In this thesis, the carrier dynamics in InGaN/GaN QWs are investigated. These structures often form the active layer in highly efficient LEDs. Micron-scale spatial variation in PL emission across blue- and green-emitting InGaN/GaN QWs is observed and its effects on measurements of efficiency droop are discussed. The integrated intensity can vary spatially by up to 50 %, highlighting the importance of considering the effect of the collection spot size on the repeatability of PL measurements. The temperature-dependence of the peak PL emission energy from a set of blue- and green-emitting InGaN/GaN MQWs is investigated. The typical 's-shape' is observed to flatten at carrier densities below the onset of efficiency droop, suggesting that the saturation of localised hole states is unlikely to be the primary contributor to droop. The temperature dependences of the PL emission from a set of InGaN/GaN SQW samples designed to have different net electric fields across the QWs are investigated at different excitation power densities. A flatter s-shaped peak energy temperature-dependence is observed from the sample in which simulations suggest the net field is reversed. Since this reversal should primarily affect electron localisation, this suggests that the localisation of electrons, as well as holes, influences the temperature-dependence of the PL emission. The relative importance of defect-related non-radiative recombination and localisation-enhanced Auger recombination on efficiency droop in InGaN/GaN QWs designed to have different point defect densities is investigated by comparing experimental PL measurements and theoretical calculations. The results suggest that defect-assisted processes are of secondary importance at carrier densities above 10^19 cm-3.
|Date of Award||1 Aug 2023|
- The University of Manchester
|Supervisor||David Binks (Supervisor) & Patrick Parkinson (Supervisor)|
- Quantum Wells