Single epitaxially grown CdSe/ZnSe quantum dots have been studied by using photoluminescence spectroscopy with a high spatial resolution. The lifting of the spin degeneracy due to exchange interaction results in a splitting of the exciton ground state, strongly dependent on the symmetry of the quantum dot. By applying a magnetic field in Faraday geometry, the energy splitting as well as the polarization properties of the exciton transition can be varied and remarkably, even at high magnetic field a spin coherence time of about 3 ns is found, which exceeds the recombination lifetime of single excitons significantly. As the biexciton state is a spin singlet, both its fine structure splitting as well as its degree of polarization are shown to be controlled by the final state of recombination, the single exciton state. Besides the discrete energy splitting of optical transitons in single quantum dots, we observe a rather statistical, but strongly correlated energy shift was well as a correlated on-off switching behavior of the exciton and the biexciton emission on a typical time constant of seconds. These effects are related to the influence of charge carriers in the nanoenvironment of the dot and to thermal or Auger-driven carrier escape into trap states in the vicinity of the dot, respectively.

The results of investigation of photocurrent spectra of quantum well and quantum dot In_xGa_1-xAs/Ga/As heterostructures obtained by the use of a scanning tunneling microscope (STM) are presented.

Transient changes in absorption of PbS-doped glasses are investigated by means of absorption pump-probe spectroscopy. Two opposite nonlinear effects, bleaching and induced absorption, are observed and their dynamics are investigated in the vicinity of the lowest optical transition of carriers quantum-confined in PbS nanocrystals of different size. Applicability of this composite material as saturable absorber is studied and the nonlinear absorption of the PbS- doped glass is compared with that of solutions of dyes commonly used as saturable absorbers. A potential of utilization of PbS-doped glass in mode locking is discussed and long-time stability of the medium under intense laser irradiation is demonstrated.

Photoluminescence (PL) spectra of the systems of Si nanocrystals imbedded into SiO₂ and (alpha) -Si matrices were investigated. The first system was fabricated by the Si⁺ implantation into thermal SiO₂ films on Si with subsequent annealing, and the other- by the irradiation of c-Si with heavy ions near the amorphization dose. For the first system, the influence of implantation does and additional phosphorus or boron implantation on the PL intensity was studied. The series of experiments aimed to clearing out the mechanisms of phosphorus induced PL enhancing was provided, namely: the influence of the order of P⁺ implantation and annealing, the effect of the pumping intensity on the degree of the PL enhancement. It was established that additional boron implantation makes PL weaker. The model of phosphorus and boron doping influence is suggested. For the second system, the effects of the Kr⁺ does and of the annealing temperature variation were revealed.

Thin films of erbium-doped YAG (Y₃Al₅O₁₂) were grown by pulsed laser deposition, followed by high temperature (>1100 degree(s)C) post-annealing. The deposition was carried out on MgO and MgAl₂O₄ substrates in ultra-high vacuum chamber with KrF excimer laser at fluences 2.5-3 J/cm². Influence of growth conditions (substrate temperature, gas environment, annealing temperature) on structural, topographical, and optical properties was investigated by using optical spectroscopy, X-ray diffraction, and atomic force microscopy.

Optimization of (i) intensity of illumination and (ii) thickness of resist was made looking for the conditions when high spatial resolution could be achieved by optical near- field lithography. Standard set-up of near-field illumination through a tapered Al-coated fiber tip was employed for the exposure of positive resist OFPR-5000 (EG), which is photo-sensitive for wavelength (lambda) < 450 nm. Tip was scanned along the line at near-field conditions of constant sample-to-tip separation to produce adjustable exposure dose of the spin-coated resist film. Femtosecond, 120 fs, pulses of the power P <1 mW (at 82 MHz repetition rate) at 400 nm were coupled into a fiber (<1 m length) and delivered to the surface of the resist for illumination. The issues of NSOM fabrication using tapered Al-coated tips are addressed. To achieve a reproducible and high aspect ratio (approaching 1:1) NSOM-based lithography there should be found resists allowing to produce thin films (<100 nm) with low surface roughness (>10 nm).

