Monolithic Integration of Group-III Nitrides on Metallic TiN (MINT)

The MINT project — Monolithic Integration of Group-III Nitrides on Metallic TiN: A Path Towards Advanced (Opto-)Electronics — addresses key challenges in integrating III-nitride semiconductors with metal electrodes to create high-performance, scalable device platforms. By combining complementary expertise from the Paul-Drude-Institut (PDI) and partners at CNRS-CRHEA (Centre de Recherche sur l’Hétéro-Épitaxie et ses Applications), the collaboration has secured funding under the ANR–DFG programme, a bilateral initiative supporting outstanding French-German research partnerships.

Group-III nitride semiconductors such as GaN and AlN are central to modern optoelectronics and RF devices due to their wide bandgaps, high electron mobility and robustness. However, realizing fully epitaxial semiconductor-on-metal architectures has been limited by structural and chemical mismatches between conventional metals and nitride crystals. The MINT project overcomes these barriers by using conductive titanium nitride (TiN) thin films as integrated bottom electrodes that serve multiple functions: they provide robust electrical contact, enhance heat dissipation during device operation, and act as efficient back reflectors for emitted light.

To achieve high crystalline quality at the semiconductor–metal interface, molecular beam epitaxy (MBE) is used to grow defect-free GaN and AlN seed nanowires on refractory TiN films. These nanowire templates are then overgrown laterally using metal-organic chemical vapor deposition (MOCVD) to produce either well-defined hexagonal micro-platelets or fully coalesced films. Structural and optical investigations will evaluate defects and interface quality, providing essential feedback to optimize both growth conditions and nanowire morphology.

A key innovation of the MINT approach is its potential to simplify device fabrication: by integrating a conductive bottom electrode directly into the epitaxial stack and minimizing processing to essentially top contact deposition, devices such as GaN-based micro light-emitting diodes (µLEDs) and AlN-based bulk acoustic wave (BAW) components can be produced with improved performance and manufacturability. In the final phase, the team will explore integrating the semiconductor-on-metal platform on silicon substrates, advancing scalability and industrial relevance.

By uniting advanced epitaxial growth techniques with comprehensive structural and optoelectronic characterization, the MINT project aims to establish a versatile semiconductor-on-metal platform that can underpin next-generation (opto-)electronic technologies. Its outcomes will strengthen Europe’s research leadership in semiconductor materials science and contribute to the broader strategic goals of the European Research Area (ERA).