More electrons come into the silicon from the wire at the
right, and mor holes are generated at the left as electrons
migrate from the p-silicon into the wire of the external
circuit. Continuous current flow is possible from right
to left.
When holes and excess electrons have been eliminated, further
current flow is impossible because there is nothing to carry
the current through the silicon, which becomes an insulator.
Continuous current flow from left to right is not possible.