germanium photodiode
A germanium-based PN- or PIN-junction photodiode.
Note 1: Germanium photodiodes are useful for direct detection of optical wavelengths from approximately 1 
m to several tens of m.
Note 2: Germanium-based detectors are noisier than silicon-based detectors. Silicon-based detectors are therefore usually preferred for wavelengths shorter than 1 m. [After FAA]