Home – Home – Jornals – Avtometriya 2009 number 4

A method of nanostructuring of silicon-on-insulator (SOI) layers on the basis of gas etching in XeF₂ or SF₆:CFCl₃ is developed for the purpose of obtaining SOI nanowire structures. SOI nanowire transistors (SOI NWTs) with free channels, used as sensors in electron detectors, are fabricated and tested. The results of experiments show that the method used to fabricate nanowires requires no hightemperature operations for elimination of defects after nanostructuring of SOI layers. The sensitivity of SOI NWTs to test molecules of bovine serum albumin is 10⁻¹⁵ mole/liter, which is one of the best results for nanowire biosensors.

Chiral metamaterials of the terahertz range are formed by means of rolling of strained nanofilms. Structural elements of these metamaterials are metal-semiconductor microhelices. Resonant optical activity of new metamaterials in the terahertz range is demonstrated. Arrays of model wire helices are formed and tested in the microwave range.

Molecular beam epitaxial growth of HgCdTe solid solutions on silicon substrates of 76.2 mm diameter was studied. Conditions for producing HgCdTe/Si(310) heterostructures for the spectral range of 3-5 μm which are suitable for fabricating high-quality devices were determined. A 4× 288 photodetector was fabricated by hybrid assembly of an array photosensitive element with a multiplexer. Results on the sensitivity and stability of this photodetector to thermal cycling are given.

Current-voltage characteristics of IR photodiodes and distributions of charge carriers in n⁺-n⁻-p-structures based on vacancy p-doped Hg_1−xCd_xTe films with x = 0.22 are examined. Threedimensional numerical modeling of the distribution of charge carriers and current-voltage characteristics during photodiode annealing is performed. The calculations predict that large tunnel currents in diodes after implantation can result from an elevated (more than 10¹⁵ cm⁻³) concentration of donors in the n⁻-layer, which enhances tunneling by decreasing the thickness of the space charged region of the n-p-junction, and also from a small (less than 3 μm) depth of the p-n-junction.

The photomagnetic effect and photoconductivity in a magnetic field are studied at a liquid nitrogen temperature for the Voigt geometry on p-HgCdTe films with graded-gap boundary regions where the content of cadmium (x) is increased above its mole fraction in the central area of the structure with a uniform distribution of x. A case with dominating Shockley-Read recombination is considered. It is demonstrated on the basis of experimental data that the film structure in studying these effects can be replaced by the central area with an identical value of x, by introducing effective velocities of surface recombination and surface generation of excess charge carriers on the interfaces between the central area and the graded-gap regions.

A combined theoretical and experimental analysis of the crystalline phase fraction in nanocrystalline films grown by low-energy plasma-enhanced chemical vapor deposition is presented. The effect of the key parameters, such as temperature, silane flux, and hydrogen dilution ratio, is analyzed. An atomic-scale Monte Carlo model is developed, where the crystallization probability depends on the local environment of the nanocrystalline film. Good agreement is found between the experiments and theory, despite the use of a single fitting parameter.

The self-organization of germanium nanoislands on the surface of calcium fluoride was studied using atomic-force microscopy and reflection electron diffraction. A Ge/CaF₂/Si(111) structure was grown by molecular beam epitaxy. The surface of the calcium fluoride film was modified by submonolayer carbon coverage to stimulate the formation of germanium nanoislands. The arameters of an array of nanoislands were found to depend on the coverage.

A model is proposed to predict the critical parameters (shape, size, element composition) of nanoislands for dislocation nucleation. The onset of plastic relaxation of three-dimensional islands formed during heteroepitaxy in the Stranski-Krastanov mode are considered theoretically for the Ge/Si(100) heterosystem as an example. The study is based on a combination of numerical and analytical approaches to the calculation of strains in three-dimensional island containing a dislocation. It is confirmed that dislocation nucleation in three-dimensional SiGe islands is not limited by the kinetic barrier.

The parameters of a structure consisting of a doped GaAs channel and an AlGaAs buffer located between the substrate and the channel are optimized using the Synopsys Sentaurus TCAD simulator. It is shown that the use of this buffer increases the breakdown voltage and power of the transistor compared to the basic structure transistor without an AlGaAs buffer. It is also shown that the transistor breakdown voltage is most greatly affected by the buffer composition (the fraction of aluminum in the Al_xGa_1−xAs) solid solution and, that the maximum breakdown voltage is obtained for a buffer containing no less than 18 % aluminum.

Nanowhisker formation on substrates activated by catalyst drops is studied by Monte Carlo simulation. Dependences of the whisker growth rate on diameter are investigated for various growth modes. The influence of deposition conditions on whisker morphology is examined. It is shown that straight thin whiskers of uniform thickness can be obtained only using a catalyst having a large contact angle with the whisker material. In such a physicochemical system, variation of growth conditions can result in nanotube formation. An atomic mechanism for the formation of a hollow whisker is proposed. Ranges of model growth conditions suitable for the growth of nanowhiskers and nanotubes are determined.

It is shown that the blocking layer of the flash memory element based on silicon nitride has an optimal value of the dielectric constant, which allows the maximum memory window in the write/erase regime to be reached.

This paper reports the results of experimental studies and calculations of components of a model system for detection and imaging in the terahertz range, including a free-electron laser and devices for laser radiation diagnostics, film shields with absorbing coatings for intermediate thermal imaging, and prototype sensitive elements based on PbSnTe:In films.

A vertical-cavity surface-emitting laser on the basis of Al_xGa_1−xAs solid solutions is developed. The laser displays stable single-mode operation at a wavelength of 795 nm, which offers the prospects of its application in miniature chip-scale atomic clocks.

Monte Carlo simulations of atomic processes on the surface of silicon nanochannel membranes during molecular-beam epitaxy and subsequent thermal oxidation are performed. It is demonstrated that silicon deposition on Si(001) wafers with 1-100 nm cylindrical pores results in constriction of channel inlets. The rates of reduction of the nanochannel diameter are estimated as functions of the wafer temperature, silicon deposition rate, and initial nanochannel diameter. Optimal conditions of silicon deposition on nanochannel membranes are determined: the wafer temperature of 250-450 °C and silicon flux intensity of 10⁻² to 10 monolayers (ML) per second. Under these conditions, the rate of reduction of the nanochannel inlet diameter is 0.13-0.15 nm/ML, which allows membrane channel modifications over a wide range down to several nanometers. Simulations of nanochannel membrane oxidation in an oxygen flux shows that precise reduction of nanochannel inlet diameters down to complete sealing of the channel due to oxide growth is only possible for small diameters of the initial pores. For channels with large lateral sizes, the effect of reduction of the channel inlet diameter due to oxidation is insignificant. Oxidation of pores enhances their stability to subsequent high-temperature treatment.

This paper gives experimental results of quantum key distribution on a fiber-optic setup at a telecom wavelength of 1555 nm. A self-compensated two-channel optical circuit is used. Quantum key distribution was performed by coding the phase states of single photons radiated by a pulsed semiconductor laser in two alternative nonorthogonal bases. Specially developed single photon counters based on InGaAs:InP avalanche photodiodes were employed as high-sensitivity photodetectors. The results of investigation of the quantum efficiency, probability of afterpulses, and noise level for various operating modes of the detectors at temperatures from −40 to −60 °C are given. A key distribution rate of 450 bit/s was obtained for a single-mode fiber-optic quantum communication channel between the receiver and sender 25 km long at a laser pulse clock frequency of 5 MHz and an average number of photons per pulse of about 0.2. For the achieved photodetector characteristics, the average number of errors in the quantum key did not exceed 3.7 %.