Abstract Ultraviolet (UV) optoelectronic devices based on binary GaN quantum wells have been widely reported in the literature. The internal quantum efficiency (IQE) of such structures is relatively low due to the large dislocation densities generated during heteroepitaxial deposition on to non lattice-matched substrates. Enhancement of IQE is possible through the use of expensive lattice-matched substrates or by using complex dislocation density reducing mechanisms. In this paper we have investigated growth mechanisms of GaN/AlN multiple quantum wells (MQWs) using Plasma Assisted Molecular Beam Epitaxy. Specifically the modulation of the surface diffusivity of adatoms has been carried out through choice of appropriate growth parameters, such as the group-III to group-V flux ratio. Our results indicate that this leads to modification of not only the surface morphology, but also the abruptness of the well-barrier interface. Under conditions of growth where surface morphology was atomically flat, the interfaces are relatively diffuse. The IQE for such structures, as measured by the ratio of room temperature photoluminescence intensity to that measured at 4 K, is rather low typically ~10%. Use of near stoichiometric growth conditions however lead to a reduction of the surface diffusivity of adatoms, and the formation of spontaneous nanostructures in the form of nano-dots of about 20 nm in diameter and high levels of uniformity. The IQE for GaN/AlN MQWs grown under such conditions is increased to as high as 28% even for samples with large dislocation densities. Thus, growth under such conditions can mitigate the detrimental effects of non-radiative recombination centers associated with dislocations by spatial localization of electron-hole pairs. These results are important to many applications, including UV light emitting diodes.

中文翻译：

---

通过分子束外延生长的 GaN/AlN 多量子阱：生长动力学对辐射复合效率的影响

摘要 基于二元 GaN 量子阱的紫外 (UV) 光电器件已在文献中得到广泛报道。由于在非晶格匹配衬底上异质外延沉积期间产生的大位错密度，这种结构的内量子效率 (IQE) 相对较低。通过使用昂贵的晶格匹配衬底或使用复杂的位错密度降低机制，可以提高 IQE。在本文中，我们使用等离子体辅助分子束外延研究了 GaN/AlN 多量子阱 (MQW) 的生长机制。具体而言，通过选择合适的生长参数（例如 III 族与 V 族通量比）来调节吸附原子的表面扩散率。我们的结果表明，这不仅会导致表面形态的改变，还会导致井-势垒界面的突变。在表面形态原子平坦的生长条件下，界面相对扩散。此类结构的 IQE（通过室温光致发光强度与 4 K 下测量的强度之比测量）相当低，通常约为 10%。然而，使用接近化学计量的生长条件会导致吸附原子的表面扩散率降低，并形成直径约 20 nm 的纳米点形式的自发纳米结构和高度的均匀性。即使对于具有大位错密度的样品，在这种条件下生长的 GaN/AlN MQW 的 IQE 也增加到高达 28%。因此，在这种条件下的生长可以通过电子-空穴对的空间定位来减轻与位错相关的非辐射复合中心的不利影响。这些结果对许多应用都很重要，包括紫外线发光二极管。