Size-dependent conductivity type inversion in CU₂O nanoparticles

X-ray photoemission spectroscopy and optical absorption studies have been carried out on Cu₂O nanoparticles prepared using the activated reactive evaporation technique. A strong shift of the valence band edge (from 0.7 to 1.8 eV) has been observed on reduction of the nanoparticle size from 20 nm to 4 nm. The size-dependent modifications in the energy level diagram and metal-Cu₂O nanoparticle Schottky junction characteristics confirm the observation of the inversion of conductivity type from p-type bulk conductivity to n-type conductivity in Cu₂O nanoparticles at lower dimensions. This study can initiate a further methodology for tailoring the semiconductor properties of a material by controlling the nanoparticle size.