Empty Valence‐Band Pocket in p‐Type Cu2O(111) Probed with Scanning Tunneling Spectroscopy

Abstract

Scanning tunneling spectroscopy is used to probe the surface electronic structure of (√3×√3)‐reconstructed cuprous oxide films on Au(111). In analogy to bulk Cu2O(111), the films show a pronounced p‐type nature with the valence‐band top pinned to the Fermi level and the conduction‐band onset located at +2.0 V. A conductance dip appears directly at zero bias in the dI/dV spectra, followed by an asymmetric dI/dV maximum inside the lower half of the bandgap. Several scenarios are considered to explain this unusual conductance behavior. The most likely interpretation is based on the accumulation of hole states in the p‐type material in response to the tip‐electric field and the development of an empty valence‐band pocket directly below the tip. Tunneling into these states leads to a finite dI/dV intensity even inside the Cu2O bandgap. A 1D tunneling model that accounts for this field‐dependent transport mechanism successfully reproduces the experimental data and rationalizes the impact of current setpoint, oxide thickness, and surface reconstruction on the observed spectral response.