Abstract
The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging
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Citation Formats
Luber, S M.
III - V semiconductor structures for biosensor and molecular electronics applications.
Germany: N. p.,
2007.
Web.
Luber, S M.
III - V semiconductor structures for biosensor and molecular electronics applications.
Germany.
Luber, S M.
2007.
"III - V semiconductor structures for biosensor and molecular electronics applications."
Germany.
@misc{etde_20865472,
title = {III - V semiconductor structures for biosensor and molecular electronics applications}
author = {Luber, S M}
abstractNote = {The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed by a thorough topographical and electrical characterization of fabricated devices which includes the electrostatic trapping of single gold nanoclusters between the electrodes. A first application to molecular electronics is presented by conductance measurements on a molecular layer of oligophenylenvinylene derivatives. Simulations on model molecules applying extended Hueckel theory and the nonequilibrium Greens function formalism reveal a good qualitative agreement between theory and experiment. Furthermore, promising extensions to the present fabrication method are discussed. These include the processing and characterization of broken T-shaped electrodes suitable for measurements on single molecules, and the transition to pure semiconductor electrodes based on indium arsenide. (orig.)}
place = {Germany}
year = {2007}
month = {Jan}
}
title = {III - V semiconductor structures for biosensor and molecular electronics applications}
author = {Luber, S M}
abstractNote = {The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed by a thorough topographical and electrical characterization of fabricated devices which includes the electrostatic trapping of single gold nanoclusters between the electrodes. A first application to molecular electronics is presented by conductance measurements on a molecular layer of oligophenylenvinylene derivatives. Simulations on model molecules applying extended Hueckel theory and the nonequilibrium Greens function formalism reveal a good qualitative agreement between theory and experiment. Furthermore, promising extensions to the present fabrication method are discussed. These include the processing and characterization of broken T-shaped electrodes suitable for measurements on single molecules, and the transition to pure semiconductor electrodes based on indium arsenide. (orig.)}
place = {Germany}
year = {2007}
month = {Jan}
}