Highly efficient GaN-based cascaded LEDs

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The aim of the project is the development of GaN-based cascaded LEDs. Thereby, several pn junctions are connected in series by using transparent tunnel junctions. In contrast to conventional LEDs, which show a drastical reduction of the efficiency at high current densities, cascaded LEDs have the potential to achieve high conversion efficiencies even at high electrical input powers, since high-power devices are operated at high voltage and and low current-density at the same time. Thus, the number of electrons and holes injected is not increased for higher brightness, but only the number of photons generated.The cascaded LEDs will be manufactured by using the only industrially relevant process of metalorganic vapor phase epitaxy in a monolithic process. A main focus is on the optimization of the doping profiles and an efficient activation of the buried GaN:Mg layers in order to ensure a minimal voltage penalty at the tunnel junctions. The project aims to increase the light output by more than 90 % per additional pn transition, while the operating voltage increases by less than 4 V. Ultimately, we aim to realize a cascaded LED with an operating voltage of 12 V and an input power of 2.4 W, which has a 70 % higher optical output power and an at least 350 % higher external quantum efficiency compared to a conventional LED.