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- ItemAdvanced GeSn/SiGeSn Group IV Heterostructure Lasers(Weinheim : Wiley-VCH, 2018) von den Driesch, Nils; Stange, Daniela; Rainko, Denis; Povstugar, Ivan; Zaumseil, Peter; Capellini, Giovanni; Schröder, Thomas; Denneulin, Thibaud; Ikonic, Zoran; Hartmann, Jean-Michel; Sigg, Hans; Mantl, Siegfried; Grützmacher, Detlev; Buca, DanGrowth and characterization of advanced group IV semiconductor materials with CMOS-compatible applications are demonstrated, both in photonics. The investigated GeSn/SiGeSn heterostructures combine direct bandgap GeSn active layers with indirect gap ternary SiGeSn claddings, a design proven its worth already decades ago in the III–V material system. Different types of double heterostructures and multi-quantum wells (MQWs) are epitaxially grown with varying well thicknesses and barriers. The retaining high material quality of those complex structures is probed by advanced characterization methods, such as atom probe tomography and dark-field electron holography to extract composition parameters and strain, used further for band structure calculations. Special emphasis is put on the impact of carrier confinement and quantization effects, evaluated by photoluminescence and validated by theoretical calculations. As shown, particularly MQW heterostructures promise the highest potential for efficient next generation complementary metal-oxide-semiconductor (CMOS)-compatible group IV lasers.
- ItemComparison of Ultraviolet B Light‐Emitting Diodes with Single or Triple Quantum Wells(Weinheim : Wiley-VCH, 2021) Kolbe, Tim; Knauer, Arne; Ruschel, Jan; Rass, Jens; Kyong Cho, Hyun; Hagedorn, Sylvia; Glaab, Johannes; Lobo Ploch, Neysha; Einfeldt, Sven; Weyers, MarkusLight-emitting diodes (LEDs) with an emission wavelength of 310 nm containing either a single or a triple quantum well are compared regarding their efficiency and long-term stability. In addition, the influence of the thickness of the lower quantum well barrier and the quantum well thickness in single quantum well (SQW) LEDs is investigated. Electroluminescence measurements show a 28% higher initial output power for the SQW LEDs compared with the triple quantum well (TQW) LEDs because of larger spatial overlap of the carriers in the SQW as revealed by electro-optical simulations of the LED heterostructures. However, TQW LEDs show a higher output power than SQW LEDs after 1 h operation under harsh conditions. For SQW LEDs, it is found that for a thicker lower quantum well barrier (65 nm instead of 25 nm) the initial output power decreases by ≈15%. A thicker SQW (3 nm instead of 1.6 nm) reduces the initial output power by even 45% but increases the lifetime by a factor of 6 which is attributed to reduced Auger recombination from an enhanced spatial separation of electrons and holes in the quantum wells due to the quantum-confined Stark effect.
- ItemAxial GaAs/Ga(As, Bi) nanowire heterostructures(Bristol : IOP Publ., 2019) Oliva, Miriam; Gao, Guanhui; Luna, Esperanza; Geelhaar, Lutz; Lewis, Ryan BBi-containing III-V semiconductors constitute an exciting class of metastable compounds with wide-ranging potential optoelectronic and electronic applications. However, the growth of III-V-Bi alloys requires group-III-rich growth conditions, which pose severe challenges for planar growth. In this work, we exploit the naturally-Ga-rich environment present inside the metallic droplet of a self-catalyzed GaAs nanowire (NW) to synthesize metastable GaAs/GaAs1-xBi x axial NW heterostructures with high Bi contents. The axial GaAs1-xBi x segments are realized with molecular beam epitaxy by first enriching only the vapor-liquid-solid (VLS) Ga droplets with Bi, followed by exposing the resulting Ga-Bi droplets to As2 at temperatures ranging from 270 °C to 380 °C to precipitate GaAs1-xBi x only under the NW droplets. Microstructural and elemental characterization reveals the presence of single crystal zincblende GaAs1-xBi x axial NW segments with Bi contents up to (10 ± 2)%. This work illustrates how the unique local growth environment present during the VLS NW growth can be exploited to synthesize heterostructures with metastable compounds. © 2019 IOP Publishing Ltd.
