Positive and negative charge carriers may even be present at the same time, as happens in an electrochemical cell.
2.
If V _ { GB } is high enough, a high concentration of negative charge carriers forms in an " inversion layer " located in a thin layer next to the interface between the semiconductor and the insulator.
3.
It can be seen that in some conductors, such as ionic solutions and plasmas, there are both positive and negative charge carriers, so an electric current in them consists of the two polarities of carrier moving in opposite directions.