Excitonic recombination processes in III-nitride quantum wells

今天，III族氮化物在技术上代表了宽禁带半导体的一个高度复杂的例子。与大的带隙一起，还有其他突出的特性，特别是电子和空穴的大有效质量以及小的介电常数。作为一个直接的后果，一个强大的电子-空穴相互作用出现导致大激子结合能，最突出的是在低维结构。对于大多数半导体，激子由于其小的结合能而被认为是低温现象。相比之下，III族氮化物量子威尔斯阱中的大激子结合能使得人们甚至在室温下也期望大部分激子。在本项目中，激子形成对复合过程的影响，包括辐射和非辐射复合，将被研究。我们预计结合动力学的巨大变化与强烈增加的重组概率相结合。此外，激子的形成对温度依赖性的强烈影响是预期的。在实验上，应进行作为载流子密度和温度的函数的复合动力学的系统研究，以澄清电子-空穴相互作用对辐射和非辐射过程的影响。一个系统的变化的组成，结构，掺杂，和结晶取向计划研究不同的激子结合能的影响。实验工作应辅以模型计算侧重于激子增强复合过程。激子对复合过程的影响可能会对III族氮化物发光二极管的性能产生相当大的影响。在那里，人们观察到“下垂”现象，即在大电流密度下量子效率的强烈降低。一个明确的证据激子增强复合过程可能会揭示新的光这些现象。此外，新的战略，以克服下垂可能会演变从一个更深的理解。

Today, group-III-nitrides technologically represent a highly sophisticated example of wide-gap semiconductors. Together with the large bandgap there are further outstanding properties, in particular large effective masses for electrons and holes as well as a small dielectric constant. As an immediate consequence, a strong electron-hole interaction emerges leading to large exciton binding energies, most prominently in low-dimensional structures. For most semiconductors, excitons are regarded a low-temperature phenomenon owing to their small binding energy. In contrast, the large exciton binding energy in III-nitride quantum wells makes one expect a large fraction of excitons even at room temperature. In the present project the consequences of exciton formation on recombination processes, including both radiative and nonradiative recombination, shall be studied. We expect dramatic changes of the ecombination kinetics combined with strongly increased recombination probabilities. In addition, a strong impact of exciton formation on the temperature dependence is anticipated. Experimentally, systematic studies of the recombination kinetics as a function of carrier density and temperature shall be performed, inorder to clarify the influence of the electron-hole interaction on both radiative and nonradiative processes. A systematic variation of composition, structure, doping, and crystallographic orientation is planned to study the influence of varying exciton binding energies. The experimental efforts shall be complemented by model calculations focused on the excitonic enhancement of recombination processes. The influence of excitons on recombination processes may have considerable impact on the properties of III-nitride lightemitting diodes. There, one observes the "droop" phenomenon, i.e. a strong decrease of the quantum efficiency at large current densities. An unambiguous proof of excitonic enhancement of recombination processes may shed new light onto these phenomena. Moreover, new strategies to overcome the droop may evolve from a deeper understanding.