Dependences of structural and electrical properties on thickness of polycrystalline Ga-doped ZnO thin films prepared by reactive plasma deposition

Polycrystalline Ga-doped (Ga content: 4 wt%) ZnO (GZO) thin films were deposited on glass substrates at 200 ∘C by a reactive plasma deposition with DC arc discharge technique. The dependences of structural and electrical properties of GZO films on thickness, ranging from 30 to 560 nm, were investigated. Carrier concentration, nn, and Hall mobility, μμ, increases with increasing film thickness below 100 nm, and then the nn remains nearly constant and the μμ gradually increases until the thickness reaches 560 nm. The resistivity obtained of the order of 10−4 Ω cm for these films decreases with increasing film thickness: The highest resistivity achieved is 4.4×10−4 Ω cm with nn of 7.6×1020 cm−3 and μμ of 18.5 cm2/V s for GZO films with a thickness of 30 nm and the lowest one is 1.8×10−4 Ω cm with nn of 1.1×1021 cm−3 and μμ of 31.7 cm2/V s for the GZO film with a thickness of 560 nm. X-ray diffraction pattern for all the films shows a hexagonal wurtzite structure with its strongly preferred orientation along the cc-axis. Full width at half maximum of the (002) preferred orientation diffraction peak of the films decreases with increasing film thickness below 100 nm.