Novel nitride materials for electronic devices

• Applicant: Dr.-Ing. Saskia Schimmel
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512083685

The overall goal of the project is to develop selected emerging nitride semiconductors alongside with an improved and more generalizable understanding of ammonothermal growth of nitrides. The project evaluates the fundamental properties of selected emerging ternary nitrides with regard to prospective applications in electronic devices. Bulk crystals will be grown via the ammonothermal method. Alongside with gaining access to the materials, a deepened understanding of the ammonothermal synthesis and doping of binary and ternary materials will be established. The targeted nitrides are suitable for heteroepitaxial integration with each other, which prospectively enables novel combinations of materials properties in electronic devices. Building on previous results on GaN, the material system GaN-AlN-AlGaN will first be investigated. AlGaN will serve as an exemplary case for studying ways of controlled crystallization of ternary nitrides via solute transport in ammonothermal solutions. Methods of intentional doping and conductivity control during ammonothermal crystal growth will be investigated using AlN as an example. The low growth temperatures enabled by ammonothermal synthesis represent a prospective pathway to conductive AlN substrates via doping with Si, which could enable significant improvements in the energy efficiency of vertical power electronic devices. The use of custom high-pressure optical cells creates unique capabilities for monitoring ammonothermal reactions in situ. In the case of Ga, these will be utilized to deepen the fundamental understanding. In situ monitoring will also be applied for expanding the fundamental understanding to the constituent elements of the ternary nitrides targeted in the project, specifically Al, Si, Mg, Mn and Zn. In parallel, in situ monitoring methods for investigating complex systems will be developed further, namely simultaneous in situ measurements with complementary techniques such as x-ray absorption, UV-Vis- and Raman spectroscopy. In addition, the roles of pressure and ammonia density for crystallization will be clarified and the feasibility of crystallization at significantly lower pressures will be evaluated. Within the project, the obtained understanding of the crystallization of ternary nitrides and their transport in ammonothermal fluids will be utilized for the crystallization of three emerging ternary nitride materials of the composition II-Si-N2 (II = Mg, Mn, Zn). Their synthesis as single crystals of good structural quality enables the experimental evaluation of their bulk properties. Building on the obtained knowledge of the properties of these materials, their application prospects in electronic devices will be evaluated further, including a first evaluation of the application potential of epitaxial heterostructures of the investigated materials.

• DFG Programme: Independent Junior Research Groups