The 2023 terahertz science and technology roadmap

Journal of Physics D: Applied Physics IOP Publishing 56:22 (2023) 223001

Authors:

Alfred Leitenstorfer, Andrey S Moskalenko, Tobias Kampfrath, Junichiro Kono, Enrique Castro-Camus, Kun Peng, Naser Qureshi, Dmitry Turchinovich, Koichiro Tanaka, Andrea G Markelz, Martina Havenith, Cameron Hough, Hannah J Joyce, Willie J Padilla, Binbin Zhou, Ki-Yong Kim, Xi-Cheng Zhang, Peter Uhd Jepsen, Sukhdeep Dhillon, Miriam Vitiello, Edmund Linfield, A Giles Davies, Matthias C Hoffmann, Roger Lewis, Masayoshi Tonouchi

Abstract:

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz-∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

Narrowband, angle-tuneable, helicity-dependent terahertz emission from nanowires of the topological Dirac semimetal Cd3As2

ACS Photonics American Chemical Society 10:5 (2023) 1473-1484

Authors:

Chelsea Xia, Dharmalingam Prabhakaran, Laura Herz, Thorsten Hesjedal, Michael Johnston

Abstract:

All-optical control of terahertz pulses is essential for the development of optoelectronic devices for next-generation quantum technologies. Despite substantial research in THz generation methods, polarisation control remains difficult. Here, we demonstrate that by exploiting bandstructure topology, both helicity-dependent and helicity-independent THz emission can be generated from nanowires of the topological Dirac semimetal Cd3As2. We show that narrowband THz pulses can be generated at oblique incidence by driving the system with optical (1.55 eV) pulses with circular polarisation. Varying the incident angle also provides control of the peak emission frequency, with peak frequencies spanning 0.21 – 1.40 THz as the angle is tuned from 15° - 45°. We therefore present Cd3As2 nanowires as a promising novel material platform for controllable terahertz emission.

Temperature dependent reversal of phase segregation in mixed-halide perovskites

Advanced Materials Wiley 35:19 (2023) 2210834

Authors:

Adam D Wright, Jay B Patel, Michael B Johnston, Laura M Herz

Abstract:

Understanding the mechanism of light-induced halide segregation in mixed-halide perovskites is essential for their application in multijunction solar cells. Here, photoluminescence spectroscopy is used to uncover how both increases in temperature and light intensity can counteract the halide segregation process. It is observed that, with increasing temperature, halide segregation in CH3NH3Pb(Br0.4I0.6)3 first accelerates toward ≈290 K, before slowing down again toward higher temperatures. Such reversal is attributed to the trade-off between the temperature activation of segregation, for example through enhanced ionic migration, and its inhibition by entropic factors. High light intensities meanwhile can also reverse halide segregation; however, this is found to be only a transient process that abates on the time scale of minutes. Overall, these observations pave the way for a more complete model of halide segregation and aid the development of highly efficient and stable perovskite multijunction and concentrator photovoltaics.

Open-circuit and short-circuit loss management in wide-gap perovskite p-i-n solar cells

Nature communications Springer Nature 14:1 (2023) 932

Authors:

Pietro Caprioglio, Joel A Smith, Robert DJ Oliver, Akash Dasgupta, Saqlain Choudhary, Michael D Farrar, Alexandra J Ramadan, Yen-Hung Lin, M Greyson Christoforo, James M Ball, Jonas Diekmann, Jarla Thiesbrummel, Karl-Augustin Zaininger, Xinyi Shen, Michael B Johnston, Dieter Neher, Martin Stolterfoht, Henry J Snaith

Abstract:

In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (VOC) and short-circuit current (JSC) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external VOC is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n-interface, suppressing the QFLS-VOC mismatch, and boosting the VOC. Concurrently, the use of an ionic interlayer or a self-assembled monolayer at the p-interface reduces the inferred field screening induced by mobile ions at JSC, promoting charge extraction and raising the JSC. The combination of the n- and p-type optimizations allows us to approach the thermodynamic potential of the perovskite absorber layer, resulting in 1 cm2 devices with performance parameters of VOCs up to 1.29 V, fill factors above 80% and JSCs up to 17 mA/cm2, in addition to a thermal stability T80 lifetime of more than 3500 h at 85 °C.

Charge-carrier dynamics of solution-processed antimony- and bismuth-based chalcogenide thin films

ACS Energy Letters American Chemical Society 8:3 (2023) 1485-1492

Authors:

Z Jia, M Righetto, Y Yang, Cq Xia, Y Li, R Li, Y Li, B Yu, Y Liu, H Huang, Mb Johnston, Lm Herz, Q Lin

Abstract:

Chalcogenide-based semiconductors have recently emerged as promising candidates for optoelectronic devices, benefiting from their low-cost, solution processability, excellent stability and tunable optoelectronic properties. However, the understanding of their fundamental optoelectronic properties is far behind the success of device performance and starts to limit their further development. To fill this gap, we conduct a comparative study of chalcogenide absorbers across a wide material space, in order to assess their suitability for different types of applications. We utilize optical-pump terahertz-probe spectroscopy and time-resolved microwave conductivity techniques to fully analyze their charge-carrier dynamics. We show that antimony-based chalcogenide thin films exhibit relatively low charge-carrier mobilities and short lifetimes, compared with bismuth-based chalcogenides. In particular, AgBiS2 thin films possess the highest mobility, and Sb2S3 thin films have less energetic disorder, which are beneficial for photovoltaic devices. On the contrary, Bi2S3 showed ultralong carrier lifetime and high photoconductive gain, which is beneficial for designing photoconductors.