Investigations on the Crystallographic Orientation Induced Surface Morphology Evolution of ZnO Thin Films and Their Wettability and Conductivity

The intrinsic zinc oxide (ZnO) thin films with controllable crystallographic orientation have been synthesized on Si(100) substrates using plasma-enhanced chemical vapor deposition (PECVD) system without any buffer layer. Based on X-ray diffraction (XRD) results, the evolution of crystallographic orientation of ZnO thin films from polar c-plane (0002), polar c-plane and nonpolar m-plane (101̅0) coexist to nonpolar m-plane and a-plane (112̅0) coexist was achieved by a simple factor of controlling synthesized temperature. The plane-view morphological images exhibited that the surface texture and grain shape of ZnO thin films could have evolved from hexagonal to stripelike grains when the ZnO crystallographic orientation changed from perpendicular to parallel to the substrate. The characterization analysis indicated that the zinc precursor [diethylzinc (DEZn), Zn­(C2H5)2] played a key role on the crystallographic orientation evolution of ZnO thin films during the early stage of the growth process because DEZn not only can serve as Zn precursor but also can be employed as passivating agent to influence the crystal growth under different synthesized temperatures. Room-temperature Hall effect measurement showed that intrinsic ZnO thin film with stripelike grains possessed the lowest value of resistivity ∼7.11 × 102 Ω cm, which had an estimated carrier concentration and mobility of about 5.73 × 1014 cm–3 and 15.34 cm2/V s, respectively. The water contact angle (CA) measurement was also provided to determine the surface wettability and surface free energy of ZnO thin films, indicating that CA could be adjusted via different crystallographic orientation of ZnO thin film.