Effects of oxygen partial pressure on film growth and electrical properties of undoped ZnO films with thickness below 100Â nm

The dependences of electrical and structural properties on film thickness below 100 nm have been studied on polycrystalline undoped zinc oxide (ZnO) thin films on glass substrates at 200 °C prepared by plasma-assisted electron-beam deposition. From Hall effect measurements, we find that resistivity decreases from 0.47 to 0.02 Ω cm with increasing film thickness, whereas carrier concentration remains almost constant, 1.65-2.0 × 1019 cm− 3, Hall mobility increases from 1.7 to 16.7 cm2/Vs with increasing film thickness. From both high-resolution out-of-plane and in-plane X-ray diffraction (XRD) data, we find substantial changes in the lattice parameters with increasing film thickness below 40 nm; a reduction in the lattice parameter of the a-axis and an increase in the lattice parameter of the c-axis. Williamson-Hall analysis reveals an increase in in-plane grain size with increasing film thickness. This indicates that the dominant scattering mechanism that determines electrical properties is a boundary scattering mechanism.