Doping (semiconductor)



In extrinsic. A semiconductor which is doped to such high levels that it acts more like a conductor than a semiconductor is called degenerate.

Some ion implantation, the latter method being more popular in large production runs due to its better controllability.

The number of dopant atoms needed to create a difference in the ability of a semiconductor to conduct is very small. Where a comparatively small number of dopant atoms are added (of the order of 1 every 100,000,000 atoms) then the doping is said to be low, or light. Where many more are added (of the order of 1 in 10,000) then the doping is referred to as heavy, or high. This is often shown as n+ for n-type dopant or p+ for p-type doping. A more detailed description of the mechanism of doping can be found in the article on semiconductors.

Dopant elements

Group IV semiconductors

For the group IV semiconductors such as gallium are used to dope silicon. Boron is the p-type dopant of choice for silicon integrated circuit production, since it diffuses at a rate which makes junction depths easily controllable. Phosphorus is typically used for bulk doping of silicon wafers, while arsenic is used to diffuse junctions, since it diffuses more slowly than phosphorus and is thus more controllable.

By doping pure silicon with group V elements such as phosphorus, extra p-type semiconductor. In this context then, a group V element is said to behave as an electron donor, and a group III element as an acceptor.

Compensation

In most cases, many types of impurity will be present. If an equal number of donors and acceptors are present in the semiconductor, the extra core electrons provided by the former will be used to satisfy the broken bonds due to the latter, so that doping produces no free carriers of either type. This phenomenon is known as compensation, and occurs at the p-n junction in the vast majority of semiconductor devices. Partial compensation, where donors outnumber acceptors or vice-versa, allows device makers to repeatedly reverse the type of a given portion of the material by applying successively higher doses of dopants.

Although compensation can be used to increase or decrease the number of donors or acceptors, the electron and hole mobility is always decreased by compensation because mobility is affected by the sum of the donor and acceptor ions.

Doping in organic conductors

Main article: Conductive polymer

electrochemical doping in which a polymer-coated, working electrolyte) to enter the polymer in the form of electron addition (n doping) or removal (p doping).

The reason n doping is so much less common is that solvent in a sealed flask; however, there are likely no commercialized n doped conductive polymers.

History

Doping was originally developed by John Robert Woodyard working at Sperry Gyroscope Company during World War II.[3] The demands of his war work on radar denied Woodyard the opportunity to pursue this line of research but, post-war, his patent proved the grounds of extensive litigation by Sperry Rand.[4]. Related work was done at Bell Labs by Teal and Sparks.[5]

See also

References

  1. ^ http://www.computerhistory.org/semiconductor/timeline/1955-Photolithography.html
  2. ^ http://www.computerhistory.org/semiconductor/timeline/1954-Diffusion.html
  3. ^ US Patent No.2,530,110, filed, 1944, granted 1950
  4. ^ Morton, P. L. et al. (1985). John Robert Woodyard, Electrical Engineering: Berkeley. University of California: In Memoriam. Retrieved on 2007-08-12.
  5. ^ Sparks, Morgan and Teal, Gordon K. “Method of Making P-N Junctions in Semiconductor Materials,” U. S. Patent 2,631,356 (Filed June 15, 1950. Issued March 17, 1953)
 
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