晶格匹配的层状合金做为新型高效光源材料的理论探索

In the past a few decades, III-nitride lighting emitting diodes (LEDs) have achieved remarkable advances together with developments in solid state lighting. For example, the discovery of GaN as a novel blue LED material was awarded Nobel Prize in Physics in 2014. However, there are several outstanding issues for the use of III-nitride alloys as white LED materials. Therefore, the discovery of new white LED materials is not only scientifically important, but also has great impacts in the industry and our modern life. Our recent theoretical and experimental study shows that layered systems have unique advantages over conventional bulk materials for lighting. For example, we discover that the light emission intensity of layered hexagonal BN is at least two orders of magnitude higher than that of wurtzite AlN thin film. In terms of our finding, we propose to design new, high-efficiency, white LED materials based lattice-matched layered alloys. Based on first-principles methods and beyond, we will systemically study several important physical properties of these alloys as LED materials, including alloy structures, electronic and optical properties, defect and doping issues, and the initial nucleation and growth of these layered alloys on substrates. Our research will not only extend our current knowledge of white LED materials, but also will provide fundamental theory for the future experimental synthesis of these lattice-matched layered alloys.

在过去的几十年，以传统氮化物为基础的固态照明取得了长足的发展和巨大的成就, 比如2014年的诺贝尔物理学奖授予了关于蓝光氮化镓材料的研究。然而，传统氮化物合金在白光照明领域有着难以克服的弊端。探索和设计比传统氮化物更好的白光材料不仅在基础研究方面有着重要的意义，同时也会对我们的日常生活产生显著的影响。我们最近的理论和实验工作表明层状材料的发光强度比传统氮化物高两个量级以上。因此，在本研究计划中我们首次提出了采用晶格匹配的层状合金来做为新型白光光源材料的想法。我们将通过以第一性原理计算为主的多种理论手段对层状合金的结构，光学和电学性质，缺陷和掺杂性质，及其在衬底上最初的成核和生长动力学等物理性质进行系统和深入的研究，从而在理论上确立这些新型材料做为白光光源的可行性。我们的研究不仅将拓展人们对现有发光材料的认知，并且也为今后实验合成这些晶格匹配的层状合金提供理论基础。

本项目的基础科学问题是如何实现高效的层状白光光源材料。围绕着这个基础科学问题，我们探索了一系列光学材料，包括一些二维BNC合金材料，低维聚合物形成的非线性光学材料，低维电子化合物材料。最终，我们成功从理论上给出了利用二维BNC合金来实现层状白光光源材料的完整的理论方案。我们从理论上发现当BNC二维合金外延生长在hcp相的Cr(0001)衬底上时，并且生长温度控制在1200 K，BNC系统将出现固溶相。有意思的是，在固溶相下BNC体系的能隙可以连续的从0 调控到 6 eV，从而可以实现各个可见光和紫外光波段的发光。因此，通过外延生长三种不同合金浓度的BNC二维合金固溶相，我们可以实现红、蓝和绿色的光源材料，进而可以实现白光光源材料。