Structural and electronic properties of bulk YN and of the YN/ScN superlattice

The structural and electronic properties of YN are investigated using two different first principles methods, the full potential linear augmented plane waves (FPLAPW) method and a recent version of the first principles full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions. Our calculations show that the ground state configuration of YN is the rocksalt (B1) structure and that it is a semiconductor. We have also investigated the A3 hexagonal structure which is nearly five-times coordinated and found it more stable than the previous wurtzite phase. So we confirm the presence of another local minimum, but in this A3 phase and not in the wurtzite (B4). Nevertheless, the transition from rocksalt (B1) to CsCl (B2) structure is found to be possible at high pressure. The zinc blende structure (B3) has also been investigated and is found to have a large and direct fundamental gap. The resemblances between YN and ScN and their small lattice mismatch led us to perform predictive investigations on rocksalt/rocksalt ScN/YN heterostructure superlattices. The latter shows interesting features: these systems constituted from indirect bandgap bulk materials are found to have a direct bandgap suggesting that the reason is probably the zone folding phenomena which is suspected to be at the origin of a similar effect observed in the popular Si/SiGe systems. To our knowledge, rocksalt/rocksalt superlattice systems have not received particular attention before. (author)