Abstract
Growth of GaAs nanowires (NWs) on Si substrates has potential applications in novel photovoltaic devices and optoelectronic integrated circuits with low cost. Over the past several years, the synthesis of GaAs NWs on Si has predominantly been investigated by using metal organic vapor phase epitaxy via the Au-catalyzed vapour-liquid-solid (VLS) mechanism. Much fewer studies have employed the molecular beam epitaxy (MBE) technique. In this study, we present a systematic study on the MBE growth of high quality GaAs NWs on Si (111) substrates by Au-assisted VLS method. The morphology and crystal structure of GaAs NWs were investigated as a function of the substrate temperature, growth time, and V/III flux ratio during MBE growth, as well as the Au film thickness, using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. We found that the nanowires grown with a As/Ga flux ratio of 25 at 540 °C exhibit a defect-free Zinc blende structure. Furthermore, we demonstrated the growth of defect-free GaAs core-shell nanowires with uniform diameter. The GaAs core was first grown at 540 °C with a As/Ga flux ratio of 25, followed by the GaAs shell grown at 400 °C using a lower As/Ga flux ratio of 8.33. Finally, we investigated the incorporation of Si and Be in nanowires, which lead to n-type and p-type GaAs NWs, respectively.