Ultrasonic Microspectroscopy of LiTaO_3 Single Crystals for Optoelectronic Devices

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Ultrasonic microspectroscopy technology, especially using the line-focus-beam (LFB) acoustic microscopy system, is very useful and unique for quantitative material characterization by measuring the velocity of leaky surface acoustic waves (LSAWs) , excited on the water-loaded specimen, through V (z) curve analysis. This system has been applied to material problems in the scientific and industrial fields of LiTaO_3 crystals for establishment of the crystal growth conditions and for evaluation of the optoelectronic device fabrication processes such as proton-exchanged and domain-inversion layrs.1.The reliable LFB system with high measurement accuracy in LSAW velocity has been established, resulting in the absolute accuracy within(]SY.+-。[)0.01% and the relative accuracy within(]SY.+-。[)0.001%.2.Three LiTaO_3 crystals of 3-inch-diameter, grown with the different compositions of the starting materials of 48,48.5,49 Li_2O-mol%, have been employed for velocity measurements. It has been shown … More that the velocities on the three basic crystal surfaces of X-, Y-, and Z-cut planes increase for all the surfaces and all the propagation directions monotonically as the Li_2O concentration increases, and the corresponding density decrease monotonically.3.The measured LSAW velocities have been compared with the measured, Curie temperatures, chemical composition, and densities. It has been shown that the LFB system has a much greater sensitivity and resolution in the determination of chemical composition than any other conventional methods such as differential thermal analysis (DTA) , X-ray fluorescence anlysis (XRF) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) .4.Acoustic homogeneity of an optical-grade congruent LiTaO_3 single crystal with 4-inch diameter has been evaluated by LSAW velocity distributions. The velocities have increased by 0.45 m/s, corresponding to the chemical composition change of +0.015 Li_2O-mol%, along the crystal length of 60mm.5.The system has been applied to characterization of proton-exchanged and domain-inverted layrs fabricated on Z-cut LiTaO_3 substrates. It has been demonstrated that the system has the capability to resolve the change of diffusion depth of 1 nm for the proton-exchanged layr and the change of the domain-inverted layr thickness of 1 nm.6.The computer program of numerical calculations of the LSAW propagation characteristics for the layred structures described above has been developed. Less