Far-infrared photon absorption by phonons in ZnTe crystals

Abstract One-phonon and two-phonon contributions to polarization are determined for ZnTe crystals in the frequency range of 1–4 THz using the existing experimental data on far-infrared absorption and neutron scattering. The two-phonon contribution in the 1.7 THz band is higher than the first-order absorption related to the ion dipole (TO mode) resonance (comparable in the 3–4 THz band). LA → TO phonon difference transitions are concluded to dominate in the 1.7 THz band, whereas TA → TO, TA → LO and mixed-mode A → O difference transitions are of primary importance in the 3–4 THz band. The contributions of the 2TA-overtone and other two-phonon-sum processes are comparatively weak. Matrix element squares for partial inter-phonon-band transitions are compared, and the photon–two-phonon coupling coefficients are estimated.