Rectifier diodes are electronic devices that are used to control the current flow direction in an electrical circuit. Two commonly used materials for diodes are germanium and silicon. While both germanium diodes and silicon diodes perform similar functions, there are certain differences between the two that must be taken into consideration before installing one or the other into an electronic circuit.
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.
Germanium diodes are manufactured in a manner similar to silicon diodes. Germanium diodes also utilize a p-n junction and are implanted with the same impurities that silicon diodes are implanted with. Germanium diodes, however, have a forward-bias voltage of 0.3 Volts.
Germanium is a rare material that is typically found with copper, lead or silver deposits. Because of its rarity, germanium is more expensive to work with, thus making germanium diodes more difficult to find (and sometimes more expensive) than silicon diodes.
Which Diode Should I Use?
Germanium diodes are best used in low-power electrical circuits. The lower forward-bias voltage results in smaller power losses and allows the circuit to be more efficient electrically. Germanium diodes are also appropriate for precision circuits, where voltage fluctuations must be kept to a minimum. However, germanium diodes are damaged more easily than silicon diodes.
Silicon diodes are excellent general-purpose diodes and can be used in nearly all electrical circuits where a diode is required. Silicon diodes are more durable than germanium diodes and are much easier to obtain. While germanium diodes are appropriate for precision circuits, unless there is a specific requirement for a germanium diode, it is typically preferable to use silicon diodes when fabricating a circuit.