Enhanced Performance of Field-Effect Transistors Based on Black Phosphorus Channels Reduced by Galvanic Corrosion of Al Overlayers

Two-dimensional (2D)-layered semiconducting materials with considerable band gaps are emerging as a new class of materials applicable to next-generation devices. Particularly, black phosphorus (BP) is considered to be very promising for next-generation 2D electrical and optical devices because of its high carrier mobility of 200-1000 cm² V^-1 s^-1 and large on/off ratio of 10⁴ to 10⁵ in field-effect transistors (FETs). However, its environmental instability in air requires fabrication processes in a glovebox filled with nitrogen or argon gas followed by encapsulation, passivation, and chemical functionalization of BP. Here, we report a new method for reduction of BP-channel devices fabricated without the use of a glovebox by galvanic corrosion of an Al overlayer. The reduction of BP induced by an anodic oxidation of Al overlayer is demonstrated through surface characterization of BP using atomic force microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy along with electrical measurement of a BP-channel FET. After the deposition of an Al overlayer, the FET device shows a significantly enhanced performance, including restoration of ambipolar transport, high carrier mobility of 220 cm² V^-1 s^-1, low subthreshold swing of 0.73 V/decade, and low interface trap density of 7.8 × 10¹¹ cm^-2 eV^-1. These improvements are attributed to both the reduction of the BP channel and the formation of an Al₂O₃ interfacial layer resulting in a high-k screening effect. Moreover, ambipolar behavior of our BP-channel FET device combined with charge-trap behavior can be utilized for implementing reconfigurable memory and neuromorphic computing applications. Our study offers a simple device fabrication process for BP-channel FETs with high performance using galvanic oxidation of Al overlayers.