H A L L E F F E C T M E A S U R E M E N T

The "Hall effect" was discovered by Edwin Hall, a professor at the Johns Hopkins university USA in 1879 while working on his doctoral thesis in physics.

Hall's experiments consisted of exposing thin gold leaf (and, later, using various other materials) on a glass plate and tapping off the gold leaf at points down its length. The effect is a potential difference (Hall voltage) on opposite sides of a thin sheet of conducting or semiconducting material (the Hall element) through which an electric current is flowing.

This was created by a magnetic field applied perpendicular to the Hall element. The ratio of the voltage created to the amount of current is known as the Hall resistance, and is a characteristic of the material in the element. In 1880, Hall's experimentation was published as a doctoral thesis in the American Journal of Science and in the Philosophical Magazine.

Today, the Hall Effect Measurement is still of a high value to semiconductor materials manufacturers and researchers. The Hall effect is used in magnetic field sensors, produced in large quantities. In the presence of large magnetic field strength and low temperature, the quantum Hall effect can be observed, which is the quantization of the Hall resistance.

Hall effect in semiconductors and photovoltaic applications

When a current-carrying semiconductor is kept in a magnetic field, the charge carriers of the semiconductor experience a force in a direction perpendicular to the magnetic field and current. At equilibrium, a voltage appears at the semiconductor edges.

The simple formula for the Hall coefficient becomes more complex in semiconductors where the carriers are generally both electrons and holes which may be present in different concentrations and have different mobilities.

The following electrical parameters can be measured

& Monitored. They will precisely characterize an electronic

conductive or semiconductive layer and provide

much interesting information.

- Resistivity (in Ohm.cm)

- Conductivity (in Ohm-1.cm-1)

- Bulk Concentration (in cm-3)

- Sheet Concentration (in cm-2)

- Mobility (in cm2/V.s)

- P/N Testing

- Magneto-Resistance

- Hall Coefficient

Who need to use “Hall effect” systems?

 College students studying Physics, Materials, Electronics, etc.

 Research LAB in the Universities majoring mainly in Physic and Materials.

 R&D engineers who are working on thin-film and wafer industry mainly semiconductor.

 Enginers working on conductive coated layers, glass coating...

 Solar cell research labs and factories, photovoltaic applications

Theory and pratical requirement for Hall effect measure :

  1- Samples should be trefle or square and the contact configuration should be as shown

  2- The layer to caracterize should be uniform

  3- The four contacts should be ohmic as much as possible to assure accurate measure.

  Some systems can determine the quality of ohmic contact via I-V or I-R curves

  between each contact point.

Some additive materials can be used to optimize the ohmic contact at each point

by using Indium, Gold paste, silver paste, Carbon paste etc ...

 - Magnet: Permanent magnet (low footprint, high magnet flow up to 1T, economical) or electromagnet (allows measures with various magnet fields)

 - Measurement range : depending of what magnet flow is present, what electronic and electrical isolation is used;, the typical range for semiconductor materials is 10e-4 up to 10e7 Ohm.cm, mobility from 10 up to 10e7 cm2/Vs and density of 10e9 up to 10e21.

 - Temperature : The Measurement can be done only at room temperature however the values of Mobility and Density versus temperature gives interesting information on the materials. So some systems allow temperatures from 70K up to 600 K. and even down to few °K. with a cryogenic design. The temperature variation is often used on solar cells and photovoltaic materials characterization

For smart & efficient solutions to Hall Effect Measurement, follow this link :

www.microworld.eu