K doping effect on structural and optical properties of ZnO nanorods grown on semipolar (11(2)over-bar2) 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 (11 (2) over bar2) GaN films using a hydrothermal growth method. The X-ray diffraction theta-2 theta 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 (11 (2) over bar2) direction, but also along the c-axis [0001] and m-axis [10 (1) over bar0] 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. (C)2015 Optical Society of America