Absorption coefficient as a function of resistance for optical germanium at 10.6microm.

Room-temperature transmittance measurements at 10.6 microm were made of germanium single-crystal samples. The samples were cut from very large doped single-crystal slabs that had been grown from +40-?-cm charge material of unknown purity for use as infrared windows and image-forming elements. The dependence of the absorption coefficient on sample resistivity was calculated from measured transmittances of ninety-two samples with resistivities ranging from 0.9 ?-cm to 57 ?cm. Maximum transmittance at 10.6 microm was obtained for the samples that were doped to a resistivity of 5-10 ?-cm and n-type conductivity.