Papers by Detlev Grützmacher
Proceedings of SPIE, Mar 14, 2016
This is a repository copy of Direct bandgap GeSn light emitting diodes for shortwave infrared app... more This is a repository copy of Direct bandgap GeSn light emitting diodes for shortwave infrared applications grown on Si.
Applied Physics Letters, Jul 16, 2012
Optics Express, Jan 15, 2016
We present results on CVD growth and electro-optical characterization of Ge 0.92 Sn 0.08 /Ge p-in... more We present results on CVD growth and electro-optical characterization of Ge 0.92 Sn 0.08 /Ge p-in heterostructure diodes. The suitability of Ge as barriers for direct bandgap GeSn active layers in different LED geometries, such as double heterostructures and multi quantum wells is discussed based on electroluminescence data. Theoretical calculations by effective mass and 6 band k•p method reveal low barrier heights for this specific structure. Best configurations offer only a maximum barrier height for electrons of about 40 meV at the Γ point at room temperature (e.g. 300 K), evidently insufficient for proper light emitting devices. An alternative solution using SiGeSn as barrier material is introduced, which provides appropriate band alignment for both electrons and holes resulting in efficient confinement in direct bandgap GeSn wells. Finally, epitaxial growth of such a complete SiGeSn/GeSn/SiGeSn double heterostructure including doping is shown.
Journal of Crystal Growth, Jun 1, 2011
We investigated the growth of the topological insulator Bi 2 Te 3 on Si(1 1 1) substrates by mean... more We investigated the growth of the topological insulator Bi 2 Te 3 on Si(1 1 1) substrates by means of molecular-beam epitaxy (MBE). The substrate temperature as well as the Bi and Te beam-equivalent pressure (BEP) was varied in a large range. The structure and morphology of the layers were studied using X-ray diffraction (XRD), X-ray reflectivity (XRR) and atomic force microscopy (AFM). The layerby-layer growth mode with quintuple layer (QL) as an unit is accomplished on large plateaus if the MBE growth takes place in a Te overpressure. At carefully optimized MBE growth parameters, we obtained atomically smooth, single-crystal Bi 2 Te 3 with large area single QL covering about 75% of the layer surface. Angular-resolved photoelectron spectroscopy reveals a linear energy dispersion of charge carriers at the surface, evidencing topologically insulating properties of the Bi 2 Te 3 epilayers.
ECS transactions, Mar 15, 2013
The epitaxial growth of Ge and GeSn on Si(100) is studied in the low temperature regime by reduce... more The epitaxial growth of Ge and GeSn on Si(100) is studied in the low temperature regime by reduced pressure chemical vapor deposition using showerhead technology. Most emphasis is placed on the growth kinetics in the low temperature regime of 375oC to 500oC which is characterized by surface limited reactions. Using Ge2H6 precursor low activation energy of 0.7 eV was determined for H2 carrier gas which further decreases to 0.5 eV if N2 is used. GeSn layers with 10 and 6.5 at.% Sn are obtained at growth temperatures of 375oC and 400oC respectively, using Ge2H6 and SnCl4 as precursors. All Ge and GeSn layers are of high crystalline quality.
ECS Journal of Solid State Science and Technology, 2013
ABSTRACT The epitaxial growth of Ge and GeSn alloys on Si(100) by Reduced Pressure Chemical Vapor... more ABSTRACT The epitaxial growth of Ge and GeSn alloys on Si(100) by Reduced Pressure Chemical Vapor Deposition is discussed. Particular emphasis is placed on the growth kinetics in the temperature window between 375°C and 475°C. Using Ge2H6 precursor and H2 carrier gas a low activation energy of 0.7 eV was found for the Ge growth which further decreases to 0.5 eV for N2 carrier gas. Thin Ge layers with high crystalline quality are aimed which may be used as buffers for the epitaxial growth of GeSn layers. Furthermore, GeSn alloys with up to 10 at.% Sn are synthesized on Si(100) at growth temperatures of 375°C employing Ge2H6 and SnCl4 precursors. All Ge and GeSn layers exhibit high crystalline quality as revealed by X-ray reciprocal space mapping and are nearly fully strain relaxed.
