Rare-earth nitride based heterostructures for integrated thermoelectrics

This project aims to establish novel rare-earth transition-metal (TM) nitrides and mixed TM/group-IIIa nitrides as a promising class of high-temperature thermoelectric materials for integrated nitride-device technologies. 

Based on the applicants' recent advances in the areas of thin-film TM-nitride growth and thermoelectric transport characterization, the focus of this project is to explore the narrow-gap TM-nitrides (ScN, CrN) and mixed allotropes with isoelectronic group-IIIa elements, given their significant potential in high-temperature thermoelectric applications. Particular attention will be paid to creating phonon-glass/electron-crystal-like compounds by controlling disorder effects, alloying, and developing advanced heterostructures using ultrahigh-purity molecular beam epitaxy methods, thereby tailoring the key thermoelectric parameters, such as electrical and thermal conductivity, and thermoelectric power factor over large temperature ranges. Three connected approaches will be pursued that logically build upon each other in forming complex TM-nitride thermoelectrics with enhanced performance: 

• The investigation of binary rocksalt thin films (ScN, CrN) and the tunability of lattice disorder through the introduction of defects (e.g., vacancies and other point defects) and substitutional doping.
• The development of mixed-TM/group-IIIa nitride alloys within and beyond the spinodal decomposition limit and the phase-mismatch-induced formation of nanocomposite structures, to tune thermoelectric properties towards the alloy limit.
• The exploration of two-dimensional quantum-well (superlattice) heterostructures to exploit beneficial quantum confinement and energy filtering concepts in enhancing thermopower, while suppressing thermal conductivity through phonon scattering at artificial interfaces. 

This project is funded by Deutsche Forschungsgemeinschaft (DFG) under project number 563156864.