Doping effects on electrical and optical properties of spin-coated ZnO thin films

• ZnO, ZnO(Ga), ZnO(In), ZnO(Ga,In) films were obtained by spin-coating technique.
• Increase of Ga and In content leads to the decrease of ZnO grain size.
• Introduction of indium in ZnO and ZnO(Ga) results in the decrease of resistivity.
• Addition of small Ga amount in ZnO and ZnO(In) leads to the transmittance increase.
• Co-doping of ZnO with Ga and In is preferable comparing to single-doping.

Undoped ZnO, as well as Ga-, In-doped and (Ga,In) co-doped ZnO thin films were deposited on glass substrates by the spin-coating technique. The effect of cation composition on the structural, morphological, optical and electrical properties of ZnO-based films was studied. Introduction of 1.0–1.3 at% of Ga in ZnO and ZnO(In) results in the enhancement of electrical and optical properties of the films. Introduction of indium leads to the decrease of resistivity. Introduction of both elements allows to improve the optical properties (the average transmittance achieves 97% in the range 400–800 nm) and to increase the conductivity up to 3.6 S/cm that is three orders of magnitude higher than the corresponding value for undoped ZnO. The effect of conductivity increase may be caused by the increase of donor elements solubility in ZnO structure for co-doped films as compared to single-doped ZnO due to the decrease of the lattice strain.