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micro-Hall sensors

We use micro-Hall sensors made up of AlGaAs/GaAs heterostructures. The high mobility 2-DEG is about 80nm below the surface of the wafer. Optical lithography and etching techniques are used to fabricate the sensors (see below).

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For the measurement, a sample is placed with one of its ends close to the Hall-sensor cross (10x10 um in the figure below). A current of about 1-2 uA is applied through two opposite leads and the Hall-voltage (which proportional to the field transverse to the plane of the sensor) is measured through the other two leads (see figure below). A lock-in amplifier is used to read the low amplitude voltage. A very high sensitivity can be achieved with these sensors. Recently, a micro-Hall sensor has been used to measure the magnetic response of an individual magnetic nanoparticle.
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See the next paper about micro-Hall magnetometers:
                     A. D. Kent et al., J. Appl. Phys. 76, 6656 (1994)  pdf_logo07
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