MBE Arsenic
Quantum Hall Effects (high mobility samples), cleaved etch overgrowth CEO and advanced gating (ion implantation)
Contact: Dr. Christian Reichl
Next to silicon, GaAs/AlAs is one of the most significant and well understood material system in semiconductor physics. Being common in many different application fields, e.g. in communications such as cell phones or satellites, high-efficiency photovoltaics and laser technology, As-based semiconductor heterostructures are currently investigated by many research groups. From a more fundamental point of view, high quality III/V compound semiconductor heterostructures are one basis to study the physics of correlated electrons in systems of reduced dimension.
We fabricate complex GaAs/AlGaAs heterojunctions using MBE with single atom layer precision. Perpetual optimization of the MBE growth to improve the charge carrier mobility and overall sample performances is one key research area within our group.
Very high mobility samples are the foundation to observe a multitude of fragile fractional quantum Hall states (FQHS). The number of defects and impurities incorporated during the MBE growth process needs to be minimized, while the material composition needs to be optimized to obtain highest mobility samples. As the potential disorder created by remote ionized donors is currently considered to be the main factor prohibiting the development of FQH states and especially the ν = 5/2 state, we continue our efforts to reduce the impact of remote ionized impurities on the magneto-transport properties.
For flexible control and spatial definition of 2DEGs, gating techniques are a powerful tool. We focus on gating technologies which are suitable to combine with MBE. This technology allows us to produce structured (buried) back gates which are overgrown by a desired heterostructure. Additionally, since modulated doping has a large impact on the quality of highest-mobilty 2DEGs we also produce and investigate gate-induced electron systems.
The study of one dimensional (1D) physics of cleaved edge overgrowth (CEO) [Deutschmann01,Wegscheider06] quantum wires (QWR) using AlGaAs/GaAs Molecular Beam Epitaxy (MBE) is another current project. Those very pure and atomically precise quantum systems are expected to reveal new physics of 1D Luttinger Liquids. Especially we are interested in the creation of separately gateable coupled QWRs.
[Deutschmann01]: R. A. Deutschmann, W. Wegscheider, M. Rother, M. Bichler, G. Abstreiter, Phys. Rev. Lett. 86, 1857-1860 (2001).
[Wegscheider06]: W. Wegscheider, M. Rother, R. Deutschmann, and T. Feil, physica status solidi (b) 243 (2006)
Indium arsenide quantum dots
Contact: Dr. Stefan Fält
A self-assembled InAs quantum dot (QD) in GaAs allows confinement of carriers in all directions and the formation of a 0-dimensional "artificial atom". With the addition of gates [Kinnischtzke16], the QD can be charged by with electron or holes, which can be identified by shifts in the optical transition in the QD (see figure).
The spin of a single electron [Vamivakas10] or hole [Delteil15] in the QD can be used as a qubit. We aim to improve the material quality and structure of the epitaxially grown QDs. One approach is to use tunnel-coupled QDs charged with two electrons and use the singlet and triplet spin configurations as these are protected from magnetic and electric decoherence processes [Delley15].
[Kinnischtzke16] L. Kinnischtzke et al., Appl. Phys. Lett. 108, 211905 (2016)
[Vamivakas10] A. N. Vamivakas et al., Nature 467, 297 (2010)
[Delteil15] A. Delteil et al., Nature Physics 12, 218 (2015)
[Delley15] Y. L. Delley et al., arXiv:1509.04171 [cond-mat.mes-hall]