Epitaxial growth of nonlayered 2D MnTe nanosheets with thickness-tunable conduction for p-type field effect transistor and superior contact electrode

Abstract

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit diverse structures, encompassing a broad spectrum of electronic types ranging from metal, semiconductor, to insulator and topological insulator. They hold immense potential for both Moore and more-than-Moore device applications. Among them, manganese telluride (MnTe), an emerging nonlayered 2D material, has garnered considerable attention due to its exceptional properties and significant application potential in next-generation electronic and optoelectronic devices. However, the controllable synthesis of ultra-thin 2D MnTe remains a great challenge, which hindering the comprehensive exploration of its fundamental properties and potential applications. In this study, we present the synthesis of large-area MnTe nanosheets through chemical vapor deposition growth, showcasing its thickness-dependent properties and device applications. By increasing the growth temperature from 500 to 750 ​°C, the MnTe nanosheets’ thickness transitions from thin-layer to a thick flake, the domain size increases from 10 to 125 ​μm, the morphology changes from triangle to hexagon, culminating in a highly symmetrical round shape. Structural characterization and second harmonic generation measurements reveal that the obtained MnTe nanosheets exhibit high crystallization quality and superior second-order optical nonlinearity. The field effect transistor (FET) constructed with thin-layer MnTe demonstrates a p-type semiconductor characteristic, transitioning to a semimetal feature as the thickness increases to a thick flake. Leveraging these thickness-dependent electrical conduction transition features, we explore diverse applications of MnTe with varying thicknesses. The semiconductive thin-layer MnTe, serving as the photosensitive channel in a device, achieves superior photoresponse, showcasing considerable potential for photodetection appliations. The semimetallic thick-layer MnTe, acting as the contact electrode in a MoS₂ FET, significantly enhances device performance, with carrier mobility increasing from 12.76 ​cm² ​V⁻¹ ​s⁻¹ (Au contact) to 47.34 ​cm² ​V⁻¹ ​s⁻¹ (MnTe contact). This work lays the foundation for the controllable synthesis of nonlayered 2D MnTe and provides insights into its prospective development for constructing innovative electronic and optoelectronic devices.