缺陷主导的GaN和AlN纳米线发光微观机理研究

Both GaN and AlN nanowires (NWs) have very promising device application in solid state lighting, solar sells, photodetectors and field emission. We will aim at all of possible defects included in GaN and AlN NWs and solve three key issues related to their light emission dominated by defects. (1) What is the physical origin of the PL peak at 3.45 eV in GaN NWs? (2) How to understand the microscopic mechanism of the broad yellow luminescence band centered at 560 nm in polar GaN NWs? (3) What is the real physical reason of the asymmetric and broad blue luminescence band in the region of 2-4 eV in AlN NWs? Considering the large surface-to-volume ratio, the quantum size effects, the random characteristics of surface atom arrangements and bond configurations together with the dielectric mismatch between the NW and its environment, we will investigate the influence of defects on the electronic structures and optical properties of GaN and AlN NWs by using first-principles calculations. Our purpose here is to clarify the nature of defects and give an atomic-level understanding for some special PL spectra observed recently in GaN and AlN NWs and pave a new way for improving the performance of GaN and AlN NW-based nano-LED and photovoltaic devices. Our results are very useful for understanding the novel physical phenomena in low-dimensional nanomaterials and fundamental investigation together with improving the characteristics of nano-devices. The current research is a real challenge due to the difficulty of the charged defects involved in NW systems.

GaN和AlN纳米线在发光、太阳能电池、探测和场发射等方面有广泛的应用前景，引起高度重视。本项目将瞄准GaN和AlN纳米线可能存在的各种缺陷，致力于解决实验提出的三个亟待解决且有较大争议的缺陷主导纳米线发光问题：(1)GaN纳米线3.45eV发光峰、(2)极性六角GaN纳米线黄发光带(中心在560 nm)和(3)AlN纳米线2-4eV宽的非对称蓝发光带的微观起因。考虑到纳米线大的比表面、量子尺寸效应、表面原子排列和键组态的无规性及纳米线与环境的介电失配效应，基于第一性原理计算，研究缺陷对GaN和AlN纳米线电子结构和光学性质的调控和影响，澄清缺陷的本质，阐明缺陷主导的特定PL光谱的微观物理起因，探索改进相应的纳米线基发光和光伏器件性能的新途径，以丰富人们对小尺度纳米体系奇妙物理现象的认识，不仅对低维纳米结构的基础研究，而且对基于这些结构的高效纳米器件的应用都意义重大，且具有极大的挑战性。

瞄准低维纳米半导体的缺陷、发光、低载流子迁移率、磁性、压力异常光谱和宽带隙半导体AlN和ZnO的p型掺杂及InN带隙争议等问题开展研究。我们发现：GaN纳米线表面微线中的受限电子到晶体场劈裂空穴带的跃迁导致了E||c偏振的3.45 eV发射线，VGa、CN和CN-ON共同决定了GaN纳米线中心在2.2 eV的黄发光带；从激子基态到VN,VAl,ON和3ON-VAl缺陷能级的光跃迁（1.96,2.16,2.74和2.94 eV）共同决定了AlN纳米线宽的非对称蓝发光带；如果用掺杂NX或AgZn的超薄ZnX(X=S,Se,Te)层插入ZnO形成短周期的(ZnO)m/(ZnX)n(m>n)超晶格来代替传统的ZnO材料，则p-型ZnO可以实现；Mg受主激活能能够从高铝Al0.83Ga0.17N合金的0.44 eV降低到MgGa delta-掺杂的纳米尺度(AlN)5/(GaN)1 超晶格的0.26 eV（已被实验精确验证）；InN宽带隙范围0.6-2.3 eV的物理起因是由于样品表面纳米结构诱导的量子受限效应；构建二维InSe/BP范德华异质结，可以提高InSe空穴迁移率3个数量级达104 cm2V-1s-1；范德华间隙过渡金属原子Sc-Zn掺杂可以在InSe/BP中诱导出铁磁、反铁磁和顺磁性；扶手椅型InSe纳米带是非磁直接带隙半导体，具有高电子迁移率103 cm2V-1s-1，锯齿形纳米带表现出本征铁磁性，自旋极化灵敏依赖于纳米带边缘结构；对二维InSe施加适当的压应变，可以显著提高空穴迁移率约2-3个数量级达103-104 cm2V−1s−1，在约6%压应变下，二维单（少）层InSe转变为直接带隙；少层hBN的低温缺陷PL谱表现出异常发光行为，由于层内和层间相互作用的不同竞争导致了单光子发射线有一个宽的谱范围570-730 nm，并呈现出三种不同的压力响应，压力系数可以是负的（红移），正的（蓝移）或从负到正改变符号（红移到蓝移）。这些结果阐明了纳米半导体中几个令人困惑的现象背后的物理机理，解决了宽带隙半导体中的几个关键问题，对未来的科学研究和相关光电器件的应用具有重要指导意义。