Excitonic recombination processes in III-nitride quantum wells

• Applicant: Professor Dr. Andreas Hangleiter
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392680433

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.

• DFG Programme: Research Grants