New interferometric technique based on the polarization of self-modulation (PSM) effect in photoconductive electrooptic crystals for the linear detection of small out-of-plane vibrations of a rough surface caused by ultrasound is described. The technique is more advantageous than the widely used photorefractive two-wave mixing technique. Basing on the vectorial theory of light diffraction in photorefractive crystals of cubic symmetry, the procedure of the PSM-interferometer optimization is proposed. The highest sensitivity of a PSM interferometer with fast semiconductor crystals is achieved in the transversal configuration when both the external electric field and grating vector are parallel to the <110> axis. The sensitivity of the adaptive PSM-interferometer is only two times smaller than the sensitivity of the classical homodyne interferometer.

Remarkable impact of external mechanical pressure to the transmitted radiation intensity has been observed for glowing fibers with various silica core diameters and side- scattering efficiencies. A physical model on deformation- simulated light scattering has been developed and discussed. The results of experimental studies confirmed the basic model assumptions.

Advanced fiber-optical displacement sensors are being developed. We propose to use a reflection fiber-optical sensor of new configuration- two pairs of fibers creating the defined angle between the tips of fibers to indicate and measure angular and linear displacement. The latter can e also used as refractometer to provide drastic improvement of measurement sensitivity in comparison with the recently developed three-fiber measurement method. We describe the design of the measurement set-up and signal processing electronics. Results of computer simulation and experimental investigation are presented. Attained sensitivity of the displacement sensor 1702 mV/micrometers . Obtained refractometer sensitivity 2(DOT)10^-6RIU.

The initial atomic-layer-chemical-vapor-deposition growth of titanium dioxide from TiCl₄ and water on quartz glass substrates is monitored in real time by incremental dielectric reflection. An interesting means for bringing the growth from the very beginning into a time-homogeneous mode is proposed and preliminarily studied. It consists in an in situ TiCl₄-treatment procedure. The crystal structure and surface morphology of the prepared ultrathin films are characterized.

The high-frequency electrodes light sources (HFELS) are widely used as bright radiators of narrow and intensive spectral lines covering spectral region from VUV to IR. In this work we shall give a short overview of our experience in preparation of HFELS, containing He, H, Rb, Hg, Zn, Pb, As, Sb, Bi, Tl, Hg-Cd, Hg-Zn, Hg-Cd-Zn, Se-Te for different applications. Special attention would be paid for HFELS use in Zeeman mercury analyzer, in Atomic absorption analyzer and Angle and glass refractive index measurement system.

Electrodeless iodine, mercury iodide, and mercury radio- frequency discharge lamps have been made to provide effective sources of atomic spectra for analytical spectroscopy providing powerful resonance radiation of iodine and mercury in the 120-253 nm region. The lamps are required and can be used for spectral calibration, resonance absorption, and fluorescence detection techniques, for investigation of atomic characteristics (e.g., branching ratios) and other purposes where intense monochromatic spectra are needed. Production technology, development, and investigation of the UV and VUV emission are described.

The paper discusses the peculiarities in measuring the refractive index of a liquid by means of detector using a plane-parallel plate as a simple measuring element and collimated light beam from laser diode. It is shown that, thanks to the splitting of refracted beam into two components at the exit face of the measuring element, it is possible to achieve resolution of the detector about 10^-5 within the whole range of refractive index measurements.

We have designed and manufactured a simple device, named frequency tracer, (FT) for fs pulse temporal phase measurements. FT is able to present a determination of the instantaneous frequency dependence on time fs pulse together with an accurate data sufficient for a complete characterization of light field. The main feature of our designed FT device is the simplicity: no spectral apparatus is needed and fs pulse phase distortion determination does not require complicated iterative mathematical algorithms. Using a single-shot real-time implementation of this technique the multi-pass amplifier (MPA) compressor of fs Ti:sapphire laser system was adjusted.

Strong localization effects are observed in epilayers of GaN and InGaN. We relate them to microstructure characteristics of samples studied. The same mechanism of localization is shown to be the dominant in GaN and in InGaN. Influence of strong localization effects on light emission properties is discussed.

The far infrared optical properties of a selection of thin epitaxial layers of GaN deposited on GaAs substrates by molecular epitaxy (MBE) have been studied by polarized oblique-incidence reflection spectroscopy at 77 and 300 K. The epilayers were grown in the cubic ((beta) -GaN) and wurtzite ((alpha) -GaN) phases. The vibrational and electronic properties of the samples have been determined by using standard optical transform matrix method to fit computed reflectivity spectra of the layered samples to the measured spectra. The model was extended to deal with anisotropic dielectric functions to account for the phonon and plasmon responses of (alpha) -GaN. In s-polarized measurements, the bulk plasma response gives direct information on the free carrier dynamics in the plane of the epilayer. The normal componento f the free carrier dielectric response couples strongly to Brewster and Berreman interface modes at frequencies close tot he LO phonon frequency. In p-polarization measurements, these interface modes have been observed and assigned with the aid of dispersion curve calculations. It is shown that Brewster and Berreman interface modes can be used to characterize the structural and electronic properties of the samples.

