Ohmic contact

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The following important information is missing from this article or section:
  • more detailed descriptions of the formation of the band displacements
  • Explanations of current flow in both directions at the ohmic contact.
  • Descriptions of the framework conditions for the creation of an ohmic contact (work function of the materials, possibly with value examples)
  • Information on the influence of surface / interfacial charges
  • ohmic contacts through a highly doped intermediate semiconductor layer
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In semiconductor electronics, an ohmic contact is understood to be a transition between a metal and a semiconductor with low electrical resistance , which behaves like an ohmic resistance and does not have a rectifying effect like the Schottky contact . It is used to contact electronic components based on semiconductors and to connect them electrically to other components. Applications are in all semiconductor components such as integrated circuits or even discrete components such as transistors . Without ohmic contacts with a low transition resistance and mechanically stable contacts, semiconductor components could not be used.

General

Idealized energy band diagram for an ohmic contact between a metal and a highly p-doped semiconductor (left) before the contact and (right) after the contact in thermal equilibrium for the case Φ m > Φ s .
Idealized energy band diagram for an ohmic contact between a metal and a highly n-doped semiconductor (left) before the contact and (right) after the contact in thermal equilibrium for the case Φ m <Φ s .

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 junctions.

With different dopings and selected metals, linear, ohmic metal-semiconductor junctions can also be created, which electrically have a linear behavior like an ohmic resistance. The resistance value is minimized in order to have as little influence as possible on the rest of the electronic circuit.

Whether a rectifying or an ohmic contact is formed depends on the band gap and the Fermi level of the two materials brought into contact. The thickness of the space charge zone decreases in inverse proportion to the square root of the density of the doping atoms in the doped semiconductor, which means that if the semiconductor is heavily doped, the barrier becomes so narrow 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 area of the Schottky junction to an ohmic contact can be.

materials

For available semiconductors, different contact metals are used to form ohmic contacts. In the semiconductor silicon , which is most widely used today , aluminum is largely used as the contact material. Silicides as ohmic contact are used less often due to the diffusion processes that are more difficult to control. For III-V and II-VI compound semiconductors, there are significantly fewer proven materials available for ohmic contact than for silicon. Some technically important semiconductors and their contact material for the formation of ohmic contacts are listed in the table:

semiconductor Contact material
Si Al , Al-Si, TiSi 2 , TiN , W , MoSi 2 , PtSi, CoSi 2 , WSi 2
Ge In , AuGa, AuSb
GaAs AuGe, PdGe, Ti / Pt / Au
GaN Ti / Al / Ti / Au, Pd / Au
InSb In
ZnO InSnO 2 , Al
CuIn 1-x Ga x Se 2 Mo , InSnO 2
HgCdTe In

Individual evidence

  1. ^ Simon M. Sze : Physics of Semiconductor Devices . 2nd Edition. Wiley-Interscience, 1981, ISBN 0-471-05661-8 , pp. 307 (The table is also available online at: Ohmic Contact Technologies . EESemi.com. 2004, accessed February 6, 2018).

literature

  • Simon M. Sze: Physics of Semiconductor Devices . 2nd Edition. Wiley-Interscience, 1981, ISBN 0-471-05661-8 .