Controllable Growth and Characterization of α- and β-phase MnSe by Chemical Vapor Deposition

Theory predicts that Mn_xSe_y is strongly magnetic thin film with a high T_C of nearly 250 K and stability in ambient conditions, unlike many other leading 2D ferromagnets. Despite the material’s suitability as a large-scale, high T_C magnetic thin film, much is still unknown and the crystallographic phases of thin-film Mn_xSe_y and their properties are still not well understood. In this work, we demonstrate the controllable growth of α- and ß-phase MnSe in a three-zone chemical vapor deposition system using Se and MnCl₂ precursor powders in an argon- and hydrogen-rich atmosphere on a sapphire substrate. A thorough characterization of each phase is performed with Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. We observe distinct Raman peaks at 129 cm^-1 and 253 cm^-1 for the α and ß phases using a 532 nm laser excitation source with a 10 mW spot power, which have been reported previously in the literature as the longitudinal acoustic αMnSe mode and  A_1g Mn-Se stretching mode, respectively. Finally, we discuss the primary parameters impacting crystal nucleation for each growth phase: chamber pressure, growth time, and, in particular, the effects of argon/hydrogen atmospheric partial pressure and precursor vapor pressures. Magnetic characterization reveals the antiferromagnetic behavior of the ß-phase, suggesting antiferromagnetism for multi-layer films and ferromagnetism in the monolayer limit.