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Dr Kun Peng
Postdoctoral Research Fellow
Clarendon Laboratory Room 245
Phone (office): +44 (0) 1865 272339
Phone (lab): +44 (0) 1865 282649
Email:
kun.pen@physics.ox.ac.uk
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Research interests
Semiconductor nanowire spectroscopy and devices
Publications
- Direct and integrating sampling in terahertz receivers from wafer-scalable inas nanowires,
K Peng, NP Morgan, FM Wagner, T Siday, CQ Xia, D Dede, V Boureau, V Piazza, AFI Morral, MB Johnston
Nat. Commun., 15:103 (2024)
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pdf | doi:10.1038/s41467-023-44345-1 ]
Terahertz (THz) radiation will play a pivotal role in wireless communications, sensing, spectroscopy and imaging technologies in the decades to come. THz emitters and receivers should thus be simplified in their design and miniaturized to become a commodity. In this work we demonstrate scalable photoconductive THz receivers based on horizontally-grown InAs nanowires (NWs) embedded in a bow-tie antenna that work at room temperature. The NWs provide a short photoconductivity lifetime while conserving high electron mobility. The large surface-to-volume ratio also ensures low dark current and thus low thermal noise, compared to narrow-bandgap bulk devices. By engineering the NW morphology, the NWs exhibit greatly different photoconductivity lifetimes, enabling the receivers to detect THz photons via both direct and integrating sampling modes. The broadband NW receivers are compatible with gating lasers across the entire range of telecom wavelengths (1.2-1.6 mu m) and thus are ideal for inexpensive all-optical fibre-based THz time-domain spectroscopy and imaging systems. The devices are deterministically positioned by lithography and thus scalable to the wafer scale, opening the path for a new generation of commercial THz receivers. Authors report on nanofacet engineering of wafer-scalable InAs nanowires enabling the operation of THz photodetectors in direct or integrating sampling mode, with performance comparable to commercial InP technology. - The 2023 terahertz science and technology roadmap,
A Leitenstorfer, AS Moskalenko, T Kampfrath, J Kono, E Castro-camus, K Peng, N Qureshi, D Turchinovich, K Tanaka, AG Markelz, M Havenith, C Hough, HJ Joyce, MB Johnston, J Cunningham
J. Phys. D-Appl. Phys., 56:223001 (2023)
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pdf | doi:10.1088/1361-6463/acbe4c ]
Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz-similar to 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. - Optimised spintronic emitters of terahertz radiation for time-domain spectroscopy,
FM Wagner, S Melnikas, J Cramer, DA Damry, CQ Xia, K Peng, G Jakob, M Klaui, S Kicas, MB Johnston
J. Infrared Millim. Terahertz Waves, 44:52–65 (2023)
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pdf | doi:10.1007/s10762-022-00897-9 ]
Spintronic metal thin films excited by femtosecond laser pulses have recently emerged as excellent broadband sources of terahertz (THz) radiation. Unfortunately, these emitters transmit a significant proportion of the incident excitation laser, which causes two issues: first, the transmitted light can interfere with measurements and so must be attenuated; second, the transmitted light is effectively wasted as it does not drive further THz generation. Here, we address both issues with the inclusion of a high-reflectivity (HR) coating made from alternating layers of SiO2 and Ta2O5. Emitters with the HR coating transmit less than 0.1% of the incident excitation pulse. Additionally, we find that the HR coating increases the peak THz signal by roughly 35%, whereas alternative attenuating elements, such as cellulose nitrate films, reduce the THz signal. To further improve the emission, we study the inclusion of an anti-reflective coating to the HR-coated emitters and find the peak THz signal is enhanced by a further 4%. - The application of one-dimensional nanostructures in terahertz frequency devices,
K Peng, MB Johnston
Appl. Phys. Rev., 8:041314 (2021)
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pdf | doi:10.1063/5.0060797 ]
One-dimensional nanostructures commonly refer to nanomaterials with a large length-to-diameter ratio, such as nanowires, nanotubes, nanorods, and nanopillars. The nanoscale lateral dimensions and high aspect ratios of these (quasi) one-dimensional nanostructures result in fascinating optical and electrical properties, including strongly anisotropic optical absorption, controlled directionality of light emission, confined charge-carrier transport and/or ballistic transport, which make one-dimensional nanostructures ideal building blocks for applications in highly integrated photonic, electronic, and optoelectronic systems. In this article, we review recent developments of very high (terahertz) frequency devices based on these one-dimensional nanostructures, particularly focusing on carbon nanotubes and semiconductor nanowires. We discuss state-of-the-art nanomaterials synthesis, device-fabrication techniques, device-operating mechanisms, and device performance. The combination of nanotechnology and terahertz science is a nascent research field which has created advanced THz sources, detectors, and modulators, leading to terahertz systems with extended functionalities. The goal of this article is to present the up-to-date worldwide status of this field and to highlight the current challenges and future opportunities.</p> - Three-dimensional cross-nanowire networks recover full terahertz state,
K Peng, D Jevtics, F Zhang, S Sterzl, DA Damry, MU Rothmann, B Guilhabert, MJ Strain, HH Tan, LM Herz, L Fu, MD Dawson, A Hurtado, C Jagadish, MB Johnston
Science, 368:510--513 (2020)
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pdf | doi:10.1126/science.abb0924 ]