Strain Energy Band Engineering of Group III-N heterostructures should allow us to prevent defect formation at the heterointerfaces ad to reduce the built-in electric field in the quantum wells. The strain, caused by lattice mismatch, may be decreased by incorporation of In into AlGaN. To monitor structural perfection of the quaternary compound AlInGaN and to evaluate electronic potential profile, we employed optical methods: reflectivity, site- selectively excited photoluminescence, photoluminescence excitation and time-resolved luminescence. AlGaN with the molar fraction of Al of 9% and two samples with the lattice mismatch reduced by partial substitution of Al by 1% and 2% of In were investigated. In AlGaN, the luminescence excited resonantly with the exciton position is red shifted. The photoluminescence excitation spectra indicate that the mobility edge is above the optical band gap, and the localization vanishes. These results show that the incorporation of approximately equals 2% indium into AlGaN leads to the disappearance of the band tail states and smoothing of the potential profile.

Transient and quasi-steady-state photoluminescence of a dense electron-hole plasma was studied in GaN epilayers under high photoexcitation at room-temperature. High initial carrier heating up to 1100 K was observed. Decay of nonthermalized electron-hole plasma was analyzed both in homo- and heteroepitaxial GaN layers. The heating is shown to significantly influence the luminescence peak position and the rate of spontaneous and stimulated recombination. After the thermalization process is completed, the luminescence decay is exponential and the room-temperature carrier lifetime can be extracted. The lifetime in the heteroepitaxial layer grown on sapphire was found to be 190 ps, while the homoepitaxial layer exhibited an essentially higher value of 890 ps, which is one of the highest reported for free-carrier recombination in GaN. Additionally, optical gain spectra were studied using variable-stripe method. The threshold for stimulated emission was found to be considerably lower and the gain at a certain pump intensity was shown to be much higher in the homoepitaxial layer than in the heteroepitaxial one. Maximum net gain value of 300 cm^-1 was observed.

We have observed an apparent rotational anisotropy of the second harmonic generation (SHG) at signal at (lambda) = 405 nm back-reflected from the surface (0001) of 3 micrometers -thick GaN grown by metalorganic chemical vapor deposition (MOCVD). The focusing depth of 2 micrometers was aimed to probe the 10-15 nm-thick buffer layer where both cubic and hexagonal phases of GaN are coexisting. Typical angular dependency clearly indicated the presence of both isotropic and six-fold contributions. The isotropic I^(2(omega ))(qq) component has a minor one-fold modulation due to a ca. 2 degree(s) disorientation of the top surface with respect to the hexagonal planes. We attribute the substantial isotropic component to the SHG yield from the bulk of GaN. The occurrence of six-fold I^(2(omega )) (qq) anisotropy, however, indicates a complementary nonlinearities, most likely due to hexagonal phase, which is coexisting with the hexagonal one in the buffer layer region. In general, both surface and bulk nonlinearities are contributing to the reflected SH yield. The symmetry of surface can differ from that in the bulk, exhibiting a corresponding angular dependence of harmonic generation. SHG mapping of GaN (ooo1) surface was measured from the ablated pattern. Space-Time-Spectra resolved photoluminescence (PL) was used to characterize the InGaN layers and GaN/InGaN MQW laser structures. Two-photon absorption (TPA) excited mapping of the dislocation network in GaN layers is demonstrated.

Nonlinear optical characteristics of single crystalline GaN were measured at the wavelength of 530 nm using Z-scan techniques. Two photon absorption coefficient at that wavelength was found to be 9 cm/GW, whereas the bound and free electron nonlinear refractive indexes were estimated as 2.5 X 10^-14 cm²/W and 5 X 10^-22 cm³, respectively. Moreover, single color dynamical Z-scan measurement was used for the determination of the photoexcited carrier trapping time, which was estimated as 1 ns.

