Structural and electron transport properties of single-crystalline In2O3 films compensated by Ni acceptors

Abstract

For device applications, the ability to grow semi-insulating or p-type indium oxide (In2O3) is highly desirable. With this in focus, high quality single-crystalline Ni-doped In2O3 films have been grown by plasma-assisted molecular beam epitaxy and structurally and electrically characterized. Within a concentration range of approximately 1017–1019 cm−3, Ni is fully incorporated in the In2O3 lattice without the formation of secondary phases. At doping higher than roughly 1020 cm−3, secondary phases seem to start forming. No film exhibits p-type conductivity at room temperature. Instead, Ni is shown to be a deep compensating acceptor—confirming theoretical calculations, the effect of which only becomes apparent after annealing in oxygen. Combined Hall and Seebeck measurements reveal the compensation of bulk donors already at low Ni concentrations (∼1018 cm−3) and a residual film conductance due to mainly the interface region to the substrate. This residual conductance is gradually pinched off with increasing Ni doping, eventually resulting in semi-insulating films at excessive Ni concentrations (∼1021 cm−3).