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- ItemAdvances in electron channelling contrast imaging and electron backscatter diffraction for imaging and analysis of structural defects in the scanning electron microscope(London [u.a.] : Institute of Physics, 2020) Trager-Cowan, C.; Alasmari, A.; Avis, W.; Bruckbauer, J.; Edwards, P.R.; Hourahine, B.; Kraeusel, S.; Kusch, G.; Jablon, B.M.; Johnston, R.; Martin, R.W.; Mcdermott, R.; Naresh-Kumar, G.; Nouf-Allehiani, M.; Pascal, E.; Thomson, D.; Vespucci, S.; Mingard, K.; Parbrook, P.J.; Smith, M.D.; Enslin, J.; Mehnke, F.; Kneissl, M.; Kuhn, C.; Wernicke, T.; Knauer, A.; Hagedorn, S.; Walde, S.; Weyers, M.; Coulon, P.-M.; Shields, P.A.; Zhang, Y.; Jiu, L.; Gong, Y.; Smith, R.M.; Wang, T.; Winkelmann, A.In this article we describe the scanning electron microscopy (SEM) techniques of electron channelling contrast imaging and electron backscatter diffraction. These techniques provide information on crystal structure, crystal misorientation, grain boundaries, strain and structural defects on length scales from tens of nanometres to tens of micrometres. Here we report on the imaging and analysis of dislocations and sub-grains in nitride semiconductor thin films (GaN and AlN) and tungsten carbide-cobalt (WC-Co) hard metals. Our aim is to illustrate the capability of these techniques for investigating structural defects in the SEM and the benefits of combining these diffraction-based imaging techniques.
- ItemHigh-temperature annealing of AlN films grown on 4H-SiC(New York, NY : American Inst. of Physics, 2020) Brunner, F.; Cancellara, L.; Hagedorn, S.; Albrecht, M.; Weyers, M.The effect of high-temperature annealing (HTA) at 1700 °C on AlN films grown on 4H-SiC substrates by metalorganic vapor phase epitaxy has been studied. It is shown that the structural quality of the AlN layers improves significantly after HTA similar to what has been demonstrated for AlN grown on sapphire. Dislocation densities reduce by one order of magnitude resulting in 8 × 108 cm-2 for a-type and 1 × 108 cm-2 for c-type dislocations. The high-temperature treatment removes pits from the surface by dissolving nanotubes and dislocations in the material. XRD measurements prove that the residual strain in AlN/4H-SiC is further relaxed after annealing. AlN films grown at higher temperature resulting in a lower as-grown defect density show only a marginal reduction in dislocation density after annealing. Secondary ion mass spectrometry investigation of impurity concentrations reveals an increase of Si after HTA probably due to in-diffusion from the SiC substrate. However, C concentration reduces considerably with HTA that points to an efficient carbon removal process (i.e., CO formation). © 2020 Author(s).
- ItemThe Impact of AlN Templates on Strain Relaxation Mechanisms during the MOVPE Growth of UVB-LED Structures(Weinheim : Wiley-VCH, 2020) Knauer, Arne; Mogilatenko, Anna; Weinrich, Jonas; Hagedorn, Sylvia; Walde, Sebastian; Kolbe, Tim; Cancellara, Leonardo; Weyers, MarkusStrain relaxation mechanisms in AlGaN based light emitting diodes emitting in the ultraviolet B spectral range (UVB-LEDs) grown on different AlN/sapphire templates are analyzed by combining in situ reflectivity and curvature data with transmission electron microscopy. In particular, the impact of dislocation density, surface morphology, and lattice constant of the AlN/sapphire templates is studied. For nonannealed AlN/templates with threading dislocation densities (TDDs) of 4 × 109 and 3 × 109 cm−2 and different surface morphologies strain relaxation takes place mostly by conventional ways, such as inclination of threading dislocation lines and formation of horizontal dislocation bands. In contrast, a TDD reduction down to 1 × 109 cm−2 as well as a reduction of the lattice constant of high temperature annealed AlN template leads to drastic changes in the structure of subsequently grown AlGaN layers, e.g., to transformation to helical dislocations and enhanced surface enlargement by formation of macrofacets. For the growth of strongly compressively strained AlGaN layers for UVB-LEDs the relaxation mechanism is strongly influenced by the absolute values of TDD and the lattice constant of the AlN templates and is less influenced by their surface morphology.
