Monolithic Integration of Group III-Nitrides on Metallic TiN: A Path Towards Advanced (Opto-)Electronics

• Applicant: Dr. Philipp John
• Subject Area: Experimental Condensed Matter Physics ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568879259

The project “MINT” aims at demonstrating novel types of group III-nitride based (opto-)electronic devices by developing a fully epitaxial semiconductor-on-metal platform. Conductive TiN thin films serve as integrated bottom electrodes to power GaN-based micro light emitting diodes (µ-LEDs) for novel display applications, and epitaxial AlN-based bulk acoustic wave devices for beyond 5G communication. This innovative concept reduces the device processing mainly to top deposition, resulting in an active region sandwiched between two electrodes that is vertically powered. During device operation, the TiN bottom electrode additionally provides effective heat dissipation and back-reflection of emitted light. To ensure a high crystalline quality of the active region despite the chemical and structural differences between metal and semiconductor, we use molecular beam epitaxy to grow GaN and AlN seed nanowires free of structural defects on the refractory TiN film. Subsequently, lateral overgrowth by metal-organic chemical vapor deposition yields either hexagonally shaped µ-platelets or fully coalesced GaN and AlN layers. The possible formation of structural defects, such as threading dislocations or inversion domains, is revealed by detailed structural and optical investigations of the semiconductor-metal interface, as well as the coalescence boundaries between adjacent grains. This information will provide important feedback to optimize growth conditions and seed nanowire morphology. Furthermore, microstructural investigations of processed devices will identify the impact of such defects on the device performance. In the final project phase, we will explore the possibility to realize flexible devices by transferring the established growth and processing protocols to graphene and polycrystalline Ti foils as substrates, with the latter potentially allowing for very large-scale fabrication.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Dr. Ileana Florea