- ItemTowards Oxide Electronics: a Roadmap(Amsterdam : Elsevier B.V., 2019) Coll, M.; Fontcuberta, J.; Althammer, M.; Bibes, M.; Boschker, H.; Calleja, A.; Cheng, G.; Cuoco, M.; Dittmann, R.; Dkhil, B.; El Baggari, I.; Fanciulli, M.; Fina, I.; Fortunato, E.; Frontera, C.; Fujita, S.; Garcia, V.; Goennenwein, S.T.B.; Granqvist, C.-G.; Grollier, J.; Gross, R.; Hagfeldt, A.; Herranz, G.; Hono, K.; Houwman, E.; Huijben, M.; Kalaboukhov, A.; Keeble, D.J.; Koster, G.; Kourkoutis, L.F.; Levy, J.; Lira-Cantu, M.; MacManus-Driscoll, J.L.; Mannhart, J.; Martins, R.; Menzel, S.; Mikolajick, T.; Napari, M.; Nguyen, M.D.; Niklasson, G.; Paillard, C.; Panigrahi, S.; Rijnders, G.; Sánchez, F.; Sanchis, P.; Sanna, S.; Schlom, D.G.; Schroeder, U.; Shen, K.M.; Siemon, A.; Spreitzer, M.; Sukegawa, H.; Tamayo, R.; van den Brink, J.; Pryds, N.; Granozio, F.M.[No abstract available]
- ItemStructural and electronic properties of epitaxial multilayer h-BN on Ni(111) for spintronics applications([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Tonkikh, A.A.; Voloshina, E.N.; Werner, P.; Blumtritt, H.; Senkovskiy, B.; Güntherodt, G.; Parkin, S.S.P.; Dedkov, Yu. S.Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to a large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and to close-packed surfaces of fcc-Ni(111) and hcp-Co(0001). Epitaxial deposition of h-BN on ferromagnetic metals is aimed at small interface scattering of charge and spin carriers. We report on the controlled growth of h-BN/Ni(111) by means of molecular beam epitaxy (MBE). Structural and electronic properties of this system are investigated using cross-section transmission electron microscopy (TEM) and electron spectroscopies which confirm good agreement with the properties of bulk h-BN. The latter are also corroborated by density functional theory (DFT) calculations, revealing that the first h-BN layer at the interface to Ni is metallic. Our investigations demonstrate that MBE is a promising, versatile alternative to both the exfoliation approach and chemical vapour deposition of h-BN.
- ItemTerahertz spin currents and inverse spin Hall effect in thin-film heterostructures containing complex magnetic compounds(Singapore [u.a.] : World Scientific Publishing, 2017-08-23) Seifert, T.; Martens, U.; Günther, S.; Schoen, M.A.W.; Radu, F.; Chen, X.Z.; Lucas, I.; Ramos, R.; Aguirre, M.H.; Algarabel, P.A.; Anadón, A.; Körner, H.; Walowski, J.; Back, C.; Ibarra, M.R.; Morellón, L.; Saitoh, E.; Wolf, M.; Song, C.; Uchida, K.; Münzenberg, M.; Radu, I.; Kampfrath, T.Terahertz emission spectroscopy (TES) of ultrathin multilayers of magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport and spin–orbit interaction at highest frequencies, but has also paved the way for applications such as efficient and ultrabroadband emitters of terahertz (THz) electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable figure of merit, we systematically compare the strength of THz emission from X/Pt bilayers with X being a complex ferro-, ferri- and antiferromagnetic metal, that is, dysprosium cobalt (DyCo5), gadolinium iron (Gd24Fe76), magnetite (Fe3O4) and iron rhodium (FeRh). We find that the performance in terms of spin-current generation not only depends on the spin polarization of the magnet’s conduction electrons, but also on the specific interface conditions, thereby suggesting TES to be a highly interface-sensitive technique. In general, our results are relevant for all applications that rely on the optical generation of ultrafast spin currents in spintronic metallic multilayers.