Patrick was external examiner for Zizhuo Liu, a PhD candidate in Prof. Huiyun Liu‘s group at University College London. Zizhuo defended his thesis entitled “High-performance III-V Quantum structures and devices grown 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
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
We have uploaded a new paper on quantum-dot-in-nanowire structures to the arXiv. Working with colleagues at University College London, the University of Warwick, the University of Sheffield and the University of Copenhagen, this work demonstrates the growth of high-quality GaAs quantum dot inclusions in a GaAsP nanowire, with evidence for single photon emission at low temperatures and emission to room temperature.
Reference: Defect-Free Axial GaAs/GaAsP Nanowire Quantum Dots with Strong Carrier Confinement, Zhang et al., arXiv:2002.07071
Group PhD student Stefan Skalsky gave a talk at the UK Semiconductors meeting in Sheffield. His talk, on “Nanosecond lasing and mm-scale optical coherence length in GaAsP/GaAs Quantum-Well Nanowire Lasers” descibed his recent work using interferometric time-resolved spectroscopy to reveal the end-facet reflectivity in nanowire lasers.
A new paper has been accepted for publication in ACS Nano. This work, led by Dr. Yunyan Zhang and Prof. Huiyun Liu at University College London, describes the growth and characterisation of quantum-well tube nanowires based on GaAs-GaAsP heterostructures.
This work brings together partners from UCL, Sheffield, Warwick, Lund (Sweden), Imperial College London, the Danish Defence Research Centre and Manchester to design new materials for III-V nanowire lasers. Unlike previous quantum-well lasers based on GaAs or InP cores, here both the barrier and core material are of higher energy than the emission wavelength, dramatically reducing the cavity losses. Furthermore, the strained quatum wells are highly effective at confining carriers, which provide a new platform for the ultimate goal of room-temperature, continuously-operating nanowire lasers for on-chip applications.
Reference: Highly-Strained III-V-V Co-Axial Nanowire Quantum Wells with Strong Carrier Confinement, Zhang et al. ACS Nano (2019) doi: 10.1021/acsnano.9b01775