Electron hopping interactions in amorphous ZnO films probed by x-ray absorption near edge structure analysis

The x-ray absorption near edge structures of amorphous ZnO (a-ZnO) films were examined. The near-edge structure, which reflects the virtual electron hopping interactions in the photoabsorption final states, increased in intensity compared to crystalline ZnO. Theoretical path-by-path analyses revealed that this reflects the extinction of the multiple hopping processes found in paths such as Zn→O→ O′ →Zn or Zn→O→ Zn′ →Zn while the Zn-(O or Zn) hopping interactions remain. This suggests that the structural disorders in a-ZnO can induce the localization of the conduction band through the limited hopping interactions.