Energy-level variations of Cu-doped ZnO fabricated through sol-gel processing

We evaluated the properties and energy levels of Cu-doped ZnO (CZO) crystals synthesized in different Cu ion additions through sol-gel processing. Different CZO crystals were synthesized with Zn-OH and Cu-OH as precursors under sol-gel reactions in base solutions. The properties of the synthesized CZO samples were characterized and the energy levels of the samples were determined. Results showed that the grain size and bandgap energy (Eg) of the CZO crystals decreased, as the proportion of Cu in the ZnO increased. The lattice volume of the CZO crystals was distorted in the presence of Cu. The lowest resistivity of the CZO sample films was determined for the CZO sample with 3% Cu addition (3CZO). The conduction band energy (Ec), valence band energy (Ev), and Fermi energy (EF) levels were estimated and varied because of the presence of Cu in ZnO. The lower resistivity of CZO was analyzed and attributed to the energy level variations that occurred on the basis of the lattice distortion in the CZO crystals.