Gate-Controlled Metal to Insulator Transition in Black Phosphorus Nanosheet-Based Field Effect Transistors

Carrier-carrier interactions or disorders strongly affect the quantum localization-delocalization of carriers which leads to the metal to insulator transition (MIT) in two-dimensional (2D) systems. However, the physical origin of MIT in 2D systems remains controversial. Here, we report the MIT in black phosphorus (BP) nanosheet-based devices with and without the encapsulation of hexagonal boron nitride (hBN). In hBN encapsulated BP devices, we perform critical scaling analysis to elucidate the microscopic origin of 2D MIT by considering the significant role of carrier-carrier interactions over disorder. We find the critical exponents z nu = 2.49 +/- 0.05 and z nu = 2.65 +/- 0.06 in metallic and insulting phases, respectively, supporting the quantum percolation (z nu = 7/3). In hBN unencapsulated BP devices, the Mott variable range hopping dominates the charge transport in the insulating phase, suggesting that the disorder plays a significant role over the carrier-carrier interactions. The extracted conductivity exponent of 1.31 +/- 0.01 at 10 K approaches the 2D percolation exponent value of 4/3, which supports the classical percolation-based 2D MIT. Our findings pave the way toward the utilization of BP with and without hBN encapsulation as a model system with which to study the 2D MIT as well as various classical and quantum transports in 2D nanoelectronic devices.