Thickness dependence of properties of ZnO thin films on porous silicon grown by plasma-assisted molecular beam epitaxy

Zinc oxide (ZnO) thin films with different thicknesses were grown on Si and porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The effects of the thickness and PS on the properties of the ZnO thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL). The ZnO thin films grown on PS exhibit a very smooth surface morphology even at a growth time of 5 min, which indicates that the films are in the 2D mode of grain growth. It is suggested that the optical properties, as well as the structural properties, of the ZnO thin films are enhanced by introducing PS. Also, the structural and the optical properties are improved as the thickness is increased.