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PHOTOVOLTAIC METHOD FOR THE MEASUREMENT OF RESISTIVITY IN GERMANIUM AND SILICON.
Final rept. Dec 66-Dec 67,
NATIONAL BUREAU OF STANDARDS GAITHERSBURG MD
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A photovoltaic method was examined to determine its potential for improving the detection of resistivity inhomogeneities responsible for reduced silicon device performance and reliability. The method involves the use of a light probe which is swept over the sample. Theory relates the photovoltage and photoconductivity measured as a function of probe position to the resistivity gradient along the sample for bar shaped samples where the probe is a thin line of light extending over the width of the bar. This method, which has been used on germanium, was extended to silicon samples. Resistivity gradients of about 0.1 ohm-cmcm could be detected in 10 ohmcm material and the resistivity profiles obtained generally agreed to within a few percent with profiles obtained from the two-point probe method. The theory has not been developed to obtain a resistivity profile on non-bar shaped samples, such as circular slices. Nevertheless, it was possible to detect and qualitatively map resistivity inhomogeneities on such slices of both germanium and silicon. Results have indicated the feasibility of the method to make not only precise measurements of resistivity profiles along bar shaped samples of germanium and silicon but quantitative resistivity measurements on circular slices as well, both in a matter of minutes with a resolution of about a diffusion length and without contacting the regions measured. This preliminary work should be extended to refine the method and determine the limits for making precise measurements in bar shaped samples and quantitative measurements in samples with other geometries. Author
APPROVED FOR PUBLIC RELEASE