The tunneling ionization of deep impurity centers induced by high-intensity terahertz radiation is investigated in the frequency range of transition between the quasi-static and the high frequency regime. A drastic enhancement of the terahertz tunneling ionization of deep impurities in semiconductors has been observed in the high frequency limit of (omega) (tau) <<T 1 ((omega) is electric field frequency and (tau) is the tunneling time). For a given constant tunneling rate an increase of frequency by a factor of seven leads to a drop of the required electric field strength by three orders of magnitude. In the opposite limit of (omega) (tau) <<T 1 within a broad range of intensity, frequency and temperature, the terahertz electric field of the radiation acts like a static field. The ionization can be described as phonon-assisted tunneling in which carrier emission is accompanied by defect tunneling in configuration space and electron tunneling in the electric field of the radiation. At high intensities the ionization is caused by the direct tunneling without involving phonons. Phonon assisted tunneling in high frequency as well as static electric fields is suggested as a method for the characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature dependences of the ionization probability allows to obtain defect parameters like tunneling times, the Huang-Rhys factor as well as the basic structure of the defect adiabatic potentials.

We investigated by the thermally stimulated currents (TSC) high purity high resistivity GaAs films, grown by vapor phase epitaxy (VPE). To reveal the single levels the thermal emptying of the defects by fractional heating was used. We also investigated the thermally stimulated depolarization currents (TSD) in samples, which were excited and polarized by light in the presence of an electric field. The following prevailing levels below the conductivity band were found: 0.21-0.23, 0.31-0.33, 0.35-0.38, 0.45-0.49 and 0.54 eV. We demonstrate that the TSC and TSD current spectra depend sensitively on the excitation conditions. So light excitation with quantum energy higher than 0.83 eV reveals the level with an activation energy of 0.21-0.23 eV, which dominates over the temperature range from about 95 to 200 K. Most probably these defects are located within the VPE layer, and have relatively small effective electron capture and generation coefficients. Moreover, at low temperatures their effective ionization energy is supposed to increase because of the existence of potential barriers. By contrast, if the quantum energy is 0.5-0.83 eV the influence of this level diminishes, and the contribution of donor levels at about 0.13 and 0.17 becomes visible. This is evidence of carrier redistribution between different defects. Furthermore, peculiarities of the TSC were observed which could not be explained by a homogeneous semiconductor model. The existence of different polarization sources in different temperature ranges is demonstrated by TSD. In particular, the inhomogeneous sample polarization causes the scattering of the activation energy values. Our results prove the influence of the potential relief of the band gap, appearing due to microinhomogeneities of the samples. Furthermore, excitation by 0.5-0.83 eV light could lead to the formation of different (p-type) conductivity channels around dislocations through the metastable transformation of the EL2 level.

The electronic excitations in complex cuprates are analyzed in the fragment approximation. The fine structure of complex cuprates is considered as the total sum of contributions origination from the electronic excitations in structural and electronic analogues with more simple characteristic units. The analysis was performed on the basis of ellipsometric measurements in the range 0.5-5.0 eV.

Evidences are given that two classes of the transient IR- absorption bands: (a) with max. at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps according G. Jacobs or due to bound polarons according E.V. Korovkin and T.A. Lebedkina) and (b) with max. at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I (due to on-center STE localized at iodine dimer according M. Hirai and collaborators) are caused by the same defect- atomic alkali impurity center [M⁺]_c⁰e^- (electron e^- trapped by a substitutional smaller size alkali cation impurity [M⁺]_c⁰). The Mollwo-Ivey plots (for the transient IR-absorption bands) of the zero-phonon line energy E₀ (for NaCl, KCl, KBr, RbCl and NaBr, KCl:I) and/or the low-energy edge valued E₀ (for NaI, RbCl:I, RbBr:I) versus anion-cation distance (d) evidence that two types of the [M⁺]_c⁰e^- centers are predominant: (a) [Na⁺]_c⁰e^- in the KX and RbX host crystals with the relation E₀approximately equals 6.15/d^2.74, (b) [Li⁺]_c⁰3^- in the NaX host crystals - E₀approximately equals 29.4/d^4.72. The Mollwo-Ivey relation E₀approximately equals 18.36/d(superscript 2.70 is fulfilled as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI if we use the F' center optical binding energy values E₀.

