Oleg A. Ryabushkin

Identification of eigenmodes of volume piezoelectric resonators in resonant ultrasound spectroscopy

Eigenmodes of volume piezoelectric resonators used in resonant ultrasound spectroscopy (RUS) are considered. A novel method for the identification of these modes is proposed, which is based on the measurement of a temperature shift of the resonance frequency. A good coincidence of the measured and calculated eigenmode spectra is demonstrated for a quartz crystal. In comparison to the other methods of identification, the proposed approach is simple to implement and provides reliable results in solving RUS problems.

Optical reflection in semiconductor structures modulated by radio-frequency electric fields

We propose a contactless technique of modulation spectroscopy for semiconductors which is based on the AC electric field effect on the probing light beam reflection. This technique allows one to investigate the distribution of both built-in and induced electric fields as well as the electron-hole interaction effects in various layers of the semiconductor structure. The measured spectra are explained by a combination of the interband transitions in the high-field (Franz-Keldysh effect) and low-field regimes, the transitions via exciton states and the temperature effect. The model is developed which allows one to describe quantitatively the spectra observed on the modulation-doped heterostructures GaAs/AlGaAs.

RF spectroscopy of polymer-clad silica optical fibers

Radio-frequency (RF) impedance spectroscopy has been used to measure the dielectric permittivity of a polymer coating on optical fibers. It is established that the temperature dependences of permittivity in the RF range in polymers and fused silica significantly differ. The principal possibility of independent measurements of the temperature of a polymer cladding and silica core of an optical fiber is confirmed.

The light reflection from semiconductor heterostructures modulated by a double polarized radiofrequency field

An rf modulation optical spectroscopy method for the study of semiconductor heterostructures is suggested which employs the effect of the light reflection coefficient modulation under the action of two rf fields with different configurations. The dependence of the rf-modulated light reflection spectra at the fundamental absorption edge of a semiconductor on the rf field polarization allows various layers of the heterostructure to be selectively studied. A model is proposed that explains the features observed in the reflection spectra of the light modulated by longitudinal and transverse rf electric fields in a GaAs/AlGaAs heterostructure.

Effect of lateral transport of photoinduced charge carriers in a heterostructure with a two-dimensional electron gas

It is shown that the nonequilibrium charge carriers produced by a local optical disturbance of the heterostructure with a two-dimensional electron gas are transported in the plane of the structure over an extremely large distance from the excitation location, which greatly exceeds the diffusion length in the bulk. The effect is attributable to the fact that the photogenerated electrons and holes are separated by the built-in electric field of the heterojunction to opposite edges of the buffer layer, where they are transported along parallel planes. The distance over which the nonequilibrium carrier density spreads reaches large values because of 1) the high conductivity of two-dimensional electrons, 2) the barrier for electron-hole recombination, and 3) hole drift in the electric field produced by the charge of nonequilibrium carriers in the plane of the structure.

Effect of local optical excitation on semiconductor heterostructures with 2D electron gas

An effect of local illumination on layered semiconductor heterostructures with 2D electron gas is investigated by measuring the spatial distribution of the photoreflectance and photoluminescence intensity varying the distance between the excitation spot and the probing position.

Novel family of optical and optoelectronic elements for information processing using the current filament in semiconductors

A new family of optical and optoelectronic elements is offered thats operation is based on controlling the current filament in semiconductors having an S-shaped current-voltage characteristic (CVC). The current filament is controlled by the action of fields (optical radiation, magnetic or electric field). The S-shaped CVC is a result of low-temperature avalanche ionization of shallow impurities in semiconductor epitaxial layers induced by an electric field (E approximately equals 1 - 10 V/cm). New elements, we shall call them cryo-elements, possess a low specific dissipated power on the order of 10-9 W/micrometers 3. The characteristic time of current filament formation is about 10-9 s. For controlling the current filament an extremely low (several photons per square micrometer in the region of fundamental absorption) light intensity is sufficient. The filament control is possible in a band from UV to IR.

Novel elements for optical and optoelectronic detection and signal processing using the current filament in semiconductors

A new family of optical and optoelectronic elements is offered whose operation is based on controlling the current filament in semiconductors having an S-shaped current-voltage characteristic (CVC). The current filament is controlled by the action of external fields (optical radiation, magnetic or electric field). The S-shaped CVC is a result of low- temperature impurity breakdown (LTIB) in semiconductor epitaxial layers induced by an electric field (E 1 - 10 V/cm). New elements, we shall call them LTIB-elements, possess a low specific dissipated power on the order of 10-9 W/micrometers 3. The characteristic time of current filament formation is about 10-9 s. For controlling the current filament an extremely low (several photons per square micrometer in the region of fundamental absorption) light intensity is sufficient. The filament control is possible in a band from UV to IR.

Optoelectronic and optical bistabilities of photocurrent and photoluminescence at low-temperature avalanche breakdown in GaAs epitaxial films

Epitaxial films of n-GaAs are studied at helium temperature by means of low-temperature impurity breakdown to study optical and optoelectronic bistabilities. During switching the carrier concentration is found to increase by about one order of magnitude, and the donors become ionized while achieving increased carrier mobility. The bistabilities are shown to be of interest for the design of switching elements that could include memory elements for information processing.

Photocryosar: bistable element for optoelectronic computing

Bistabilities of photocurrent and photoluminescence at the low-temperature impurity breakdown suggests all elements necessary for optoelectronic and optical processing. It was found that such elements may possess record low energy and power characteristics with a good speed of operation. However, the necessity of using a low temperature (for many semiconductors it is a helium temperature) seriously limits the range of applications of these elements.