CIRS

Structures containing layers of porous silicon with two metal contacts are investigated. Porous silicon is manufactured by anodizing p-type crystalline silicon plates of resistivity of 0.4 Ω cm. Contacts for the samples are made by additional boron doping of the surface and by thermal evaporation of aluminium. Resistance and current-voltage characteristics are investigated. Response of the porous silicon layer containing structures under action of pulsed microwave radiation was investigated for the first time. The origin of the response is discussed.

Iron-containing nanoparticles and clusters were formed in silica with porosity, which was predetermined by different procedures of sol-gel technology and the chemical composition of precursors. Bulk and layer-type samples of different porosity were synthesized and investigated. The morphology, magnetic, and optical properties were studied to characterize the samples and to analyze the formation of Fe-oxides. Experimental results showed that both Fe2O3 and Fe3O4 were formed in the samples and that their relative amount was dependent on preparation technology.

A photomagnetoelectric effect has been investigated in semiconductors InAs and CdxHg1-xTe (x=0.2 and 0.26) excited by Q-switched neodymium-YAG laser. The photomagnetoelectric signal undergos double-sign-inversion when the intensity of the exciting light pulses exceeds a critical value Ic=5×1024 photons/(cm2 s) for InAs and (1-4)×1024 photons/(cm2 s) for CdxHg1-xTe samples. It is shown that a frequency spectrum of photomagnetoelectric response is broadened significantly in the region of high frequencies. In general three frequency bands were distinguished. From this investigation it follows that using laser pulses of a duration topt∼1-10 ps the photomagnetoelectric signal in the terahertz range may be generated.

We present a photoluminescence study of optical transitions in Be acceptor-doped GaAs/AlAs multiple quantum wells at room and liquid nitrogen temperatures. We investigate excitonic spectra and reveal acceptor-impurity induced effects in multiple quantum wells having different width.

We report on the results of experimental study of free carrier heating in degenerate GaAs tunnel p-n diodes when the carriers are excited by pulsed microwave radiation. Free carrier heating is responsible for the electromotive force in the diode. The magnitude of the electromotive force linearly depends on pulsed microwave power and increases with the decrease in semiconductor lattice temperature. It is almost independent of the pulsed microwave frequency and of p-n junction plane orientation in respect to electric field direction. In the tunnelling regime the dark current in the diode is reduced, however, at high enough forward bias the diffusive current is stimulated due to hot carrier phenomenon.

It is demonstrated that polycrystalline La0.33Ca0.67MnO3 thin film sensors can be used to measure pulsed strong magnetic fields with microsecond duration rise and decay times. The response characteristics of these sensors were investigated using 0.7-1.0 ms duration bell-shaped magnetic field pulses of 10-20 T amplitudes and by using special waveform magnetic field pulses with amplitudes of 40 T and decay times of 50 mus. The response of these magnetic field sensors was compared with those of conventional loop sensors and Faraday rotation sensors using Bi12SiO20 single crystals as a known standard.

The considered chaotic oscillator consists of an amplifier, 2nd order LC resonator, Schottky diode and an extra capacitor in parallel to the diode. The diode plays the role of a nonlinear device. Chaotic oscillations are demonstrated numerically and experimentally at low as well as at high megahertz frequencies, up to 250 MHz.

Influence of strong electric field in wide frequency range (from DC to 35 GHz) on electrical resistance of thin La0.67Ca0.33MnO3 polycrystalline manganite films was investigated in the range of (78 divided by 300) K. Different behavior of resistance change vs. temperature was observed when pulsed DC electric field and microwaves were applied to the films. When pulsed DC electric field is applied the electric-field-induced resistance change ("electroresistance") of manganite film depended nearly monotonically on temperature. However, in microwave electric fields a non-monotonic character of the electroresistance temperature dependence was observed. The dependence of the electroresistance on quality of manganite films was observed in case of microwaves. The experimental findings are explained assuming different electrical current mechanisms in case of DC and microwave fields. The applied voltage drops mainly across the grains of polycrystalline film due to a presence of displacement currents in case of microwaves, whereas in DC case the voltage drop is across the grain boundaries.

High crystalline quality films of n-La2/3Ce1/3MnO3, p-La2/3Ca1/3MnO3 and related p-n diode structures were grown heteroepitaxially on lattice-matched SrTiO3(100) substrates by dc magnetron sputtering and pulsed laser deposition. The La2/3Ce1/3Mn O3/La2/3Ca1/3MnO3 bilayer was patterned into a strip-like geometry to investigate electrical properties of the interface. Significant magnetoresistance values and nonlinear current-voltage characteristics were indicated for the interface of the p-n diode heterostructure.

Si and GaAs avalanche diodes containing microplasmas are investigated. Microwave field applied to the diode in addition to reverse dc bias results in considerable spread of noise spectrum and in the increase of noise power. The microplasma noise spectra cover very high (30 to 300 MHz) and ultrahigh (300 to 1000 MHz) frequency bands, while the effective noise temperature is about 10(8) K.