Enhancing ambipolar carrier transport of black phosphorus field-effect transistors with Ni-P alloy contacts

Reducing power consumption and leakage current in complementary metal-oxide semiconductors (CMOSs) has gained importance for further increasing the transistor density. An effective strategy to achieve this is to use ambipolar carrier transport that can exploit both holes and electrons in a single transistor. We report the enhancement of ambipolar behavior in black phosphorus (BP) field-effect transistors (FET) by forming a low-resistance Ni₂P alloy contact via low-vacuum annealing at 250 °C, where the transformation of BP into Ni₂P alloy selectively occurred at the source/drain electrodes with the BP channel remaining pristine. The N-channel current on/off ratio and field-effect electron carrier mobility of BP FETs were improved by 98% and 1290%, respectively. Our results suggest that high-performance ambipolar BP FETs with low-resistance ohmic contacts can be achieved via low-temperature vacuum annealing for next-generation CMOS applications.