Germanium is used in specific applications such as communication, spectroscopy, etc. They have largely been replaced with silicon. Germanium diodes are more expensive compared to silicon.
Germanium diodes have a lower forward bias voltage compared to silicon 0.15 volts. This enables the use of the Germanium diode at low voltages where silicon cannot be used.
Germanium is also used in photoelectronics application. Germanium diodes have a smaller band gap 0.66 eV. This means that the electrons can be excited even by near-infrared radiation.
Germanium is used in solar cells to capture the energy in near-infrared regions of the light spectrum. Germanium based sensors are used spectroscopy to detect light radiation at low frequencies.