Contact resistance

The term contact resistance refers to the contribution to the total resistance of a system which can be attributed to the contacting interfaces of electrical leads and connections as opposed to the intrinsic resistance, which is an inherent property, independent of the measurement method. This effect is often described by the term Electrical Contact Resistant or ECR. The idea of potential drop on the injection electrode was introduced by William Shockley to explain the difference between the experimental results and the model of gradual channel approximation. In addition to the term ECR, "Interface resistance", "transitional resistance", or just simply "correction term" are also used. The term "parasitic resistance" has been used as a more general term, where it is usually still assumed that the contact resistance has a major contribution.

Here we need to distinguish the contact resistance evaluation in two-electrode systems (e.g. diodes) and three-electrode systems (e.g. transistors).

For two electrode systems the specific contact resistivity is experimentally defined as the slope of the I-V curve at V=0:

where J is the current density = current/area. The units of specific contact resistivity are typically therefore in ${\displaystyle \Omega \cdot {\text{cm}}^{2}}$ where ${\displaystyle \Omega }$ stands for ohms. When the current is a linear function of the voltage, the device is said to have ohmic contacts.

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