The construction of a silicon diode starts with purified silicon. Each side of the diode is implanted with impurities (boron on the anode side, arsenic or phosphorus on the cathode side), and the joint where the impurities meet is called the "p-n junction."
Silicon diodes have a forward-bias voltage of 0.7 Volts. Once the voltage differential between the anode and the cathode reaches 0.7 Volts, the diode will begin to conduct electrical current across its p-n junction. When the voltage differential drops to less than 0.7 Volts, the p-n junction will stop conducting electrical current, and the diode will cease to function as an electrical pathway.
Because silicon is relatively easy and inexpensive to obtain and process, silicon diodes are more prevalent than germanium diodes.