Sensitive contactless eddy-current conductivity measurements on Si and HgCdTe

Abstract

A high-sensitivity high-spatial-resolution eddy-current apparatus has been set up for contactless conductivity measurements on Si and HgCdTe. The inductive sensitivity limit has been demonstrated, on Si slices, to a very low σt (product of conductivity and thickness) of 0.0004 Ω−1 and the spatial resolution was shown to be about 4 mm, both a threefold improvement over past published results. HgCdTe bulk slices and epitaxial films have been measured over a wide range of σt from 0.001 to 1 Ω−1 at 77 K. The conductivity mapping measurements on HgCdTe material were also demonstrated for the first time. The sensitivity of eddy-current probes consisting of miniature commercial rf coils were shown to be not only temperature independent, but also very stable after repeated thermal cyclings between 300 and 77 K. This feature makes the eddy-current method an ideal technique for routine contactless conductivity measurements on HgCdTe material at 77 K. We also show that both the sensitivity and the spatial resolution of eddy-current probes can be explained quantitatively by a simple theory which treats coils as magnetic dipoles.