Elucidating the Conductivity-Type Transition Mechanism of p-Type Cu2O Films from Electrodeposition

Narrow bandgap Cu2O films of p- and n-type conductivities are electrodeposited on conducting glass substrates from aqueous Na2SO4 solutions. These Cu2O films exhibit photoelectrochemical responses under visible light illumination. The p- and n-type films have different preferred out-of-plane orientations of [111] and [100], respectively. X-ray absorption fine structure spectroscopic analysis shows that the n-type Cu2O contains a higher degree of lattice disorder. Ultraviolet photoelectron spectroscopy along with the Mott-Schottky electrochemical impedance analysis determines the energy-level diagrams of both the p- and n-type films. On the basis of the structural features obtained, this paper finds that strong Cu2+ absorption on the unstable surface states resulting from the Cu vacancies of Cu2O can lead to the formation of an inversion layer and thus conductivity transition from p to n type. As a consequence of this p-n transition mechanism, Cu2O films containing nanocavities for strong Cu2+ absorption exhibit an n-type conductivity, while intact Cu2O films are p type. A conductivity-type diagram is constructed to show that a subtle change in the deposition parameters can tune the crystal orientation and conductivity type of Cu2O films. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3125800] All rights reserved.