ECS transactions, Aug 7, 2014
Progress in epitaxial methodology as well as in nanotechnology opened new routes to custom design... more Progress in epitaxial methodology as well as in nanotechnology opened new routes to custom design novel device structures harboring highly mismatched layers as well as materials far beyond the solubility limit. In this paper we discuss III/V nanostructures as well as SiGeSn alloys grown on Si(100). Taking GaAs/InAs core shell nanowires as an example, the possibility to control the crystal structure enables to fabricate advanced radial/axial heterostructures by phase selective epitaxy. Controlling (GaIn)As/(GaIn)Sb core shell nanowires offer broken and staggered bandgap alignments for the design of advanced tunnel FETs. Finally (Si)GeSn alloys of extraordinary structural quality with Sn concentration up to 14% were deposited by reactive gas source epitaxy. PL and absorption data give evidence for a fundamental direct band gap in these materials. The potential of these materials for ultra-low power electronic devices as well as for optoelectronics is demonstrated.
Journal of Crystal Growth, Dec 1, 2009
The influence of the growth temperature in metal organic vapor-phase epitaxy (MOVPE) on intention... more The influence of the growth temperature in metal organic vapor-phase epitaxy (MOVPE) on intentional Cr incorporation during GaN growth is studied in the range 900-1125 1C. The structural properties are investigated and compared to those obtained from undoped layers deposited at the same growth conditions and using the same growth procedure; Whereas, the best surface morphology and the best crystal quality are found at 1125 1C for undoped GaN layers, the best structural and morphological properties are obtained for the Cr-doped GaN (GaN:Cr) layers grown at 950 1C. GaN:Cr layers deposited at this temperature additionally exhibit the highest Cr concentration in the series as well as a Cr accumulation in the beginning stage of GaN:Cr growth. The accumulation may be responsible for the changed growth mode and the improved structural characteristics as well as for the observed V-shaped defects usually associated with strain relaxation. Thermo-remanent magnetization and a hysteresis loop were observed even above room temperature. The magnetic properties correlate to the structural properties of GaN:Cr layers.
Journal of Applied Physics, 2011
InGaN/GaN nanowire ͑NW͒ heterostructures grown by plasma assisted molecular beam epitaxy were stu... more InGaN/GaN nanowire ͑NW͒ heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy ͑HRTEM͒ images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence ͑PL͒ spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However,-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.
2016 IEEE Nanotechnology Materials and Devices Conference (NMDC), 2016
The transport in InAs nanowires is investigated at low temperatures. On wires with different n-ty... more The transport in InAs nanowires is investigated at low temperatures. On wires with different n-type doping information on Rashba and Dresselhaus spin-orbit coupling is gained from weak antilocalization measurements. By using a short local gate quantum point contacts are formed, which show quantized conductance. From bias-depended measurements the g-factor is extracted for different subbands.
Physics, Chemistry and Application of Nanostructures - Reviews and Short Notes - Proceedings of the International Conference on Nanomeeting-2007, 2007
ABSTRACT
CLEO:2011 - Laser Applications to Photonic Applications, 2011
Photonic devices, such as photoconductive switches and integrated photodetectors, have been inten... more Photonic devices, such as photoconductive switches and integrated photodetectors, have been intensively studied in recent years [1], as they play the essential role in high-speed, short-haul optical communication systems due to their high bandwidth, low crosstalk, and superior ...
AIP Conference Proceedings, 2013
We used InAs nanowires with two different charge carrier concentration to fabricate Josephson jun... more We used InAs nanowires with two different charge carrier concentration to fabricate Josephson junctions with superconducting Nb electrodes. For highly doped nanowire junctions a supercurrent is observed up to T ∼ 5 K, for low doped nanowire junctions we were able to tune the Josephson current by a back gate voltage. Owing to the transparent interface between Nb and InAs nanowires subharmonic gap structures due to multiple Andreev reflection have been observed. Furthermore, the effect of magnetic field on the Josephson current was investigated and a monotonous decrease of Josephson current was found. The observed behavior has been compared with a theoretical model.
SPIE Proceedings, 2014
ABSTRACT Due to their strong spin-orbit coupling III-V semiconductor nanowires are excellent cand... more ABSTRACT Due to their strong spin-orbit coupling III-V semiconductor nanowires are excellent candidates for electrical spin manipulation. Therefore, a major goal is to tailor spin-orbit coupling in these devices. Direct electrical spin injection into quasi one-dimensional nanowires is demonstrated. Furthermore, the weak antilocalization effect was investigated in InAs nanowires. The quantum corrections to the conductivity are interpreted by developing a quasi-one-dimensional diffusive model. It turns out that by means of doping and electric gating the spin-lifetimes can be tuned significantly. By creating few-electron quantum dots inside these devices the impact of the confinement on the spin relaxation properties is investigated.
