Modeling of carbon nanotube Schottky barrier modulation under oxidizing conditions

A model is proposed for the previously reported lower Schottky barrier Phi(Bh) for hole transport in air than in vacuum at a junction between the metallic electrode and semiconducting carbon nanotube (CNT). We consider the electrostatics in a transition region between the electrode and CNT in the presence or absence of oxygen molecules (air or vacuum), where an appreciable potential drop occurs. The role of oxygen molecules is to increase this potential drop with a negative oxygen charge, leading to lower Phi(Bh) in air. The Schottky barrier modulation is large when a CNT depletion mode is involved, while the modulation is negligible when a CNT accumulation mode is involved. The mechanism prevails in both p- and n-CNT's, and the model consistently explains the key experimental findings.