Crystal quality and conductivity type of (0 0 2) ZnO films on (1 0 0) Si substrates for device applications

摘要

Undoped high quality (0 0 2) zinc oxide thin films were grown on (1 0 0) silicon substrates by pulsed laser deposition (PLD). The films were developed at low growth temperatures between 200 and 300 ℃, and a range of oxygen pressures from 8.5 × 10~(-5) to 2.6 × 10~(-4)Torr. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and room temperature photoluminescence (PL) have been carried out in order to verify the formation of ZnO layers and evaluate the structural and optical properties of the grown layers. Four-point Van Der Pauw Hall effect measurements were performed to evaluate the electrical conduction in the films. The grown ZnO films on Si were found to be perfectly (0 0 2) aligned polycrystalline structures with a best full-width at half-maximum (FWHM) value of 0.24° obtained for the optimum growth conditions. The PL study showed high optical quality with a substantially suppressed defect related emission band for the optimized conditions. Hall effect measurements showed that samples prepared at oxygen pressures of 1.0 × 10~(-4) Torr and above had p-type conductivity at room temperature, whereas samples grown at lower pressures were n-type. All samples showed n-type conductivity at low temperature (77 K) regardless of the growth conditions, which suggests a thermal competition between donor-like oxygen vacancies and/or oxygen vacancy complexes with hydrogen, and acceptor-like oxygen interstitials and possibly Zn vacancies.