Resistivity measurement and mapping

Resistivity mapping and measurement

The electrical resistivity directly depends on the density of the semiconductor and is therefore a useful parameter to monitor doping profiles and homogeneity. The lifetime and diffusion length depend  on the doping density as well. Since doping shifts the fermi level, it increases the rate of SRH recombination in most cases. In addition, since Auger recombination is more likely in heavily doped material, the recombination process itself is enhanced as the doping increases.

In our systems the resistivity is measured via the non-contact eddy current method. Eddy current is caused when a sample is exposed to a changing magnetic field due to variations of the field with time, for example if an AC current flows in a coil in close proximity to the sample. This causes a current within the bulk of the sample and the circulating eddies of current create induced magnetic fields that oppose the change of the original magnetic field. The greater the electrical conductivity of the sample , the greater are the currents that are developed and the greater the opposing field will be. In other words the electrical loss in the material is measured, which is directly related to the resistivity of the sample.

Note that the measurement depends also on the distance from the coil to the sample and therefore on geometrical features of the sample.