Semiconductor Quantum Nanomaterials - Research
Group leader: Dr. Gregor Koblmueller (Chair of Prof. Dr. Jonathan Finley)
Our research activities on semiconductor quantum nanomaterials aim at four different domains:
A major workhorse for our research on advanced nano-systems/devices are innovative semi-conductor nano- & quantum-heterostructures created by design using accurately controlled synthesis methods. Specifically we employ ultrahigh-purity molecular beam epitaxy (MBE) dedicated to III-V compound semiconductors (arsenides/antimonides), group-III nitrides and, soon to come, new classes of emerging 2D materials. Currently, a substantial effort in synthesis is on III-V nanowires (NW), which offer unique capabilities in heterostructure and crystal phase engineering, as well as site-selective growth and deterministic incorporation of atomically engineered low-dimensional quantum systems. The following selection of key public-cations gives a brief view into ongoing activities in growth/synthesis research of 1D-NWs and their quantum heterostructures.
F. Del Giudice, D. Ruhstorfer, T. Stettner, H. Riedl
T. Stettner, et al., “Coaxial GaAs-AlGaAs core-multi-shell nanowire lasers with epitaxial gain control”, Appl. Phys. Lett. 108, 011108 (2016).
J. Treu, et al.: “Lattice-matched InGaAs-InAlAs core-shell nanowires with improved luminescence and photoresponse properties”, Nano Letters 15, 3533 (2015).
B. Loitsch, et al., “Tunable quantum confinement in ultrathin, optically active semiconductor nanowires via reverse-reaction growth” Advanced Materials 27, 2195 (2015).
To establish the as-grown quantum nano-structures for various different devices, it is important to clearly understand their structure-property relationships to predict their performance. This requires advanced high-resolution spectroscopy and imaging methods to resolve properties quantitatively and at the nanoscale. Here, we employ a whole toolbox of different nano-metrology techniques to link specific structural and morphological features with electrical, optical, mechanical and thermal properties. Examples of such methods include electrical scanning probe microscopy (SPM) techniques, high-resolution electron and ion-beam microscopy, µRaman spectroscopy, time- and spatially resolved µPL spectroscopy (vis-to-midIR), absorption spectroscopy, etc. Typical examples of research in this field are illustrated in various selected publications.
J. Becker, F. Del Giudice, D. Ruhstorfer, T. Stettner
J. Becker, et al., “Correlated chemical and electrically active dopant analysis in catalyst-free Si-doped InAs nano-wires”, ACS Nano DOI:10.1021/-acsnano/7b08197 (2018).
B. Loitsch, et al.: “Suppression of alloy fluctuations in GaAs-AlGaAs core-shell nanowires”, Appl. Phys. Lett. 109, 093105 (2016).
T. Yang, et al., “Size, composition, and doping effects on In(Ga)As-nanowire/Si tunnel diodes probed by conductive atomic force microsccopy” Appl. Phys. Lett. 101, 233102 (2012).
PHOTONIC PROPERTIES / DEVICES
One of our current research directions is to develop high-performance integrated photonic, quantum photonic and optoelectronic devices based on on-chip monolithically integrated quantum nanomaterials, in particular nanowires (NW). Specific examples include NW-based lasers and non-classical single photon emitters based on NW-QD (-quantum dot) devices for next-generation information technology, quantum communication and sensing. Hereby, an important task is to explore the optical and photonic responses of the respective systems using advanced confocal luminescence spectroscopy, where e.g. the effects of the quantized electronic structure, light-matter interactions, or the coupling of light to on-chip photonic circuits are probed. The following key publications illustrate our current work on integrated photonic NW-based devices and their properties.
J. Bissinger, P. Schmiedeke, T. Stettner, A. Thurn
T. Stettner, et al., “Direct coupling of coherent emission from site-selectively grown III-V nanowire lasers into proximal silicon waveguides”, ACS Photonics 4, 2537 (2017).
B. Loitsch, et al.: “Microscopic nature of crystal phase quantum dots in ultrathin GaAs nanowires by nano-scale luminescence characterization”, New J. Phys. 18, 063009 (2016).
B. Mayer, et al., “Monolithically integrated high-b nanowire lasers on silicon” Nano Letters 16, 152 (2016).
ELECTRONIC PROPERTIES / DEVICES
The materials under investigation are also prime candidates for advanced quantum transport studies and future electronic devices with performance perspectives that go well beyond those of classical field-effect transistors. A major focus of our work aims therefore at developing high-mobility III-V based NW channels as well as systems with large spin-orbit interaction (e.g. InAs NW) for topological superconductor-semiconductor interfaces. Important goals here are to understand and optimize the semi-classical & quantum transport phenomena in dependence of channel & device design, quantum confine-ment, structural properties, etc. using low-noise, temperature- and field-dependent transport spectroscopy. In addition, we also explore the thermoelectric transport properties in these systems. Recent highlights are summarized in the respective selection of key publications.
J. Becker, S. Fust, C. De Rose, D. Ruhstorfer
D. Irber, et al.: “Quantum transport and sub-band structure of modulation-doped GaAs-AlAs core-superlattice nanowires” Nano Letters 17, 4886 (2017).
J. Ju, et al.: “Thermoelectric properties of In-rich InGaN and InN/InGaN superlattices” AIP Advances 6, 045216 (2016).
S. Morkötter, et al., “Demonstration of confined electron gas and steep-slope behavior in d-doped GaAs-AlGaAs core-shell nanowire transistors” Nano Letters 15, 3295 (2015).