EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Ultra-thin InGaN/GaN quantum wells (QW) arranged in short-period superlattices (SPS) are considered promising material systems for advanced optoelectronics and topological insulator applications due to their 2D character. The optoelectronic properties of pseudomophically grown InGaN/GaN SPSs are directly related to the composition and thickness of the QWs and GaN barriers. Such properties can be exploited only by controlling the indium content in monolayer (ML)-scale. Therefore, it is deemed necessary to associate the strain state of such QWs to their composition. To this end, total energy and force calculations were performed using both empirical potentials and Density Functional Theory (DFT) calculations. Biaxially strained InGaN/GaN supercells were constructed considering both ordered configurations and randomly distributed indium atoms in the QWs, spanning the whole compositional range. Ordered configurations constitute the ground states while supercells with randomly distributed indium atoms allow to investigate QWs at the experimentally relevant growth temperatures. Moreover, the impact of local clustering phenomena on the strain can be addressed due to random alloys fluctuations. The calculations revealed a breakdown of the anisotropic elasticity in QWs with thickness limited to one ML. The strain of random structures presented remarkable convergence to that of ordered ones with similar indium content, despite the ML-scale compositional inhomogeneities. The strain behavior of QWs with two MLs was also determined while the strain distribution on the abutting barrier MLs as function of the indium content and QW thickness was revealed. Moreover, these results provided additional insight into the local bond distortions and strain behavior of metal and non-metals sublattices in the QWs. The calculations were verified against experimental observations by high resolution scanning transmission electron microscopy (HRSTEM).

Supported by the IKY project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432) and the project “INNOVATION-EL” (MIS 5002772).