- ItemHighly linear fundamental up-converter in InP DHBT technology for W-band applications(New York, NY [u.a.] : Wiley, 2020) Hossain, Maruf; Stoppel, Dimitri; Boppel, Sebastian; Heinrich, Wolfgang; Krozer, ViktorA fundamental up-converter with high linearity is presented, realized as full Gilbert cell (GC) mixer using a 800 nm transferred substrate (TS) InP-DHBT technology. The LO input of the Gilbert cell conducts from 75 to 100 GHz and requires 5 dBm of input power. The GC attains a single sideband (SSB) conversion gain of 10 ± 1 dB within the frequency from 82 to 95 GHz with a saturated output power of -1 dBm at 86 GHz and >5 dB conversion gain between 75 and 100 GHz. The up-converter exhibits 25 GHz of IF bandwidth. The DC power consumption is only 51 mW. © 2020 The Authors. Microwave and Optical Technology Letters published by Wiley Periodicals, Inc.
- ItemContinuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser(New York, NY : Springer, 2020) Gwaro, Jared O.; Brenner, Carsten; Theurer, L.S.; Maiwald, M.; Sumpf, Bernd; Hofmann, Martin R.We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample.
- ItemBandwidth Improvement of MMIC Single-Pole-Double-Throw Passive HEMT Switches with Radial Stubs in Impedance-Transformation Networks(Basel : MDPI, 2020) Tsao, Yi-Fan; Würfl, Joachim; Hsu, Heng-TungIn this paper, we propose a new configuration for improving the isolation bandwidth of MMIC single-pole-double-throw (SPDT) passive high-electron-mobility transistor (HEMT) switches operating at millimeter frequency range. While the conventional configuration adopted open-stub loading for compensation of the off-state capacitance, radial stubs were introduced in our approach to improve the operational bandwidth of the SPDT switch. Implemented in 0.15 m GaAs pHEMT technology, the proposed configuration exhibited a measured insertion loss of less than 2.5 dB with better than 30 dB isolation level over the frequency range from 33 GHz to 44 GHz. In terms of the bandwidth of operation, the proposed configuration achieved a fractional bandwidth of 28.5% compared to that of 12.3% for the conventional approach. Such superior bandwidth performance is mainly attributed to the less frequency dependent nature of the radial stubs.
- ItemEuPRAXIA Conceptual Design Report(Berlin ; Heidelberg : Springer, 2020) Assmann, R. W.; Weikum, M. K.; Akhter, T.; Alesini, D.; Alexandrova, A. S.; Anania, M. P.; Andreev, N. E.; Andriyash, I.; Artioli, M.; Aschikhin, A.; Audet, T.; Jafarinia, F. J.; Jakobsson, O.; Jaroszynski, D. A.; Jaster-Merz, S.; Joshi, C.; Kaluza, M.; Kando, M.; Karger, O. S.; Karsch, S.; Khazanov, E.; Bacci, A.; Khikhlukha, D.; Kirchen, M.; Kirwan, G.; Kitégi, C.; Knetsch, A.; Kocon, D.; Koester, P.; Kononenko, O. S.; Korn, G.; Kostyukov, I.; Barna, I. F.; Kruchinin, K. O.; Labate, L.; Le