Contactless measurement of bulk carrier lifetime in thick silicon wafers by an induced eddy current

In order to examine the bulk carrier lifetime in a silicon single crystal, a contactless method of determining the carrier lifetime for wafers up to 20 mm thick has been developed. This method is based on the measurement of the photoconductive decay of the eddy current induced in a wafer by a high-frequency magnetic flux. The experimental results show that the maximum values of measurable bulk carrier lifetime are longer than the known values for high-quality silicon crystals. The measurable maximum values are comparable with those satisfying the American Society for Testing and Materials designation, i.e. 11 ms for p-type and 32 ms for n-type wafers. The minimum value of measurable bulk carrier lifetime is found as a function of the wafer thickness. This functional dependence of the minimum value on the wafer thickness is also examined and discussed in some detail.