Contactless measurement of carrier lifetime in silicon thick wafers

Contactless methods of measuring bulk carrier lifetime with a reliable accuracy have scarcely been reported thus far. A contactless method has been studied for Si wafers with thickness of up to 10 mm. This method makes use of the eddy current in the wafer induced by the magnetic fluxes (5 MHz) passing through a thick wafer. To confirm the reliability of this method, the decay of photoconductivity Δσ0 and injection level Δσ0/σ measured by this method are compared with those of the dc method. In the eddy current method, the bulk lifetime and diffusion coefficient are obtained as 1.88 ms and 12.4 cm2/s for an n-Si crystal, and 26 ms and 37.3 cm2/s for a p-Si crystal. The latter value, 26 ms, for bulk lifetime is almost in agreement with the value, 29 ms, obtained by the American Society for Testing and Materials (ASTM) dc method. The sensitivity of this method and the desired thickness of wafer for evaluating the bulk lifetime are discussed.