Anorganische Hybridsysteme als Funktionsstrukturen für die integrierte Optoelektronik
Zusammenfassung der Projektergebnisse
In this paper we have demonstrated the feasibility of a hybrid system of a microcavity OLED and a garnet functionalized planar waveguide in which a modulation of 18 per 3.3 mT is possible. The device is encapsulated and can work under normal atmosphere. The garnet growth has been optimized to reduce cracks and roughness in the system. The surface morphology and the substrate influence have been studied. The influence of the substrate orientation on the nucleation is evident but has only small effects on the surface roughness. More important is an adjustment of the lattice constant which leads to a 30% reduced BIG roughness. The reduction of crack density in the surface was possible by choosing a substrate with an appropriate thermal expansion coefficient. A buffer system based on GGG was developed to study the stress release in BIG compared to YIG. The garnets were patterned using laser structuring and ion beam etching. As garnets are comparatively stable against chemical etching these methods seemed feasible. We obtained the best results for laser structured garnet films. Each structuring process was repeated several times to optimize the wall roughness. The optical properties of BIG have been analyzed using ellipsometric measurements. The optical constants could be derived from ellipsometric data and confirmed by optical transmission measurements. The Faraday rotation of BIG scales linearly with the film thickness, thus it is possible to adjust the needed rotation and the BIG thickness for optimal performance. To find the best values for the microcavity OLED stack various setups have been simulated. Especially the transition from a normal OLED to a microcavity has been investigated for different anode materials. From the simulations regarding the organic layer thickness of microcavity OLEDs the optimized parameters for light coupling into the substrate could be found. The simulations were verified by the fabrication of selected OLED stacks, which showed very good electrical and optical behavior. The diode characteristic of the microcavity OLED was clearly visible and luminance started at 2.5 V having values comparable to non-cavity OLEDs. In the end we demonstrated the modulation of the OLED light in the garnet functionalized waveguide in response to an external magnetic field. As the absorption in the waveguide is high at 532 nm wavelength the thickness of the garnet layer had to be adjusted for best performance. For our model system a 125 nm thick garnet core was embedded between two glass slides. As BIG shows high absorption in the visible spectral range a wavelength shift in the luminance of the microcavity OLED is desirable. This is an interesting prospect for further research in this area. A microcavity OLED with near infrared light emission could solve the problem of absorption and thus lead to an all garnet waveguide.
