Abstract：High mobility GaAs/AlGaAs structures grown with molecular beam epitaxy (MBE) are required to study phenomena such as the exitonic superfluid in electronic bilayers, and the “5/2” fractional quantum Hall state which is a prime candidate for topological quantum computing. Up to now only a few laboratories have achieved the desired electron mobilities. The reason is that the available techniques do not have the sensitivity to analyze the impurity level of the residual gas or of the starting materials. Thus the MBE growers rely on experience and simply on “gut” feeling in designing their MBE systems and optimizing the process. In this talk I will describe the measures with which we increased the electron mobility from 106 cm2/Vs to 2′107 cm2/Vs in two different MBE systems. I will discuss the requirements on the MBE-vacuum system and the modifications which led to improvement in sample purity. Equally important is the collaboration with materials suppliers to obtain the best possible starting materials. Correct operating the MBE systems is obviously also relevant. I will detail the measures which we had taken and will assess their relative importance. Based upon the high-mobility wafers we could study the 5/2 state and the excitonic superfluid state.
About speaker (Prof. Dr. Werner Dietsche)：
Physics Study at the University Karlsruhe, at the Research Center Jülich and at University of Ottawa, Canada, PhD from University Karlsruhe
1975-1989 Research Work at the Technical University Munich and at the University of Illinois, USA
1989-2011 Max-Planck-Institute Stuttgart (von Klitzing department)
Research highlights:
1. Experiments with ballistic and monochromatic phonons (1975-1995)：clarification of the anomalous Kapitza transmission, phonon properties of amorphous solids， phonon wave vector spectroscopy of 2DEGs, phonon imaging
2. Molecular Beam Epitaxy(1990-2011):HiTc-layers with MBE, High mobility GaAs based MBE
3. Quantum-Hall effect (1990-2011):Decorating the hot spots with superfluid helium, Imaging the QHE: electro-optically, Current induced nuclear polarization at the fractional quantum Hall effect,
Frictional drag between electron layers, Excitonic superfluid in quantum Hall bilayers