Diodes are mainly made up of silicon like semiconductors. It has a crystalline structure. Different types of diodes are available. For example pn junction, zener, point contact, tunnel, photo diode, LED, shockley, etc. When silicon is there it has 4 electrons in the valence shell and is bonded with 4 electrons of adjacent silicon atoms. By doping, that is adding impurities (group 13 or group 15) elements, we can increase the conductivity of a semiconductor by introducing p and n regions which shows holes and electrons were the majority charge carriers.
The semiconductor used in very early crystal diodes used as detectors in radios was galena (lead sulphide crystal) and used a stiff sharply pointed "cat's whisker" point contact. Naturally present impurities in the galena made doping unnecessary.
During WW2 germanium crystal point contact diodes were introduced for use in military radios. Naturally present impurities in the germanium made doping unnecessary.
Germanium junction diodes were introduced in the early 1950s (along with germanium junction transistors), silicon junction diodes and transistors were introduced in the late 1950s and took most of the market in the early 1960s.