Electronic and Magnetic Properties of the Fe/GaAs(110) Interface
by Tim Iffländer
Date of Examination:2015-10-30
Date of issue:2016-02-29
Advisor:Prof. Dr. Rainer G. Ulbrich
Referee:Prof. Dr. Rainer G. Ulbrich
Referee:Prof. Dr. Hans Christian Hofsäss
Persistent Address:
http://dx.doi.org/10.53846/goediss-5503
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Abstract
English
Metal-semiconductor interfaces are present in every semiconductor device and are therefore of fundamental importance in modern technology. In this thesis we investigate the structural, electronic, and magnetic properties of the low-temperature (LT) grown Fe/GaAs{110} interface. In order to check the validity of theoretical models describing the microscopic process of Schottky barrier formation, the LT grown Fe/GaAs{110} interface serves as an ideal model system that is studied by means of atomically resolved cross-sectional scanning tunneling microscopy (XSTM) and spectroscopy (XSTS). Highly resolved LT XSTS measurements show a continuum of states inside the band gap of the p-type semiconductor. That these states are metal-induced gap states (MIGS) is demonstrated in a control experiment across a p-type GaAs edge without Fe film where no gap states are observed. Furthermore, we combine XSTS along the space charge region of the semiconductor with three-dimensional finite element simulations of the electrostatic potential inside the space charge region. In this way we take into consideration the tip-induced band bending, determine the Schottky barrier (SB) height of the ideal p-type Fe/GaAs(110) interface, and obtain a spatial and energetic map of the local density of states inside the valence band of the same interface. A comparison of the XSTS data and density functional theory (DFT) calculations reveals the relevance of both MIGS and bond polarization models. Moreover, the very good agreement between the XSTS and DFT data demonstrates that the XSTS technique is an excellent approach to investigate the microscopic process of SB formation. In this thesis, we also investigate the influence of different growth conditions on the structure, the SB height, and the charge distribution at p-type interfaces by means of XSTM and XSTS. Furthermore, in this thesis, the magnetic anisotropy of ultrathin (2—3 monolayer thin) LT grown Fe films on the GaAs{110} surface is investigated by means of in situ magneto-optic Kerr effect measurements in longitudinal, polar, transverse and mixed geometry. These measurements exhibit an out-of-plane magnetization which is unidirectionally coupled to the in-plane magnetization component along the <001> direction and directly related to the inversion asymmetry of the GaAs{110} surface in the same direction. Magneto-optic simulations show that this magnetic anisotropy cannot be explained by a simple canted magnetization of the Fe film.
Keywords: cross-sectional scanning tunneling microscopy; cross-sectional scanning tunneling spectroscopy; STM; STS; ideal metal-semiconductor interface; Schottky barrier; metal-induced gap states; bond polarization; in situ magneto-optic Kerr effect; MOKE; ultrathin magnetic films; magnetic anisotropy of thin films; Fe; GaAs(110); tip-induced band bending; 3D finite element simulation; space charge region