Comparisons of Structural and Optical Properties of ZnO FilmsGrown on Sapphire and Si (001)

Zinc oxide films were grown on sapphire and Si (001) substrates by reactive electron beam evaporation at low substrate temperatures. Atomic force microscopy (AFM), x-ray diffraction (XRD), and photoluminescence excitation (PLE) are employed to characterize the as-grown films. The AFM measurements have shown that all of the ZnO films present the pillar-like growth properties, but the dimensional uniformity of the ZnO crystal pillars grown on sapphire was better than
that on Si (001). The XRD results indicated that the prepared ZnO films both on sapphire and Si (001) were all highly c-axis oriented, their linewidth of ZnO (002) are only 0.19° and 0.28°, respectively. The PLE characterizations revealed the continuum absorption of the samples grown on sapphire. However, in the PLE spectra of the ZnO films grown on Si(001) substrates, a broad peak appears at the high energy region, which indicates the formation of ZnO quantum dot structures on Si(001).