Univ.-Prof. Dr. rer. nat. Thomas Riedl

EFRE Project: PerovsKET - Improvement of the microstructure of perovskites by thermal nanoimprint as a key technology for large-area perovskite optoelectronics.

The birth of microelectronics in the early 1970s was the starting point of a paradigm shift that continues to fundamentally shape our everyday lives in many aspects. The modern information society, the much-cited digitalization of private and public life would be unthinkable without microelectronics. The carriers of information in microelectronics are charged particles, the so-called electrons. The improvement of microelectronics through miniaturization, which has progressed over decades, is now on the verge of reaching its physical limits - progress is stalling. In the future, photonic circuits could trigger a revolution of similar scope to the introduction of microelectronics. Here, carriers of information are light particles, so-called photons. The combination of electronic and photonic circuits on a microchip (integrated optoelectronics) holds out the prospect of functionalities that are capable of eclipsing everything known to date in terms of speed and efficiency. In addition to information and communication technology, there is a wide range of possible applications in the field of sensor technology, including so-called lab-on-chip solutions.

However, integrated optoelectronics lacks the central component: a suitable (laser) light source that can be integrated into silicon chips. Recently, new semiconductors from a class of materials known as minerals since the 19th century have entered the stage of optoelectronics and caused a sensation in the scientific community - perovskites. What makes perovskite lasers so special? They can be processed from a solution and have shown their great potential for integration into silicon electronics in initial very promising pioneering work.

As important preliminary work, a novel fabrication process for particularly low-defect perovskite layers was developed in cooperation between the Chair of Electronic Devices (headed by Prof. Riedl) and the Microstructure Technology group (headed by Prof. Scheer). In this process, the perovskite layers deposited from a solution are recrystallized by means of a thermal imprint process. In this process, the initially very rough and defect-rich perovskite layers are recrystallized and smoothed under simultaneous application of temperature (< 150°C) and pressure (approx. 100 bar). This not only reduces optical losses due to light scattering, but also eliminates structural defects in the perovskite semiconductor that make laser activity difficult or impossible. It also makes it possible to pattern the perovskite layers with photonic resonator structures needed for a laser. Such a structuring process at low temperatures around 100°C would be completely futile for established semiconductors and is made possible solely by the specific crystal properties of the perovskites.

The PerovsKET project aims to better understand the process technology developed and to replace the lead still present in perovskites with other metals. Project partner NB Technologies is contributing a patented nanoimprint process with innovative stamps to the project, which should enable upscaling of the process and thus lay the foundation for later series production. AMO GmbH is applying innovative patterning techniques to integrate the improved perovskite materials into silicon-based chip systems. The nano-photonic devices are expected to demonstrate significantly improved performance and achieve record levels even on larger active areas than before. Ideally, our work will also make a significant contribution in the global race for the first perovskite laser diode. However, the overarching goal remains integrated optoelectronics, to combine the best of the worlds of electronics and photonics.

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