Search for a Metallic State on a GaAs Surface by Electrolytic Gating

Undergraduate #283
Discipline: Physics
Subcategory: Materials Science

Michelle R. Bundy - Saint Augustine's University
Co-Author(s): Gordon Stecklein and Paul Crowell, University of Minnesota, Minneapolis, MN

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Electronics categorizes materials into three main types: metals, insulators, and semiconductors. A Metallic surface state was recently discovered in Si, our hypothesis is that it should also be discovered in GaAs because it has a higher mobility. We then designed an experiment in which we gate an ionic liquid to investigate if this induces a metallic surface state on insulating n -GaAs. We measured the resistivity from 2-300 K using the Physical Property Measurement System (PPMS) and a Van der Pauw method. Ohmic contacts to the GaAs substrate were created by annealing Ge/Au/Ni. In an experiment with 1×1016 cm-3 n-GaAs, applying a positive gate voltage increased the resistivity, but this increase in resistivity could not be reversed by applying a negative voltage. In experiments with 3×1015 cm-3 n-GaAs, the resistivity at 2 K decreased upon applying a gate voltage of 2 V, but there was not a monotonic change in resistivity with applied voltage. The temperature-dependence of the resistivity showed no evidence of a change from insulating to metallic behavior. But when a magnetic field was applied to a new sample of 3×1015 cm-3 n-GaAs, the resistivity was increased by a factor of 1000. This is a positive sign that with continuing further investigations using a magnetic field we will then be able to increase the bulk resistance high enough to induce a metallic surface state.

Funder Acknowledgement(s): This work was supported primarily by the National Science Foundation MRSEC and REU programs under Award Numbers DMR-1263062 and DMR1420013.

Faculty Advisor: Melton,