AVS 52nd International Symposium
    Applied Surface Science Tuesday Sessions
       Session AS+BI-TuM

Paper AS+BI-TuM3
Characterization of a Chemically Passivated GaAs Based Sensor Device in Air and Electrolytes

Tuesday, November 1, 2005, 9:00 am, Room 206

Session: Surface Characterization of Organic and Biological Systems
Presenter: M. Tornow, Walter Schottky Institut, TU Muenchen, Germany
Authors: S.M. Luber, Walter Schottky Institut, TU Muenchen, Germany
D. Gassull, TU Muenchen, Germany
D. Schuh, Universitaet Regensburg, Germany
M. Tanaka, TU Muenchen, Germany
M. Tornow, Walter Schottky Institut, TU Muenchen, Germany
G. Abstreiter, Walter Schottky Institut, TU Muenchen, Germany
Correspondent: Click to Email
Functionalized field effect devices are promising candidates to act as smart substrates for sensor applications. For a use in biological systems a functional layer has to provide stability against electrochemical decomposition, and allow effective coupling of the surface potential to the conductive channel. We present a resistor device passivated with a 4'-substituted 4-mercaptobiphenyl (MBP) self-assembled monolayer (SAM) for sensing applications. Base material is a GaAs-AlGaAs heterostructure containing a quasi 2D electron gas 60nm beneath the surface. In the first part of our study we investigated the influence of the MBP-SAM on the electronic surface properties of n-doped GaAs samples employing the Kelvin probe technique. We changed the dipole moment of the MBP molecules using various substituents (-H, -OH, -CH@sub 3@) and found a linear effect on the electron affinity. In the second part we tested the stability of the resistor device based on the GaAs-AlGaAs heterostructure in aqueous solutions. Whereas a bare device degraded rapidly the coated samples showed a remarkable increase in stability. Furthermore we characterized samples coated with monolayers with CH@sub 3@ (MBP-CH@sub 3@) and OH (MBP-OH) substituents in buffered electrolyte solutions with varying pH. For the MBP-OH coated sample, a change in pH induced a change in the resistance of the device. Interestingly, the sample grafted with an MBP-CH@sub 3@ SAM also showed a clear response on pH which can be attributed to the adsorption of OH@super -@ ions on CH@sub 3@ groups.