Propagation Direction Of Acoustic Wave Research Articles

Acoustoelectric Investigation of Deep Centers in Bulk and Multilayered Semiconductors

Two basic versions of the acoustic deep-level transient spectroscopy (A-DLTS) technique based on the acoustoelectric effect resulting from the interaction between an acoustic wave and interfaces have been used to study deep centers in semiconductor structures. The former uses the high frequency transverse acoustoelectric signal (TAS) arising from the interaction of surface acoustic wave electric field and free carriers at the structure interfaces. The latter uses an acoustoelectric response signal (ARS) produced by the structure interface when a longitudinal acoustic wave propagates through the structure. An additional version of A-DLTS uses the acoustoelectric effect on light beam generated interface in high resistivity and along with photosensitive semiconductors. Planar Si MIS structure and GaAs/AlGaAs heterostructure capacitors and high resistivity GaAs were investigated by these versions of the A-DLTS technique. Several deep centers were found and their activation energies and corresponding cross-sections determined. Both the appearance of some A-DLTS peaks and the shift of practically all peaks of the A-DLTS spectra with increasing bias voltage in investigated structures can be considered to be the characteristic features of interface states. The polarization and the propagation direction of acoustic waves generated on the light beam produced interface appears as important condition of detected deep centers.

Measurements of the acoustic vector wave field in the shallow ocean made by a single ocean sub‐bottom seismometer (OSS)

In the shallow oceans, acoustic waves are strongly coupled with the seabed. If the vector wave field within the seabed is measured at a point, the direction of acoustic wave propagation can be accurately determined. To test this idea, we have measured the vector wave fields that are induced by ULF/VLF (0.01–1 Hz) ambient acoustic noise and acoustic pulses (0.05–1000 Hz) generated by an airgun using a single ocean sub‐bottom seismometer in shallow water 13 m deep. The maximum entropy principle is applied to the three orthogonal components of the vector field induced by the ambient noise to calculate the directional spectra. We were capable of detecting the noise field propagating from many directions that were substantiated from other independent measurements. The measured acoustic vector wave field induced by a moving source were compared with the model predictions by a WKBJ code. In the model calculations, the geoacoustic data obtained from the bottom shear modulus profiler method (Yamamoto and Trevorrow, in this conference) were used. Excellent agreements are obtained between the measured seismograms and the synthetic seismograms indicating that moving acoustic sources can be accurately determined using only two OSSs in the shallow oceans. [Work supported by ONR.]

Bragg coupling efficiency for guided acoustooptic interaction in GaAs

The guided acoustooptical interaction on the (100) plane of GaAs is investigated as a function of waveguide thickness type of mode, acoustic frequency, direction of acoustic wave propagation, and substrate refractive index Our calculated results indicate that best efficiency is obtained for TE(0) ? TE(0) optical modes and for acoustic surface wave propagating along the ?01l? direction at a waveguide thickness close to cut-off Under these conditions, approximately 75 mW of acoustic power is required for 100% diffraction. For a transducer aperture giving 50 Omega of radiation resistance, the rf bandwidth of the diffraction is limited essentially by the frequency bandwidth of the interdigital transducer. A comparison of the calculated results with experimental data at 1.06-microm optical wavelength is also given.

Noncollinear acousto-optic filter with large angular aperture

A new type of noncollinear acousto-optic filter with large angular aperture is described. By an appropriate choice of acoustic wave propagation direction, the momentum mismatch caused by the angular deviation of the incident light from the matching condition in a noncollinear interaction can be compensated by the angular change of optical birefringence. A TeO2 noncollinear acousto-optic filter was constructed that had a half-power bandwidth of 40 Å at an f/4 (±7°) aperture. Tuning from 700 to 450 nm is obtained by changing the acoustic frequency from about 100 to 180 MHz. About 95% maximum transmission is obtained with an electrical power density of 1 W/cm2 applied to the transducer.

The effect of inhomogeneities in acoustic-surface-wave amplification

We present the results of a theoretical analysis of acoustic-surface-wave amplification by a sheet of electrons whose density and drift velocity vary along the common direction of acoustic wave propagation and electron drift. Such inhomogeneities not only may result from doping variations but are inherent for drifting electrons at the surface of a semiconductor because of fringing electric fields due to the applied dc potential. We propose the results as a possible explanation of the observed inability of such amplifiers to reach the maximum gain predicted by the homogeneous amplifier theory.