Examination of relationship between resistivity and photocurrent induced magnetic field in silicon wafers using laser SQUID

Using the laser SQUID method, we examined the relationship between silicon wafer resistivity and magnetic field. By irradiating the wafer with a 3.2 W high-power laser beam, we were able to generate a measurable magnetic field perpendicular to the wafer, even for the wafers without p-n junctions. For samples having resistivities of 130 Ω·cm or less, we observed magnetic field distributions in the form of concentric circles. Histogram analysis showed that as resistivity decreases, mean value of magnetic field and standard deviation increase. For p-type wafers having resistivities of up to 300 Ω·cm, both mean value of magnetic field and standard deviation vary as a power law with respect to resistivity. However, for samples having resistivities of 300 Ω·cm or higher, the relationship was saturated, and determining resistivity was difficult. Since the laser SQUID method can be used to measure resistivity without electrical contact, it works well even for wafers with surface oxide films, and does not cause contamination.