The luminescence induced by alpha particles in GaAs/Al_0.35Ga_0.65As multiple quantum well (MQW) semiconductor was detected and investigated. The luminescence was observed at liquid nitrogen and at room temperatures as light flashes induced by individual (alpha) -particles. The MQW samples studied, in addition, were investigated using standard photoluminescence method to show that (alpha) - particle created flashes are associated with a radiative decay of 2D excitons in quantum wells. Since the number of detected light quanta in a flash is critical, a discussion of the collection efficiency of photons created by a single (alpha) -particle is presented.

Changes in the photostimulated luminescence (PSL) spectrum of an electron irradiated KBr:Tl single crystal in relation to the A-luminescence spectrum upon direct activator ion excitation in the A-absorption band (AL) are found. Based on the view about the spatial correlation between F and activator hole centers, it is suggested that anion vacancy is an additional perturbing factor fot he activator (Tl⁺) excited (p-electron) state which is already subject to the dynamical Jahn-Teller effect. Dependences of the PSL efficiency on activator (In⁺) concentration in KBr:In samples irradiated by UV-light (6.30-6.45 eV), X-rays (30 keV or electrons (5.6 keV), are compared. The possible role of 6.45 eV photons is discussed in context with the hypothesis of efficient exciton energy transfer at room temperature (RT).

The excitation-energy dependences and relaxation times of photoinduced changes of excitonic lines in type-I GaAs/AlAs QW structures are studied by the photo- and wavelength- modulated reflectance spectroscopies. The optical data indicate that photoinduced broadening/quenching of excitonic lines dominates in the modulation spectra under photoexcitation within the QW by He-Ne laser. It was found that characteristic time of these photoinduced changes varies form milliseconds at 300 K to seconds at 120 K and reduces under illumination above the AlAs band gap. Moreover, different time constants and their temperature dependences were obtained for QW- and buffer layer-related optical features. It was suggested that photoinduced changes of excitonic spectra could be associated with the T- X electron transfer effects and creation of excess holes in the QW under He-Ne excitation.

Discussion of ways to achieve mid and far IR intraband lasing just by lateral electric field carrier (electron or hole) heating in multiple quantum well (MQW) structures is given. It is argued that the Gunn diodes are low frequency indirect transition lasers based on hot electron population inversion arising under electron intervalley transfer. In the MQW structures direct optical transitions exist while hot carrier population inversion can be achieved due to inter-valley/real space transfer. The two MQW structures are considered in this work: GaAs/AlAs and GaAs/InGaAs systems. In the first the hot electron (Gamma) -X intervalley/real space transfer from GaAs layers to AlAs layers provides population inversion while in the second the inversion can arise due to interlevel/interlayer transfer. Evaluations via the Monte-Carlo simulation of the hot electron phenomena in some of the structures are given and observation of the hot carrier phenomena of the type (including far and mid IR emission and absorption) are presented. Consideration of the appropriate laser design which provides also a way to cope with the low frequency (Gunn type) current oscillations is given.

We review performance and physical characteristics of yttrium barium copper oxide (YBCO) compound as an infrared (IR) photodetector. YBCO has been used as the IR detector material in both superconducting (oxygen-rich) and semiconducting (oxygen-depleted) phases. YBCO in its crystalline, Yba₂Cu₃O_6+x phase with x>0.95 is a high-temperature superconducting material with the superconducting transition T_capproximately equals 90K. The superconducting YBCOIR detectors operate as either nonequilibrium (quantum) or bolometric (thermal) devices. The nonequilibrium devices are characterized by very short, single-picosecond photoresponse times and are expected to find applications in optoelectronics and imaging, as well as ultrafast optical-to-electrical transducers for digital input applications. The bolometric mechanism results in relatively slow but very sensitive detectors with possible applications in astronomy. In addition to superconducting IR sensors, interest in uncooled YBCO devices is growing very rapidly. Despite somewhat lower sensitivity and significantly reduced speed of response, as compared to the superconducting counterpartners, the uncooled IR detectors are characterized by much lower operating cost and weight due to lack of cooling cryogens and are compatible with existing silicon-based processing and fabrication. The last point is of paramount importance if the IR-sensitive pixels are to be integrated with CMOS read-out circuitry for monolithic focal plane arrays and infrared cameras. Amorphous uncooled YBCO photodetectors operate as either photoconductive bolometers of unbiased pyroelectric devices.

