Early semiconductor developments used germanium as the commercial, semiconductor material. Due to its ease of processing and more stable temperature characteristics, silicon became the semiconductor of choice.
And as a consequence of that, most early germanium semiconductors were replaced with silicon. These were primarily transistors and diodes.
However, germanium diodes have the advantage of an intrinsically low forward voltage drop, typically 0.3 volts; this low forward voltage drop results in a low power loss and more efficient diode, making it superior in many ways to the silicon diode. A silicon diode forward voltage drop, by comparison, is typically 0.7 volts. This lower voltage drop with germanium becomes important in very low signal environments (signal detection from audio to FM frequencies) and in low level logic circuits. As a result germanium diodes are finding increasing application in low level digital circuits.
With this increased interest, certain general germanium characteristics should be understood. First and most important is that of an increased leakage current for germanium at a reverse voltage. This is mitigated to some degree by the fact that in low level circuits the reverse voltage applied to a germanium diode is also usually very low, resulting in a low reverse leakage current (leakage current is directly proportional to reverse voltage). However the leakage current is still larger than with silicon. A properly designed circuit can lessen this factor.