Preparation of ZnO thin films using MOCVD technique with D2O/H2O gas mixture for use as TCO in silicon-based thin film solar cells

Zinc oxide (ZnO) thin films have been successfully grown by metal organic chemical vapor deposition (MOCVD) technique using deuterium water (D2O) and water (H2O) mixtures as oxidants for diethylzinc (DEZ). B2H6 was also employed as a dopant gas. It was found that the crystal orientation of ZnO films strongly depends on D2O/H2O ratio. As a result, the surface morphology of ZnO changed from textured surface morphology to smooth surface morphology with increase in the ratio of D2O/H2O. Moreover, it was also observed that the carrier concentration of ZnO films did not change with the ratio of D2O/H2O, while the mobility of these films was strongly dependent on the D2O/H2O ratio. Without D2O addition, the resistivity of films had its lowest value and the minimum sheet resistance was 10 Ω/square. All films showed transmittance higher than 80% in the visible region. Moreover, the haze values of these films could be controlled by the ratio of D2O/H2O. These results indicate that the crystal orientation and surface morphology of the low resistivity ZnO films can be modified by using a mixture of D2O and H2O without changing the deposition temperature. Thus, the obtained ZnO films are promising for use as a front TCO layer in Si-based thin film solar cells.