Extreme polarisation gradients (Akronym: „Polrock“): surface and interface analytics on rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-based heterostructures

• Applicants: Professor Dr. Oliver Ambacher; Professor Dr. Stefan Krischok
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530081697

Within the project, rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-based heterostructures will be epitaxially grown, and their interface properties will be investigated. We aim to prove the theoretically predicted extreme polarization gradients and polarization-induced sheet charge densities at the interface between different crystal structures. Furthermore, they should be adjusted in a controlled manner for applications in electronic and optical devices. The novel combination of ScxAl1-xN-layers with rock salt structure (without polarization, P(rs) = 0) and GaN or ScxAl1-xN layers with wurtzite structure (which can show very high polarization along the [0001]-direction: Pmax(wz) ~~ 1,4 C/m2 ) within one pseudomorphic heterostructure, enables to achieve very high polarization gradients (∆P = Pmax(wz)) and polarization induced sheet charge densities up to σ/e ~~ 8 x10^14 cm-2. These sheet charge densities are about two orders of magnitude higher than sheet charges confined at interfaces of pseudomorphic GaAlN/GaN-heterostructures, which correspond to state-of-the-art. Simulations of band edge profiles are necessary to prove extreme polarization gradients by experimentally measurable charge carrier profiles. They need precise knowledge about band discontinuities, surface potentials, and doping. Analyzing band discontinuities and specific surface and interface properties requires a detailed analysis of the single layers and their heterostructures. Based on optimized nitrogen- and metal-polar coatings and layer systems, we will determine the structural and electronic properties of the ScxAl1-xN-material system and the dispersion of the band transitions and phonons in dependence of the Sc-content. Simulations will support the exact determination of the electronic and phonon band structure. The gained insight will help prove the band discontinuities, band bending, and charge carrier profiles at the interfaces of rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-heterostructures and enable the validation of extreme polarization gradients and their controlled variation.

• DFG Programme: Research Grants