Blanc, C.; Lechner, C.; Lee, P.; Leemans, W.; Lehrach, A.; Li, X.; Li, Y.; Libov, V.; Bartocci, S.; Lifschitz, A.; Lindstrøm, C. A.; Litvinenko, V.; Lu, W.; Lundh, O.; Maier, A. R.; Malka, V.; Manahan, G. G.; Mangles, S. P. D.; Marcelli, A.; Bayramian, A.; Marchetti, B.; Marcouillé, O.; Marocchino, A.; Marteau, F.; Martinez de la Ossa, A.; Martins, J. L.; Mason, P. D.; Massimo, F.; Mathieu, F.; Maynard, G.; Beaton, A.; Mazzotta, Z.; Mironov, S.; Molodozhentsev, A. Y.; Morante, S.; Mosnier, A.; Mostacci, A.; Müller, A. -S.; Murphy, C. D.; Najmudin, Z.; Nghiem, P. A. P.; Beck, A.; Nguyen, F.; Niknejadi, P.; Nutter, A.; Osterhoff, J.; Oumbarek Espinos, D.; Paillard, J. -L.; Papadopoulos, D. N.; Patrizi, B.; Pattathil, R.; Pellegrino, L.; Bellaveglia, M.; Petralia, A.; Petrillo, V.; Piersanti, L.; Pocsai, M. A.; Poder, K.; Pompili, R.; Pribyl, L.; Pugacheva, D.; Reagan, B. A.; Resta-Lopez, J.; Beluze, A.; Ricci, R.; Romeo, S.; Rossetti Conti, M.; Rossi, A. R.; Rossmanith, R.; Rotundo, U.; Roussel, E.; Sabbatini, L.; Santangelo, P.; Sarri, G.; Bernhard, A.; Schaper, L.; Scherkl, P.; Schramm, U.; Schroeder, C. B.; Scifo, J.; Serafini, L.; Sharma, G.; Sheng, Z. M.; Shpakov, V.; Siders, C. W.; Biagioni, A.; Silva, L. O.; Silva, T.; Simon, C.; Simon-Boisson, C.; Sinha, U.; Sistrunk, E.; Specka, A.; Spinka, T. M.; Stecchi, A.; Stella, A.; Bielawski, S.; Stellato, F.; Streeter, M. J. V.; Sutherland, A.; Svystun, E. N.; Symes, D.; Szwaj, C.; Tauscher, G. E.; Terzani, D.; Toci, G.; Tomassini, P.; Bisesto, F. G.; Torres, R.; Ullmann, D.; Vaccarezza, C.; Valléau, M.; Vannini, M.; Vannozzi, A.; Vescovi, S.; Vieira, J. M.; Villa, F.; Wahlström, C. -G.; Bonatto, A.; Walczak, R.; Walker, P. A.; Wang, K.; Welsch, A.; Welsch, C. P.; Weng, S. M.; Wiggins, S. M.; Wolfenden, J.; Xia, G.; Yabashi, M.; Boulton, L.; Zhang, H.; Zhao, Y.; Zhu, J.; Zigler, A.; Brandi, F.; Brinkmann, R.; Briquez, F.; Brottier, F.; Bründermann, E.; Büscher, M.; Buonomo, B.; Bussmann, M. H.; Bussolino, G.; Campana, P.; Cantarella, S.; Cassou, K.; Chancé, A.; Chen, M.; Chiadroni, E.; Cianchi, A.; Cioeta, F.; Clarke, J. A.; Cole, J. M.; Costa, G.; Couprie, M. -E.; Cowley, J.; Croia, M.; Cros, B.; Crump, P. A.; D’Arcy, R.; Dattoli, G.; Del Dotto, A.; Delerue, N.; Del Franco, M.; Delinikolas, P.; De Nicola, S.; Dias, J. M.; Di Giovenale, D.; Diomede, M.; Di Pasquale, E.; Di Pirro, G.; Di Raddo, G.; Dorda, U.; Erlandson, A. C.; Ertel, K.; Esposito, A.; Falcoz, F.; Falone, A.; Fedele, R.; Ferran Pousa, A.; Ferrario, M.; Filippi, F.; Fils, J.; Fiore, G.; Fiorito, R.; Fonseca, R. A.; Franzini, G.; Galimberti, M.; Gallo, A.; Galvin, T. C.; Ghaith, A.; Ghigo, A.; Giove, D.; Giribono, A.; Gizzi, L. A.; Grüner, F. J.; Habib, A. F.; Haefner, C.; Heinemann, T.; Helm, A.; Hidding, B.; Holzer, B. J.; Hooker, S. M.; Hosokai, T.; Hübner, M.; Ibison, M.; Incremona, S.; Irman, A.; Iungo, F.This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.
