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Institute of Semiconductor and Solid State Physics
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Nanoscale Semiconductors Group.
 

Group Members
 

Group Leader:
Univ. Prof. Dr. Armando Rastelli

Post-Docs:
Dr. Ievgen Brytavskyi
Dr. Saimon Filipe Covre da Silva
Dr. Santanu Manna

PhD Students:
M.Sc. Dee Rocking Cyrlyson's

DIin Julia Freund
DIin Barbara Lehner, opens an external URL in a new window
DI Christian Schimpf
DI Tobias Maria Krieger
DI Gabriel Undeutsch

Undergraduate Students:
Maximilian Aigner, B.Sc.
Ailton José Garcia Junior, B.Sc.
Andreas Kitzmüller, B.Sc.
Lars Neuser, B.Sc.
Thomas Oberleitner, B.Sc.
Melina Peter, B.Sc.
Christoph Plattner, B.Sc.
Kajetan Schweighofer, B.Sc.

Research Fields

Semiconductor Quantum Dots (QD) for quantum photonics

Our focus is to explore and push the limits of semiconductor nanostructures as scalable sources of single and entangled photon pairs for application in emerging quantum technologies.

We mostly focus on GaAs QDs in AlGaAs matrix, which we grow by Molecular Beam Epitaxy (MBE), opens an external URL in a new window in the cleanroom of our institute. After having tried out different strategies over the past years (hierarchical self-assembly, opens an external URL in a new window, Ga-droplet etching, opens an external URL in a new window), we have selected Al-based droplet etching, opens an external URL in a new window as the most promising route to produce high-quality QDs. The  main reasons are: 1) the whole fabrication process takes place at high temperature, minimizing the occurrence of crystal defects; 2) the QDs can be seamlessly embedded in photonic and optoelectronic structures similar to conventional InGaAs QDs in GaAs matrix, a property which have recently used to enhance light extraction, opens an external URL in a new window and to achieve electrical injection, opens an external URL in a new window; 3) the size of the QDs, opens an external URL in a new window can be changed to achieve any desired wavelength in the range 680-805 nm; 4) QDs with high in-plane symmetry, opens an external URL in a new window can be obtained, facilitating the generation of entangled photons; 5) the radiative recombination times can be substantially shorter than conventional QDs, which is beneficial for fast operation and generation of indistinguishable, opens an external URL in a new window and entangled photons, opens an external URL in a new window.

To control the properties of the QDs after growth we have been exploring different strategies ranging from permanent tuning via laser annealing, opens an external URL in a new window to reversible tuning via electric fields, opens an external URL in a new window and piezoelectric-induced strains, opens an external URL in a new window. Post-growth strain engineering is a powerful method to control the emission wavelength of QDs, for instance in light-emitting diodes, opens an external URL in a new window, and to obtain highly-entangled photons, opens an external URL in a new window from QDs by removing the effect of residual asymmetries. Besides using commercially available piezoelectric substrates, we have patented microstructured piezoelectric actuators, opens an external URL in a new window, which allow the in-plane stress tensor of a semiconductor membrane, opens an external URL in a new window to be fully controlled. This has allowed the demonstration of a QD-based wavelength-tunable source of entangled photons, opens an external URL in a new window. With such a method we envision the possibility of using separate sources to build-up quantum-relays, opens an external URL in a new window. As a first step in this direction, we have performed two-photon interference, opens an external URL in a new window between photons emitted by two separate QDs.

GaAs QDs are also ideally suited for fundamental studies, opens an external URL in a new window, as their structural properties can be conveniently obtained from scanning probe microscopy and they are practically unstrained. Combined with post-growth strain engineering, the optical selection rules, opens an external URL in a new window for excitons confined in these QDs can be widely tuned to match specific applications.