Contact resistance in semiconductor diodes refers to the parasitic electrical resistance that arises at the interfaces between the semiconductor material and the metal contacts (electrodes) that are attached to it.

These metal-semiconductor interfaces are critical for injecting current into or extracting current from the active regions of the diode.

The origin of this resistance is multifaceted, stemming from the inherent properties of the junction itself.

When metal and semiconductor come into contact, a potential barrier, known as the Schottky barrier, often forms due to the difference in their work functions. This barrier impedes the flow of carriers (electrons or holes), creating a resistance.

Even in Ohmic contacts, which are designed for low-resistance current flow, some finite resistance exists due to factors such as surface states, interfacial oxides or contaminants, and the specific doping profile of the semiconductor region immediately beneath the contact.

A high contact resistance is detrimental to diode performance, as it leads to power loss in the form of Joule heating, reduces the overall efficiency, and can cause undesirable voltage drops that shift the operating characteristics of the device.

It is typically quantified using specific contact resistivity (Pc), a fundamental parameter measured in Ω·cm², which allows for the evaluation of the contact quality independent of the contact area.

Minimizing contact resistance is therefore a primary goal in semiconductor device fabrication, achieved through meticulous surface preparation, selection of appropriate metal alloys, and the use of highly doped semiconductor layers to thin the Schottky barrier and promote efficient carrier transport via quantum mechanical tunneling.

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