New Paper: Defect-Free Axially Stacked GaAs/GaAsP Nanowire Quantum Dots with Strong Carrier Confinement

Transmission electron microscopy and room-temperature photoluminescence of a dot-in-wire structure.

In a new collaboration between Yunyan Zhang and Profs. Huiyun Liu (UCL), Ana Sanchez (Warwick) and David Mowbray (Sheffield) we report the fabrication and measurement of a GaAs/GaAsP quantum dot-in-wire structure in Nano Letters.

While many material architechtures have been explored for single photon emission, the GaAsP-GaAs system provides strong carrier confinement and sharp interfaces, and can be grown directly onto a silicon substrate. This is a new route to silicon integrated single photon devices.

Reference: Defect-Free Axially Stacked GaAs/GaAsP Nanowire Quantum Dots with Strong Carrier Confinement, Yunyan Zhang, Anton V. Velichko, H. Aruni Fonseka, Patrick Parkinson, James A. Gott, George Davis, Martin Aagesen, Ana M. Sanchez, David Mowbray, and Huiyun Liu, Nano Lett. (2021), DOI: 10.1021/acs.nanolett.1c01461

New Publication: Self-Catalyzed AlGaAs Nanowires and AlGaAs/GaAs Nanowire-Quantum Dots on Si Substrates

A new collaborative paper led by Giorgos Boros and the team of Xuezhe Yu and Huiyun Liu at University College London has been published in J Phys Chem C. In this work, Giorgos reported the development of high quality ternary nanowires (AlGaAs) grown via MBE. While the AlGaAs/GaAs heterostructure system is well known in planar films, it has proven challenging to explore in the nanowire architecture.

Reference: Self-Catalyzed AlGaAs Nanowires and AlGaAs/GaAs Nanowire-Quantum Dots on Si Substrates, Giorgos Boros et al., J Phys Chem C. 2021, DOI: 10.1021/acs.jpcc.1c03680

New Paper : Facet-Related Non-uniform Photoluminescence in Passivated GaAs Nanowires

(Left) SEM image of a single 250nm diameter GaAs nanowire with {112} facets highlighted and (Right) recombination measured in the {110} region (blue) and {112} region (red), showing emission quenching at these surfaces.

Our collaborative work on spatially inhomogeneous recombination in semiconductor nanowires has been published in a special issue of Frontiers in Chemistry. The work, led by Dr. Nian (Jenny) Jiang at the University of Cambridge reports the spatially varying emission intensity from passivated nanowires. By comparing the bulk emission to buried quantum well emission, we show that the a reduction in emission is related to {112}-faceted surfaces at the base of the wires.

This work solves a long-standing question in optoelectronic nanowires – why does the emission vary for nominally uniform structures? It provides two routes to avoiding this variation, through quantum well emission and by tuning the surface reconstruction to favour {110} side-walls.

Reference: Facet-Related Non-uniform Photoluminescence in Passivated GaAs Nanowires, Nian Jiang, Hannah Joyce, Patrick Parkinson, Jennifer Wong-Leung , Hark Hoe Tan and Chennupati Jagadish, Frontiers in Chemistry, 8, 1136 (2020), DOI: 10.3389/fchem.2020.607481

New Paper: Carrier dynamics and recombination mechanisms in InP twinning superlattice nanowires

(a) Twinning superlattice nanowire on substrate, (b) high-resolution SEM and (c) TEM image showing superlattice.

A new paper has been published in Optics Express, led by collaborator Xiaoming Yuan at Central South University (Changsha) and growth colleagues in the group of Prof. Jagadish at Australian National University.

In this work, novel “twinning-superlattice” nanowires are grown. Once passivated, this growth method produces extremely high quality nanowires, with carrier lifetimes of over 7ns. This work made use of the Manchester iTCSPC spectrometer, built by group PhD student Stefan Skalsky to study the low fluence dynamics at room temperture.

This growth method opens up a new facet in crystal-phase engineering for nanowire optoelectronics.

Reference: Carrier dynamics and recombination mechanisms in InP twinning superlattice nanowires, Xiaoming Yuan, Kunwu Liu, Stefan Skalsky, Patrick Parkinson, Long Fang, Jun He, Hark Hoe Tan, and Chennupati Jagadish, Optics Express 28, 16795 (2020) DOI: 10.1364/OE.388518

New Project: Big-Data for nano-electronics

Patrick has been awarded a 4-year research fellowship from UKRI for a project on “big-data for nano-electronics”. This Future Leaders Fellowship will enable Patrick to focus on building a research group to develop a new methodology for accelerating the study of functional nanotechnology.

Project Summary

The modern world runs on nanotechnology; we are connected by a fibre-network using nanostructured lasers, and use computers and phones made of nanometre scale transistors. The next generation of nanotechnology promises to incorporate multiple functionalities into single nanomaterial elements; this is “functional nanotechnology”. Here, the size of the material itself provides functionality – for instance for sensing, computing, or interacting with light.  The most powerful and scalable approaches to making these structures use bottom-up or “self-assembled” methods; however, as this production technique emerges from the laboratory and into industry, issues such as yield, heterogeneity, and functional parameter spread have arisen.

Functional performance in these nanomaterials is determined by geometry. As such, variations in size or composition affect performance in complex ways. In this project, I will combine high-speed and high-throughput techniques to measure the shape, composition and performance of hundreds of thousands of functional nanoparticles from each production run. By combining this big data with statistical analytics, I will create a new methodology to understand and then optimize cutting-edge functional nanomaterials, working with academic partners in Cambridge, University College London, Strathclyde, Lund (Sweden) and the Australian National University, and industrial partners including AIXTRON and Nanoco.

The ultimate goal of this project is to enable demonstration and scale-up of transformative devices based on novel nanotechnology, for sensing, computing, telecommunication and quantum technology.

New Paper: Heterostructure and Q-factor engineering for low-threshold and persistent nanowire lasing

Group PhD student Stefan Skalsky’s paper on semiconductor nanowire lasing has just been published in Light: Science and Applications. In this new work, Stefan used his newly developed Interferometric Time-Correlated Single Photon Counting system (i-TCSPC) to measure the coherence length of laser emission from nanowires grown by the Liu group at UCL. These measurements allowed the direct calculation of the nanowire mirror reflectivity.

During this study, Stefan found that it was possible to use indirect bandgap materials as a holding state for carriers before they relax into the emissive wells; this finding both allows multi-nanosecond lasing after a sub-picosecond excitation, and record low lasing thresholds through resonant excitation.

This work was supported by TEM provided by the Sanchez group at Warwick.

Reference: Heterostructure and Q-factor engineering for low-threshold and persistent nanowire lasing, Skalsky et al., Light: Science and Applications, 9, 43 (2020) https://doi.org/10.1038/s41377-020-0279-y

New Paper: Characterisation, Selection and Micro-Assembly of Nanowire Laser Systems

Our collaborative work on the selection, transfer and testing of semiconductor nanowire lasers has now been published in Nano Letters.

In this work, growth colleagues at ANU prepared nanowire lasers which were characterised at Manchester. This characterisation was used to select bins of nanowires, which were transferred using a cutting edge pick-and-place tool at the University of Strathclyde. The transferred wires were re-tested in Manchester; while some wires showed identical behaviour, some showed a change in lasing mode.

This work will guide the heterointegration of nanowire lasers with photonic circuits, targetting high-yield and industrial applicability.

Reference: Characterisation, Selection and Micro-Assembly of Nanowire Laser Systems, Jevtics et al., Nano Letters (ASAP), DOI: 10.1021/acs.nanolett.9b05078