Investigation of the interaction of powerful laser radiation with semiconductors allows us to develop a number of novel techniques for active spectroscopy of semiconductors. Different approaches, based on light induced modulation of refractive or absorptive index of the semiconductor via photothermal, photorefractive, resonant exitonic or free carrier based effects has been used to reach the goal. In this paper we review some applications of two nondestructive techniques for characterization of bulk semiconductors and structures: transient free carrier grating technique and combined optical-microwave technique, both based correspondingly on refractive or absorption indices modulation by free carriers. The case of coexisting refractive index modulation mechanisms by free carriers (FC) and by light induced space-charge (SC) electric fields is analyzed concerning the role of defects in photorefractive GaAs crystals. The applications of those techniques given below are mainly based on investigations, performed at the Laboratory of Optical Diagnostics of Semiconductors at Vilnius University or in collaboration with other research institutions.

Ellipsometry is well known to be a very powerful technique for investigation of films, surfaces, interfaces and so on. Thanks to its principals and high quality of standard polarization prisms, ellipsometry has a sensitivity about one hundred's part of monolayer or some hundred's parts of angstrom if this sensitivity is recalculated for the thickness measurements. This very convenient and sensitive method of investigations also is very simple in realization. Unfortunately, ellipsometry is an indirect method. It may be the best method for investigations of little changes in well defined systems, but obtaining the optical parameters of an investigated system from the measured ellipsometrical angles (psi) and (delta) can be very difficult. Thus all results of ellipsometrical measurements have to be interpreted on the basis of some physical model and obtained optical parameters are only the parameters of the concrete chosen model. Difficulties in investigations of thin films and sub-monolayer coverings are: the nonuniformity of a substrate, the choice of an appropriate model for having the meaningful physical description, and a selection of measurement conditions for obtaining all parameters of this model. This article does not pretend to review all of the problems of the thin films ellipsometry and does not have a somehow full list of references; it is only a short look over some aspects of the ellipsometry of thin films.

Optical diagnostics of HgCdMnTe, HgCdMnSe narrow-gap semiconductors have been performed by means of FIR vibrational spectroscopy and IR luminescence for the case of low manganese content. Primary attention is given to the spectral features attributed to structural disordering or defects presence both in perfect and in real crystalline structures of HgCdTe(Se).

A technique for determination of stimulated by laser radiation phase-transition thermodynamic parameters of film structures is proposed. The amorphous films of W,Mo,Ni and Fe oxides are examined. The influence of laser wavelength on the thermodynamic parameters of phase transition in nonequilibrium conditions of laser irradiation is shown. The thermodynamic parameters in equilibrium conditions of all known differential thermal analysis techniques may be received. The equipment and measurement techniques for structure formation examination with simultaneous use of Rayleigh scattering and differential thermal analysis methods of high sensitivity are developed.

A device for spectral diagnostics of surface quality of real structures (crystals, ceramics, films) being used in modern microelectronics has been proposed. It consists of several selective IR leading semiconductor sources, an optical system, is executed on the basis of IR fibers, an unselective pyroelectric IR detector and a block of signal processing.

The mechanism and nature of photochemical transformation in cadmium iodide with copper impurity crystal followed by optical properties change were investigated. It was determined that the main mechanism is photostimulated decay of `copper-defect' complexes almost without activation and forming of Cu_i defect which are the lightsensitivity and absorption centers. The influence of copper-including complexes formed by isomorphic and anisomorphic replacement in anionic and cationic sublattices on cadmium iodide crystals lightsensitivity was studied. It was determined that cationic Eu coactivator causes the light insensitive defects forming, that is conditioned by [Cu_Cd] centers stabilization due to crystal lattice deformation by europium. The influence of anionic sulphur coactivator leads to absorption increase that is conditioned by single [Cu_i]-including defects and complexes stabilization.

A construction and the action principle of the sensor of the form and position of the light beam is described. On the basis of the two such sensors there has been constructed an apparatus for measuring profiles and roughness of the quasi-mirror surfaces. The inhomogeneities detection was realized by the change of the energy center position of the beam and its form, the beam being reflected from the examined surface. The measurements results are appendixed.

