what are the carrier concentration limitation of p doped silicon for thin film transistor ad solar cell applications?
Dear Qaisar,
Welcome!
Doping of silicon enabled the seen revolution in the electronic devices and integrated circuits. Doping is a technological parameters that can be used to control the conduction type and carrier concatenation in the a large margin from the intrinsic concentration ni to the maximum solid solubility of the doping element in the silicon.
As for p-type doping, one can use the trivalent elements such as Boron, Gallium, Aluminum and indium. The highest doping achieved is limited as said before by the maximum solid solubility. Boron has the e highest solid solubility among the mentioned p-type dopants.
The heavily doped layers are used as emitter regions in the bipolar junction transistor. It is so that as the doping increases the emitter injection efficiency is raised until an optimum doping has been reached after which an increase in the doping will lead to a decrease in the injection efficiency. This optimum doping is about 10^19/cm^3.
This includes also the e emitter of the solar cell
The other application is the source and drain regions in the field effect transistor. It is so that these region must have a negligible resistance compared to that of the channel. Also, polysilicon gate region must be heavily doped to act metal like.
An important application of the heavily doped layers is to produce ohmic MS contacts. To make the metal semiconductors contacts ohmic irrespective of the doping of the semiconductor one produces a heavily doped layer at the surface of the semiconductor directly under the metal electrodes. In such applications it is required to get the highest possible doping to reduce the resistance of such layers to a minimum.
wish you success
For Si photo detector, heavily doped (P+) emitter is also required for faster response
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