Exchange interaction between localized magnetic moments mediated by free charge carriers is responsible for a non-monotonic dependence of the low-temperature energy band-gap in dilute magnetic semiconductors. We found that in weakly doped Mn-ZnO films, increasing the exchange interaction by increasing the concentration of free charge carriers results in a red-shift of the near-band-edge emission peak at room temperature. An increase of Mn concentration widens the band gap, and a blue-shift prevails. Exchange interaction can be used to tune the room-temperature optical properties of the wide-band gap semiconductor ZnO.

We present a detailed investigation of the electrical properties of epitaxial ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3∕\mathrm{Sr}{\mathrm{Ti}}_{0.98}{\mathrm{Nb}}_{0.02}{\mathrm{O}}_3$ Schottky junctions. A fabrication process that allows reduction of the junction dimensions to current electronic device size has been employed. A heavily doped semiconductor has been used as a substrate in order to suppress its series resistance. We show that, unlike standard semiconductors, high-quality oxide-based Schottky junctions maintain a highly rectifying behavior for doping concentration of the semiconductor larger than ${10}^{20}{\mathrm{cm}}^{-3}$. Moreover, the junctions show hysteretic current-voltage characteristics.