Preparation of transparent conducting Ga-doped ZnO and Al-doped ZnO Bilayers by using r.f. magnetron sputtering with ZnO buffer layers on polymer substrates

Al-doped ZnO (AZO) and Ga-doped ZnO (GZO) thin films were sequentially deposited on polymer (polyethylene terephthalate: PET) substrates with ZnO buffer layers by using a radio-frequency (r.f.) magnetron sputtering technique, and the effects of the buffer layer thickness on the microstructure and the electrical and the optical properties of the GZO/AZO/ZnO multilayers films were investigated to develop transparent conductors for flexible display applications. The optimum buffer layer thickness with which the lowest resistivity of the GZO/AZO/ZnO films was obtained was determined to be 140nm. The carrier concentration, the carrier mobility and the electrical resistivity of the GZO film with a 150-nm-thick ZnO buffer layer were 6.8 x 10(20) cm(-3), 11.0 cm(2) /Vs and 8.3 x 10(-4) Omega cm, respectively. The transmittance of the GZO/AZO/ZnO films was found to be higher than 85% and to be nearly independent of the ZnO buffer layer thickness.