Velocity surface measurements for ZnO films over {001}-cut GaAs

Abstract

Articles you may be interested inAnnealing effects on electrical and optical properties of ZnO thin-film samples deposited by radio frequency-magnetron sputtering on GaAs (001) substrates Growth and characterization of hypothetical zinc-blende ZnO films on GaAs(001) substrates with ZnS buffer layers A potential application for a piezoelectric film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO, .or Si,NdGaAs (001):cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope.Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the (110) propagation direction tbe autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the (100) direction. The passivation layer of SiOz or Si,N4 (CO.2 ,um thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by O&l.3 dB/@ at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theoretical calculations. We have also obtained the'anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 ,um thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Temperature dependent angular dispersions of surface acoustic waves on GaAs

“…We attribute the bigger discrepancy in ZnO/GaAs between our result and the literature data to the different ZnO film thickness. Our ZnO layer is as thick as 0.079𝜆 SAW (316 nm), thinner than the 0.13𝜆 SAW ZnO layer (1.6 𝜇m for 𝜆 SAW = 12 𝜇m) used by Kim et al 8 . We consider that the difference in measured velocity on GaAs in Fig.…”

“…Our RT results (filled circle and filled square in 8 . We consider that the difference in measured velocity on GaAs in Fig.…”

“…In addition, both our and the literature ZnO/GaAs devices exhibit a strong concave-upward parabolic behavior except with different fitting coefficients, which is opposite to a mild concave-downward behavior in the GaAs device. Thus, the beam diffracts more in the ZnO/GaAs system, unlike in GaAs, where it is autocollimating 8 . pSAWs suffer from the energy loss to the bulk, which reduces driving power efficiency.…”

“…[6] ZnO/GaAs ZnO/GaAs Ref. [8] Bulk ZnO signal values of ZnO/GaAs are worse than those of GaAs. We think that the ZnO film quality from our sputtering process may not be as cleans as that of the GaAs wafers.…”

“…6,7) Angular dispersions are related to diffraction of SAWs on surface, for example, a downward parabolic dispersion on GaAs leads to autocollimating behavior of SAWs. 8) Depending on propagation direction in GaAs, there are two different SAW modes: 6,7) (1) pure Rayleigh SAWs and (2) pseudo or leaky SAWs denoted as pSAWs. pSAWs are partially localized near the surface, but they lose energy into the bulk by transverse shear waves.…”