A^IVB^VI (chalcogenides of IV-group elements) semiconductors are well-known materials having applications in infrared optoelectronics. Major efforts in the field of physics of the condensed matter are aimed at elucidating the influence of defects and impurities on the properties of semiconductor materials. In many cases, impurities can dramatically change the properties of semiconductor materials. Pb_1-x-ySn_xGe_yTe is a well- known narrow-band-gap semiconductor with usually high (n>=10¹⁶ cm^-3) intrinsic defects. The introduction of indium into these solid solutions establishes an impurity level that is a function of the Sn and Ge concentration and of temperature. For x>0.22, the In impurity level lies within the forbidden band (dielectric state) and exhibits the attendant sharp drop in the electron density. In the dielectric state (temperatures below 25 K) the In-doped alloys are unique in that they are photosensitive with a decrease in the electrical resistivity and an increase of carrier lifetime by several orders of magnitude (10^-3-10⁴ s) depending on the temperature. The long relaxation time of the non- equilibrium concentration of electrons, manifested as persistent photoconductivity (PPC) effect. One of the advantages of PPC effect is the possibility of increasing the signal/noise ratio by an increase of the charge integration time. Therefore one of the major challenges in developing array photodetectors operating in the television standard with a frame time ~ carrier lifetime is to insure signal accumulation in each element of the array. As it is seen we have unequal possibility to realize novel type of array photodetectors over a wide range of the IR spectrum (up to 30 micrometers ), in which each element provides radiation detection and its accumulation.

The cut-off effect in slightly asymmetric systems prevent the wider practical usage of long range surface polaritons (LRSP) in the infrared region. Due to asymmetry caused by the presence of even a few nanometers wide air gap the LRSP mode disappear. We propose a solution of this problem by using an effective medium approach. The basic idea is to compensate for the air gap induced asymmetry by introducing an additional layer into the system. That allows us to shift the cut-off to values sufficiently for experimental observation of LRSP. FTIR spectra of end-fire coupled LRSPs in the GaAs/Au/GaAs multilayer system were measured in the (800-3000) cm^-1 range. Various geometric and polarization sensitive effects of the infrared system capable of influencing the LRSP coupling is discussed. A pronounced increase in the p and s polarized light transmission ratio at long-wavelengths is explained as an increase in the propagation distance L of LRSPs. A fairly good fit between experimental and calculated curves was achieved at long wavelengths. The width of the air gap was used as a parameter in the calculations.

Our study is concerned with the photo-thermovoltaic effects caused by the absorption of CO₂ laser light in narrow gap A^IVB^VI semiconductors. We report on results of experimental study of photoresponse induced in n-type and p- type lead telluride with Ni contacts. We show that in the case of ohmic contacts (n-PbTe-Ni and p-PbTe-Ni at 300K) the detected signal originated from thermoemf due to created crystal lattice temperature gradient. In the case of p- PbTe-Ni at 80K we have Schottky contacts and the photoresponse consists at least of two components: fast and great in value photoemf- due to carrier generation resulting from two-photon absorption, and slow as well as of lower magnitude thermoemf.

Pulsed laser deposition technique has been employed to fabricate a continuous series of solid solutions with basic composition of La_0.7(Pb_{1- x}Sr_x)_0.3MnO₃, which undergo metal-to-insulator transition near the room temperature. These films exhibit colossal magnetoresistivity (CMR) and strong temperature dependence of resistivity in the vicinity of phase transition. Temperature coefficient of resistivity (TCR) has been tailored by precise compositional control tog et maximum value close to room temperature. Film with TCR as high as 7.4%K¹ at 295 K and magnetoresistance of 30% at 7kOe has been used to make uncooled bolometer demonstrator. The responsivity as high as 0.6 V/W, noise equivalent power of 3x10^-8W/(root)Hz, detectivity of 9x10⁶ cm(root)Hz/W, and noise equivalent temperature difference as low as 120 nK/(root)Hz at 30 Hz frame frequency have been achieved for non-optimized bolometer based on 4.5-micrometers - thick film grown on 2.5x2.5x0.5 mm³ LaAlO₃(001) substrate. Measurements of optical responsivity in frequency and time domains yield substrate-to-thermostat thermal conductance G = 3x10^-3 W/K and three relaxation times responsible for heat transfer from film thermistor to substrate, from substrate to thermostat, and heat exchange via leads to be 0.5 s, 1.9 ms and 90 microsecond(s) correspondingly. Improving bolometer design by micromachining technique, one can expect that reducing of thermal conductance G down to 10^-6 W/K for bolometer with resistance of 500 (Omega) , should result in the increasing of responsivities to 3.9 A/W and 2.8x10³ V/W and detectivities to 2.5x10⁸ cm(root)Hz/W and 9.3x10⁸ cm(root)Hz/W at 30Hz in voltage and current biasing regime correspondingly.