Proceedings of the International Semiconductor Conference, CAS, 2010
ABSTRACT We investigated the quantum transport in InAs nanowires. From the universal conductance ... more ABSTRACT We investigated the quantum transport in InAs nanowires. From the universal conductance fluctuations at 0.5 K a phase-coherence length of 300 nm was extracted. By averaging the gate-dependent conductance fluctuations a magnetoconductance peak due to weak antilocalization was found indicating the presence of spin-orbit coupling. In a nanowire quantum dot formed by three gate fingers single electron tunneling was confirmed.
Physica Status Solidi (C) Current Topics in Solid State Physics, 2012
The conductivity and crystal structure of nominally undoped InAs nanowires deposited by three dif... more The conductivity and crystal structure of nominally undoped InAs nanowires deposited by three different methods – 1. selective area metal organic vapor phase epitaxy (SA MOVPE), 2. gold assisted vapor liquid solid (VLS) MOVPE and 3. extrinsic catalyst free VLS molecular beam epitaxy (MBE) – is investigated. The influence on conductivity by stacking faults and different growth conditions is analyzed to determine the main impact. It is found that in terms of crystal structure, nanowires deposited by VLS MOVPE and VLS MBE behave similarly showing a zinc blende (ZB) phase while nanowires deposited by SA MOVPE feature a high density of stacking faults and a tendency to higher amounts of wurtzite (WZ) when grown with a decreased growth rate. However, the conductivity of wires deposited by VLS MOVPE is found to be much higher and statistically less dispersive compared to the other two wire types. An electrical similarity between nominally undoped wires in VLS MOVPE and previously reported intentionally doped wires in SA MOVPE is observed and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasmonics, 2011
Semiconductor self-assembled Ge-on-Si quantum dot structures coated with Au film were successfull... more Semiconductor self-assembled Ge-on-Si quantum dot structures coated with Au film were successfully employed as surface-enhanced Raman scattering (SERS) substrates to characterize ultramarine blue inorganic art pigment. To assign the bands and to reveal the enhancement mechanisms, the quantum-chemical calculations of vibration spectra of linear and cyclic model compound of SiO4 and AlO4 tetrahedra were carried out. The overtones are observed
Nanotechnology, 2010
In the literature, there are controversies on the interpretation of the appearance in InN Raman s... more In the literature, there are controversies on the interpretation of the appearance in InN Raman spectra of a strong scattering peak in the energy region of the unscreened longitudinal optical (LO) phonons, although a shift caused by the phonon-plasmon interaction is expected for the high conductance observed in this material. Most measurements on light scattering are performed on ensembles of InN nanowires (NWs). However, it is important to investigate the behavior of individual nanowires and here we report on micro-Raman measurements on single nanowires. When changing the polarization direction of the incident light from parallel to perpendicular to the wire, the expected reduction of the Raman scattering was observed for transversal optical (TO) and E(2) phonon scattering modes, while a strong symmetry-forbidden LO mode was observed independently on the laser polarization direction. Single Mg- and Si-doped crystalline InN nanowires were also investigated. Magnesium doping results in a sharpening of the Raman peaks, while silicon doping leads to an asymmetric broadening of the LO peak. The results can be explained based on the influence of the high electron concentration with a strong contribution of the surface accumulation layer and the associated internal electric field.
Nanotechnology, 2012
We investigated the transport properties of GaAs/InAs core/shell nanowires grown by molecular bea... more We investigated the transport properties of GaAs/InAs core/shell nanowires grown by molecular beam epitaxy. Owing to the band alignment between GaAs and InAs, electrons are accumulated in the InAs shell as long as the shell thickness exceeds 12 nm. By performing simulations using a Schrödinger-Poisson solver, it is confirmed that confined states are present in the InAs shell, which are depleted if the shell thickness is below a threshold value. The existence of a tubular-shaped conductor is proved by performing magnetoconductance measurements at low temperatures. Here, flux periodic conductance oscillations are observed which can be attributed to transport in one-dimensional channels based on angular momentum states.
Nanotechnology, 2013
We report on the technology and growth optimization of GaAs/InAs core/shell nanowires. The GaAs n... more We report on the technology and growth optimization of GaAs/InAs core/shell nanowires. The GaAs nanowire cores were grown selectively by metal organic vapor phase epitaxy (SA-MOVPE) on SiO(2) masked GaAs (111)B templates. These were structured by a complete thermal nanoimprint lithography process, which is presented in detail. The influence of the subsequent InAs shell growth temperature on the shell morphology and crystal structure was investigated by scanning and transmission electron microscopy in order to obtain the desired homogeneous and uniform InAs overgrowth. At the optimal growth temperature, the InAs shell adopted the morphology and crystal structure of the underlying GaAs core and was perfectly uniform.
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Papers by Detlev Grützmacher