PMC

Operational principle of the conventional and polarization inversion technique (PIT) models: (a) Conventional structure with a single piezoelectric layer, (b) polarization-inverted layer structure with a 0.25 inversion ratio (front-side inversion model), (c) polarization-inverted layer structure with a 0.25 inversion ratio (back-side inversion model), and (d) the PIT with a 0.5 inversion ratio (half-inversion model). Note that the time and frequency responses of the radiated ultrasound waves at interface A for each case were also demonstrated by computational simulation, as shown in .

Relationship between the ray length across each layer and inversion errors of S2–S3. Three layers: Red, black, and blue circles denote the errors of the first layer, the second layer, and the third layer, respectively. The magenta curve indicates the fitted curve by using the power function. Five layers: Red, black, blue, yellow, and green squares denote the errors of the first layer, the second layer, the third layer, the fourth layer, and the fifth layer, respectively. The magenta dotted curve indicates the fitted curve by using the power function. Two layers: Red and black diamonds denote the errors of the first layer and the second layer, respectively. The magenta dotted curve indicates the fitted curve by using the power function.

(a) Internal depleted layer at the β-Ga₂O₃/Au phase boundary; (b) corresponding band diagram; E_inv—energy of the inversion level, E_F—energy of the Fermi level, E_C—energy of the lower edge of the conduction band, E_V—energy of the upper edge of the valence band, L_D—width of the depleted layer, d_inv—width of the inversion layer, ○—holes, ●—electrons, eV_S—height of the potential barrier at the surface of the grain.

Temperature inversion errors. The red, black, blue, green and purple curves indicate the errors of the first layer, the second layer, the third layer, the fourth layer, and the fifth layer, respectively. (a–c) correspond to the results of a–c, respectively.