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Semiconductor Nanostructures and Quantum Systems

Prof. Jonathan Finley

Research Field

Our group explores a wide range of topics related to the fundamental physics of nanostructured materials and their quantum-electronic and -photonic properties. We study the unique electronic, photonic and quantum properties of materials patterned over nanometer lengthscales and explore how sub-components can be integrated together to realise entirely new materials with emergent properties. This convergence of materials-nanotechnology, quantum electronics and photonics is strongly interdisciplinary, spanning topics across the physical sciences, as well as materials science and engineering.

Address/Contact

Am Coulombwall 4/I
85748 Garching b. München
+49 89 289 12771
Fax: +49 89 289 12704

Members of the Research Group

Professor

Office

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Students

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Teaching

Course with Participations of Group Members

Offers for Theses in the Group

3D-Structured III-V Nanowires for Ultrahigh-Efficiency Solar Cells

At the Walter Schottky Institute (WSI-TUM) we recently launched a research project directed to the exploration of new types of high-efficiency solar cell systems based on 3D-structured III-V semiconductor nanowires.

Conventional single-cell photovoltaic devices are known to have performance limits due to large thermal and spectral losses, light trapping issues and charge carrier losses. To overcome these problems 3D-structured nanowire (NW) solar cells have emerged as promising systems with improved light trapping and absorption properties beyond the ray-optic limit, as well as better carrier collection efficiencies.

The goal of this M.Sc. project is to exploit the advantages of 3D-structured III-V semiconductor NWs and work towards a novel hot carrier solar cell (HCSC), which allows to selectively cool charge carriers and reduce thermal losses. Hereby, you will be closely working together with two PhD students to first design proper bottom-up III-V NW heterostructures from the group-III-V family of semiconductors. Exploiting the full geometrical and energy-selective parameter space, the design will be directly guided by in-depth simulations for enhanced photoabsorption and effective carrier thermalization properties. NW heterostructures on lithographically patterned substrates should then be realized by top-down/bottom-up nanofabrication processes and further characterized by various optical spectroscopy methods (photoluminescence, FTIR, and UV-Vis-NIR absorption spectroscopy). Finally, the goal is to identify correlations between array-geometry, NW dimensions, and electronic properties of the selected heterostructure material (band gap and strain) and the corresponding optical and charge carrier responses.

You will gain & learn:

  • Knowledge in electromagnetic (FDTD) and electronic band structure simulations (nextnano)
  • Advanced lithography / clean-room processes for state-of-the art 3D structured NWs
  • Diverse optical spectroscopy (micro-Photoluminescence, FTIR, UV-Vis-NIR absorption)
  • Correlated microscopy methods (SEM, He-Ion Microscopy)

Experience in the area of clean room fabrication, optical spectroscopy or nanoanalytics, as well as experience in simulations is a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de and Jonathan.Finley@wsi.tum.de. Please include your CV, and a transcript of records (Bachelor & Master).

May 2019

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Gregor Koblmüller
Advanced Nano-Thermoelectrics based on III-V Semiconductor Nanowires

At the Walter Schottky Institute (WSI-TUM) we currently conduct an extensive research program on the realization of high carrier mobility III-V semiconductor nanowires and their application in next generation ultrascaled nanoelectronics and thermoelectric energy conversion.

An important step towards high performance nano-thermoelectric devices is the development of suitable high carrier mobility materials which simultaneously allow high electrical conductivity and large Seebeck coefficient, while minimizing thermal conductivity. In this regard, 1D-semiconductor nanowires are very promising nano-thermoelectric systems, since they exhibit reduced density of states (DOS) and complex core-multishell structure design enabling to meet all these relevant criteria.

The goal of this M.Sc. project is to explore novel modulation doped InAs/AlSb core-multishell nanowire heterostructures and investigate their potentials in nano-thermoelectrics by a combination of semi-classical and quantum transport experiments as well as characterization of thermal transport. Interacting closely with two PhD students you will be designing the proper InAs/AlSb nanowire materials and further transform these into 2- or 4-terminal nanowire-field effect transistor (NWFET) devices together with resistively coupled heaters using advanced nanolitho­graphy methods in state-of-the art cleanroom facilities. These nano-thermoelectric devices should be then characterized with respect to their internal structure and 1D-DOS, contact behavior, carrier density and channel length in order to identify different regimes of transport and thermopower using temperature-dependent electrical transport spectroscopy. In addition, thermal transport on these systems will also be characterized using a novel non-destructive optical technique (Raman spectroscopy).

