Home – Home – Jornals – Avtometriya 2011 number 5

The current status of ellipsometric methods and hardware tools developed at the Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences is considered. A unique static scheme for ellipsometric measurements is presented, which is used as a basis for instruments designed for various purposes: spectral and laser ellipsometers and also ellipsometers for local measurements. The capabilities of ellipsometric instruments are illustrated by results of studying various objects and fast processes. It is demonstrated that complete experiments can be performed with the use of static-type ellipsometers with determination of all parameters of partly depolarized light.

A retrospective analysis of growing of multilayered and variband structures based on the mercury cadmium telluride compounds by the method of molecular beam epitaxy with ellipsometric control and methodical developments in the field of ellipsometry of inhomogeneous structures is presented. Calculations are performed, and solutions of direct and inverse problems for some cases important for practice are obtained. The high accuracy of determining the thickness and composition of the layers in growing heterostructures of nanometer-scale thicknesses is demonstrated. In some cases, it is proposed to use the relative derivative of ellipsometric parameters measured in the course of growing the structure to increase the accuracy of solving the inverse problem. This procedure allows the profiles of the optical constants of structures with gradient compositions to be determined. Theoretical calculations for periodic layered structures are performed, and the possibility of their controlled growing is demonstrated in experiments.

This paper presents a brief review of the progress in the development of two types of semiconductor emitters based on semiconductor Bragg microcavities. The first type of these emitters is a vertical-cavity laser based on Al_xGa_1−xAs. The laser demonstrates stable single-mode lasing ata wavelength of 795 nm, which opens prospects for its use in miniature atomic frequency standards on the basis of Rb⁸⁷. The second type is a single-photon emitter based on semiconductor quantum dots. The design of such an emitter was developed on the basis of a semiconductor Bragg microcavity providing a high level of external quantum efficiency of the emitter (up to 80%) and high performance due to the Purcell effect.

Results of experimental studies presenting data on the effect of electron trapping centers on the properties of Pb_1−xSn_xTe : In with x ≈ 0.24-0.29 at temperatures below 20 K are described. A model is developed that consistently explains a number of phenomena in Pb_1−xSn_xTe : In solid solutions, including current-voltage characteristics in the absence of light resulting from the injection from contacts and space-charge limited current when electrons are captured in traps distributed in energy in the bandgap, photoelectric phenomena in the infrared and terahertz spectral ranges, features of galvanomagnetic phenomena, and fluctuations and autooscillations of current in the absence or presence of light.

The interaction of the GaSb(001) surface with fluxes of As₂, As₄, and Sb₄ molecules is studied using reflection high-energy electron diffraction. It is shown that As₂ molecules interact with a GaSb surface predominantly by an exchange mechanism, and As₄ molecules by the vacancy mechanism. It is established that for the reproducible generation of In-Sb heterointerfaces in InAs/GaSb superlattices, one needs to use a flux of As₄ molecules rather than As₂ molecules.

The plasma oxidation of a silicon surface in an inductive plasma generation reactor were studied using spectroscopic ellipsometry and atomic emission spectroscopy. The effect of inert gases on the formation kinetics of ultrathin SiO2 films is discussed. The effect of intense oxidation of Si in the plasma formed by nominally pure helium was found. It is suggested that this effect is due to the photostimulated acceleration of the reaction at the silicon-oxide interface by the intrinsic optical emission from the helium plasma.

A possibility of using a new method of film synthesis in a supersonic flow of a hydrocarbon plasma generated by a disk-type magnetohydrodynamic accelerator is demonstrated. Two methods are used for characterization of diamond-like carbon films: nondestructive spectroscopic ellipsometry and atomic-force microscopy.

The surface of biochips prepared on the basis of silicon wafers for studies of reactions of pre-immobilized oligonucleotides and protein molecules was analyzed by high-resolution scanning ellipsometry. The hybridization interactions of nucleic acid (duplex formation in the reaction of an amplicon of the influenza A virus matrix protein gene with probe molecules), sorption of protein molecules, and protein-protein interactions on the surface of the biochip were detected. It was shown that pre-sorption of gold nanoparticles led to greater efficiency of immobilization of protein molecules on the biochip. The experimental data suggest that that ellipsometry is a highly sensitive, nondestructive and inexpensive label-free method for the detection of the biochip surface, which is suitable for quantitative analysis of reactions of biomolecules.

