Plasma (physics) potential in the space between charged particles, independent of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (formula_6), but on the scale of the Debye length
Depletion region the bulk semiconductor, then a spontaneous depletion region forms if the gate is electrically shorted to the substrate, in much the same manner as described for the p–n junction above. The principle of charge neutrality says the sum of positive charges must equal the sum of negative charges: where "n" and "p" are the number of free electrons and holes, and formula_28 and formula_29 are the number of ionized donors and acceptors "per unit of length", respectively. In this way, both formula_28 and formula_29 can be viewed as doping spacial densities. If we assume full ionization and that formula_32, then: