Far Infrared Measurement of the Dielectric Properties of GaAs and CdTe at 300 K and 8 K

The real refractive index n and power absorption coefficient alpha of high resistivity GaAs and CdTe have been directly measured at 300 K and 8 K in the wavelength region from 12.5 micro to 300 micro. This spectral region contains the fundamental lattice resonance of both materials: 37.2 micro for GaAs and 71.4 micro for CdTe. This resonance causes large dispersion in the linear material properties. Single Drude-type oscillators have been visually fit to the measured n data with the results that for GaAs, epsilon(dc)' = 12.8 +/- 0.5 at 300 K and 12.6 +/- 0.5 at 8 K, and epsilonalpha(') = 10.9 +/- 0.4 at 300 K and 8 K ; for CdTe, epsilon(dc)' = 9.4 +/- 0.4 at 300 K and 9.0 +/- 0.4 at 8 K, and epsilon(alpha)' = 6.7 +/- 0.3 at 300 K and 8 K. The GaAs data clarifies the role of dispersion in n in the 5-20 micro region where previous results differ considerably. For both materials the n and alpha data in the region past 30 micro are the first to be reported.