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Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Schapers T.,Jülich Research Center | Schapers T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 4 more authors.
Crystal Growth and Design | Year: 2014

We present a novel type of core-shell nanowires in which only certain parts of the core are covered by the shell. This is achieved by the crystal phase selective growth of the InAs shell on zinc blende GaAs nanowires with controlled wurtzite inclusions. The shell grows on the zinc blende phase, but its growth is hindered on the wurtzite crystal phase. Nucleation of InAs occurs exclusively on the zinc blende GaAs regions. The wurtzite segments are placed inside self-catalyzed GaAs nanowires by partially consuming and refilling the Ga droplet. The crystal phase selective growth of InAs on the side facets of the GaAs nanowires is explained by the local environment of each new In atom. Because of unbalanced neighbors on the wurtzite side facets, the growth of a highly lattice mismatched material is hindered. This happens not only on the wurtzite segments, but also on regions being characterized by a high density of twins. © 2014 American Chemical Society.


Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Lepsa M.I.,Jülich Research Center | Lepsa M.I.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 4 more authors.
Journal of Crystal Growth | Year: 2013

The control of the Ga droplet during the MBE growth and its impact on the crystal structure of self-catalyzed GaAs nanowires (NWs) were investigated. The consumption of the droplet proceeds in two steps. First, the contact angle decreases to 901 keeping the NW diameter constant. The crystal structure changes from zinc blende (ZB) to wurtzite (WZ). Then, the contact angle keeps constant while the top radius of the NW decreases and the NW grows again in ZB configuration. During the last step, {110}, {211}B and {100} facets develop at the top. Calculations show that the Ga desorption from the droplet has to be taken into account during its consumption. With this information, several WZ segments of different lengths were placed into ZB GaAs NWs via partial droplet consumption. For this purpose, we supplied As and Ga separately, in order to partially consume and refill the Ga droplet. The same mechanism was applied to self-catalyzed InAs NWs resulting in short WZ segments inserted in a ZB twinning superlattice. © 2012 Elsevier B.V. All rights reserved.


Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Heiderich S.,Jülich Research Center | Heiderich S.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 7 more authors.
Journal of Crystal Growth | Year: 2012

We present detailed results about the molecular beam epitaxy (MBE) growth of GaAs nanowires (NWs) on GaAs (111)B substrates prepared for the growth by a new method using hydrogen silsesquioxane (HSQ). Before the growth, HSQ is converted to SiO x by thermal treatment. The NWs are grown via the vapor-liquid-solid (VLS) mechanism. The influence of five growth parameters are described: SiO x thickness, growth time, substrate temperature and Ga and As 4 beam fluxes. It is shown that the nanowire density can be tuned by two orders of magnitude by adjusting the SiO x thickness. Additionally, the results demonstrate that the axial growth is controlled by the As 4 beam flux whereas the lateral growth is controlled by the Ga beam flux. The observed NW tapering is mainly determined by the V/III beam flux ratio. Our study gives important information about the VLS growth mechanism, which is extended by considering the secondary adsorption process of Ga adatoms. The nanowires have predominantly zinc blende crystal structure with rotational twins. A wurtzite segment is always found at the top of the NWs being associated with the growth after the Ga shutter has been closed. © 2012 Elsevier B.V. All rights reserved.


Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Rosenbach D.,Jülich Research Center | Rosenbach D.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 10 more authors.
Nano Letters | Year: 2016

We demonstrate the growth and structural characteristics of InAs nanowire junctions evidencing a transformation of the crystalline structure. The junctions are obtained without the use of catalyst particles. Morphological investigations of the junctions reveal three structures having an L-, T-, and X-shape. The formation mechanisms of these structures have been identified. The NW junctions reveal large sections of zinc blende crystal structure free of extended defects, despite the high stacking fault density obtained in individual InAs nanowires. This segment of zinc blende crystal structure in the junction is associated with a crystal phase transformation involving sets of Shockley partial dislocations; the transformation takes place solely in the crystal phase. A model is developed to demonstrate that only the zinc blende phase with the same orientation as the substrate can result in monocrystalline junctions. The suitability of the junctions to be used in nanoelectronic devices is confirmed by room-temperature electrical experiments. © 2016 American Chemical Society.


Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Rosenbach D.,Jülich Research Center | Rosenbach D.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 8 more authors.
Nano Letters | Year: 2015

By applying a texturing process to silicon substrates, we demonstrate the possibility to integrate III-V nanowires on (100) oriented silicon substrates. Nanowires are found to grow perpendicular to the {111}-oriented facets of pyramids formed by KOH etching. Having control of the substrate orientation relative to the incoming fluxes enables not only the growth of nanowires on selected facets of the pyramids but also studying the influence of the fluxes on the nanowire nucleation and growth. Making use of these findings, we show that nanowires with different dimensions can be grown on the same sample and, additionally, it is even possible to integrate nanowires of different semiconductor materials, for example, GaAs and InAs, on the very same sample. © 2015 American Chemical Society.


Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Luysberg M.,Jülich Research Center | Schapers T.,Jülich Research Center | And 6 more authors.
Nano Letters | Year: 2012

We present results about the growth of GaAs/InAs core-shell nanowires (NWs) using molecular beam epitaxy. The core is grown via the Ga droplet-assisted growth mechanism. For a homogeneous growth of the InAs shell, the As4 flux and substrate temperature are critical. The shell growth starts with InAs islands along the NW core, which increase in time and merge giving finally a continuous and smooth layer. At the top of the NWs, a small part of the core is free of InAs indicating a crystal phase selective growth. This allows a precise measurement of the shell thickness and the fabrication of InAs nanotubes by selective etching. The strain relaxation in the shell occurs mainly via the formation of misfit dislocations and saturates at ∼80%. Additionally, other types of defects are observed, namely stacking faults transferred from the core or formed in the shell, and threading dislocations. © 2012 American Chemical Society.


Lepsa M.I.,Jülich Research Center | Lepsa M.I.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Rieger T.,Jülich Research Center | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | And 8 more authors.
2016 Compound Semiconductor Week, CSW 2016 - Includes 28th International Conference on Indium Phosphide and Related Materials, IPRM and 43rd International Symposium on Compound Semiconductors, ISCS 2016 | Year: 2016

We present results about the growth, structural and strain relaxation properties and room temperature electrical transport of GaAs/InSb core-shell nanowires grown self-catalyzed by molecular beam epitaxy on Si (111) substrates. Due to the high lattice mismatch of about 14%, the growth of the shell proceeds from an island-based nucleation to a closed and rather smooth layer. High resolution transmission electron microscopy in combination with geometric phase analyses are used to identify different types of dislocations responsible for the strain relaxation on zinc blende and wurtzite core-shell nanowire segments. While on the wurtzite phase only Frank partial dislocations with bWZ,FP = c/2[0001] are found, the strain on the zinc blende phase is relaxed by perfect and Schokley and Frank partial dislocations with bZB,p = a/2(110), bZB,SP = a/6(112) and bZB,FP = a/3(111), respectively. Electrical transfer characteristics of the core-shell nanowires show an ambipolar behavior whose strength depends strongly on the dimensions of the nanowires. © 2016 IEEE.


Davydok A.,University of Siegen | Rieger T.,PGi | Rieger T.,Julich Aachen Research Alliance for Fundamentals of Future Information Technology JARA FIT | Biermanns A.,University of Siegen | And 6 more authors.
Journal of Applied Crystallography | Year: 2013

Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO x layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

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