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Silicon-Germanium Alloys for Infrared Detectors.

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Final rept. 15 Aug 77-14 Aug 79,

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Silicon-germanium alloys in the range of 10 at . Ge have been prepared by Czochralski growth. Material that was not intentionally doped exhibited resistivities as high as 1700 ohm-cm, but, because of the uptake of boron impurities from the crucible during growth, higher resistivities could not be achieved. Therefore, even though the alloys had absorption coefficients for 1.06 micron radiation around 50 per cm in contrast to 14 per cm for silicon, they were not well suited to preparing p-i-n detectors for 1.06 micron applications because the resistivities were too low to provide suitable long depletion regions. We prepared some alloy crystals by a crucible-free process which would lead to high resistivity akin to float zoning. The maximum Ge content achieved was about 2.5 at . while this value could be increased by equipment modification and process development, a fundamental drawback of the method is an axial variation of the germanium content as the germanium initially present in the zone is depleted. Measurements of minority carrier diffusion lengths in device structure made of p-type Si-Ge and of p-type Si showed essentially equivalent recombination life-times for both materials as processed to make the devices the lifetime values were close to 100 nsec. At room temperature, the mobility in p-type Si-Ge is degraded by 10 to 20 from the Si value. At cryogenic temperature, the mobility reduction is much larger, but is consistent with the disorder scattering estimate from room temperature measurements.

Subject Categories:

  • Infrared Detection and Detectors
  • Crystallography

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