  A first-principles study has been performed to evaluate the electronic and
optical properties of wurtzite Zn1-xCdxO up to x=0.25. We have employed the
Perdew-Burke-Ernzerhof (PBE) form of generalized gradient approximation within
the framework of density functional theory (DFT). Calculations have been
carried out in different configurations. With the increasing Cd concentrations,
the band gap of Zn1-xCdxO is decreased due to the increase of s states in
conduction band. The results of imaginary part of dielectric function indicate
that the optical transition between O 2p states in the highest valence band and
Zn 4s states in the lowest conduction band has shifted to low energy range as
the Cd concentrations increase. Besides, the optical band gap decreases from
3.2 to 2.84 eV with increasing Cd concentrations from 0 to 0.25. Meanwhile, the
bowing parameter b, which has been obtained by fitting the results of optical
band gap, is about 1.21 eV. The optical constants of pure ZnO and
Zn0.75Cd0.25O, such as optical conductivity, loss function, refractive index
and reflectivity, have been discussed.