Terahertz (THz) radiation is an interesting region of the electromagnetic spectrum lying between microwaves and infrared. Non-ionizing and transparent to most fabrics, it is finding application in security screening and imaging but is also being developed for communication and chemical sensing. To date, most THz detectors have focused just on signal intensity, an effort that discards half the signal in terms of the full optical state, including polarization. Peng et al. developed a THz detector based on crossed nanowires (arranged in a hash structure) that is capable of resolving the full state of the THz light. The approach provides a nanophotonic platform for the further development of THz-based technologies.Science, this issue p. 510Terahertz radiation encompasses a wide band of the electromagnetic spectrum, spanning from microwaves to infrared light, and is a particularly powerful tool for both fundamental scientific research and applications such as security screening, communications, quality control, and medical imaging. Considerable information can be conveyed by the full polarization state of terahertz light, yet to date, most time-domain terahertz detectors are sensitive to just one polarization component. Here we demonstrate a nanotechnology-based semiconductor detector using cross-nanowire networks that records the full polarization state of terahertz pulses. The monolithic device allows simultaneous measurements of the orthogonal components of the terahertz electric field vector without cross-talk. Furthermore, we demonstrate the capabilities of the detector for the study of metamaterials. - Light absorption and recycling in hybrid metal halide perovskite photovoltaic devices,
JB Patel, AD Wright, KB Lohmann, K Peng, CQ Xia, JM Ball, NK Noel, TW Crothers, J Wong-leung, HJ Snaith, LM Herz, MB Johnston
Adv. Energy Mater., 10:1903653 (2020)
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pdf | doi:10.1002/aenm.201903653 ]
The production of highly efficient single- and multijunction metal halide perovskite (MHP) solar cells requires careful optimization of the optical and electrical properties of these devices. Here, precise control of CH3NH3PbI3 perovskite layers is demonstrated in solar cell devices through the use of dual source coevaporation. Light absorption and device performance are tracked for incorporated MHP films ranging from approximate to 67 nm to approximate to 1.4 mu m thickness and transfer-matrix optical modeling is utilized to quantify optical losses that arise from interference effects. Based on these results, a device with 19.2% steady-state power conversion efficiency is achieved through incorporation of a perovskite film with near-optimum predicted thickness (approximate to 709 nm). Significantly, a clear signature of photon reabsorption is observed in perovskite films that have the same thickness (approximate to 709 nm) as in the optimized device. Despite the positive effect of photon recycling associated with photon reabsorption, devices with thicker (>750 nm) MHP layers exhibit poor performance owing to competing nonradiative charge recombination in a "dead-volume" of MHP. Overall, these findings demonstrate the need for fine control over MHP thickness to achieve the highest efficiency cells, and accurate consideration of photon reabsorption, optical interference, and charge transport properties. - Single $n^+$-i-$n^+$ {InP} nanowires for highly sensitive terahertz detection,
K Peng, P Parkinson, Q Gao, JL Boland, ZY Li, F Wang, S Mokkapati, L Fu, MB Johnston, HH Tan, C Jagadish
Nanotechnology, 28:125202 (2017)
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pdf | doi:10.1088/1361-6528/aa5d80 ]
Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n(+)-i-n(+) InP nanowires. The axial doping profile of the n+-i-n+ InP nanowires has been calibrated and characterized using combined optical and electrical approaches to achieve nanowire devices with low contact resistances, on which the highly-sensitive InP singlenanowire photoconductive THz detectors have been demonstrated. While the n+-i-n+ InP nanowire detector has a only pA-level response current, it has a 2.5 times improved signal-tonoise ratio compared with the undoped InP nanowire detector and is comparable to traditional bulk THz detectors. This performance indicates a promising path to nanowire-based THz electronics for future commercial applications. - Broadband phase-sensitive single {InP} nanowire photoconductive terahertz detectors,
K Peng, P Parkinson, JL Boland, Q Gao, YC Wenas, CL Davies, ZY Li, L Fu, MB Johnston, HH Tan, C Jagadish
Nano Lett., 16:4925-4931 (2016)
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pdf | doi:10.1021/acs.nanolett.6b01528 ]
Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (similar to 1260 cm(2) V-1 s(-1)) and low dark current (similar to 10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution. - Single Nanowire Terahertz Detectors ,
K Peng, P Parkinson, L Fu, Q Gao, N Jiang, Y Guo, F Wang, H Joyce, JL Boland, M Johnston, H Tan, C Jagadish
, 2015:STu4H.8 (2015)
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pdf | doi:10.1364/CLEO_SI.2015.STu4H.8 ]
Photoconductive terahertz detectors based on single GaAs/AlGaAs nanowire were designed, fabricated and incorporated into the pulsed time-domain technique, showing a promise for nanowires in terahertz applications such as near-field terahertz sensors or on-chip terahertz micro-spectrometers. - Single Nanowire Photoconductive Terahertz Detectors,
K Peng, P Parkinson, L Fu, Q Gao, N Jiang, Y Guo, F Wang, HJ Joyce, JL Boland, HH Tan, C Jagadish, MB Johnston
Nano Lett., 15:206-210 (2015)
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pdf | doi:10.1021/nl5033843 ]
Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as diverse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors. - Single GaAs/AlGaAs Nanowire Photoconductive
Terahertz Detectors ,
K Peng, P Parkinson, L Fu, Q Gao, N Jiang, Y Guo, F Wang, HJ Joyce, JL Boland, MB Johnston, HH Tan, C Jagadish
, 2014:221-222 (2014)
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pdf | doi:10.1109/COMMAD.2014.7038695 ]
Photoconductive terahertz detectors based on single GaAs/AlGaAs core-shell nanowire have been designed and fabricated. The devices were characterised in a terahertz time-domain spectroscopy system, showing excellent sensitivity comparable to the standard bulk ion-implanted InP receiver, with a detection bandwidth of 0.1 ~ 0.6 THz. Finite-difference time-domain simulations were performed to understand the origin of the narrow bandwidth of current detectors as well as optimize antenna designs to improve detector performance.
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