John Ambrose Fleming Invented P-n Junction Diode
P-n Junction Diode was invented in 1904.
P-n Junction Diode is  a PN junction with p-type on one side and n-type on the other. When a positive voltage is applied to the p-type side (forward bias), it shrinks and overcomes the depletion zone, causing the current to flow from the p-type to the n-type side.