Nitride Multilayers as a Platform for Parallel Two-Dimensional Electron-Hole Gases: MgO/ScN(111)

At interfaces between insulating oxides LaAlO$_3$ and SrTiO$_3$, a two dimensional electron gas has been observed and well studied, while the predicted hole gas has not been realized due to the strong tendency of holes in O-2p orbitals to localize. Here we propose, via ab initio calculations, an unexplored class of materials for the realization of parallel two dimensional (2D), two carrier (electron+hole) gases: nitride-oxide heterostructures, with (111)-oriented ScN and MgO as the specific example. Beyond a critical thickness of five ScN layers, this interface hosts spatially separated conducting Sc-3d electrons and N-2p holes, each confined to about two atomic layers-- the transition metal nitride provides both gases. A guiding concept is that the N$^{3-}$ anion should promote robust two carrier 2D hole conduction compared to that of O$^{2-}$: metal mononitrides are mostly metallic and even superconducting while most metal monoxides are insulating. Our results, provide guidance for new exploration, both experimental and theoretical, on nitride-based conducting gases that should promote study of long sought exotic states viz. new excitonic phases and distinct, nanoscale parallel superconducting nanolayers[1].\newline [1]A.S. Botana, V. Pardo, W.E. Pickett, arXiv/1509.08518(2015)