Nonstructural acousto-injection luminescence in metalized lithium niobate

Abstract

The observation of a nonstructural acousto-injection luminescence (NAIL) from metallized LiNbO3 wafers is reported. The X- and Y-cut plates with linear dimensions of a few mm and silver paste electrodes on opposite surfaces are investigated. The experiments are done at room temperature. The fundamental shear modes are excited at MHz-frequencies. We measure the spectra of NAIL, acousto-electric resonance/antiresonance properties, X-ray diffraction rocking curves, acoustic emission accompanying NAIL, and photoluminescence. The NAIL and associated effects appear above a certain threshold acoustical strain of e = 10-5. The results are explained in the terms of considerable piezoelectric fields, yielding the charge injection from the metal contacts into crystal along with the strong mechanical stresses leading to dislocations motion. The acoustic emission and X-Ray rocking curves disclose the dislocation motion under e > 10-5. The involvement of the microstructural non-uniformities in the effects observed is experimentally identified by the X-ray rocking curves taken at different ultrasound amplitudes and photo-luminescence spectra taken from the different micro-regions of samples. Photoluminescence reveals the charged point defects that may promote an electrical conduction. The distribution of crystal defects along wafers is not uniform, and has a quasi-periodical component with tens to hundreds of microns spacing between their extremal locations.