Hall Effect in a Semiconductor

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This project is constructing an experiment to measure the Hall effect in a semiconductor crystal. This experiment replaces the current experiment to measure the Hall effect in a plasma, which is seriously limited by the inability of students to evaluate their data accurately in the absence of an understanding of plasma hydrodynamics. In the Hall effect in a semiconductor experiment students make measurements of the resistivity of a germanium crystal and the Hall voltage that develops when a magnetic field is applied transverse to the applied current through the crystal. Taking these measurements at a variety of temperatures between liquid nitrogen and room temperatures, the students determine the value of the band gap in germanium, the density of impurities in the crystal, the temperature dependence of the resistivity and the electron and hole mobilities, and the dependence of the magnetoresistance on temperature and applied magnetic field. Through the Hall effect experiment, students not only extend their knowledge of the fundamentals of semiconductor physics but also become better acquainted with the techniques used in modern condensed matter research. They learn how to measure and control temperatures between liquid nitrogen and higher than room temperatures and how to make electrical measurements, including null measurements, in materials. The experiment also improves their data reduction and analysis skills.