Asymmetrically-necked GaAs/Al_0.25Ga_0.75As modulation-doped structures are examined as possible active parts of the detector for operation within 10 GHz -3 THz frequency range. The estimations of the device parameters are performed for real structure planned to be used in the experiments. Calculations show that i) Sensitivity of the diodes based on modulation doped structures at liquid nitrogen temperature is significantly higher than at room temperature; ii) this trend remains over the microwave frequency range of operation; iii) narrowing of the necked- size of the device with 300 nm size of the necked-part, the sensitivity could reach 4000 V/W for microwaves and 100 v/W at 1 THz at room temperature with respect to absorbed power. At liquid nitrogen temperature the frequency dependence of voltage sensitivity at the same conditions becomes more pronounced for microwaves- it is 30 000 V/W while in terahertz frequency range the voltage sensitivity drops to the value of 240 V/W.

It is shown that the photocurrent amplification in Schottky diodes (SD) with low barriers is due to the avalanche of minority carriers in the depletion layer (DL) of a semiconductor. The simple physical model of carrier generation in the DL of the diode is proposed for the experimental results interpretation. The theoretical estimates of the current amplification coefficient are in a good agreement with experimental data.

This report demonstrates that optically triggered switches based on high T_c superconductor thin films can be used for the generation of sub-nanosecond rise time high-power pulses. Presented in this article are the experimental investigations of the light-induced switching dynamics in YBCO thin films biased by high-current nanosecond duration pulses. This research indicates that a high-power superconducting opto-electronic opening switch can operate in several regimes. The following transitions between the various states of the film are realized: superconducting to normal (S-N), super-conducting to mixed (S-M), low resistance mixed to high resistance mixed (M_LR-M_HR) and mixed to normal (M-N). When the superconductor is biased with a high current, the value of the light intensity needed for triggering the switch decreases by several times. The explanation of the main light-induced switching characteristics and their behavior is based on a model, which takes into account the simultaneous action of the light and the bias current on the superconducting film. The report also includes a discussion f the ultra-fast film damaging phenomenon which appears as a result of the dissipation of intense power during switching. Discussed is also how this process limits the highest amplitude of the generated pulse. The possible application of high-power superconducting opto-electronic switches for the creation of jitter free radar is also discussed.

Photoluminescence properties of short-period asymmetric GaAs/AlAs superlattices with the well and barrier thickness varied from 10 to 3 monolayers were studied at high optical excitation. It was shown that an asymmetric structure of the superlattice, in which the well layers are at least twice wider than the barrier ones, allows us to maintain the direct band gap and, hence, to improve emission properties for any well width. This is important for utilization of such structures in light-emitting devices. The stimulated emission at 80 K was observed for a GaAs/AsAs superlattice with the well and barrier thickness of 6 and 3 monolayers, respectively. At the same time, investigations of the dependences of the emission intensity on the pump intensity for different superlattices revealed an enhancement of nonradiative recombination with decreasing the well thickness due to an enhanced influence of interface roughness.

The ultrafast dynamics of As-ion implanted and annealed GaAs is investigated using transmission pump-probe measurements. Carrier recombination time was found to increase from 4 to 40 ps with increasing annealing temperature. At lower annealing temperatures the transmitted optical signal is dominated by induced absorption, at higher annealing temperatures this effect is replaced by induced transparency. We explain these features by the saturation of the arsenic antisite related electron traps and by the appearance of the second type of defects, respectively.

We have studied the optical response of two single-barrier AlAs/GaAs tuneling-based light-emitting diodes (TLED's) excited by very fast electrical pulses (transition times of less than 100 ps). The grown TLED's were identical except for the barrier width, which was chosen to be 4 and 6 nm, respectively. Streak-camera time-resolved spectra were recorded at room and liquid-nitrogen temperature, while simultaneously monitoring the current and voltage pulses. Both diodes show very fast switch-on and switch-off, with the room temperature 3-dB modulation bandwidth of 3 GHz for the 6 nm sample and 1.8 GHz for the 4 nm TLED.

