First-principles calculations of Cd-doped ZnO thin films deposited by pulse laser deposition

Zn1−xCdxO thin films are deposited on quartz substrate by pulse laser deposition. Their band structure and optical properties are experimentally and theoretically investigated. By varying Cd concentration, the band gap of Zn1−xCdxO films can be adjusted in a wide range from 3.219 eV for ZnO to 2.197 eV for Zn0.5Cd0.5O, which produces different emissions from ultraviolet to Kelly light in their photoluminescence spectra. Simultaneity, the electronic structure and band gap of Zn1−xCdxO are investigated by the density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach, which precisely predicts the band-gaps of ZnO and Zn1−xCdxO alloys. Both the experimental results and theoretical simulation reveal that with increasing Cd concentration in Zn1−xCdxO alloys, their absorption coefficients in visible light range are evidently enhanced. The adjustable photoluminescence emission and enhanced visible light absorption endow Zn1−xCdxO alloys potential applications in optoelectronic and photocatalytic fields.

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► A combined experimental and theoretical model investigated for Cd-doped ZnO thin films.
► Our results show that Cd-doped ZnO is n-type impurity dopants, CdO and Cdi are donors and they can compensate p-type doping.
► The experimental observed very wide visible light emission may be attributed to the crystalline defects introduced by Cd doping.
► The optical band gap and optical transition of ZnO and Zn1−xCdxO alloys have been accurately reproduced by GGA + U approach.