Ohmic contact

An ohmic contact is a non-rectifying electrical junction: a junction between two conductors that has a linear current–voltage (I-V) curve as with Ohm's law. Low resistance ohmic contacts are used to allow charge to flow easily in both directions between the two conductors, without blocking due to rectification or excess power dissipation due to voltage thresholds.

By contrast, a junction or contact that does not demonstrate a linear I-V curve is called non-ohmic. Non-ohmic contacts come in a number of forms (p–n junction, Schottky barrier, rectifying heterojunction, breakdown junction, etc.).

Generally the term "ohmic contact" implicitly refers to an ohmic contact of a metal to a semiconductor, where achieving ohmic behaviour is possible but requires careful technique. Metal–metal ohmic contacts are relatively simpler to make, by ensuring direct contact between the metals without intervening layers of insulating contamination or oxidation; various techniques are used to create ohmic metal-metal junctions (soldering, welding, crimping, deposition, electroplating, etc.). This article focuses on metal–semiconductor ohmic contacts.

Low-resistance, stable ohmic contacts to semiconductors are critical for the performance and reliability of semiconductor devices, and their preparation and characterization are major efforts in circuit fabrication. Poorly prepared junctions to semiconductors can easily show rectifying behaviour by causing depletion of the semiconductor near the junction, rendering the device useless by blocking the flow of charge between those devices and the external circuitry. Ohmic contacts to semiconductors are typically constructed by depositing thin metal films of a carefully chosen composition, possibly followed by annealing to alter the semiconductor–metal bond.

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