Synthesis and Magnetic and Optoelectronic Properties of Ultrathin Nonlayered α-MnSe

Two-dimensional (2D) nonlayered semiconductors─distinct from traditional van der Waals layered materials─offer transformative opportunities for spintronics and advanced optoelectronics due to their unconventional quantum confinement and magneto-optical coupling. However, achieving atomic-scale thickness control in nonlayered 2D semiconductors remains a critical challenge. Here, we epitaxially grow rock-salt α-MnSe nanosheets via atmospheric pressure chemical vapor deposition (APCVD), achieving an ultrathin thickness of 0.75 nm (≈1 unit cell) on mica substrates. Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) confirm single-phase, high-crystalline α-MnSe with atomic flatness, a rare attribute in nonlayered systems. Magnetic measurements reveal unusual low-temperature ferromagnetism with a phase transition at ∼120 K. The α-MnSe photodetector exhibits 0.16 A·W–1 responsivity and 3 × 109 Jones detectivity under 640 nm illumination, while β-Ga2O3-gated FETs demonstrate p-type conductivity with a record-high mobility of 170 cm2 V–1 s–1. This work establishes nonlayered α-MnSe as a versatile platform for magnetic memory and energy-efficient optoelectronic devices, expanding the frontiers of 2D material science.