We describe the photoresponse of GaN-based surface acoustic wave (SAW) delay-line oscillator operating in the 200 MHz range. The decrease in oscillator frequency under ultraviolet illumination of GaN transducer is caused by the SAW velocity decrease due to the acoustoelectronic interaction with photoconductivity electrons. The oscillator frequency shift reaches its maximum value at 365 nm and drops to zero above 400 nm with visible/ultraviolet rejection ratio more than 100. The optical quenching of the photoconductivity in GaN was observed. These results demonstrate the potential of the GaN-based SAW oscillators for applications as visible–blind remote UV sensors.

The attenuation of surface acoustic waves propagating along crystallographic X axis in proton-exchanged 128° rotated Y-cut lithium niobate during the evaporation of copper film on the crystal surface has been measured as a function of sheet resistivity of the film. From the magnitude of attenuation maxima, the effective electromechanical coupling coefficients for samples with different thicknesses of HxLi1−xNbO3 layers have been evaluated, and from the position of maxima in the resistivity scale, the effective dielectric permittivities of the structure have been estimated. The electromechanical coupling coefficient is found to be reduced practically to zero with increasing thickness of protonated layer and acoustic frequency, and the dielectric permittivity is not significantly affected by the proton exchange.

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The electromechanical coupling coefficient for surface acoustic waves propagating in GaN-on-sapphire structure has been evaluated using in situ measurements of the SAW attenuation during the evaporation of a metal film on the GaN surface. The extracted values for samples with GaN layer thicknesses of 2.2-2.4 mm were in the range of 0.06-0.09% at SAW frequencies of 200-300 MHz.Introduction Surface acoustic waves (SAWs) have found important applications in material research, signal processing, and telecommunications areas. There is a considerable interest in SAW investigations in thin-film structures based on GaN family of semiconductors. The key parameter for SAW devices is the electromechanical coupling coefficient, K 2 . The efficiency of the SAW interdigital transducer (IDT) is characterized by its radiation conductance G a ðf 0 Þ ¼ 8K 2 f 0 C T N at center frequency f 0 , where C T is the IDT static capacitance and N is the number of the IDT electrode pairs. The electromechanical coupling coefficient for SAWs can be expressed as K 2 ¼ 2DV=V, where DV is the magnitude of the SAW velocity change that occurs when the free surface of the piezoelectric is shorted by a thin highly conducting metal film, and V is the unperturbed SAW velocity. The K 2 values for SAWs in GaN-on-sapphire structures have been evaluated from transducer performance analysis and extracted from the velocity measurements by several authors [1][2][3][4]. However, there is a considerable disagreement in the results, and further investigations are necessary. For this purpose, we have chosen the technique, different from those mentioned above. We report on the evaluation of the electromechanical coupling coefficient for GaNon-sapphire structures using in situ measurements of the SAW attenuation during the evaporation of a metal film on the surface of the piezoelectric [5,6].