The various optical components with dielectrical coatings (mirrors, anti-reflection coatings, filters, polarizing and dichroic splitters, etc.) are used broadly in the quantum electronic, laser technique and other branches of optical instrument making. The successful designing of the multi-layer coatings with definite spectral and physicochemical properties are dependent on the authenticity of the parameters of the individual layers. It is known that considerable information about peculiarity of the coating design may be gotten by the measuring of the refractive, transmission and absorption spectra. At this report the results of the investigation of the refractive spectra of multi-layer dielectrical mirrors with symmetrical periods are presented and possibilities of the diagnostic of the structure and some parameters of the individual layers are shown.

A constructed high resolution (<EQ 10^-3 cm^-1) laser spectrometer, based on IV-VI cryogenic injection lasers, is described in applications to early medical onco-hematological diagnostics and nondestructive control of oxygen concentration and its distribution across Si-wafers. In this kind of spectrometer the dispersive elements are absent. Scanning of the radiation wavelength is realized by changing of the injection current. The width of the spectral scanning band is determined by the value of the laser injection current and the duration of the injection current pulse. Using these kinds of spectrometers it is possible to realize not only the measurements of infrared spectra with high resolution, but also high speed of the measurements. One spectrum in the range of (Delta) (lambda) approximately equals 0.55 micrometers can be measured during 15 ms. High resolution (10^-3 - 10^-4 cm^-1) makes it possible to resolve the superfine structure of absorption bands.

The method of determining optical constants of a thin film, deposited on a transparent, or slightly absorbing substrate, is proposed. It requires us to make measurements under normal incidence of the transmittance, the air-incident and substrate-incident reflectances, and film thickness. In the UV spectral region the additional measurements of reflectance for the opaque to light films are needed. It permits us to receive more precise optical constant values even for the high absorbing films. To illustrate the method, optical constants of the GeSe₂ and GeSe₂Ag_0.75 thin films were determined in the wide region of the spectrum.

A new method is proposed for studying surfaces in the region of resonance interaction of electromagnetic radiation with surface elementary excitations. In this method the sample surface is illuminated through the ATR prism having a thin metallic layer on its base and ellipsometric angles of reflected beam are measured. We have studied ellipsometric parameters and sensitivity of GWP ellipsometry in measuring refraction and absorption indices at the surface. A substantial bettering of sensitivity was demonstrated.

It is shown that spectroellipsometry (SE) as a non-destructive and contactless optical method may be used for characterization of transition layer properties, determination of optical bands positions and free-carrier concentration, evaluation of composition of compound materials and so on. A set of computer programs for the determination of dielectric functions (epsilon) ₁ ((omega) ) and (epsilon) ₂((omega) ) from ellipsometric angles (psi) and (Delta) was developed for the system with one, two and three interfaces. Computer simulations of electron band structure of monoatomic and compound materials (Si, C, SiC), including microcrystalline ones, were also made. The composition of some compound materials (SiC,HTSC) have been obtained from comparison of spectroellipsometry data with theory predictions.

A method of structure analysis of vitreous films is proposed, which enables us to obtain the information on the kinds and concentrations of the main structural components of the material, and to create the statistical picture of the most probable arrangement of the atoms in film lattice. The method is based on the computer analysis of the shape of IR-absorption spectrum. The capabilities of the method are demonstrated on the example of structure analysis of amorphous silicon-oxygen phase.

Photoluminescence investigations of silicon subjected to such industrial treatments as implantation, high temperature postimplantation annealing, treatment in high frequency discharge plasma, as well as the prolonged thermal annealing with the formation of thermal donors were carried out. It was shown that photoluminescence can be used for direct observation of the implanted impurity activation under various postimplantation treatments. Photoluminescence also proved to be useful for indirect control of thermal donors generation in Si:Ge.

