Growth and characterisation of InP-based core-shell nanowires for optoelectronic device applications

Abstract

In order to achieve high performance III-V nanowire heterostructure based devices, it is essential that the heterostructures are of good structural and optical quality. Hence controlling the morphology and crystal structure is a critical factor in the nanowire heterostructure growth. Au-nanoparticle assisted vapour-liquid-solid (V-L-S) technique is one of the superior methods used in recent years for nanowire growth.

This thesis investigates InP-based core-shell nanowire growth by the metal organic chemical vapour deposition (MOCVD) on (111)B InP substrates via V-L-S growth mechanism. The microstructure of core-shell nanowires is characterised by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Micro-photoluminescence and micro-Raman measurements are carried out to study the optical properties.

The growth of InP/In<subscript>xGa{u2081}-<subscript>xAs and InP/In<subscript>xGa{u2081}-<subscript>xP core-shell nanowires is investigated in this work to study the effect of shell composition on nanowire morphology, crystal structure and optical properties. The morphology of InP/In<subscript>xGa{u2081}-xAs nanowires depends on the shell composition. It is found that along with the InGaAs shell growth, significant axial growth of the InGaAs also occurs and with the increase in In composition, this axial component increases proportionately. The InP nanowire core and the InGaAs shell have a wurtzite crystal structure but the axial section of InGaAs has a defect free zinc-blende phase underneath the Au particle. InP/In<subscript>xGa{u2081}-xAs core-shell nanowires showed PL emissions from both InP core and the InxGa{u2081}-<subscript>xAs shell at 4K with a 40meV redshift in the InP PL emission from nanowires with xv,In{u2265}0.51.

In the case of InP/In<subscript>xGa{u2081}-xP core-shell nanowires, with higher In composition (xv,In> 0.50) in the In<subscript>xGa{u2081}-xP shell, uniform and smooth shell formation around the core is observed. Room temperature photoluminescence is observed from the nanowires (0 < x<subscript>v,In < 0.90) which indicates the good crystal quality. Core-shell nanowires with x<subscript>v,In < 0.50 show PL emission at {u223C}1.46eV at 300K, corresponding to the emission peak of wurtzite InP nanowires. A dramatic blueshift in the photoluminescence emission is observed from samples with x<subscript>v,In> 0.50 , ranging from 1.48eV to 1.55eV, which is comparable with photoluminescence observed from In<subscript>xGa{u2081}-xP epilayer grown with x<subscript>v,In > 0.50. Raman scattering results showed no evidence of strain induced shift in the InP-like phonon modes. Show more