Temperature dependence of the absorption coefficient of GaAs and ZnSe at 10.6 μm

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Abstract
The temperature (T) dependence of the absorption coefficient β at 10.6 μm of Czochralski-grown high-resistivity GaAs and chemical vapor deposited (CVD) ZnSe is measured by laser calorimetry. Experimental data are compared with theoretical curves for intrinsic multiphonon absorption. The temperature dependence of β for GaAs is found to possibly exhibit multiphononlike behavior below ∼450°K, but deviates rapidly from theoretical predictions above ∼500°K. The latter effect may be attributed to an increase in free-carrier density via thermal ionization from a level near 0.37 eV. The absorption coefficient of CVD ZnSe is found to be independent of T over the temperature range investigated, and therefore this material appears to be impurity or surface loss dominated.