In a temperature interval of 4.2 - 400 K spectral-luminescence characteristics, luminescence time decay, and the main scintillate parameters of the cadmium tungstate (CdWO₄) monocrystals were studied. In the special conditions grown (when a composition of components near to a stoichiometry composition) nominally `pure' CdWO₄ crystals were examined, and the crystals CdWO₄ with an impurity of different elements (Ni, Cs, Ag, Bi, Mo, Pr, Sm) cations were examined too. The spectra of photo- and x-ray luminescence, the spectras of photoexcitation, the spectra and the thermoluminescent glow curves, light output and energy resolution, when (gamma) -radiation processing have been analyzed. The temperature and long-duration x-ray and (gamma) -irradiation processing influence on some characteristics have been examined. The information obtained made it possible to discuss opportunities of the luminescence methods of scintillate crystals CdWO₄ diagnostics.

Advantages and limitations of a computer-controlled versalite modular laboratory set-up for spectroscopic diagnostics of materials developed in the Institute of Physics In Kyiv are discussed. Comparison with the options of standard optical multichannel analyzer is made. To illustrate the operation of the system the results on luminescence of direct-gap II-IV semiconductors within a wide (up to 6 orders of magnitude) range of excitation levels are presented.

The x-ray luminescence of the unintentionally doped polycrystalline ZnSe samples has been studied at the wide spectral range. Comparative study of x-ray luminescence and photoluminescence spectra has been made. The analysis of purity and quality of ZnSe by x-ray luminescent measurements is advantageous because of the bulk character of the x-ray excitation and the possibility of testing big squares. The peculiar features of x-ray spectra of unintentionally doped ZnSe lead us to conclude that this material has high optical quality.

In this paper a new method of impurities defect interaction monitoring by analyzing the low temperature many-bands photoluminescence spectra (PL) under the nonuniform external perturbation of the defect system is presented. As an example a PL spectra of cadmium telluride monocrystal plates after annealing in evacuated ampoule, cadmium and gallium atmosphere are discussed versus a coordinate of diffusion. The same well known background impurities such as Cu, Li, P and their complexes with native defects were studied under non- uniform deviation from stoichiometric composition of material toward the sample thickness.

In this review an independent method of vibrational spectroscopy, the spectroscopy of hyper- Raman scattering, is presented. The method was essentially developed and applied to study a number of physical problems. Some new possibilities for the study of material properties are demonstrated. This method is useful for the investigation of centrosymmetric and noncentrosymmetric crystals, glasses, liquids and gases at any conditions and under various external actions.

The use of Raman scattering and low temperatures photoluminescence is used to characterize the properties of thin n-AlGaAs films grown from Ga-Bi-Al solution-melt by LPE on SI GaAs substrates. By using these optical methods the Al concentration dependence for AlGaAs films with change of Bi concentration and for two fixed Al concentrations were obtained.

Direct measurements of radial optical inhomogeneity in long narrow elements (gas-discharge tubes, optical fibers, filamental crystals, etc.) entail some difficulties conditioned both by geometry and by littleness of optical properties absolute variations, especially critical in absorptive photothermospectroscopy. At the same time, in many such cases transverse optical inhomogeneity is close to lens-like type. It allows us to realize convenient and accurate procedure for measuring such inhomogeneity, disposing the inhomogeneous sample into the laser resonator and observing the inhomogeneity effect on the characteristics of generated radiation. This report presents general theoretic foundations for the proposed approach. Some variants of this procedure are analyzed and their advantages over common ones are shown. Experimental examination of the proposed method with an example of the He-Ne discharge element has shown its validity and usefulness.

It has been shown the evidence for the energy location of low-temperature photoluminescence (PL) of bound exciton complexes lines can be used as a technique of internal stress diagnostic in high quality bulk CdTe the substrates material for epitaxial growth photosensitive HgCdTe layers. The obtained deformation dependencies of the energy location and PL lines intensities allow us to estimate the value and sign of elastic stresses as well as defects type.

Peculiarities of the birefringence in Si-crystals caused by mechanical stress are investigated, using a method based on polarization modulation by means of a photoelastic modulator. Samples with the external operated stress and conventional Si-plates with the nonregular residual inner stress were tested by employing this method. Registration of the stress with the value more than 10^-3 kg/cm², investigation of the value of the stress spatial distribution and determination of the direction of the strain caused by this stress are available.