The ultimate efficiency of a three-pin solar cell based on the GaAs/Si structure is calculated by means of numerical simulation in a diffusion-drift approximation. Dependences of the efficiency on the GaAs layer thickness and the density of dislocations threading in this layer, which are known to affect the lifetime of nonequilibrium charge carriers. It is shown that the maximum limit efficiency (27 %) of such a structure is reached at the GaAs layer thickness of about 1.4 µm and the density ofthreading dislocations of less than 106 cm⁻².

Optical properties of Ga- and N-polar triple nitrides Al_xGa_1−xN with molar fractions of aluminum from 0 to 0.6 are studied by a nondestructive contactless method of spectroscopic ellipsometry. Correlation dependences of the shift of the fundamental absorption edge and the behavior of the real and imaginary parts of the pseudodielectric function on the composition x and polarity of the Al_xGa_1−xN layers are revealed. It is verified that the polarity of the layers grown by molecular beam epitaxy is defined by the formation of the AlN nucleating layer.

The mechanism of formation of silicon nanoclusters in layers of nonstoichiometric composition is studied by Monte Carlo simulation. Interest in silicon nanoclusters (Si-nc) coated with an oxide layer is due to their applications in modern optoelectronics and nanoelectronics. A lattice Monte Carlo model is proposed to study atomic processes in the Si-SiO₂ system. The formation of silicon nanoclusters during annealing of single SiO layers and SiO₂-SiO-SiO₂ layered structures is studied. Along with the diffusive motion of particles, the model takes into account the formation and collapse of mobile molecules of silicon monoxide. It is shown that accounting for transport of silicon under high-temperature annealing due to the motion of SiO accelerates the formation of Si-nc. Dependences of the size of nanoclusters on temperature, annealing time, and the composition of the SiO_x layer are obtained. It is found that annealing of silica films containing layers of nonstoichiometric composition can lead to the formation of silicon nanoclusters or cavities.

Technical parameters and possible applications of an infrared scanning microscope with a spatial resolution of up to 3 µm are considered. It is shown that the device works with both array and linear photodetectors. Original PC software was designed to control the scanning process interactively and receive and process images of objects in the infrared range,.

Operation of a photodetector in an infrared microscope has a number of features preventing the application of calibration methods known for thermal imaging devices. A differential method of calibration is proposed which gives an opportunity to consider the nonlinearity of the transfer characteristics of the photodetector reading unit and electronic path and the variation of the background radiation flux.

The mechanism of occurrence of sensitivity of microbolometer detector arrays based on vanadium oxide to terahertz radiation are analyzed. Experimental data are given showing the possibility of increasing the sensitivity of microbolometer detectors in the terahertz range by using an additional thin metal absorbing layer applied on the microbolometer membrane. A polarization dependence of the sensitivity of microbolometers in the terahertz and far infrared spectral ranges is found. It is shown that the sensitivity of microbolometers in the terahertz range is due to the absorption of radiation in the narrow metal runs placed on the support legs of the microbolometers and playing the role of an ohmic contact between the heat-sensitive layer and the processing curcuit.

Thin films obtained by centrifugation of blood serum of healthy people and patients with diffuse pathology of liver with different degrees of fibrosis are studied by means of spectroscopic ellipsometry. The physical properties of the films are found to depend on the bio-organic composition of blood serum, which, in turn, is determined by pathological processes proceeding at different degrees of liver fibrosis. Correlations between the bio-chemical parameters of blood serum and ellipsometric data are obtained. Pilot ellipsometric experiments on studying blood serum with observations of the plasmon resonance of patients with intestinal tract tumors are performed. A persistent specific interaction between antigens of patient's blood serum and SD24 monoclonal antibodies is found, which alters the position of the surface plasmon resonance. It is demonstrated that ellipsometry is a high-sensitivity nondestructive inexpensive express method of screening, i.e., preliminary diagnostics of disease stages for patients with pathologies of internals.

This paper describes an automated photoelectromagnetic set of instrumental and methodological tools designed to determine the electrical and recombination-diffusion parameters of charge carriers in epitaxial films and p-type mercury-cadmium-tellurium film structures with thickness comparable to the diffusion length of minority carriers. The complex includes the following methods: the Hall effect, magnetoresistance, the photomagnetic effect, and photoconductivity in a magnetic field for the Faraday and Voigt geometries. The following parameters were determined: equilibrium concentration, the mobility of majority and minority charge carriers (holes and electrons, respectively), the bulk lifetimes electrons and holes, surface recombination velocities on the free boundary of the film and the interface with the substrate.