New Paper: Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires

Optoelectronic materials form the building blocks of crucial components of modern technology, including solar cells, CCDs, lasers and LEDs. The past decade has seen significant developments in materials science that enable the shrinking of these materials to the nano-scale. These advancements have also created entirely new technologies based around light manipulation. We can now create nano-scale light sources, nano-scale light detectors and nano-scale optics: so we can build a chip that performs processes using light instead of electrical signals.

An important component of these devices are nanowires: these can act as on-chip light sources and tiny optical fibers, essentially the power and wiring of a light based circuit. As materials are shrunk towards the nano-scale, their performance is affected strongly by their size, providing a handle to tune performance of these nanowires  to suit the application. However, herein lies one of the major challenges of this technology; it remains difficult to accurately and repeatedly control the size of these nano-materials when they are made leading to  an unwanted spread in their performance.

High-throughput experiments to study inhomogeneity

Stephen Church of the OMS Lab worked with colleagues in the Joselevich group at the Weizmann Institute in Israel to developed a methodology to optimize these nano-materials by harnessing the inherent variation using big data approaches. He has developed an automated microscope that can study the properties of more than 10,000 individual nano-wires with a suite of different optical experiments. This approach produces a vast dataset that, when considered together, describes the nano-material and can therefore be used to establish the best way to optimize their performance. Crucially, this approach requires very little prior knowledge of the sample and can be applied generally to new nano-materials.

Soft nanowires and the impact of strain

In their recent paper, we demonstrate this approach on wires made of halide perovskites, an emerging material touted for its superior light emission and detection. The material is also “soft”, deforming to fit on its substrate; this causes further spread in properties as the thickness of the wire changes. The big data approach shows the impact of this deformation on the color and the efficiency of light emission from the nano-wires, and shows how the degree of deformation varies across the population.

Open data

This publication is made up of more than just a journal report. The raw data has been made available via FigShare, and the analysis code via github. It is possible to explore and manipulate the raw data using the Google Colab platform.

Reference: Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires, Stephen A. Church, Hoyeon Choi, Nawal Al-Amairi, Ruqaiya Al-Abri, Ella Sanders, Eitan Oksenberg, Ernesto Joselevich and Patrick W. Parkinson, ACS Nano (2022) DOI: 10.1021/acsnano.2c01086

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 Conference Proceeding: Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells

Rachel Barrett (a PhD student in the Binks group in Manchester) has had a conference proceeding published in collaboration with the OMS group. The study, on micro-scale spectroscopy of GaN-based quantum wells was presented at Photon 2020 and was carried out in collaboration with the Department of Materials Science at Cambridge.

Reference: Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells, Barrett et al., J Phys Conference Series, 1919, 012011 (2021), DOI:10.1088/1742-6596/1919/1/012011

New Review : Measuring, controlling and exploiting heterogeneity in optoelectronic nanowires

Interwire and intrawire inhomogeneity

Group PhD students Ruqaiya Al-Abri and Hoyeon Choi have written an invited review article for JPhys Photonics, published today.

Lead author Ruqaiya Al-Abri describes this work:

Among the one-dimensional structures, semiconductor nanowires have attracted great attention; from the growth process to the production of functional devices they have been widely studied. The growth condition of the nanowires can lead to non-uniformity (disorder) in the crystal structure, morphology, and geometry of the nanowire. Consequently, this affects the functionality of individual and/or ensembles of nanowires. However, researchers have benefited from disorder; it has been shown that disorder can enhance the performance of ensemble of nanowires such as in photovoltaic devices. This review article attempts to understand the disorder in these structures, investigates the origin of the inhomogeneity within “interwire” and between “intrawire” nanowires, and outlines different approaches to correlate disorder to functional parameters and hence optimize the performance of the nanowires.

Reference: Measuring, controlling and exploiting heterogeneity in optoelectronic nanowires, Ruqaiya Al-Abri, Hoyeon Choi and Patrick Parkinson, JPhys Photonics, (2021) DOI:10.1088/2515-7647/abe282

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 Paper: Visualizing the role of photoinduced ion migration on photoluminescence in halide perovskite grains​

Group student Hoyeon has had a paper accepted in the RSC Journal of Materials Chemistry C, studying the photo-brightening effect in perovskite grains using correlated optical and chemical mapping. In collaboration with the Flavell group and the NanoSIMS group at Manchester, this study linked luminescence lifetime and emission energies to local changes in oxygen and iodine density close to the surface of methyammonium lead iodide grains; a prototypical next-generation photovoltaic material.

This new study unambiguously links the emission efficiency improvement under illumination – the so-called photo-brightening effect – to light-induced migration of iodine into the bulk of the crystal and an increase in oxygen levels close to the surface of the grains. By mapping the emission efficiency and chemical levels on the sub-micron scale, we find that grain size has a decreasing role with light-soaking.

Reference: “Visualizing the role of photoinduced ion migration on photoluminescence in halide perovskite grains​“, J. Mater. Chem. C (2020), DOI:10.1039/d0tc01441a

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)