Understanding and Optimization of III-V nanowire growth in Aerotaxy

III-V semiconductor nanowires are high aspect ratio nanostructures with superior properties that can potentially enhance the functionality of next-generation opto-electronic devices. At present, the most reliable method for fabricating III-V semiconductor nanowires is the particle-assisted vapor-liquid-solid growth using a substrate-based growth process. However, a substrate-based process limits the number of nanowires that can be produced per cycle and is an obstacle to the industrial production of III-V nanowires. A viable alternative technology for the high-throughput synthesis of III-V nanowires is vital to exploit the true potential of III-V semiconductor nanowires. Aerotaxy is a gas-phase vapor-liquid-solid growth technology that can mass-produce III-V semiconductor nanowires without a substrate. It reduces the cost of production by eliminating the need for a crystalline substrate and can produce nanowires at a phenomenal rate.
This thesis explores the fundamental limits of the Aerotaxy technology in producing III-V nanowires. GaAs and GaAsP material systems were adopted to explore the fundamentals of Aerotaxy nanowire growth. Growth experiments were designed to probe the growth parameter dependence of nanowire properties like morphology, crystal structure and composition. In addition to that, the efficiency of in situ doping (p- and n- type) in Aerotaxy was evaluated using optical and electrical characterization techniques. The growth parameter space was explored to demonstrate the reproducibility and efficiency of Aerotaxy nanowire growth. To better understand the growth, a pseudo-particle continuum model for Aerotaxy growth was developed. The results from the model shows good agreement with experimental quantitative and qualitative observations.
The studies presented in the thesis also explores the fabrication of complex nanostructures like branched GaAsP nanowires. By tuning the diameter of the initial catalytic particle, we were able to induce branching in GaAsP nanowires. Apart from that, GaAs nanowires grown from alternative metal particles like Ga, AuAg and Ag in Aerotaxy shows promising initial results. Mass-producing III-V nanowires using alternative seed metals that are compatible with Si could bring novel functionalities while reducing production costs. The importance nano-safety is also highlighted in the context of a high-throughput production environment.