Theory and application of a two-layer Hall technique

The electrical characterization of epitaxial layers on substrates of the opposite conductivity type presents serious problems if the p-n junction at the interface has significant leakage current such that it cannot be used to effectively electrically isolate the two regions. In order to meet the need for nondestructively characterizing such structures, a modification of the conventional Hall technique was developed in which the Hall measurements are made simultaneously on both the epitaxial layer and its substrate, the interface impedance is measured, and the interaction between the two regions is modeled and taken into account. This technique can be used to verify those cases in which the perturbing effects of a high-resistivity substrate are negligible, thus justifying conventional measurements on the epitaxial layer. In principle, it can be used to measure the resistivity and Hall coefficient of each layer separately if the assumptions of the model are realized in practice. The use of this technique is discussed and applied to the case of a thin n-type silicon epitaxial layer on: 1) a conducting substrate of indium-doped silicon that had a significant amount of leakage at the interface p-n junction and 2) a high-resistivity silicon substrate that had negligible influence on the measurement of the Hall coefficient of the epitaxial layer.