Mohanchand Paladugu

Structural characteristics of GaSb∕GaAs nanowire heterostructures grown by metal-organic chemical vapor deposition

Highly lattice mismatched (7.8%) GaAs/GaSb nanowire heterostructures were grown by metal-organic chemical vapor deposition and their detailed structural characteristics were determined by electron microscopy. The facts that (i) no defects have been found in GaSb and its interfaces with GaAs and (ii) the lattice mismatch between GaSb/GaAs was fully relaxed suggest that the growth of GaSb nanowires is purely governed by the thermodynamics. The authors believe that the low growth rate of GaSb nanowires leads to the equilibrium growth. (c) 2006 American Institute of Physics.

Nature of heterointerfaces in GaAs/InAs and InAs/GaAs axial nanowire heterostructures

The Australian Research Council was acknowledged for the financial support of this project.

Evolution of Epitaxial InAs Nanowires on GaAs (111)B

A systematic investigation of the Au catalyst-assisted growth of epitaxial InAs nanowires (NW) on GaAs substrates was presented. Scanning electron microscopy (SEM) images of InAs NWs with different growth times show no vertical NWs in the sample with 1 min growth of InAs. High resolution transmission electron microscopy (HRTEM) investigations performed at the trace/substrate interface to determine the strain status show many misfit dislocations at the InAs/GaAs interface. The interfacial energy of InAs/Au is found to be higher than that of GaAs/Au, and these energetic considerations result in the Au catalysts retaining contact with GaAs. Vertical NWs initiate at trace intersections where the Au catalysts can not retain interfaces with the GaAs substrate. HRTEM image showing the junction between the base and InAs trace clearly present the epitaxially grown base on the InAs trace.

Polytypic InP Nanolaser Monolithically Integrated on (001) Silicon

On-chip optical interconnects still miss a high-performance laser monolithically integrated on silicon. Here, we demonstrate a silicon-integrated InP nanolaser that operates at room temperature with a low threshold of 1.69 pJ and a large spontaneous emission factor of 0.04. An epitaxial scheme to grow relatively thick InP nanowires on (001) silicon is developed. The zincblende/wurtzite crystal phase polytypism and the formed type II heterostructures are found to promote lasing over a wide wavelength range.

Polarity driven formation of InAs/GaAs hierarchical nanowire heterostructures

The structural and morphological characteristics of InAs/GaAs radial nanowire heterostructures were investigated using transmission electron microscopy. It has been found that the radial growth of InAs was preferentially initiated on the {112}A sidewalls of GaAs nanowires. This preferential deposition leads to extraordinarily asymmetric InAs/GaAs radial nanowire heterostructures. Such formation of radial nanowire heterostructures provides an opportunity to engineer hierarchical nanostructures, which further widens the potential applications of semiconductor nanostructures.

Formation of Hierarchical InAs Nanoring/GaAs Nanowire Heterostructures

(Figure Presented) Rings around the wire: Novel hierarchical heterostructures, assembled by radial deposition of InAs on GaAs nanowires with nonplanar side walls, result in the formation of InAs nanorings. The mechanism of formation of such structures, determined by transmission electron microscopy, involves the preferential nucleation of InAs at concave regions of the GaAs surface by capillarity effects.

Evolution of InAs branches in InAs/GaAs nanowire heterostructures

The Australian Research Council is acknowledged for the financial support of this project. One of the authors M.P. acknowledges the support of an International Postgraduate Research Scholarship.

Evolution of Wurtzite Structured GaAs Shells Around InAs Nanowire Cores

GaAs was radially deposited on InAs nanowires by metal–organic chemical vapor deposition and resultant nanowire heterostructures were characterized by detailed electron microscopy investigations. The GaAs shells have been grown in wurtzite structure, epitaxially on the wurtzite structured InAs nanowire cores. The fundamental reason of structural evolution in terms of material nucleation and interfacial structure is given.

III-V nanowires for optoelectronics

The optical and structural properties of binary and ternary III-V nanowires including GaAs, InP, In(Ga)As, Al(Ga)As, and GaAs(Sb) nanowires by metal-organic chemical vapour deposition are investigated. Au colloidal nanoparticles are employed to catalyze nanowire growth. Zinc blende or wurtzite crystal structures with some stacking faults are observed for these nanowires by high resolution transmission electron microscope. In addition, the properties of heterostructure nanowires including GaAs-AlGaAs core-shell nanowires, GaAs-InAs nanowires, and GaAs-GaSb nanowires are reported. Single nanowire luminescence properties from optically bright InP nanowires are reported. Interesting phenomena such as two-temperature procedure, nanowire height enhancement of isolated ternary InGaAs nanowires, kinking effect of InAs-GaAs heterostructure nanowires, and unusual growth property of GaAs-GaSb heterostructure nanowires are investigated. These nanowires will play an essential role in future optoelectronic devices.

Microstructure and Mechanical Properties of Cast Ti25Nb3Mo3Zr2Sn Alloy

The microstructure and mechanical properties of a cast near β type titanium alloy, Ti-25Nb-3Zr-3Mo-2Sn, have been investigated in this paper. In the as cast condition, the alloy possesses coarse, equiaxed β grains and Transmission Electron Microscopy(TEM) observations showed the ω phase is also present in this condition. The alloy in the as cast condition has low strength and is highly ductile. Direct ageing at 450°C for 4 hours leads to the formation of a large number of fine scale α phase precipitates. The alloy in the aged condition is less ductile but exhibits significantly enhanced strength.