Ohmic contact

  • Detailed descriptions to form the band shifts
  • Explanations for current flow in both directions at the ohmic contact.
  • Descriptions of the conditions for the formation of an ohmic contact ( work function of the materials, possibly with values ​​examples)
  • Information on the influence of Oberflächen-/Grenzflächenladungen
  • Ohmic contacts by a highly doped semiconductor interlayer

Under an ohmic contact with low electrical resistance is to be understood in the semiconductor electronic transition between a metal and a semiconductor which behaves as an ohmic resistance and no rectifying action, such as the Schottky contact has. It serves electronic devices based on semiconductors to contact and electrically connect with other components. Applications are all semiconductor devices such as integrated circuits or discrete components such as transistors. Without ohmic contacts with low contact resistance and mechanically stable contacts could not use semiconductor devices.

General

As already mentioned, there are two main types of metal - semiconductor junctions: rectifying junctions ( Schottky contact ) with non-linear properties, and ohmic contacts, which are also called linear transitions.

Through different dopings and selected metals also linear, ohmic metal - semiconductor junctions can be created, which electrically have a linear behavior as an ohmic resistance. In this case, the resistance value is minimized in order to have the least possible influence on the remaining electronic circuit.

Whether a rectifying or ohmic contact is formed, depends on the band gap and the Fermi level of the two materials are brought into contact. The thickness of the space charge region increases inversely proportional to the square root of the density of the dopant atoms in the doped semiconductor from, whereby at high doping of the semiconductor, the barrier is so thin that it can be neglected and the contact behaves like a small ohmic resistance. By alloy formation and the formation of silicides in the contact region can be of the Schottky junction to an ohmic contact.

Materials

For available semiconductor result in the formation of ohmic contacts, different contact metals used. In the semiconductor silicon today's most used aluminum is largely used as a contact material. Silicides are used as ohmic contact, due to the applied difficult to be controlled diffusion processes rarer. For III-V and II -VI compound semiconductor are significantly less well-tested materials for the ohmic contact from silicon available. In the table some industrially important semiconductor and the contact material for the formation of ohmic contacts are listed below:

Depletion region Aluminium Titanium nitride Tungsten Germanium Indium Gallium nitride Indium antimonide Copper indium gallium selenide solar cells Simon Sze
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