Defect-induced room temperature ferromagnetism in un-doped InN film

Diluted magnetic semiconductors (DMSs), with the Curie temperature at room temperature, are of technological and fundamental importance. Defect engineering has been an effective way to introduce magnetic moments in various non-magnetic systems. Here we show firstly, InN film directly grown on (0001)-oriented Al2O3 substrate with In deficiency is ferromagnetic with its Curie temperature as high as 297K. The undesirable large lattice mismatch between the film and substrate leads to a peculiar surface structure that the film separates into distinct In-rich and In-poor regions. Our first-principles calculations suggest the defect of In-vacancy is responsible for the magnetism. A local magnetic moment of 2.5μB is found, in agreement with experimental results. Our findings demonstrate that room-temperature ferromagnetism can also be induced in narrow band gap semiconductors through defect engineering, which remains largely unexplored so far.