Diffusion redistribution of zinc during the doping of structurally inhomogeneous epitaxial layers of gallium phosphide

The distribution of zinc established during its diffusion accompanying the doping of gallium phosphide layers in the course of epitaxial growth has been numerically simulated. The internal redistribution of zinc introduced in the presence of a structural macrodefect (in particular, screw dislocation) is treated according to the dissociative model of the interstitial-lattice site diffusion. This model assumes the existence of zinc ions in two states with different diffusion mobilities that actively interact with gallium vacancies. The results of an analysis of solutions of a nonlinear boundary-value problem demonstrate the existence of sharply inhomogeneous distributions of the zinc ion concentration, which explain some experimentally observed anomalies in the reverse current of zinc-doped epitaxial GaP-based p-tn junctions.     

Binary acceptor doping of epitaxial gallium phosphide for high-temperature electronic devices

We have experimentally studied the reverse-bias branch of the current-voltage (I–U) characteristics of high-temperature two-electrode devices (rectifying diode, Zener diode, hot electron emitter), the technology of which involves the stage of binary zinc-magnesium doping. Factors leading to the development of various types of the avalanche breakdown are analyzed as dependent on the Zn/Mg ratio. Differences in the characteristics and behavior of the I–U curves are related to features of the acceptor diffusion, which always accompanies the process of doping involved in the growth of multilayer epitaxial p–n structures.     

Simulation of 125I induced DNA strand breaks in a CAP-DNA complex

The E. coli catabolite gene activator protein (CAP)-DNA complex with 125I located at the position of the H5 atom of the cytosine near the centre was incorporated into the PARTRAC track structure code. DNA strand breaks due to irradiation were calculated by track structure and radical attack simulations; strand breaks due to neutralisation of the highly charged 125Te ion were derived from a semi-empirical distribution. According to the calculations, the neutralisation effect dominates the strand breakage frequency at 2 bases away from the 125I decay site on both strands. The first breakage distribution counted from a 32P labelled end on the strand with 125I agreed well with experimental data, but on the opposite strand, the calculated distribution is more concentrated around the decay site and its yield is about 20% larger than the measured data.     

Phase-matching and femtosecond difference-frequency generation in the quaternary semiconductor AgGaGe5Se12

We present data on the linear (transmission, index of refraction) and nonlinear (second-order susceptibility) optical properties of the quaternary semiconductor AgGaGe5Se12 with orthorhombic symmetry--a solid solution in the AgxGaxGe1-xSe2 system with x = 0.17. The nonlinear coefficients are estimated from phase-matched second-harmonic generation near 3 microm. After numerical analysis of the phase-matching configurations for three-wave nonlinear interactions, the first experimental results on difference-frequency mixing, producing tunable (4-7.5-microm) femtosecond pulses at a 1-kHz repetition rate, are described. The pulses of only five optical cycles (FWHM = 84 fs) are generated near 5 microm with energy of 0.5 microJ. Because of its higher damage threshold, larger birefringence and bandgap, and greater variety of phase-matching schemes, AgGaGe5Se12 could become an alternative to AgGaS2 and AgGaSe2, more widely used in high-power and specific applications.     

Specific Features of the Pyroelectric Effect in Epitaxial Aluminum Nitride Layers Obtained on Si Substrates

Technical Physics Letters - Pyroelectric effect has been studied in quasi-bulk AlN layers with thickness of 10–170 μm produced by hydride–chloride vapor-phase epitaxy on standard...     

Mechanisms of triplex-caused polymerization arrest

Pyrimidine/purine/purine triplexes are known to inhibit DNA polymerization. Here we have studied the mechanisms of this inhibition by comparing the efficiency of Vent DNA polymerase on triplex- and duplex-containing templates at different temperatures, Mg2+concentrations and time intervals with the thermal stability of the corresponding structures. Our results show that triplexes can only be by-passed at temperatures where thermal denaturation initiates, while duplexes, in contrast, are overcome at temperatures where they are quite stable. These results show that DNA polymerase cannot untangle triplex regions within DNA templates and seems to entirely depend on their thermal fluctuations. The high stability of triplexes at physiological temperatures and ambient conditions make them a barrier to polymerization.     

Optical properties of thallium mercury iodide

We investigated the growth conditions and obtained Tl₄HgI₆ nonlinear crystals of red and black phases. We also measured the dispersion of the black-phase crystal refractive indices and analyzed possible nonlinear three-frequency processes.     

Preparation and Structure of AgGa1 – x In x Se2 Single Crystals

AgGa_{1 – x} In _x Se₂ single crystals grown by the Bridgman–Stockbarger method, using presynthesized charges with x = 0.27, 0.335, and 0.375 are studied by x-ray diffraction (phase analysis, determination of lattice parameters, structure refinement of powdered crystals by the Rietveld profile analysis method, and single-crystal structural analysis). The results suggest that the crystals may contain Se and Ag vacancies. The polarity of the crystals is found to depend on their composition.     

Preparation, Structure, and Properties of New Laser Crystals Y2SiBe2O7and Y2Al(BeB)O7

Nominally pure and activated (Yb and Nd) Y₂SiBe₂O₇and Y₂Al(BeB)O₇crystals, belonging to the melilite family, were grown by the Czochralski technique, and their structures were determined by single-crystal x-ray diffraction. The cation distribution over the crystallographic sites in the structure of Y₂Al(BeB)O₇was assessed. The crystals were found to have a tendency to be twinned.