Attenuation Of Surface Acoustic Waves Research Articles

Ultrasonic attenuation of surface acoustic waves in a thin film of superconducting Nb 3Sn

The attenuation of 660 MHz surface acoustic waves propagating in a thin film of Nb 3Sn 5000 Å thick has been measured as a function of temperature from 4.2 K to 16 K. The A 15 Nb 3Sn, electron-beam codeposited on YZ lithium niobate and annealed at 700°C, was studied using 5.1 μm wavelength interdigital electrodes. The film revealed a transition temperature of 14.2 ± 0.1 K and using the BCS theory, an energy gap 2 Δ(0) = 3.5 k B T c .

Contactless semiconductor surface characterization using surface acoustic waves

The electric field which accompanies a surface acoustic wave (SAW) propagating on a piezoelectric substrate can interact with the free charge carriers near the surface of an adjacent semi-conductor. This interaction produces a measurable DC acoustoelectric voltage across the semi-conductor and attenuates the SAW. The magnitude of these effects are dependent on the semi-conductor conductivity. Monitoring the acoustoelectric voltage or SAW attenuation while varying the conductivity by external means can yield information about the density and the dynamics of the surface and impurity states in the semiconductor. By observing the optical wavelength dependence of the acoustoelectric voltage developed across the semiconductor, the energy profile of the states in the bandgap can also be determined. Experimental results will be presented for several semiconductor samples. These include GaAs and GaP with or without added impurities and silicon. Tlie results show that the use of the SAW convolver provides a simple sensitive contactless and nondestructive means of evaluating the electrical properties of the semiconductor surface.

Estimation of surface-acoustic-wave attenuation due to platelet defects

Surface-acoustic-wave (SAW) attenuation due to platelet defects in quartz substrate (40° rotated Y cut) was investigated. The dimensions of the defects, which are formed in a lapping and polishing process, were quantitatively measured. The data was used in the analytical calculation. SAW attenuation loss in propagating on damaged substrate with deep defects was experimentally measured in the 150–400-MHz frequency range. The loss was obtained from the measured Q value of an IDT resonator, comprising the substrate. By comparing the Q value of the resonator using damaged substrate with that using undamaged substrate, the loss caused by the defects was discriminated from other losses. Steg’s scattering theory was applied to the SAW device and the calculated attenuation loss agreed well with the measured one. The theory also predicts that the attenuation constant in conventionally polished substrate, which contains about 2×104 cracks/cm2 microcracks, is about 1 dB/cm at 1 GHz.

Study of the surface properties of thermally oxidized silicon using surface acoustic wave attenuation

In the separate media space charged coupled convolver, the interaction of a surface acoustic wave (SAW) with the free carriers in an adjacent semiconductor results in attenuation of the acoustic wave. The magnitude of the attenuation is dependent on the concentration of the free carriers near the surface. An externally applied d.c. voltage changes the surface carrier concentration and this change is reflected in SAW attenuation. Analysis of the SAW attenuation caused by a continuous d.c. field gives an estimate of the surface state density. The time required for the SAW attenuation to reach steady state after the semiconductor is driven into deep depletion is an indication of the rate of carrier generation in the depletion region. Transient effects have also been observed using a synchronously applied d.c. pulse.

Ultrasonic attenuation of surface acoustic waves in superconducting zinc

The attenuation of 90-MHz elastic surface waves propagating in both 3 000 and 10 000 \AA{} films of zinc has been measured as a function of temperature from 3 to 0.38 K. The surface acoustic waves were generated and detected by using a surface-acoustic-wave device with interdigital transducers plated onto a $Y\ensuremath{-}Z$ cut lithium-niobate substrate. Utilizing the experimental results, in the BCS theory, energy gaps of $2\ensuremath{\Delta}(0)$ equal to 4.17\ifmmode\pm\else\textpm\fi{}0.20 and 3.81\ifmmode\pm\else\textpm\fi{}0.20 in units of ${k}_{B}{T}_{c}$ were calculated for the 3 000 and 10 000 \AA{} films, respectively. The transition temperatures for the 3 000 and 10 000 \AA{} films were 1.5\ifmmode\pm\else\textpm\fi{}0.01 and 1.31\ifmmode\pm\else\textpm\fi{}0.01 K, respectively.

Attenuation and phase velocity of surface acoustic waves interacting with charge carriers in thin metal films

A simple method for the simultaneous measurement of attenuation and phase-velocity changes of surface acoustic waves, based on the use of a surface-acoustic-wave oscillator, is described. The application of the method is illustrated in the case of surface acoustic waves interacting with charge carriers in thin gold fims vapor deposited on the lithium niobate substrate supporting the surface waves. Good agreement is obtained between experimental results and theory. It is shown that the product of carrier mobility and Fermi energy can be determined with good accuracy independently from three different relations involving attenuation, phase velocity, and resistivity data.

Optical image scanning by electronic control of surface acoustic wave attenuation in CdS

A new technique of reading optical images in a CdS surface acoustic wave delay line is presented. The principle is based on controlling surface-acoustic wave propagation loss by applied gate bias.

Semiconductor surface spectroscopy using acoustic surface wave: CdS

The space charge coupled interaction of surface acoustic waves (SAW) propagating on a piezoelectric substrate with a semiconductor surface placed in proximity gives rise to SAW attenuation. As a result of nonlinearity, a d.c. acousto-electric voltage and a second-harmonic r.f. convolution voltage under certain circumstances are developed across the semiconductor. The spectral response of these parameters is used to determine the static and dynamic properties of the semiconductor surface. The existence of maxima and minima in the photo-enhanced convolution voltage, acousto-electric voltage and SAW attenuation is due to the corresponding structures in the photoconductivity. A comparison is made between the spectral response of these parameters for CdS to show that, at room temperature, the transverse acousto-electric voltage has greater sensitivity to photon absorption for subband gap illumination.

Surface study of ion-implanted silicon wafers using SAW convolver

Nonlinear space-charge-coupled interaction between a surface acoustic wave (SAW) propagating on a lithium niobate substrate and ion-implanted silicon samples placed in proximity to the SAW propagating surface has been studied. A pulsed dc electric field normal to the surface has been used to bend the surface potential for accumulation and depletion of charge carriers near the surface which in effect causes a change in attenuation of SAW. Experimental results are presented using three n-type silicon samples into two of whcih boron was implanted. Experimental results are found to substantiate theoretical predictions of attenuation, calculated on the basis of partial compensation of the silicon doping by the implanted ions. Similar studies have also been made using incident light of varying intensity on the semiconductor surface.

Temperature dependence of the interaction between surface acoustic waves and nickel thin films

Measurements of the magnetic-field-dependent attenuation of 618-MHz surface acoustic waves by a 500-Å nickel film, made over the temperature range 4–350 K, are reported. Some room-temperature hysteresis-dependent interactions are also described.

Determination of energy band and surface-state locations in GaAs using the separated-medium surface-acoustoelectric effect

The wavelength dependence of the peak transverse acoustoelectric voltage and the surface acoustic wave attenuation determine the energy band and the locations of the surface states in the energy gap of GaAs. The dependence is explained by direct optical transition between the bands and optical transition from surface states. This method needs no contacts to the semiconductor surface, is simple, very sensitive, and accurate.

Electronic control of the velocity and attenuation of surface acoustic waves in piezoelectric semiconductors

The velocity and attenuation of a surface acoustic wave on a piezoelectric semiconductor may be controlled by adjusting the bias of a reverse-biased distributed diode. With the proper choice of resistivity and operating frequency, changes in velocity of 1% and attenuation of 300 dB/cm may be achieved in c-axis cadmium sulfide for bias voltages under 30 V. Theoretical behavior is presented and initial experimental results are summarized.

Measurements on surface acoustic waves in photoconducting cadmium sulfide

Measurements of the conductivity dependence of the velocity and attenuation of surface acoustic waves in photoconducting cadmium sulfide are described. The use of the surface acoustic waves as a diagnostic for photoconductivity studies is demonstrated.