A novel sensitive and easy in operation technique based on nonlinear polarization transformation at nondegenerate in polarization two-wave-mixing interaction in a macroscopically isotropic nonlinear medium is analyzed theoretically and demonstrated experimentally for diagnostics of the third-order nonlinear response of materials on bacteriorhodopsin. The technique is shown to be an effective tool for obtaining information about the real and imaginary parts of the third-order nonlinear index and some other parameters of a nonlinear material.

The experimental results obtained by methods of linear and nonlinear optics and their discussion for pure metal (Ag, Au, Cu, Al, Ni, Cr), and Fe- and Ni-based amorphous alloys are performed. It is shown that from both linear spectroreflectopolarimetric and the second- harmonic generation data, the parameters characterizing surface roughness may be evaluated, moreover in the latter the sensitivity to the surface effects is in two orders higher than that for ellipsometry. The greater the roughness, the smaller is the intensity of s-component of the second harmonic generation. The structural anisotropy of both sides of the ribbon for amorphous alloys is found. This results in the difference of the principal angles of incidence, measured for two orthogonal orientations relative to p-plane from each of the ribbon's sides.

The monopulse method for rapidly determining the threshold energy E_th and threshold power density J_th of optical destruction in optically transparent dielectrics and semiconductors is developed. This method of diagnostics is based on measuring the optical transmission and electrical conductivity of the specimen under irradiation by laser pulses. The advantages of such diagnostics over the previously developed multi-pulsed methods are analyzed. As an example, the use of the method proposed for CdS single crystals, among them the crystals with uniquely high optical strength (J_th equals 600 - 800 MW/cm²), is described.

The new scintillation x-ray and gamma-ray detectors of `semiconductor scintillator- photodiode' type are preferential as the traditional scintillator-photoelectronic impurity systems. In particular, the ZnSe(Te)-based scintillators, connected to silicone photodiode, have a light yield 1.5 - 2 times larger than the light yield for the CsJ(Te). The shortcoming of ZnSe scintillators is their relatively large inertiality. The x-ray luminescence (XL) signal relaxation is not being described by the simple exponential or hyperbolical law. After the XL extinguishing, one can observe even some XL strengthening, that leads to the significant shining time increase. To reveal the ZnSe scintillators inertiality causes, an investigation of the impurity semiconductor luminescence via computer modeling has been carried out. The kinetics, temperature dependence, and infrared irradiation influence have been investigated. The properties of the system containing the multiple charged recombination centers (MRC), in particular the amphoteric centers (AC), were compared to properties of the system containing the simple recombination centers (SRC) only.

The oscillator regularity E equals h(omega) _i (n + 1/2) at the traps energy spectra was observed in a number of complex crystals: in Ba₂NaNb₅O₁₅ and YAlO₃ one series was observed; in CsCdCl₃ -- two; in ZnWO₄, ZnWO₄:Ni -- three; in Y₃Al₅O₁₅ -- five series. Most of the h(omega) _i are coincident with the high- frequency lines of the first-order Raman spectra, others -- with the second order Raman lines or the Raman lines caused by impurities. Accuracy of coincidence is 0.1 - 3.3%. The explanation of the oscillator regularity was done within the framework of the polaron trap model. Two variations of the model are offered: the trap is either an autolocalized polaron or a polaron stabilized by the field of intrinsic or impurity defects. In both cases the polaron energy states are described by the parabolic potential curves with equidistant vibration levels. The thermal activation energy is then determined by the number of a level from which the tunneling either in the polaron band or in the excited exciton state adjacent to the luminescence center is possible.

Magnitude and kinetics of laser induced integral flow of thermal radiation of semiconductors and metal-semiconductor structures are studied. The possibilities of latent defect disclosure in metal-semiconductor structures, near-surface macrodefects in semiconductor wafers, to control surface properties of a semiconductor and metal-semiconductor interface with the help of developing the laser-thermal method of diagnostics have been shown. It is shown also that measurements of integral flow of thermal radiation allow us to draw conclusions about the condition and mechanisms for laser-stimulated diffusion, defects creation, p-n junction, and ohmical contact formation processes in semiconductor structures.

