HfO2-passivated black phosphorus field effect transistor with long-termed stability and enhanced current on/off ratio

Enhanced on/off ratio, obvious threshold voltage left shift, newly emerging bipolar field effect performance and most importantly, excellent stability in ambient condition have been reported for the HfO2-passivated black phosphorus field effect transistors. Both Raman spectra and x-ray photoelectron spectroscopy (XPS) show a thickness reduction effect after HfO2 passivation, XPS further demonstrates that the formation of P-Hf and P-O chemical bonds contributes to the thinning of layered black phosphorus (BP), in which P-Hf bonds also provide chemical protection for BP flakes from degradation. Atomic force microscopy measures the thickness of the passivation layer and also verifies the stability of the passivated BP flakes.