You will gain & learn:

  • Knowledge in design of low-dimensional III-V semiconductors with high carrier mobility
  • Fabrication of nanoelectronic & nano-thermoelectric devices using nano-lithography
  • Experience in low-noise, low-temperature electrical transport characterization
  • Experience in optical spectroscopy, specifically Raman spectroscopy
  • Diverse microscopy methods (AFM, SEM, He-Ion Microscopy)

     

      Experience in the area of clean room fabrication, nanoanalytics or (nano)electronics, as well as experience using Matlab is a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de and Jonathan.Finley@wsi.tum.de. Please include your CV, and a transcript of records (Bachelor & Master).                  May2019

M

M

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Gregor Koblmüller
Electron Spin Qubits in Quantum Dot Molecules - Towards a Quantum Repeater

 

Quantum communication using single photons provides one route towards physically secure data transmission. However, the total length of today’s quantum key distribution systems is limited to about ~300km due to photon absorption in the “quantum channel” - typically an optical fiber. To overcome this problem, one can build so-called “quantum repeaters” in which the channel is broken down into shorter segments connected by quantum links. In our group we are working towards building a quantum repeater using optically active semiconductor-based quantum dot molecules.  We aim to make use of trapped pairs of charges – singlet-triplet (S-T) spin qubits.

In the first part of this MSc. project you fabricate a quantum photodiode structure containing coupled quantum dots. This will involve clean-room fabrication, as well as electrical characterization of the fabricated diodes. In the second part, your focus will be on optical characterization of the S-T spin qubits. The goal is to measure exceedingly long coherence times (>>1µs) for special electric fields where the energy gap of the qubit is insensitive to electric and magnetic field fluctuations.

Prior knowledge in optics, clean-room fabrication and programming are helpful – but secondary to high motivation and an open and curious mindset to tackle challenging problems. You will get experience in state-of-the-art nanofabrication, optical spectroscopy at cryogenic temperatures, as well as understanding of semiconductors in the context of quantum information and technology.

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley
Quantum Emitters in 2D Materials

2D materials were shown in 2015 to host randomly occurring single-photon emitting sites. Due to unique properties, such as ultimate proximity of the light sources to the surface that result in high photon extraction efficiencies, nuclear spin-free isotopes, valley pseudospin and potential for scalability, 2D materials are extremely promising as building blocks for solid-state photon-based quantum information. They have the potential to overcome the limitations of the current systems as highly sensitive, easily integrable quantum light sources and qubits of the future1. However, in current 2D quantum emitters the photon emission energy is random2. This prevents photon indistinguishability, a non- negotiable requirement for both fundamental studies and applications. Moreover, the current fabrication process is incompatible with silicon photonics and on-chip integration. To unleash the full impact of 2D materials on quantum science and technology, we are currently attempting a novel fabrication strategy. In the first part of the project, you will realize quantum dots of 2D semiconductors top-down, with dimensions below those achievable through conventional lithography systems, using a combination of etching masks made of colloidal quantum dots and by Helium Ion Beam Lithography followed by Reactive Ion Etching. Such quantum dots will be deterministic, scalable and will overcome the critical limitations of the current solid-state quantum emitters in 2D materials. You will study the optical properties of such quantum emitters at cryogenic temperatures and in the presence of magnetic fields. Further, you will have the option of integrating such quantum emitters and their arrays with optical cavities and waveguides, realizing spin-qubits registers made of arrays of independently charged quantum-dots and studying the effect of interactions among separate quantum emitters placed at a subwavelength distance. This is a challenging but no current solid-state quantum dot system satisfies the requirements to do so.

Some experience in the areas of optics, electronics, programming or cleanroom fabrication will be beneficial, but secondary to your personal motivation and commitment to this fascinating project. You will gain skills and knowledge and probably become an expert in various scientific research tasks, including but not limited to nanoscale cleanroom fabrication and state-of-the-art electro-optical measurements at cryogenic temperatures.

You should: be a highly motivated student with a curious and open mind looking to solve. This is a challenging but potentially ground-breaking project in the framework of quantum science and technology. You will work in close collaboration with a small team of Ph.D students and a postdoc, therefore teamwork is crucial. You must enjoy working with others, have a knack for a good laugh and you shouldn’t take yourself too seriously, these skills will help with the regular frustrations arising when doing research.

You will get: experience on state-of-the-art (or beyond) nanofabrication and on performing optical spectroscopy in state-of-the-art laboratories, a sound understanding of the physics of 2D materials and solid-state quantum optical systems, and if everything goes well a nice (or even amazing) paper in a top journal. Maybe most importantly, you will also have a lot of fun along the way.

