Copper-doped germanium detector

Photon detectors consist of a thin film of semiconductor material, such as lead sulfide, lead telluride, indium antimonide, or germanium doped with copper or mercury, deposited on a nonconducting glass and sealed into an evacuated envelope. Photon flux impinging on the semiconductor increases its conductivity. Lead-sulfide detectors are sensitive to radiation below about 3 fj.m in wavelength and have a response time of about 10 /nsec. Doped germanium detectors cooled to liquid-helium temperatures are sensitive to radiation up to about 120 jitm in wavelength, and have a response time of approximately 1 nsec. 

Bode and Graham (1963) A Comparison of the Performance of Copper-Doped Germanium and Mercury-Doped Germanium Detectors by D. Bode and H. A. Graham, Infrared Phys. 3, 129-137. 

In the far-IR, where photon energies are very low, quantum detectors cannot be used at all. Two types of thermal detectors, each operating at liquid-helium temperatures, have been used. The first one is the germanium bolometer, often doped with a low level of copper, gallium or antimony. For increased responsivity, these detectors are cooled down to 1.5 K by pumping the detector cryostat. The second type is the InSb hot-electron detector. 

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