Origin of Ferromagnetism and Long-range Interactions of Cu in GaN: Chemical Bonding and Electronegativity Approaches

Abstract

The diluted magnetic semiconductors (DMS) used in microelectronics should exhibit ferromagnetism mediated by delocalized electrons. Only Mn-doped GaN has passed this requirement, although the Curie temperature of this materials is at most 170 K, which is substantially lower than room temperature. Therefore, the development of a novel DMS with a higher Curie temperature is still an important issue. Recently, the potential of Cu-doped GaN has been demonstrated both theoretically and experimentally. However, it is not clear why Cu shows ferromagnetism. Using first principles density functional calculations, this study shows that the onset of magnetism of Cu in GaN results from the tendency of electrons to leave anti-bonding states. The delocalized electrons, which can stabilize the ferromagnetic alignment of the Cu ions, are generated at the Fermi level due to the small difference in electronegativities between nitrogen and Cu ions. For comparison, localized electrons are formed in Mn-doped GaN due to the large difference in electronegativities. The difference in electronegativities between the anion and the transition-metal impurity is expected to be helpful in the design of new DMS materials.