Surfactant-mediated molecular beam epitaxy of ZnO

We investigated the effects of atomic hydrogen as a surfactant for plasma-assisted molecular beam epitaxial growth of ZnO. Atomic hydrogen was provided by dissociation of hydrogen gas, and ZnO films were grown on Zn-polar ZnO substrates. The growth mode was observed by using reflected high-energy electron diffraction (RHEED) and the presence of atomic hydrogen enhanced two-dimensional growth. Without atomic hydrogen, ZnO homoepitaxial growth directly on ZnO substrate showed a three-dimensional growth mode. Employing a low-temperature ZnO buffer layer (LT-ZnO) enabled a two-dimensional growth mode. However, with atomic hydrogen, two-dimensional growth mode was achieved without using LT-ZnO. Low-temperature epitaxial growth was also achieved. Atomic force microscopy (AFM) measurements showed that the surfaces of ZnO films grown with atomic hydrogen were quite smooth. The structural and the optical properties were characterized using high resolution X-ray diffraction and photoluminescence. Theses properties were improved by atomic hydrogen irradiation. Thus, hydrogen acts an effective surfactant to enhance the layer by layer growth mode.