Crystalline magnesium nitride ( M g 3 N 2 ): From epitaxial growth to fundamental physical properties

Single-crystalline Mg3N2 thin films are grown on MgO (100) substrates with plasma-assisted molecular beam epitaxy. To prevent the oxidation of the Mg3N2 films and allow further physical characterization, a polycrystalline MgO cap is deposited in situ. The growth orientation of the Mg3N2 films can be tuned from (100) to (111) by changing the growth conditions, and the associated epitaxial relationships have been determined by means of x-ray diffraction. The lattice constant of Mg3N2 films has been monitored as a function of temperature from 300 to 900 K, determining thereby the linear thermal expansion coefficient. Transmission measurements indicate an optical bandgap of crystalline Mg3N2 around 2.9 eV at room temperature, consistent with diffuse reflectance measurements on micrometric Mg3N2 particles. These results demonstrate the possibility of exploiting Mg3N2 as a new crystalline semiconductor in the blue-violet range.