Si图形衬底上非极性/半极性GaN材料外延生长及物性研究

In order to reduce the quantum confined Stark effect (QCSE) and the cost, growth of GaN and luminescent device on non-polar or semi-polar surface on silicon technology has attracted much attention in recent years. However, non-polar and semi-polar GaN grown on Si substrates suffer from low crystal orientation controllability, Ga-Si melt-back etching phenomenon, and high defect density. To solve such problems, we study the process of Si trench etching, and show the influence of the pattern sizes, shapes, orientation and depth on the subsequent growth behavior of non-polar and semi-polar GaN, as well as the control of crystal surface orientation and the evolution of surface morphology. We will use the insertion of intermediate layer to prevent the Ga-Si melt-back etching phenomenon during the GaN growth and to help control the growth orientation of non-polar and semi-polar GaN material. At the same time, we will also investigate the effects of epitaxial growth conditions and buffer layers on the crystalline quality, stress/strain and optical property of non-polar and semi-polar GaN. The rule of formation and evolution of defects will be uncovered. The high crystal quality non-polar and semi-polar GaN would be eventually realized on the patterned silicon substrate, and will help build a foundation for non-polar and semi-polar GaN-based LEDs on Si substrate.

由于可以消除量子限制斯塔克效应并降低生产成本，近年来硅衬底上外延非极性/半极性GaN材料及发光器件受到了越来越多的关注。但是硅基非极性/半极性材料生长过程中存在着晶体取向难控制、Ga-Si回熔刻蚀、缺陷密度高等难点。为解决这些问题，本项目首先摸索硅衬底图形刻槽工艺，研究图形尺寸、取向、深度等对非极性/半极性GaN生长行为、晶体表面取向、表面形貌的影响。其次，研究介质掩膜对GaN生长期间Ga-Si回熔刻蚀的抑制作用和晶体取向控制的辅助作用。最后探索生长工艺条件、缓冲层类型对非极性/半极性GaN材料晶体质量、应力应变和发光性质的影响机制，揭示缺陷生成与演化规律。最终在硅图形衬底上外延得到高质量的非极性/半极性GaN材料，为实现硅基非极性/半极性GaN基LED器件奠定基础。

与传统的c面GaN基LED相比，基于半极性/半极性GaN LED能够显著降低QCSE，而采用硅衬底可以降低成本并与现有工艺兼容。本项目将两者的优势结合起来，以实现硅图形化衬底上非极性/半极性GaN材料的高质量制备为目标，针对硅基非极性/半极性材料生长过程中存在着晶体取向难控制、Ga-Si回熔刻蚀、缺陷密度高等关键问题展开研究。选用(113)和(110)晶向的硅作为衬底，通过光刻和湿法腐蚀制备硅图形衬底，优化Si图形衬底腐蚀制备工艺，研究其与GaN生长行为、晶体取向控制、表面形貌演化之间的关联关系。分别采用直接生长法和高温-低温GaN层生长法在(113)硅图形衬底上MOCVD外延生长半极性(11-22)GaN，其中高温-低温GaN层生长法长出的GaN效果较好，得到了表面平整度高的半极性GaN材料，并揭示硅图形衬底非极性/半极性GaN晶体取向控制、缺陷抑制机理以及表面形貌演化规律。另外，传统的半导体材料GaN与新兴的二维材料MoS2结合成的异质结被用于一些光电器件中，使用半极性GaN制作异质结有望提高器件性能。我们分别将极性和半极性GaN与MoS2结合，制备了两种MoS2/GaN异质结并使用X射线光电子能谱分析测量了二者的带阶。