Internal Friction and Photoacoustic Effects in A₂B₆ and A₂B₇(HgI₂) Single Crystals at Different Levels of Ultrasound Strain Amplitude

Abstract
A comparison of effects in damping and Young modulus under the influence of illumination for ZnSe and HgI₂ demonstrates quite different mechanisms of photoacoustic interaction in the crystals : a drift of photocarriers in the electric field which arises due to piezoelectricity for the first case and a dislocation pinning mechanism for the second one. Spectral responses of the photoacoustic effect in both amplitude independent and dependent damping range are presented for mercury iodide crystals. The newly found acousto- and photo-optic effects in the luminescence spectrum of HgI₂ allow one to specify the photosensitive dislocation pinning centre as an exciton state of carriers on a stoichiometric point defect of the lattice (iodine or mercury vacancy or interstitial).