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Apparatus and method for measuring minority carrier lifetimes in semiconductor materials

United States Patent

August 14, 2001
View the Complete Patent at the US Patent & Trademark Office
National Renewable Energy Laboratory - Visit the NREL Technology Transfer Website
An apparatus for determining the minority carrier lifetime of a semiconductor sample includes a positioner for moving the sample relative to a coil. The coil is connected to a bridge circuit such that the impedance of one arm of the bridge circuit is varied as sample is positioned relative to the coil. The sample is positioned relative to the coil such that any change in the photoconductance of the sample created by illumination of the sample creates a linearly related change in the input impedance of the bridge circuit. In addition, the apparatus is calibrated to work at a fixed frequency so that the apparatus maintains a consistently high sensitivity and high linearity for samples of different sizes, shapes, and material properties. When a light source illuminates the sample, the impedance of the bridge circuit is altered as excess carriers are generated in the sample, thereby producing a measurable signal indicative of the minority carrier lifetimes or recombination rates of the sample.
Ahrenkiel; Richard K. (Lakewood, CO), Johnston; Steven W. (Golden, CO)
Midwest Research Institute (Kansas City, MO)
09/ 283,738
April 1, 1999
CONTRACTUAL ORIGIN OF THE INVENTION The United States Government has rights in this invention under Contract No. DE-AC36-86010337 between the U.S. Department of Energy and the National Renewable Energy Laboratory, a Division of Midwest Research Institute.