A Van der Pauw measurement is a technique used to measure the electrical properties of a material, such as resistivity or carrier concentration. It involves applying a current and measuring the resulting voltage at different points on the material's surface.
In a Van der Pauw measurement, a current is applied to the material through two contacts, while the voltage is measured at two other contacts. The current and voltage are then reversed and measured again. This process is repeated at multiple points on the material's surface to obtain a complete set of data.
The source unit in a Van der Pauw measurement is the device or instrument used to generate the current that is applied to the material being tested. This can be a power supply, current source, or other device capable of delivering a known and controlled amount of current.
A Van der Pauw measurement is useful because it allows for the characterization of a material's electrical properties without the need for complex sample preparation or specialized equipment. It can also be used to measure the properties of non-uniform or irregularly shaped materials.
Some limitations of a Van der Pauw measurement include the assumption of a homogenous material and the need for precise positioning of the contacts on the material's surface. It may also be less accurate for highly anisotropic materials or materials with very low resistivity.