Controllable Growth and Characterization of {\alpha}- and {\beta}-phase MnSe by Chemical Vapor Deposition

Abstract

Manganese selenide (MnSe) is a promising air-stable two-dimensional magnetic semiconductor for which theory predicts robust ferromagnetism in monolayers with Curie temperatures approaching 250 K. However, the crystallographic phases and magnetic properties of thin-film MnSe grown by scalable methods remain poorly understood. Here, we demonstrate the controllable growth of ${\alpha}$- and ${\beta}$-phase MnSe on C-face sapphire using a three-zone chemical vapor deposition process with elemental Se and ${MnCl_{2}}$ precursors in an $Ar/{H_{2}}$ atmosphere. Using Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, we show that our process yields phase-pure ${\alpha}$-MnSe nanorods and ${\beta}$-MnSe triangular flakes with lateral sizes up to 20 ${\mu}m$ and thicknesses of 15-30 nm. Low-temperature photoluminescence of the ${\beta}$-phase films reveals a bandgap of approximately 2.0 eV. Systematic variation of growth parameters shows that precursor vapor pressure, rather than ${H_{2}}$ partial pressure, is the dominant factor controlling lateral flake size. Vibrating-sample magnetometry measurements reveal a $N{\'e}el$ temperature of 53 K in the ${\beta}$-phase films, providing clear evidence of antiferromagnetism in the multilayer regime and establishing MnSe as a tunable platform for 2D spintronic and optoelectronic devices.