Controlling structural quality of ZnO thin film on c-plane sapphire during pulsed laser deposition

The pulsed laser deposition (PLD) of ZnO thin film on c-plane sapphire has been studied as a function of various growth parameters such as nucleation layer temperature, annealing duration, laser pulse frequency, number of steps of ZnO deposition, final growth temperature and pressure. Among various growth parameters, laser pulse frequency was found to have significant influence to form single crystal ZnO film on c-plane sapphire through elimination of misaligned crystal domains completely. Allowing relaxation to the seeding layer by slowing down laser pulse frequency to 1 Hz established the complete epitaxial relationship between ZnO and sapphire over large plan view area, which is confirmed by plan view single crystal diffraction pattern, whereas ZnO grown at 5 Hz laser pulse frequency showed significant rotation between crystallites as evident from ring diffraction pattern from plan view TEM image. Using higher pressure (10−2 Torr) forms ZnO nanobullet during second stage of growth. AFM surface roughness improved to ∼2.4 nm for the sample grown with relaxed nucleation layer. Hall mobility also increased to ∼58 cm2 V−1 s−1 for this sample.

► Pulse laser deposition of ZnO with low laser pulse frequency. ► Epitaxial improvement with low laser frequency. ► Plan view TEM images and diffraction pattern from ZnO under different growth condition.