In present paper is reported the first successful observation of the electrochromic effect of polyvanadium- molybdenum acid H₂V₁₀Mo₂O_{31+/- y}(DOT)nH₂O xerogels. Thin films of the investigated compound were produced by sol-gel technology. The transmission spectra were measured in the visible and infrared wavelength range. IN the all wavelength regions the transmission spectra changes when the dc electrical field was applied to the film. IN the visible wavelength range were observed the reversible changes of the film color. IR spectroscopy measurements of the films were carried out to obtain information about the water content in the film when the current flows through the sample. The electrochromic effect in the investigated compound is related with the proton motion through the xerogel that is acting by dc electrical field.

Thin films of tin-doped indium oxide, In₂O₃:Sn (ITO), with 9 mol% Sn were grown heteroepitaxially at 600 degree(s)C by dc magnetron sputtering on (100)-faces of lattice-matched yttrium stabilized zirconia, ZrO₂:Y (YSZ). Carrier density ranging from about 10²⁶cm^-3 to 10²⁷m^-3 has been measured after film annealing at 200divided by750 degree(s)C in oxygen or vacuum. The lowest resistivity valued down to about 4.0(DOT)10^-6 (Omega) m (at 300 K) have been indicated for the vacuum-annealed films. Optical transmittance and reflectance spectra of the films were investigated at T = 85divided by300 K in the UV, visible and near IR spectra regions ((lambda) = 0.2divided by6.0 micrometers ). The transmittance spectra in the vicinity of the band-gap were modeled in terms of direct allowed transitions taking in to account both the gap widening (the Burstein-Moss effect) and narrowing due to electron-electron and electron-ion interaction. The band- gap E_g0, of 3.47 eV and 3.54 eV has been evaluated for non-doped material at T = 300 K and 85 K, respectively.

In this research the influence of annealing on current- voltage characteristics of selenious acid (H₂SeO₃) treated Al-nGaAs contacts was investigated. Linear Al-nGaAs contacts were obtained by combination of selenious acid treatment and annealing. Dependence of the annealing and selenious acid treatment effects on nGaAs substrate dopants concentration was observed. Specific resistivity of the Al- nGaAs ohmic contact as low as 7.3(DOT)10^-6 (Omega) (DOT)cm² was achieved. Formation of the Al-nGaAs ohmic contact was explained by the interface Se reactions with both GaAs and Al.

(alpha) -C:H films were applied to fabricate photonic band gap (PBG) structures in the silicon substrate by SF₆N₂-based reactive ion etching (RIE). The influence of RIE parameters on (alpha) C:H films structure and etching rate was investigated int his study. It is shown that RIE rate for (alpha) -C:H films changes from 26 nm/min to 38 nm/min with the integrated intensity ratios I_D/I_G varied from 0.65 to 1.1. It is evident that increase in etching rate is determined by increasing quantity of sp² bonding in the synthesized (alpha) -C:H films. RIE does not change structure of the (alpha) -C:H masking films. However, non- uniform character of RIE takes place due to the non- homogeneous graphite clusters in (alpha) -C:H masking films. However, non-uniform character of RIE takes place due to the non-homogeneous graphite clusters in (alpha) -C:H masking films. By changing parameters of silicon etching, such as RF power density, pressure and negative bias voltage, anisotropy was varied in wide range and microstructures of different shape were obtained.

The synthesis of potassium substituted basic sodalites (formula available in paper) were performed. The XRD and FTIR measurements confirmed one phase results of the synthesis, but the number of water molecules in (beta) -cages was different from the expected values. The ionic radius of potassium is approximately 30% larger than radius of the sodium ion. The lattice constants of potassium substituted sodalites are about 3.6% larger than sodalite lattice constants. The thermally stimulated depolarization current technique was applied to determine dielectric relaxation process in the potassium substituted basic sodalites. We assume that all generated dipole momentum during the TSDC test belongs mainly to the potassium ions which have various possible localization positions in the (beta) -cage. The basic (formula available in paper) have similar TSDC peak positions at 335 K, but different activation energies of dielectric relaxation process. The activation energy of potassium substituted basic sodalites is larger than activation energy in basic Na sodalite which is explained by higher volume occupied by the potassium ions in the (beta) -cage. In case of the potassium substituted nonbasic sodalite the activation energy of dielectric relaxation process was about two times lower than the activation energy of dielectric relaxation process in the Na nonbasic sodalite. This fact is explained by lower number than 4 of the water molecules in (beta) -cage.