A Promising Method of Evaluating ZnO Single Crystals Using the Line-Focus-Beam Ultrasonic Material-Characterization System

Abstract

Preliminary experiments and numerical calculations were conducted for developing a new ultrasonic method of evaluating resistivity distributions in ZnO single crystals using the line-focus-beam ultrasonic material-characterization system. Velocity and attenuation of leaky surface acoustic waves (LSAWs) were measured at 225 MHz on three Z -cut ZnO specimens with different resistivities. We observed drastic LSAW velocity and attenuation changes associated with relaxation between piezoelectricity and semiconduction for LSAW propagation: 56 m/s in velocity and 0.012 in normalized attenuation around a resistivity of 8.3 m. This ultrasonic method is promising for ZnO crystal characterization.

Development of a Micro Line-Focus-Beam Ultrasonic Device

“…For the Z-cut ZnO specimen we observed results with significant velocity distribution (Fig. 5) for dimensions of 4 Â 7 Â 3 mm 3 , as seen in our previous report, 4) due to the resistivity variations. We also measured detailed velocity profiles by y-scanning in fine steps of 0.1 mm along a broken line at x ¼ À1 mm, indicated in Fig.…”

“…Higher spatial resolution is required to evaluate small surfaces of such crystals as ZnO and AlN. 4,5) Directional point-focus-beam (PFB) ultrasonic devices [6][7][8][9][10] were developed with higher spatial resolution and acceptable directionality; however, they were not suitable for quantitative evaluations due to imperfect directionality in the LSAW propagation. 2,11) It is also insufficient simply to reduce the transducer width along the unfocused direction of the LFB device because of the diffraction effect of the acoustic field.…”

Acoustic properties for Ga–Sn–Zn liquid metal coupler with low melting point and high acoustic impedance

“…As one of the evaluation methods using ultrasonic, we have developed quantitative material characterization method using the ultrasonic micro-spectroscopy (UMS) technology. [11][12][13] So far, the usefulness of the UMS system has been demonstrated through many case examples such as detecting crystal inhomogeneity in mass production, [14][15][16][17][18] improving crystal homogeneity, 19) determination of the congruent composition of LiNbO 3 and LiTaO 3 , 20,21) determination of acoustical physical constants, [22][23][24][25][26] resistivity evaluation of ZnO, 27) evaluation of coefficient of thermal expansion for TiO 2 -SiO 2 glass, 28) thin film evaluation, [29][30][31] and so on. In the UMS system, it is possible to select and evaluate the bulk wave characteristics and surface wave characteristics of materials by changing the lens shape of the ultrasonic device.…”

Ultrasonic Microspectroscopy of ZnO Single Crystals Grown by the Hydrothermal Method

“…We developed a new ultrasonic method of evaluating the resistivity of this semiconductor material through drastic velocity changes associated with piezoelectricity. 16) We also recently developed a micro-LFB device with a higher spatial resolution in order to obtain detailed information of steep variations in acoustic properties on a small specimen surface. 17) It is fundamentally important to obtain accurate acoustical physical constants of actually employed crystals for developing and designing advanced ultrasonic devices, and for preparing standard specimens and establishing this ultrasonic method for characterizing ZnO crystals.…”