Highly efficient GaN-based cascaded LEDs

该项目的目标是开发基于gan的级联led。因此，几个pn结通过透明隧道结串联起来。传统led在高电流密度下效率大幅降低，与之相反，级联led即使在高输入功率下也有潜力实现高转换效率，因为大功率器件同时在高电压和低电流密度下工作。因此，注入的电子和空穴的数量不会因为更高的亮度而增加，而只是产生光子的数量。级联led将在单片工艺中使用工业上唯一相关的金属有机气相外延工艺制造。一个主要的重点是优化掺杂分布和有效激活埋GaN:Mg层，以确保在隧道结处的电压损失最小。该项目的目标是每增加一个pn转换，光输出增加90%以上，而工作电压增加不到4 V。最终，我们的目标是实现工作电压为12 V，输入功率为2.4 W的级联LED，与传统LED相比，其光输出功率提高70%，外部量子效率提高至少350%。

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.