S-K方法外延GaN量子点的系统分析

Systematic Analysis of Epitaxial GaN QDs by S-K Method

利用S-K(Stranski-Krastanov)方法外延自组装GaN量子点会涉及到Ⅴ/Ⅲ比、生长中断、生长时间、生长流量、生长温度以及降温过程中的氨气流量等6个关键生长条件,通过调节这几个生长条件可以调控生长面的表面能和GaN沉积量,最终改变GaN量子点的形貌和密度。分析了S-K方法中各个生长条件对GaN量子点生长的影响及其起作用的内部机理,调节Ⅴ/Ⅲ比和生长中断时间可以改变生长面的表面自由能,内部机制主要在于Ga原子及GaN在表面的迁移作用和N原子对二者迁移的限制共同竞争;生长时间、流量和生长温度可以调节最终的GaN沉积量,改变生长温度可以影响沉积速率和迁移速率,但高温下GaN会与H2作用发生分解;降温过程中一定量的NH3氛围可以防止GaN量子点发生分解。最后,通过优化生长条件在MOCVD系统中找到了每个条件的生长窗口并获得了不同尺寸和密度的GaN量子点。其中温度生长窗口有两个,高温805℃生长的无帽层GaN量子点发光性能更为优良。

The S-K(Stranski-Krastanov)method of growing self-assembly GaN QDs is attributed to 6 crucial growth conditions ofⅤ/Ⅲratio,growth interruption,growth duration,flow,temperature and the NH3 flow during cooling down.The surface free energy and GaN deposition amount on growth front are tunable by adjusting the 6 conditions in epitaxial process of GaN QDs(quantum dots).In this paper,the influence of the 6 growth conditions of S-K method on GaN QDs and the mechanism of which are systematically analyzed,and the surface free energy on growth front can be changed by theⅤ/Ⅲratio and growth interruption duration,whose mechanisms are ascribed to the competition of migration and suppression by N atoms of Ga atoms and GaN.The GaN deposition amount can be changed by growth duration,flow and temperature.The temperature variation results in the GaN deposition rate and migration,but the GaN is decomposed by H2 in high temperature.The GaN decomposition is prevented by the introduction of certain amount of NH3 during cooling down.Finally,the appropriate growth windows of every condition are obtained by optimizing experiments and GaN QDs with different size and density are grown in MOCVD,where two appropriate temperature have been achieved.The GaN QDs grown in 805℃possess better luminescence performance.