BN薄膜的可控外延生长及其p型掺杂研究

Deep ultraviolet (DUV) LED, as a kind of high-efficiency source, is promising for a wide variety of applications, such as sterilization, biochemical detection, non-line-of-sight communications and special luminesce, for the benefits of environmentally friendly, low-cost and long-lifetime features. At present, DUV LED is based on AlGaN and its quantum structure, however its output power is seriously limited by the difficulty in p-type doping for high-Al-content AlGaN. As a new member of conventional III-nitride, h-BN is intrinsic p-type semiconductor, showing an alternative approach to replace the p-type AlGaN injection layer and enhance the output power of DUV LED. This proposal will focus on the growth kinetics of BN under non-equilibrium condition, fabricate high quality h-BN thin films and BGaN alloys exploiting newly-built molecular beam epitaxy (MBE) system and explore a method to realize effective p-type doping for the films. The study of the active mechanism for Mg-doping is based on in situ analysis of ARPES, exploring the band structure or surface state in dependence of layer thickness and Mg-doping conditions. Subsequently, high quality BN/GaN digital alloys will be fabricated to improve the crystalline quality and efficiency of p-type doping for BGaN alloys. Finally, we will study the Ohmic contact and vertical transport of holes in p-type h-BN and BGaN, enabling the realization of high performance DUV LED.

深紫外LED是一种绿色环保、低成本、长寿命的高效光源,在杀菌消毒、生化探测、非视距通讯及特种照明等领域有重大应用价值。目前深紫外LED基于AlGaN材料及其量子结构，其输出功率主要受制于高Al组分AlGaN的p型掺杂这一难题。而与传统III族氮化物半导体同族的h-BN，本征即表现为p型，且有望通过掺杂实现高空穴浓度p型材料，是克服掺杂困难，实现高输出功率深紫外LED的有效途径。本项目拟研究非平衡条件下BN的外延生长动力学，利用新建的BN分子束外延（MBE）设备实现高质量BN薄膜和BGaN合金的可控生长，进而研究其p型掺杂及Mg原子的激活机制；结合原位角分辨光电子能谱（ARPES），研究其表面性质和能带结构，探索掺杂规律；研究利用BN/GaN数字合金提高BGaN合金的晶体质量和提升p型掺杂效率的方法；研究p型BN和BGaN材料空穴的纵向输运规律和欧姆接触，为实现高效深紫外LED器件奠定基础。

二维BN材料具有超宽带隙和层状结构等优异的物理性质。本项目通过MBE方法实现了h-BN的高质量外延薄膜，通过高温热退火处理驱动BN薄膜重结晶，研究证实该过程中存在从e-BN到sp2-BN的相变过程，进而显著提高了BN的晶体质量，最终获得2英寸高质量h-BN单晶薄膜。研究了h-BN异质外延中的悬挂键，通过第一性原理计算得出单个O原子化学吸附在单层h-BN表面时倾向于形成N-O键和B-O-N键的结论。通过在h-BN表面引入部分O缺陷，实现了h-BN/Al2O3(0001)上高质量金属极性原子级平整的GaN外延薄膜。研究了不同h-BN厚度对外延层的应力弛豫机制，通过拉曼光谱研究发现改变h-BN厚度显著弛豫外延结构中的失配应力。在高质量BN/GaN复合模板上制备了高质量LED原型器件。相关成果发表SCI论文7篇，授权中国发明专利2项。以上研究为高质量BN材料外延生长及高性能BN基光电器件的设计与制备提供了新思路。