Atomic Magnetometry-Based Electromagnetic Imaging of Low-conductivity Semiconductors

We demonstrate non-destructive imaging and discrimination of specimens with electrical conductivities down to $5times10^2$ Sm$^{-1}$. The images are obtained with an $^{85}$Rb radio-frequency atomic magnetometer operating at room temperature, in an unshielded environment. This extends the domain of electromagnetic imaging with atomic magnetometers to low-conductivity, non-metallic materials - representing an improvement of more than two orders of magnitude from previous results. We validate the technology by imaging and identifying different concentrations of n-dopants in Si samples. Simultaneous images of specimens with a difference in conductivity up to twenty times is demonstrated. Multi-frequency image analysis allows unambiguous discrimination of different dopant levels, with a resolution of 2.5 times. These results demonstrate a viable approach for non-invasive imaging of non-metallic materials, as well as for accessing and imaging the bulk properties of large wafers of semiconductors, with the potential for full material characterisation and quality monitoring. High-impact specific applications in science and technology are identified.