Two-Phonon Difference Absorption Spectra in Ge Crystals

Abstract

Optical absorption spectra of Ge crystals have been measured in the far-infrared region at temperatures between 2 and 292 K. In the low energy region, structures in the absorption spectra have been found around 100 and 200 cm⁻¹, which are assigned as being due to the two-phonon difference processes between TA and other phonons. The absorption spectrum due to the two-phonon difference process gives us information on the optical absorption process which is complementary to the information obtained from the two-phonon summation spectrum.