Acoustoelectric Domains Research Articles

Decay of Acoustoelectric Domain and Microwave Emission in n-InSb

The relation between the motion of the acoustoelectric domain and microwave emission in acoustoelectrically oscillating n -InSb was investigated and it was found that the discontinuity at the boundary of anode plays an important role in the microwave emission. The decay of the domain and microwave emission was studied by using a double pulse technique; the built-up domain continued to exist about 1 µsec after switching off the first pulse, but the microwave emission faded out instantaneously. If the second pulse is applied during the decay of the acoustic domain, the microwave emission can be generated again. The square root of the emitted microwave power was proportional to the drift velocity of electrons. These results show that the drift motion of electrons is essential for the microwave emission from n -InSb. In some cases reflected acoustic domain from the anode was observed. Finally the decay of the acoustoelectric domain is explained by considering the contributions from both the three-phonon proce...

SOUND WAVE AMPLIFICATION IN INDIUM ANTIMONIDE

We have directly measured acoustic wave amplification of shear waves in high mobility InSb in the frequency range 0.5–2.0 GHz. At 1 GHz we have observed 10 dB net terminal gain. We find good agreement with the modified theory of White in the high magnetic field region where the acoustic wavelength λ is much larger than the Larmor radius of the electrons. In the low magnetic field limit it is necessary to use the Boltzmann transport equation approach of Spector; in this case, good agreement with the observed behavior is obtained. This effect is shown to be responsible for the two-mode threshold behavior for acoustoelectric domain oscillations in InSb.

Brillouin Scattering Studies of Acoustoelectric Domain Formation in Semiconducting CdS

AbstractThe growth of the flux intensity in acoustoelectric domains in semiconducting CdS has been followed over five orders of magnitude for frequencies between 0.2 and 5 GHz using the Brillouin scattering technique. The form of the flux domains is exponential on both sides with a halfwidth of about 300 μm. By studying their formation in the very early stage before the current decay, it was found that the frequencies and amplification factors of the flux appearing first are close to those predicted by the linear theory. After the current has started to decay, higher and lower frequencies are observed, the lower with much higher amplification and intensities. It seems that the electric field inside the domain does not have an essential influence on the flux growth. The experimental results are compared with some acoustoelectric amplification models.

FLUX-DEPENDENT ASPECTS OF THE EVOLUTION OF ACOUSTOELECTRIC DOMAINS IN n-GaAs

Optical probe studies of propagating acoustoelectric domains in n-GaAs reveal a self-narrowing of the domain during growth, and an apparent limitation to the peak acoustic density in the domain, illustrating the role of flux-dependent processes in domain evolution. A mechanism is discussed, based on evidence for changes in spectral composition of the domain at high acoustic intensity.

ERRATA: Resonant and Round-Trip Gain for Acoustoelectric Domain in n-InSb

ERRATA: Resonant and Round-Trip Gain for Acoustoelectric Domain in n-InSb

Optical Probing of Inhomogeneities in n-GaAs with Applications to the Acoustoelectric Instabilities

A study is presented of the intimate relationship between current instabilities of acoustoelectric origin in n-GaAs at 77°K and the inhomogeneity in the Ohmic resistivity of the samples. In order to correlate various aspects of the acoustoelectric instabilities with the sample inhomogeneities, two optical probing techniques were developed for determining the Ohmic-resistivity profile with good spatial resolution, ⪝0.1 mm. One involves the measurement of the local photoconductance in the sample, which is related to the local dark resistivity; the other method involves the measurement of the change in optical transmission produced by the local thermal shift in the intrinsic absorption edge when the sample is heated by a high current pulse. The change in optical transmission is related to the local resistivity. The acoustic flux distribution in the sample is determined by yet another optical probe, utilizing the modulation in transmission produced by the high acoustic-energy density in the domain. Several aspects of the acoustoelectric effects are themselves useful for gauging the homogeneity of the samples. In particular, the propagating acoustoelectric domain serves as a convenient probe of the carrier concentration. These techniques are applied to the analysis of the form of the current instabilities, the distribution of the acoustic flux in the sample, and the domain-formation process. The presence of a somewhat higher resistance, hence higher acoustoelectricgain region, at the upstream end near the cathode is shown to contribute to the formation of propagating acoustoelectric domains.

DIRECT OBSERVATION OF ACOUSTOELECTRIC DOMAINS

By combining optical strain-birefringence with stroboscopic illumination, acoustoelectric domains in CdS have been made visible. Domain widths of 50 to 200 μ have been observed in crystals with drift field perpendicular to the C axis. In crystals with E parallel to C axis the domain travels at 30° with respect to C and forms a complex reflection pattern.

