Morphology characterization and growth mechanism of Au-catalyzed GaAs and GaAs/InGaAs nanowires

Abstract

The nanowires (NWs) of heterostructure with GaAs based materials have received great attention in the past decades, due to their potential applications in electronics and optoelectronics. Therefore it becomes more and more important to investigate the technology of fabricating NWs with GaAs based materials. In our study, Au-catalyzed GaAs nanowires and GaAs/InGaAs heterostructures are grown by metal-organic chemical vapor deposition following the vapor-liquid-solid mechanism. The growth process, which is vital for morphology research, is found to be strongly affected by growth temperature via scanning electron microscope testing. The GaAs NWs are grown at varying temperatures to investigate the influence of temperature on NW morphology. It is observed that the axial growth decreases with growth temperature increasing while radial growth exhibits the opposite trend, which causes the length of NWs to decrease with temperature increasing at the same time. As radial growth rate is inhibited and radial growth rate is enhanced at relatively high temperature, the geometry of GaAs nanowires turns from columnar to taper and eventually pyramid with temperature rising. The GaAs/InGaAs nanowire heterostructures with distinct heterostructure interfaces, which are columnar and vertical to substrates, are obtained and analyzed. Energy dispersive X-ray spectroscopy (EDX) is used for element monitoring while radial growth is hardly observed during axial heterostructure fabrication, indicating well controlled fabrication technology of NWs growth. The InGaAs segments of axial heterostructures are grown after GaAs segments and occur at the bottom of NWs instead on the top, the analysis of which shows that In atoms would take part in the growth of NWs via migrating at the surface of substrate preferentially, rather than being absorbed in Au-Ga alloy catalytic droplets. Radial heterostructures of GaAs/InGaAs nanowires are grown with GaAs as cores and InGaAs as shells, respectively. Because the axial growth rate would be restricted with temperature increasing, the growth temperature of radial heterostructures is higher than that of axial heterostructures. A small amount of axial growth occurs during the growth of radial heterostructures as indicated by the EDX monitoring result, which is analyzed to be caused by the diffusion of In atoms at radial growth temperature, resulting in a segment of InGaAs nanowire at the interface of nanowires and Au-Ga alloy catalytic droplets.