As we expect a significant number of applicants, please enquire as soon as possible. For inquiries feel free to write to Dr. Matteo Barbone: Matteo.Barbone@wsi.tum.de
suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley
Quantum optics on coupled quantum dots

Solid-state qubits are a promising platform for future quantum technology applications. Among them, semiconductor-based quantum dot molecules (QDMs) - two coupled quantum dots – promise unique properties. Long coherence times (>1µs) and strong optical dipole transitions make them ideal candidates for quantum communication purposes.


Our group works towards the implementation of a multi qubit-photon interface by optically controlling spin states in QDMs.

In your Master's project, you will gain experience in nanofabrication while preparing QDM samples. However, the main part of your time you will spend in an optics lab: Besides studying the fundamental structure of QDMs, you will join in implementing resonance and pulsed excitation to the existing setup. This will enable the investigation and manipulation of charge spins in QDMs at cryogenic temperatures.

For successfully participating in the project, prior knowledge in optics and programming is beneficial. Being keen to learn about quantum optics and being able to work in a team is even more important.


If you are interested in joining the project and our group, please send your application (including CV and transcript of records) tofrederik.bopp@wsi.tum.de and finley@wsi.tum.de.

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Nuclear, Particle, and Astrophysics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley
Ultrafast Electron-Photon Dynamics in Nanowire Lasers

Wavelength-scale coherent optical sources are vital for a wide range of applications in nanophotonics ranging from metrology and sensing to nonlinear frequency generation and optical switching. Since precision metrology and spectroscopy is enabled by the ability to generate phase-stabilized trains of ultrafast laser pulses, it is of particular interest to realize such a technology on-chip. However, the complexity of conventional mode-locked laser systems has so far hindered their realization at the nanoscale. Recently, we demonstrated that subsequently emitted ultrafast laser pulses emitted from incoherently pumped GaAs-AlGaAs core-shell nanowire lasers remain mutually phase coherent over timescales that are approximately ten times longer than the emitted pulse duration1. A deeper understanding of the factors governing the electron and photon dynamics of NW lasers is now crucial for further developments.

In this project, you will, therefore, investigate the carrier relaxation and gain dynamics of novel quantum confined nanowire laser structures by employing ultrafast pump-probe spectroscopy. Thereby you will explore the influence of composition modulation and low dimensional gain media on the frequency and phase-dependent lasing characteristics. Further, you will have the option of extending the current pump-probe setup in order to study coupling and switching phenomena in NW-based silicon photonic circuits.

You will get experience in performing state-of-the-art ultrafast spectroscopy at room and cryogenic temperatures, and a solid understanding of the physics of semiconductor nanolasers.

In this thesis, you will be closely working with several other student members at WSI. Good knowledge in physics, especially optics, semiconductors, as well as previous experience with lab work related to of nanophotonics or quantum optics are a benefit, but secondary to motivation and commitment. Applications should be sent to Andreas.Thurn@wsi.tum.de, Gregor.Koblmueller@wsi.tum.de, or Jonathan.Finley@wsi.tum.de. Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

[1] Mayer, B. et al. Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser. Nat. Commun. 8, 15521 (2017)

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley
Imaging of Neural Action Potentials by Quantum Sensors and Deep Learning

Our lab is using solid state qubits to build sensors, for instance for magnetic fields. We aim to apply them to various applications, with a particular focus on life sciences.

We are seeking a MSc student to study a novel application, imaging of electric action potentials of neurons, the cells performing computation in the brain. This should involve the development of a new type of sensor, based on solid state quantum materials, smart signal processing by artificial neural networks, or a combination of both.

Techniques:

* You will learn to prepare microscopy samples of both solid state samples and cell cultures. 

* You will design an experiment to detect the weak optical signals from these samples in one of our existing microscope setups. This will involve development of advanced optics and control software.  

Depending on preference you will either

* Study fluoresent quantum materials like red fluorescent diamond and their response to external electric fields. 

* Develop signal processing protocols to enhance these signals in existing devices 

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Nuclear, Particle, and Astrophysics
  • Master’s Thesis Biophysics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Friedemann Reinhard

Current and Finished Theses in the Group

Dynamics of Superconducting Nanowires Single Photon Detectors (SNSPDs)
Abschlussarbeit im Masterstudiengang Physics (Applied and Engineering Physics)
Themensteller(in): Jonathan Finley
Planar Scanning Probes
Abschlussarbeit im Masterstudiengang Physik (Physik der kondensierten Materie)
Themensteller(in): Friedemann Reinhard
Vibrational and optical properties of freestanding atomically-thin nanomaterials
Abschlussarbeit im Masterstudiengang Physik (Physik der kondensierten Materie)
Themensteller(in): Jonathan Finley
Spectroscopy of localized interlayer excitons in van-der-Waals heterostructures
Abschlussarbeit im Masterstudiengang Physics (Applied and Engineering Physics)
Themensteller(in): Jonathan Finley
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