Hall-Effect Measurement Facility

      This facility is used for measuring the carrier concentrations and mobilities of semiconductors. It consists of a scanner switching card together with a Hall effect card (Keithley 7001/7065), a closed-cycle He refrigerator with temperature range between 10-650K, and a magnet (Alpha Scientific Magnetics Model 4800). The system is interfaced with a computer with Labview and is capable of automatically switching between the measurement configurations within a few milliseconds so that the carrier concentration and mobility can be measured as functions of time continuously. There is also a state-of-the-art SQUID magnetometer, which has been integrated with our picosecond laser spectroscopy system by an optic fiber, is used for studying the magnetic field dependence (B up to 5.5 Tesla) of the optical and electrical properties. The SQUID magnetometer is shared among four faculty members in physics and chemistry. Our goal with this setup is to study the temperature variations of carrier concentration and mobility of III-Nitride epilayers grown by our MOCVD system. We use the Hall measurement to give us specific
information about the sample we are studying. In the past, we have also used this setup to study Persistent Photoconductivity in wide band-gap semiconductors like: GaN and its alloys.

Below: A schematic of the Hall-effect measurement system

Below: A picture of the Hall measurement system