Growth and Characterisation of Gold-seeded Indium Gallium Arsenide Nanowires for Optoelectronic Applications

Abstract

III-V semiconductor nanowires have been shown as promising candidates to serve as building blocks in electronic and optoelectronic devices such as transistors, lasers, light emitting diodes, photodiodes and solar cells. Among the III-V semiconductors, ternary III-V alloy semiconductors such as InxGa1-xAs have the advantage of tunable bandgap by varying their alloy composition covering the important wavelengths used in optical telecommunication systems and sensing in near infra-red region. Therefore, it is essential to gain an understanding and control of ternary nanowires prior to incorporating them in device applications.

This thesis presents a progressive advancement of Au-seeded InxGa1-xAs nanowire growth by metal-organic vapour phase epitaxy (MOVPE), towards achieving highly uniform composition, morphology and pure crystal phase. Several techniques have been employed to investigate the nanowire properties. Scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) have been used for structural and compositional analysis, while photoluminescence (PL) has been used to provide insight into their optical properties.

Pure zinc-blende (ZB) phase InxGa1-xAs nanowires are obtained via two-temperature growth method, which involves growing an initial stub at a higher temperature followed by a lower growth temperature. Low-temperature growth is found to favour high In incorporation rate either via the vapour-liquid-solid (VLS) mode or the vapour-solid (VS). InxGa1-xAs nanowires with highly homogenous composition and pure ZB phase are achieved when the In incorporation rates in both modes are equivalent.

Homogenous composition InxGa1-xAs nanowires can also be achieved at relatively high temperatures with tunable crystal phase. Detailed TEM analysis in combination with the EDX show that the crystal phase is dependent on the V/III ratio, and correlates with the Ga incorporation rate in the nanowire. Pure wurtzite (WZ) phase, uniform and taper-free nanowires are obtained with a combination of relatively high growth temperature, low V/III ratio and small diameter Au seed particle. The optimized pure WZ phase nanowires capped with InP show luminescence properties around 1.54 um, a wavelength region of importance to the optical fibre telecommunications.

Understanding the growth evolution of InxGa1-xAs nanowires is improved by developing a model based on a nucleation kinetics approach. The modelling correlates well with the experimental results revealing the key factors governing the composition and growth rate of InxGa1-xAs nanowires.

Finally, tunable emission wavelengths of InxGa1-xAs /InGaP core-shell structures within the range of 1100 - 1420 nm are achieved by tuning the shell thickness. The growth of the complex ternary/ternary system is studied using TEM and EDX analyses, revealing some challenges in the growth of the shell. Despite the challenges, a strain related blue-shifting of the InxGa1-xAs bandgap is demonstrated.

Overall the thesis makes a significant progress in understanding the growth of Au-seeded InxGa1-xAs nanowires. From the systematic study, the growth of highly uniform InxGa1-xAs nanowires grown via Au-seeded VLS method is demonstrated. A growth model is developed to further understand the growth mechanism. The optimized nanowires in combination with an InP or InGaP shell show luminescence properties tunable within the near infra-red region, promising as future optoelectronic building blocks. Show more