Dwukierunkowe diody elektroluminescencyjne do pracy z prądem przemiennym

Bidirectional light-emitting diodes for alternating current operation The III-nitride light emitting diodes (III-N LEDs) coated with phosphor are the most efficient white light sources for domestic and outdoor lighting. However, standard LEDs require the direct current (DC) supply, while the power in the electric grid is distributed as alternating current (AC). AC/DC converters are often bulky and always a few percent of energy is lost to current rectification. Substantial efforts was put to fight with this inconvenience and different approaches to directly AC-driven light emitting devices were proposed. First of them is based on merging several III-N LEDs in a sophisticated way to form rectifiers inside an AC LED chip. Nonetheless, under AC condition only a part of all LEDs used in the circuit emit light at the same time, which effectively reduces the surface power density received from the device. The second approach is a symmetric structure, where the organic emissive layer is sandwiched between two dielectric barriers. However, a proper balance of injected carriers is difficult to achieve and thus those devices suffer from high driving voltage and low power efficiency. In this project we propose a new design of an AC-driven bidirectional light emitting diodes (BD LED), which operation is based solely on the epitaxial structure. We focus on symmetrical structures, in which an efficient InGaN quantum well (QW) constitute the light emitting region and are surrounded by two tunnel junctions (TJs) for efficient carrier injection. That way, under the positive bias the top TJ is reversely polarized, interband tunneling of carriers occurs and thus the holes are effectively injected into the QW. Simultaneously, the bottom TJ is polarized forwardly, so electrons are also injected to the QW. Under the negative bias is just the oposite the top TJ is polarized forwardly, while the bottom TJ reversely. The carriers are still injected to the QW, but in this case they come from other sides of QW. The proof-of-concept BD LED was grown by plasma assisted molecular beam epitaxy (PAMBE) on Ga-polar bulk GaN substrate. It shows very promising characteristics i.e. we have obtained light emission for both directions of current flowing through BD LED. Therefore it is essential to continue this research in order to fully explore the physics of BD LEDs and understand the impact of each element of the epitaxial structure on the optoelectronic properties of BD LEDs, so that the novel class of light-emitting devices could be developed. In this project, we will investigate BD LEDs as a new class of semiconductor light sources dedicated to direct AC operation. The structures will be grown by plasma assisted molecular beam epitaxy (PAMBE). The main part of this project will be devoted to studying the active region in BD LED structures, in particular how the built-in electric field affects the optoelectronic properties of these devices under DC and AC power conditions. In order to do that, in the first task, we will optimize doping in TJs to reduce operating voltages of single BD LED. We will test the feasibility of stacking multiple BD LEDs to meet high-power applications. Finally we will examine the BD LEDs switching dynamics to determine the limiting factors of carrier supply to the active region. Mikołaj Żak, Instytut Wysokich Ciśnień Polskiej Akademii Nauk 592241 OSF,