- ItemTemperature-Dependent Charge Carrier Diffusion in [0001¯] Direction of GaN Determined by Luminescence Evaluation of Buried InGaN Quantum Wells(Weinheim : Wiley-VCH, 2020) Netzel, Carsten; Hoffmann, Veit; Tomm, Jens W.; Mahler, Felix; Einfeldt, Sven; Weyers, MarkusTemperature-dependent transport of photoexcited charge carriers through a nominally undoped, c-plane GaN layer toward buried InGaN quantum wells is investigated by continuous-wave and time-resolved photoluminescence spectroscopy. The excitation of the buried InGaN quantum wells is dominated by charge carrier diffusion through the GaN layer; photon recycling contributes only slightly. With temperature decreasing from 310 to 10 K, the diffusion length in [0001⎯⎯] direction increases from 250 to 600 nm in the GaN layer. The diffusion length at 300 K also increases from 100 to 300 nm when increasing the excitation power density from 20 to 500 W cm−2. The diffusion constant decreases from the low-temperature value of ∼7 to 1.5 cm2 s−1 at 310 K. The temperature dependence of the diffusion constant indicates that the diffusivity at room temperature is limited by optical phonon scattering. Consequently, higher diffusion constants in GaN-based devices require a reduced operation temperature. To increase diffusion lengths at a fixed temperature, the effective recombination time has to be prolonged by reducing the number of nonradiative recombination centers.
- ItemHigh-Temperature Annealing of AlGaN(Weinheim : Wiley-VCH, 2020) Hagedorn, Sylvia; Khan, Taimoor; Netzel, Carsten; Hartmann, Carsten; Walde, Sebastian; Weyers, MarkusIn the past few years, high-temperature annealing of AlN has become a proven method for providing AlN layers with low dislocation densities. Herein, the example of Al0.77Ga0.23N is used to investigate whether annealing can also improve the material quality of the ternary alloy. A detailed analysis of the influence of annealing temperature on structural and optical material properties is presented. It is found that with increasing annealing temperature, the threading dislocation density can be lowered from an initial value of 6.0 × 109 down to 2.6 × 109 cm−2. Ga depletion at the AlGaN surface and Ga diffusion into the AlN buffer layer are observed. After annealing, the defect luminescence between 3 and 4 eV is increased, accompanied by an increase in the oxygen concentration by about two orders of magnitude. Furthermore, due to annealing optical absorption at 325 nm (3.8 eV) occurs, which increases with increasing annealing temperature. It is assumed that the reason for this decrease in ultraviolet (UV) transmittance is the increasing number of vacancies caused by the removal of group-III and N atoms from the AlGaN lattice during annealing.
- ItemImproving AlN Crystal Quality and Strain Management on Nanopatterned Sapphire Substrates by High-Temperature Annealing for UVC Light-Emitting Diodes(Weinheim : Wiley-VCH, 2020) Hagedorn, Sylvia; Walde, Sebastian; Susilo, Norman; Netzel, Carsten; Tillner, Nadine; Unger, Ralph-Stephan; Manley, Phillip; Ziffer, Eviathar; Wernicke, Tim; Becker, Christiane; Lugauer, Hans-Jürgen; Kneissl, Michael; Weyers, MarkusHerein, AlN growth by metalorganic vapor-phase epitaxy on hole-type nanopatterned sapphire substrates is investigated. Cracking occurs for an unexpectedly thin-layer thickness, which is associated to altered nucleation conditions caused by the sapphire pattern. To overcome the obstacle of cracking and at the same time to decrease the threading dislocation density by an order of magnitude, high-temperature annealing (HTA) of a 300 nm-thick AlN starting layer is successfully introduced. By this method, 800 nm-thick, fully coalesced and crack-free AlN is grown on 2 in. nanopatterned sapphire wafers. The usability of such templates as basis for UVC light-emitting diodes (LEDs) is furthermore proved by subsequent growth of an UVC-LED heterostructure with single peak emission at 265 nm. Prerequisites for the enhancement of the light extraction efficiency by hole-type nanopatterned sapphire substrates are discussed. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim