Acoustoelectric Amplification Research Articles

Semiconductor Fluorinated Carbon Nanotube as a Low Voltage Current Amplifier Acoustic Device

Acoustoelectric effect (AE) in a non-degenerate fluorinated single walled carbon nanotube (FSWCNT) semiconductor was carried out using a tractable analytical approach in the hypersound regime , where q is the acoustic wavenumber and is the electron mean-free path. In the presence of an external electric field, a strong nonlinear dependence of the normalized AE current density , on ( is the electron drift velocity and is the speed of sound in the medium) was observed and depends on the acoustic wave frequency, , wavenumber q, temperature T and the electron-phonon interactions parameter, . When , decreases to a resonance minimum and increases again, where the FSWCNT is said to be amplifying the current. Conversely, when , rises to a maximum and starts to decrease, similar to the observed behaviour in negative differential conductivity which is a consequence of Bragg’s reflection at the band edges at T=300K. However, FSWCNT will offer the potential for room temperature application as an acoustic switch or transistor and also as a material for ultrasound current source density imaging (UCSDI) and AE hydrophone devices in biomedical engineering. Moreover, our results prove the feasibility of implementing chip-scale non-reciprocal acoustic devices in an FSWCNT platform through acoustoelectric amplification.

Non-Reciprocal Acoustic Transmission in a GaN Delay Line Using the Acoustoelectric Effect

This letter reports on first-time demonstration of non-reciprocal acoustic transmission in a gallium nitride (GaN) delay line structure. The split of forward (S21) and backward (S12) transmissions is observed by applying a dc electric field through the active area with a two-dimensional electron gas (2DEG) sheet. The non-reciprocity (~20.7 dB/mm max. in this letter) varies by tuning the gate voltage to deplete the 2DEG sheet carrier density, which agrees with model prediction for the interaction between 2DEG and surface acoustic waves. Our preliminary results prove the feasibility of implementing chip-scale non-reciprocal acoustic devices in a GaN platform through acoustoelectric amplification.

Nonlinear acoustoelectric interactions in GaAs/LiNbO3 structures

Surface acoustic waves accompanied by very large piezoelectric fields can be created in a semiconductor/piezoelectric hybrid system. Such intense waves interact with the mobile carries in semiconductor quantum well structures in a manner being strongly governed by nonlinear effects. At high sound intensities, a formerly homogeneous two-dimensional electron system breaks up into well confined stripes surfing the wave. As a result, we observe a strong reduction of electronic sound attenuation. On the other hand, large momentum transfer between the electron system and the wave results in nonlinear acoustoelectric effects and acoustoelectric amplification. We describe our experimental findings in terms of a generalized theory of the acoustoelectric effect and discuss the importance for possible device applications.

Acoustoelectric Amplification in the Presence of Non-Uniform Electric Field and Carrier Concentration in Solids

Acoustoelectric amplification in a strain-dependent, transversely magnetised semiconductor is studied in the presence of non-uniform electric field and carrier concentration along the sample length. A generalised expression for the amplification coefficient in strain-dependent and piezoelectric materials is also discussed for a single carrier semiconductor. Application to a multilayered system of different single carrier semiconductors coupled to one elastic wave is also suggested. The non-uniformity in carrier concentration is found to have significant effect on the amplification coefficient in a multilayer system. Bei ungleichformigen Feldern und Ladungstragerkonzentrationen uber der Probenlange wird akustoelektrische Verstarkung in einem spannungsabhangigen, transversal magnetisierten Halbleiter untersucht. Verallgememerte Ausdrucke fur den Verstarkungskoeffizienten in spannungsabhangigen und piezoelektrischen Materialien werden fur einen Eintragerhalbleiter ebenfalls diskutiert. Die Anwendung auf ein mehrschichtiges System von unterschiedlichen Eintrager-Halbleitern, die an eine elastische Welle gekoppelt sind, wird vorgeschlagen. Es wird gefunden, das die Ungleichformigkeit in der Tragerkonzentration einen betrachtlichen Einflus auf den Verstarkungskoeffizienten eines Mehrschichtsystems hat.

Amplification of acoustic waves in magnetised piezoelectric semiconductors. Effect of nonlinearity in electron effective mass and collision frequency

AbstractAn attempt is made to provide a theoretical approach to experimental studies of the acoustoelectric amplification in magnetised piezoelectric semiconductors showing that the attenuation of an acoustic wave crosses over to its amplification when the electron drift velocity exceeds the acoustic wave velocity. First a phenomenological theory is developed to study the relative change in electron effective mass and collision frequency when an acoustic wave passes through piezoelectric semiconductors. Then, analytically, it is shown that this nonlinearity due to the electric vector of the field associated with the wave can also explain this behaviour. Numerical computations are made for n‐InSb at 78 K. It is found that the magnetic field does not have any remarkable effect on amplification.

Amplification of acoustic waves in piezoelectric semiconductors: Effect of nonlinearity in electron effective mass and collision frequency

This paper essentially seeks to provide a theoretical construct to the experimental studies on the acoustoelectric amplification in piezoelectric semiconductors showing that the attenuation of an acoustic wave crosses over to its amplification when electron drift velocity exceeds the acoustic wave velocity. In this paper, first, a phenomenological theory is developed to study the relative change in electron mass and collision frequency when an acoustic wave propagates through piezoelectric semiconductors. Then, analytically, we have shown that this nonlinearity in electron mass and collision frequency arising due to the electric vector of the field associated with the wave can also explain this behavior. Numerical computations are made for a typical case of n-InSb at 77 K.

Broadband generation of acoustic surface waves on GaAs by conversion from acoustoelectrically amplified bulk waves

This paper describes the first observation of the generation of surface waves in a broad frequency band (0.2<f<1.0 GHz) by conversion from bulk acoustic waves. The latter are obtained by acoustoelectric amplification from thermal background in GaAs samples at 300 K. The surface waves are generated in the form of narrow propagating domains. Both group and phase velocity measurements, carried out on the principal crystallographic surfaces, served to identify the surface waves.

Direct measurement of acoustoelectric amplification parameters in surface acoustic waves

It is shown that classical formulae which describe acoustoelectric amplification can give the values of the coupling coefficient the dielectric relaxation frequency and the trapping parameters if one can measure the change of phase velocity as a function of the accelerating electric field. A method based on measurement of the phase velocity in the pulsed mode is proposed, which allows the direct determination of these various parameters. Experiments are performed on photoconducting CdS operating in the Rayleigh mode. The dielectric relaxation frequency omega c is not proportional to the semiconductor conductivity. The trapping time tau varies linearly from 10-9 s to 5*10-9 s with the conductivity in the range explored.

Improvement of semiconducting films for acoustoelectric amplification

Experimental results for surface acoustoelectric amplification on a monolithic structure InSb/LiNbO3 are reported. Drift mobility, in a reproducible sequence of samples, has been found to be almost equal to the Hall mobility and reaches a value of up to 600 cm2/Vs.

Nonohmic behavior of semiconductors in a quantizing magnetic field

We have investigated the nonohmic resistivity of a nondegenerate semiconductor in quantizing magnetic fields for the case where acoustic phonons are the dominant scattering mechanism. The type of I-V characteristics found depends upon which of three mechanism are dominant. The three mechanisms are due to collisional broadening, inelasticities due to the finite phonon energy and phonon drag. When collistion broadening is important, the nonlinearities in the current voltage characteristic arise only from electron heating, while when the inelasticities are dominant, there is also an intrinsic nonlinearity in the characteristic. Finally, when phonon drag is dominant, high frequency acoustoelectric amplification will occur when the Hall velocity exceeds the sound velocity, i.e. V H > S. For the case where inelasticities dominate, a region of negative differential resistance is obtained that should persist even when there is considerable optical phonon scattering.

Acoustoelectric Amplification—A Phonon-Laser Approach: Theory of a Single Acoustic Mode

Acoustoelectric amplification in piezoelectric semiconductors can be profitably treated as the acoustic analog of a classical laser. The nonlinear acoustic gain and frequency pulling can be found by combining Maxwell's equations with the piezoelectric equations of state and solving the resulting system to third order in a perturbation expansion. Recent experimental findings (acoustic mode locking, etc.) encourage the use of such methods, which produce results analogous to those of the Lamb theory of a classical laser. We here present solutions for the case of a single acoustic mode. Diffusion effects are found to be important, especially near threshold.

Nonohmic behaviour of tellurium with intrinsic and near-intrinsic carrier concentration

Investigations of the nonohmic behaviour of intrinsic and near-intrinsic tellurium were performed by voltage probe measurements, double pulse experiments and measurements with T-shaped samples. It is shown, that the nonohmic behaviour for T > 180 K is not due to acoustoelectric amplification but is caused by a depletion layer of electrons near the cathode. The development of the depletion layer is explained by a blocking contact for electrons at the cathode contact. Mit Hilfe von Potentialsonden, Doppelimpulsen und T-förmigen Proben wurden Untersuchungen über das nichtohmsche Verhalten von Tellur im intrinsischen und nahezu intrinsischen Bereich durchgeführt. Es wird gezeigt, dass das nichtohmsche Verhalten nicht auf eine akustoelektrische Verstärkung zurückgeführt werden kann, sondern durch eine Verarmungsschicht an Elektronen in der Nähe der Kathode verursacht wird. Die Entstehung der Verarmungsschicht wird durch einen sperrenden Kontakt für Elektronen an der Kathode erklärt.

Anwendung der Weitwinkelinterferenzen zur Untersuchung von akusto-elektrischen Gitterschwingungen in Kadmiumsulfid / Application of the Pseudo-Kossel-Line-Technique for the Investigation of Acoustoelectric Lattice Jibrations in Cadmium Sulfide

Changes in absolute and relative intensities of Pseudo-Kossel lines from crystals containing lattice vibrations were observed. Since the relation between vibration amplitude and intensity modification is known theoretically, vector amplitudes and gain factors of the acoustoelectric amplification can be determined. Advantages of this method are discussed.

An explanation for the Bekefi peaks in the low-field microwave emission from InSb

The peaks in the microwave emission intensity from InSb, at 4.2 K, observed at distinct values of the applied magnetic field as reported by Bekefi et al., are explained in terms of magnetophonon resonances in the acoustoelectric amplification.

Brillouin-Scattering Studies of Acoustoelectric Gain and Lattice Attenuation in Semiconducting CdS

Brillouin-scattering measurements were used to study acoustoelectric interactions in semi-conducting CdS. In the GHz frequency range, a double-pulse technique described earlier was employed to suppress domain formation and thereby reduce down-conversion processes. In this manner considerable extension of the small-signal regime towards higher flux levels could be achieved. At lower frequencies, nonlinear effects were invoked to produce a propagating low-frequency domain whose attenuation and amplification were subsequently studied under small-signal conditions. Analysis of the time evolution of the spatial and frequency distribution of the amplified flux, measured under different conditions, provided accurate data on the frequency dependence of the acoustoelectric gain and the lattice attenuation over the broad range of 0.15-4 GHz. Comparison of the measured gain parameters with the small-signal theory of acoustoelectric amplification gave very good agreement throughout the frequency range studied. The lattice attenuation was found to follow the expected ${f}^{2}$ Akhiezer law at high frequencies and to vary much more slowly, if at all, in the low-frequency range (0.2-0.6 GHz). In this latter range the lattice attenuation is very low (\ensuremath{\sim}1 ${\mathrm{cm}}^{\ensuremath{-}1}$) and is most probably controlled by crystal imperfections. Although the studies in this paper were mostly confined to the small-signal regime, several interesting features have emerged concerning nonlinear effects. In particular, the down-converted low-frequency flux in a propagating domain was observed to lag slightly behind the high-frequency flux from which it originated. No explanation can be offered at present for this rather surprising phenomenon.

Miscellaneous : Acoustoelectric amplification in a layered structure at microwave frequencies Schummy, H., Claassen, M., Harth, W., Arch Elektron & Ubertragungstech26 (May 1972) 241 (in English)

Miscellaneous : Acoustoelectric amplification in a layered structure at microwave frequencies Schummy, H., Claassen, M., Harth, W., Arch Elektron & Ubertragungstech26 (May 1972) 241 (in English)

Measurements of acoustoelectric gain and lattice attenuation in n-GaAs

Measurements of the non-ohmic behaviour associated with acoustoelectric amplification were employed to derive the frequency dependence of the small signal electronic gain parameter alpha 0 and the lattice attenuation alpha l in n-GaAs. Samples of different carrier concentrations at different temperatures were used to vary the frequency of the amplified flux. The use of a single frequency model in the derivation of alpha 0 and alpha 1 is justified in the text.

Proposed Measurement of the Acoustoelectric Effect by Electron-Photon-Phonon Interaction for Hypersonic Phonons in Semiconductors

It is proposed that amplification of phonons of frequencies in the order of hundreds of gigahertz can be investigated by measuring expected changes in the free carrier absorption coefficient which will occur from changes in the density of thermal phonons. It is shown that for photon energies greater than the thermal energy, there is a one-to-one correspondence between the energy of the incident photons and the momentum of the phonons that are required for free carrier absorption by means of intraband electron transitions. An important result derived is that the phonon energy per unit bandwidth, at a particular phonon frequency proportional to the incident radiation energy, is directly related to the ratio of the free carrier absorption coefficients during and before acoustoelectric amplification. As a specific example, the case of CO2 laser radiation absorption in n-type Ge is considered, leading to the result that at 10 K the free carrier absorption coefficient will increase by several orders of magnitude over its thermal equilibrium value during acoustoelectric amplification. In addition, the dependence of the free carrier absorption coefficient on the phonon density suggests applications in some laser devices such as photon drag detectors and amplitude modulators.

1027. Study of the acoustoelectric amplification in tellurium with epitaxially grown selenium transducers: J Barbot et al,Phys Stat Sol (a), 8 (2), Dec 1971, 433–436

1027. Study of the acoustoelectric amplification in tellurium with epitaxially grown selenium transducers: J Barbot et al,Phys Stat Sol (a), 8 (2), Dec 1971, 433–436

Acoustoelectric amplification of Rayleigh waves in presence of a d.c. transverse magnetic field

The influence of a 20 kG d.c. transverse magnetic field on the acoustoelectric amplification of Rayleigh waves at 50 MHz has been investigated. The experimental results are in good agreement with theoretical expectations.