Comparison of electrical, optical, and structural properties of RF-sputtered ZnO thin films deposited under different gas ambients

Transparent conducting ZnO:Al thin films were prepared by rf-magnetron sputtering under different gas ambients at 300 degrees C. The electrical resistivity varied from 1.23 x 10(-1) to 2.8 x 10(-4) Omega cm introducing O-2 and H-2 gas with Ar ambient. The minimum sheet resistance of ZnO:Al film is 3.5 Omega/square. The maximum carrier concentration and Hall mobility as estimated from Hall effect measurement of the films were 2.3 x 10(21)/cm(3) and 44.4 cm(2) V-1 s(-1) respectively. Photoluminescence (PL) spectra peaks are mainly in the blue emission region and change from 432 nm (2.87 eV) and 541.5 nm (2.29 eV) with the change of gas ambients. From the X-ray diffraction (XRD) pattern exhibiting only the (002 peak of ZnO, all films were found to be c-axis-oriented. The crystallite size varies from 150 to 288 angstrom for different films calculated from (002) orientation of XRD data. The characteristic features of ZnO films prepared under Ar + H-2 ambient are their high carrier concentration, high strain values, high band gap and blue emission compared to the other ZnO films. The structural, electrical, optical properties and surface topography of ZnO thin films using XRD, Hall measurements, PL, UV-visible (vis)-near IR (NIR) spectroscopy and atomic force microscopy (AFM) have been investigated.