Diodes are electronic pieces that have two electrodes and that allow the advance of electrical current in only one direction.
In 1873, Frederick Guthrie had positively charged his electroscope and mistakenly placed a piece of hot white metal near the terminal of his electroscope. The white metal that was hot emitted electrons to the terminal and neutralized the positive charge of the electroscope causing the sheets to stick together. The negative charge of the electroscope could not be discharged, so the hot metal only emitted the electrons, that is, the negative charge. Therefore, the direction of the flow of electrons was unidirectional, thus the first diode was born.
The diode is a two-layer, two-terminal semiconductor device. When n-type and p-type semiconductor material are joined together, this forms a PN junction, which is referred to as a diode.
N-type
Positively charged
P-type
Negatively charged