Atomic structure of surfaces and interfaces

The first step in understanding the electronic and optical properties of surfaces is to know what the surface reconstruction looks like. We achieve this using different methods. In order to use electron-based methods the investigations are made in Ultra High Vacuum (UHV). The surfaces are prepared by MBE and MOVPE growth and either transferred into our chambers under UHV conditions, or cleaned within our chambers by desorbing a protective cap.

In order to gain information about the atomic surface structure we combine Scanning Tunneling Microscopy (STM) and Photoemission Spectroscopy (PES), the latter carried out at the Synchrotron radiation source at BESSY. Standart UHV techniques, such as Low Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES) are used to characterise surface symmetry and stoichiometry. Reflectance Anisotropy Spectroscopy (RAS), as an optical probe, allows to compare surfaces under UHV conditions to those in MOVPE environment and helps to monitore the surface preparation.

Based on the experimental results obtained on a specific surface, different stucture models can be tested. Together with the theoretical calculations it is possible to determine the best fitting model.

Our work focus on clean surfaces of III-V semiconductor materials like GaAs, GaP, InP and InGaP. On such defined "subtrates" we investigate the growth of ferromagnetic metals (Fe, Co, Ni). The junctions are possible candidates for new "spintronic" (spin-injection dependent) semiconductor devices.

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