Optical Observation of Acoustoelectric Domains in CdS by Brillouin Scattering Technique

Optical Observation of Acoustoelectric Domains in CdS by Brillouin Scattering Technique

Studies of Acoustoelectric Domain Formation in Semiconducting CdS

Experimental studies of acoustoelectric domain formation in semiconducting CdS were performed at room temperature by sample notching, injection of phonon packets and superposition of spike voltage pulses on the main d. c. pulses. Two different modes of current oscillations were observed. Mode I is characterized by constant oscillation period and Mode II by field-dependent period. In the notched samples, mode transition from Mode I to II was observed for appropriate notch depth. This reveals that Mode II is ascribed to locked domain sources such as electric field concentration. On the other hand, domain triggering in Mode I oscillation can be performed in the homogeneous samples either by phonon injection or by spike pulse superposition. This indicates that Mode I is attributed to travelling domain sources such as phonon concentration or shock-generated acoustic flux. Based on these experimental results, domain formations due to electric and acoustic non-uniformities were discussed.

RESONANT AND ROUND-TRIP GAIN FOR ACOUSTOELECTRIC DOMAINS IN n-InSb

Resonant and round-trip acoustoelectric gain are attainable in the high-mobility, piezoelectric semiconductor n-InSb, upon application of transverse magnetic fields. These features are demonstrated in the context of acoustoelectric domain formation and acoustoelectric instabilities. The elucidation of the basic features is greatly simplified by the use of constant-current pulses, which eliminate oscillatory effects.

ERRATA: Modulation of Optical Absorption at the Intrinsic Edge by Acoustoelectric Domains in n-GaAs

The enhancement of optical absorption by propagating acoustoelectric domains is observed in n‐GaAs at 77°K. The spectral dependence of this absorption corresponds to an exponential broadening of the intrinsic absorption edge. Several possible mechanisms for this effect are considered in terms of the electric field and the acoustic flux present in the domain.

Ultra-high frequency emission from GaAs

Abstract Ultra-high frequency emission from n-type GaAs is observed as the acoustoelectric domain hits the anode of the crystal. Emission is attributed to the piezoelectric character of the anode region. Experimental technique described here is believed to be a useful tool in analyzing the frequency components and the attenuation of the acoustoelectric domain.

MODULATION OF OPTICAL ABSORPTION AT THE INTRINSIC EDGE BY ACOUSTOELECTRIC DOMAINS IN n-GaAs

The enhancement of optical absorption by propagating acoustoelectric domains is observed in n-GaAs at 77°K. The spectral dependence of this absorption corresponds to an exponential broadening of the intrinsic absorption edge. Several possible mechanisms for this effect are considered in terms of the electric field and the acoustic flux present in the domain.

Modulation of Near Infrared Radiation by Acoustoelectric Domains in n‐Type GaAs at Room Temperature

AbstractOptical experiments have enabled measurements of the absorption coefficient of n‐type GaAs to be made at room temperature near the absorption edge by an acoustoelectric domain located at the anode. Moreover, the shape of the domain can be deduced and in addition the acoustic flux is shown to be an important factor in the variations of the absorption coefficient. Some results are also given of local resistivity variations in n‐type GaAs by the injection of free carriers when a GaAs laser beam is focused on the sample.

SOUND WAVE INTERACTIONS IN InSb

In high-mobility piezoelectric semiconductors such as InSb, a transverse magnetic field greatly reduces the electron drift velocity required to form an acoustoelectric domain. We have developed a theory which predicts this effect reasonably well. We have also shown that when these materials are used as acoustic amplifiers, the magnetic field reduces the dc power dissipation at maximum acoustic gain to such a large degree that CW amplification of sound waves can easily be achieved.

Current oscillations in CdS caused by acoustoelectric domain motion

Current oscillations caused by acoustoelectric domain motion were investigated in semiconducting and photoconducting CdS at room temperature. Oscillatory behaviors of the current are closely connected with the domain motion. Four different kinds of behavior of the domain were observed in several samples. In the homogeneous semiconducting CdS, the domain is built up through local amplification of thermal phonons due to spatial fluctuations of phonon-density distribution. Its site depends upon the applied electric field. In the inhomogeneous ones, the domain is usually formed at the region of electric-field concentration. In the homogeneous photoconducting CdS, damped oscillations of the current were observed. The domain formation may be attributed to amplification of acoustic shock wave generated at the cathode. In the inhomogeneous ones with a high-resistivity region near the anode, the domain is formed at the high-resistivity region and it seems to be dragged by some acoustic stimulations such as shock-excited acoustic waves. Formation time of the domain was also investigated in the homogeneous semiconducting CdS. Conductivity dependence of it seems to support the quantum theory but exclude White's formulation.

Note concerning the Mössbauer study of the order-disorder transformation in Ni 3Mn

It is proposed that Brillouin scattering by the bunched electrons in a CdS acousto-electric domain should be detectable if a CO2 laser is used as the radiation source.