or
or
One p-type and one n-type semiconductors
An ordinary diode requires a junction between a p-type and an n-type semiconductor material. The p-type material has a surplus of positive charge carriers (holes), while the n-type material has a surplus of electrons. This creates a depletion region at the junction where both types of carriers are depleted, acting as a barrier to current flow in one direction.
Therefore, both two p-type and two n-type semiconductors alone would not create the necessary junction for a functioning diode.
