳米柱的生长和In迁移机理的相关理论模型，揭示了Si衬底上（In）GaN纳米柱的热力学和动力学生长机理。.（3）设计了多种新型的GaN纳米柱异质结构，改善了载流子传输，并获得了高性能的PEC和LED器件。其中，GaN异质结光电极的偏置光电转换效率最高达到2.26％，注入电流为350mA时，GaN基LED的光输出功率可以达到581.71mW。. 本项目在实施过程中发表Advanced Materials，Small等SCI论文31篇，申请发明专利36项，其中授权发明专利24项，申请PCT专利1项；项目团队培养了长江学者青年学者、香江学者、广东省珠江人才等，硕博士16人次，获广东省科技进步二等奖（第一获奖人）、中国产学研合作创新成果二等奖（第一获奖人）等科研奖励。