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DDC: 530 × DDC: 540 × Type: article × WGL Institute: PDI ×

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Now showing 1 - 5 of 5
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    Optoelectronic properties and ultrafast carrier dynamics of copper iodide thin films
    ([London] : Nature Publishing Group UK, 2022) Li, Zhan Hua; He, Jia Xing; Lv, Xiao Hu; Chi, Ling Fei; Egbo, Kingsley O.; Li, Ming-De; Tanaka, Tooru; Guo, Qi Xin; Yu, Kin Man; Liu, Chao Ping
    As a promising high mobility p-type wide bandgap semiconductor, copper iodide has received increasing attention in recent years. However, the defect physics/evolution are still controversial, and particularly the ultrafast carrier and exciton dynamics in copper iodide has rarely been investigated. Here, we study these fundamental properties for copper iodide thin films by a synergistic approach employing a combination of analytical techniques. Steady-state photoluminescence spectra reveal that the emission at ~420 nm arises from the recombination of electrons with neutral copper vacancies. The photogenerated carrier density dependent ultrafast physical processes are elucidated with using the femtosecond transient absorption spectroscopy. Both the effects of hot-phonon bottleneck and the Auger heating significantly slow down the cooling rate of hot-carriers in the case of high excitation density. The effect of defects on the carrier recombination and the two-photon induced ultrafast carrier dynamics are also investigated. These findings are crucial to the optoelectronic applications of copper iodide.
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    On-chip generation and dynamic piezo-optomechanical rotation of single photons
    ([London] : Nature Publishing Group UK, 2022) Bühler, Dominik D.; Weiß, Matthias; Crespo-Poveda, Antonio; Nysten, Emeline D. S.; Finley, Jonathan J.; Müller, Kai; Santos, Paulo V.; de Lima Jr., Mauricio M.; Krenner, Hubert J.
    Integrated photonic circuits are key components for photonic quantum technologies and for the implementation of chip-based quantum devices. Future applications demand flexible architectures to overcome common limitations of many current devices, for instance the lack of tuneabilty or built-in quantum light sources. Here, we report on a dynamically reconfigurable integrated photonic circuit comprising integrated quantum dots (QDs), a Mach-Zehnder interferometer (MZI) and surface acoustic wave (SAW) transducers directly fabricated on a monolithic semiconductor platform. We demonstrate on-chip single photon generation by the QD and its sub-nanosecond dynamic on-chip control. Two independently applied SAWs piezo-optomechanically rotate the single photon in the MZI or spectrally modulate the QD emission wavelength. In the MZI, SAWs imprint a time-dependent optical phase and modulate the qubit rotation to the output superposition state. This enables dynamic single photon routing with frequencies exceeding one gigahertz. Finally, the combination of the dynamic single photon control and spectral tuning of the QD realizes wavelength multiplexing of the input photon state and demultiplexing it at the output. Our approach is scalable to multi-component integrated quantum photonic circuits and is compatible with hybrid photonic architectures and other key components for instance photonic resonators or on-chip detectors.
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    Metamaterial-enabled asymmetric negative refraction of GHz mechanical waves
    ([London] : Nature Publishing Group UK, 2022) Zanotto, Simone; Biasiol, Giorgio; Santos, Paulo V.; Pitanti, Alessandro
    Wave refraction at an interface between different materials is a basic yet fundamental phenomenon, transversal to several scientific realms – electromagnetism, gas and fluid acoustics, solid mechanics, and possibly also matter waves. Under specific circumstances, mostly enabled by structuration below the wavelength scale, i.e., through the metamaterial approach, waves undergo negative refraction, eventually enabling superlensing and transformation optics. However, presently known negative refraction systems are symmetric, in that they cannot distinguish between positive and negative angles of incidence. Exploiting a metamaterial with an asymmetric unit cell, we demonstrate that the aforementioned symmetry can be broken, ultimately relying on the specific shape of the Bloch mode isofrequency curves. Our study specialized upon a mechanical metamaterial operating at GHz frequency, which is by itself a building block for advanced technologies such as chip-scale hybrid optomechanical and electromechanical devices. However, the phenomenon is based on general wave theory concepts, and it applies to any frequency and time scale for any kind of linear waves, provided that a suitable shaping of the isofrequency contours is implemented.
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    In Situ Transmission Electron Microscopy of Disorder–Order Transition in Epitaxially Stabilized FeGe2
    (Washington, DC : Soc., 2021) Terker, Markus; Nicolai, Lars; Gaucher, Samuel; Herfort, Jens; Trampert, Achim
    Isothermal crystallization of amorphous Ge deposited on a cubic Fe3Si/GaAs(001) substrate is performed by in situ annealing within a transmission electron microscope. It was found that the formation of epitaxially aligned tetragonal FeGe2 is associated with a disorder–order phase transition mainly consisting of a rearrangement of the Fe/vacancy sublattice from a random distribution to alternating filled and empty layers. Additionally, atomically resolved high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that the vertical lattice spacing of the Ge sublattice reduces across vacancy layers, indicating that strain minimization plays a role in the phase transition process. Crystallization and ordering are both found to proceed layer-by-layer and with square-root-shaped kinetics with a smaller transition rate for the latter.
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    Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction
    (Weinheim : Wiley-VCH, 2022) Mazzolini, Piero; Fogarassy, Zsolt; Parisini, Antonella; Mezzadri, Francesco; Diercks, David; Bosi, Matteo; Seravalli, Luca; Sacchi, Anna; Spaggiari, Giulia; Bersani, Danilo; Bierwagen, Oliver; Janzen, Benjamin Moritz; Marggraf, Marcella Naomi; Wagner, Markus R.; Cora, Ildiko; Pécz, Béla; Tahraoui, Abbes; Bosio, Alessio; Borelli, Carmine; Leone, Stefano; Fornari, Roberto
    Unintentionally doped (001)-oriented orthorhombic κ-Ga2O3 epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm2V−1s−1, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga2O3 epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga2O3 and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties.