Controllable Synthesis of Transferable Ultrathin BiGe(Si)O Dielectric Alloys with Composition-Tunable High-κ Properties.

Two-dimensional (2D) alloys hold great promise to serve as important components of 2D transistors, since their properties allow continuous regulation by varying their compositions. However, previous studies are mainly limited to the metallic/semiconducting ones as contact/channel materials, but very few are related to the insulating dielectrics. Here, we use a facile one-step chemical vapor deposition (CVD) method to synthesize ultrathin BiSiGeO dielectric alloys, whose composition is tunable over the full range of just by changing the relative ratios of the GeO/SiO precursors. Moreover, their dielectric properties are highly composition-tunable, showing a record-high dielectric constant of >40 among CVD-grown 2D insulators. The vertically grown nature of BiGeO and BiSiGeO enables polymer-free transfer and subsequent clean van der Waals integration as the high-κ encapsulation layer to enhance the mobility of 2D semiconductors. Besides, the MoS transistors using BiSiGeO alloy as gate dielectrics exhibit a large / (>10), ideal subthreshold swing of ∼61 mV/decade, and a small gate hysteresis (∼5 mV). Our work not only gives very few examples on controlled CVD growth of insulating dielectric alloys but also expands the family of 2D single-crystalline high-κ dielectrics.