Growth and characterization of ZnO film on Si(1 1 1) substrate by helicon wave plasma-assisted evaporation

Abstract

We investigated ZnO film on Si(1 1 1) substrates grown by high density helicon wave oxygen plasma (>10 11/cm 2) assisted evaporation, which is a potentially promising approach for growing epitaxial oxide semiconductor films without causing surface damage. Adequate addition of Ar into oxygen plasma enhances production of excited atomic oxygen utilized for epitaxial oxide film growth. ZnO films could not be directly deposited on Si(1 1 1) substrate at temperatures greater than 600°C due to large thermal expansion coefficient difference and lattice mismatching. In this work, however, ZnO films were deposited on Si substrate up to 780°C after introducing low temperature (LT) ZnO buffer layers. In addition, adopting LT ZnO buffer layers turns out to significantly improve both crystal quality and optical properties. Structural and optical properties were characterized with the aid of X-ray diffraction (XRD), photoluminescence (PL), and field emission scanning electron microscopy (FE-SEM). As the growth temperature increases, the FWHM value of the XRD θ-rocking curve decreases significantly. The result of PL spectra for ZnO film deposited in the temperature 600–680°C range shows strong and sharp excitonic emission with very weak deep-level emission. In contrast, beyond these temperatures, relatively strong deep-level emission peak appears at 1.9 eV and the FWHM value of near-band-edge emission peak broadens. FE-SEM shows typical ZnO hexagonal columns but as growth temperature increases, each column collapsed, which influenced optical emission property.