Germanium (Ge) crystal as a kind of infrared optical material, has advantages of  high infrared refractive index, wide infrared wavelength range, small absorption coefficient, low dispersive index etc., it is a good material particularly used for military , civilian and thermal imager, infra-red radar, windows etc., high purity Ge can be used  for astronomical gamma spectrometer, nuclear energy spectrometer and Ion physical  X-ray instruments, Si－Ge10 with doped mercury, cadmium, uprum, gallium of Ge single crystal can be used to infrared detector.

Applications:

It is a perfect semiconductor material, applied in the field of aerospace measurement and control, infrared laser system, nuclear detection, optical fiber communications, infrared thermal imager, infrared optics, solar cell, biomedical sciences etc.