K doping effect on structural and optical properties of ZnO nanorods grown on semipolar (112-2) GaN films using a hydrothermal growth method

Abstract

In this work, we investigated the potassium (K) doping effect on structural and optical properties of ZnO nanorods grown on semipolar (112-2) GaN films using a hydrothermal growth method. The X-ray diffraction θ-2θ scan of the ZnO nanorods without any seeding step showed that most of the single-crystalline ZnO nanorods were highly inclined to the c-axis [0001] direction. In the case of hydrothermally-grown K-doped ZnO nanorods, growth occurred not only in the normal [112-2] direction, but also along the c-axis [0001] and m-axis [101-0] directions. As the growth proceeded even further, micron-sized ZnO pyramids having nonpolar and semipolar planes were formed on the ZnO nanorods. The optical properties of K-doped ZnO nanorods and pyramids were studied using cathodoluminescence measurements. While the near band edge peak was centered at 382 nm for pure c-plane ZnO nanorods, a significant peak shift to 418 nm for the K-doped ZnO nanorods was observed with relatively broad emissions. It is believed that the violet emissions centered at 418 nm are mainly associated with both K interstitial and Zn interstitial defects. Thus, the electron transitions from K interstitial levels to the valence band can lead to relatively strong violet emissions at 418 nm for K-doped ZnO nanorods and pyramids.