The perfection of vacuum technology of thin film structure production of different functional applications is to a great extent defined by the technical level of the devices for investigation of mechanical properties of thin films. Improvement of operational characteristic features of film structures is restrained by lack of mechanical stability which in its turn is considerably influenced by the level of internal macro- and microstresses. In this paper the method and device for thin films mechanical stability investigation are presented and the examples of PbF₂ and As₂S₃ coatings are furnished.

Structural schemes of photoacoustic microscope and photoacoustic spectrometer of original design are described and the results are presented on photoacoustic micro- and spectroscopy for porous silicon, high-temperature superconductors, layer semiconductors, elements of integrated circuits and other materials and devices for electronics.

Studies of both superclean silicon wafer surface and subsurface layer have shown high informative possibilities of the light scattering method. It was found that measurements of light scattering indicatrix vs azimuth make it possible to fix the occurrence of atomic steps on the surface studied. The possibility of detecting stacking faults in silicon single crystals is demonstrated by analyzing the intensity of the scattered light with a 442 nm wavelength during scanning of the sample surface with a focused laser beam.

In this paper, a method is proposed for determination of the performance of such optical and photo-optical systems as lenses with graded-index profiles, focusing optical fibers and micro- lenses. A device, characterized by its simplicity, for modulation or optical transfer functions measurements is described. Some micro-optical elements are evaluated by means of the suggested method and the device.

A measurement system with a rotating polaroid was constructed which allows us to detect the degree of the light polarization ((rho) ) of 0.1%. The dependencies of r were studied on pumping current (I), axial stress ((sigma) ) and temperature (T) for AlGaAs diode lasers (DL), as well as variations of (rho) with the parameters of the detecting system. The validity of the one-dimensional Cassidy's model was argued to describe the polarization phenomena in the active region of DL. The obtained data demonstrate the possibility to evaluate the mechanical strain in the active layer of DL and estimate the difference in reflectivities between transverse electric (TE) and transverse magnetic (TM) modes of the output at varying mechanical strain. The developed experimental system and technique are simple, sensitive and robust enough to be used under the conditions of industrial producing DLs.

The optical/digital system with solid state array detectors for capillary characteristics of materials and high-temperature melts measuring and diagnostics by sessile-drop method is described. Conditions of sessile drop image forming in the optical scheme of the system are defined. The spatial gradient algorithm for image spatial gradient field forming and gradient maximums localization is proposed. Three methods of sessile drop geometric parameters precise measuring and gradient maximums locations estimation are described. The results of distilled water and mercury sessile drop geometric parameters multiple measurements with the subsequent averaging of obtained data are presented. The perspectives of measurement accuracy increasing and sessile drop image processing time decreasing are discussed.

The thermovisual method for control of electronic products and informational-measuring system for performing such control are considered. The technical features of the system are described in detail.

The discharge current influence on the homogeneous broadening of the spectral lines in the gas-discharge media by direct collisions of the excited atoms with free electrons and also through collision broadening changing because of the gas heating by discharge current is considered. It was established that homogeneous broadening and hence the frequency shift of the spectral line depend essentially on the thermal condition of the laser work. The theoretical calculations are confirmed by the experimental measurements of the dependence of the homogeneous broadening of spectral line 3s₂ - 2p₄ neona in the He-Ne laser on the discharge current magnitude. For the homogeneous broadening determination by the experimentally measured Lamb dip characteristics a new computation method was developed, which can be used both in single-mode and two axial modes conditions of laser generation. It has been shown that on its basis and using known dependencies of the collision broadening of the spectral lines on the pressure, there can be realized an express-control of the main sources of the generation frequency unreproducibility in the sealed off discharge tubes, such as gas pressure and relative excitation of the laser system.

Analog television technology and computer processing are used in conventional and confocal microscopes to produce and handle high-quality amplitude contrast image. Results of comparison of various methods are obtained and one the television microscope systems is fully considered.