Conducting properties and structure of nonstoichiometric orthorhombic phase of YBa2Cu3O7−x obtained by high-temperature vacuum annealing

Neutron and x-ray diffraction studies are carried out which show when the orthorhombic phase of YBa₂Cu₃O_7−x (x≈0.02) is heat treated at temperatures of 430–550 K under tunnel high-vacuum pumping, a partial emission of oxygen from the O(1) positions (with coordinates 0;0;0.1578) and O(4) positions (with coordinates 0;1/2;0) occurs with no change in the symmetry or in the unit cell parameters. The temperature dependence of the electrical resistivity in the temperature interval 77–300 K shows a semiconducting character. Pis’ma Zh. Tekh. Fiz. 24, 90–95 (September 12, 1998)     

Possibility of nonequilibrium phase transitions in semiconductors and semiconducting superstructures in crossed electric and magnetic fields

An analysis is made of two types of negative differential conductivity in semiconductors and semiconducting superstructures containing ND shallow impurity atomic systems (centers), in crossed electric and magnetic fields corresponding to nonequilibrium phase transitions of n _e , where n _e is the average density of nonequilibrium carriers (electrons). It is observed that these semiconductors and semiconducting superstructures in crossed electric and magnetic fields may be used to fabricate various semiconductor devices and apparatus, and also memory elements for the acquisition, storage, and protection of information under extreme conditions. Pis’ma Zh. Tekh. Fiz. 25, 39–44 (August 26, 1999)     

Photoluminescence properties of AlxGa1−x As epitaxial layers grown under conditions of ultrafast flux cooling

Results are presented of studies of the photoluminescence properties of epitaxial layers of Al_xGa_1−x As solid solutions grown by liquid-phase epitaxy with nonequilibrium crystallization achieved by ultrafast rates of cooling of the flux (V∼10²–10³ °C/s). The photoluminescence characteristics obtained indicate that the epitaxial layers are of high quality. It is also observed that when samples with x _buff=0.5–0.55 are exposed to laser radiation of power density ∼1 kW/cm² at a temperature of 77 K, the spectral composition of the radiation undergoes irreversible changes caused by the formation of an arsenic vacancy (V _As)-donor impurity complex. Pis’ma Zh. Tekh. Fiz. 23, 8–13 (March 12, 1997)     

Silicon metal-dielectric-semiconductor varicaps with an yttrium oxide dielectric

This paper reports an investigation of the electrophysical properties of metal-dielectric-semiconductor varicaps with an yttrium oxide dielectric, prepared by resistive vacuum evaporation of the rare-earth metal with subsequent thermal oxidation of the film in air at 500–550 °C. It is found that the electrical conductivity of the samples follows the Poole-Frenkel law. High-frequency capacitance-voltage characteristics are used to determine the specific capacitance of the dielectric, C ₀=0.027–0.03 μF/cm², the slope of the capacitance-voltage characteristic, dC/dV=35–40 pF/V, the fixed charge in the dielectric, Q _f=(1.7−2.7)×10⁻⁸ C/cm², and the density of surface states at the flat-band potential, N _ss=(1−2)×10¹¹ cm⁻²·eV⁻¹. The capacitance tuning range factor for the metal-dielectric-semiconductor varicaps is 2.5–3. These structures are shown to be applicable as metal-dielectric-semiconductor varicaps with a low control voltage and a high quality factor. Pis’ma Zh. Tekh. Fiz. 23, 50–55 (June 26, 1997)     

Anomalies in the elastic and inelastic properties of ferromagnet-ferroelectric composites

We have studied the elastic and inelastic properties of composite materials of the Co _x (PZT)_{1 − x} system (x = 0.23–0.79) possessing a nonequilibrium nanogranular structure with an average grain size of ∼3 nm. The results of mechanical tests performed in a temperature range of 300–900 K revealed a significant increase in the level of mechanical losses (Q ⁻¹) above 750 K, which is caused by the thermoactivated migration of point defects. An additional heat treatment leads to grain coarsening and the appearance of a ferroelectric state in the dielectric matrix. The temperature dependences of Q ⁻¹ in annealed samples exhibit two maxima, one of which is due to the interaction of domain boundaries with lattice defects and the other is related to the motion of interfaces in the region of the ferroelectric phase transition.     

Fiber ring laser with locked relaxation oscillations

An investigation is made of the locking of the relaxation oscillations in a fiber ring laser with an active medium of phosphorus aluminosilicate glass doped with erbium and ytterbium ions. It is shown that stable pulse-periodic emission in the 1.5 /gmm range can be achieved at a pulse repetition frequency between 80 and 160 kHz with a pulse length of 2–3 μs. A single-mode model is used to determine the laser parameters (the pumping rate and the photon lifetime in the cavity). Pis’ma Zh. Tekh. Fiz. 25, 24–28 (January 26, 1999)     

Influence of the specific input energy on the characteristics of a nuclear-pumped Ar/Xe laser

Results are presented of experiments and model calculations on the pumping of a 1.73 μm Ar/Xe laser with 235U fission fragments over a wide range of specific powers. An analysis is made of the mechanism for quenching of the lasing at high specific input energies. Pis’ma Zh. Tekh. Fiz. 24, 16–20 (July 26, 1998)     

Alternation of nonequilibrium and sequences of structural transitions

An analysis is made of the law of alternating nonequilibrium, dictating an oscillatory change in the degree of nonequilibrium for a wide range of influence. With increasing influence, intervals of decreasing degree of nonequilibrium at their onset correspond to structural transitions and accompanying anomalous states. This law can be used to identify a wide variety of new nonequilibrium effects. Pis’ma Zh. Tekh. Fiz. 23, 17–21 (May 26, 1997)     

Critical importance of the single-level approximation to account for the highly nonmonotonic dependences of carrier lifetimes on recombination impurity concentration

This paper is a continuation of an analysis regarding an increase in the lifetimes of nonequilibrium electrons π_n and holes πp by several orders of magnitude, observed with increasing concentration of recombination centers. It is shown that a substantial increase in πn and πp may also occur for three charge states of the recombination impurities N, and the curves πn=f(N) and π n=f(N) may each have two minima and maxima. Pis’ma Zh. Tekh. Fiz. 23, 39–45 (April 12, 1997)     

Two-section InGaAsP/InP Fabry-Perot laser with a 12 nm tuning range

Wavelength tuning over a 12 nm range is obtained for a two-section InGaAsP/InP Fabry-Perot laser (λ=1.55 μm). The method used to vary the gain profile of the laser allows one to predict the range of possible wavelength tuning. Pis’ma Zh. Tekh. Fiz. 23, 10–15 (March 26, 1997)     

Possibility of fabricating an inductive high-speed detector for electromagnetic radiation using thin YBa2Cu3O7−δ films

It is shown that an inductive high-speed nonequilibrium detector for electromagnetic radiation can be fabricated using thin YBaCuO films. An electronic detection regime has been obtained for the first time using a low-temperature inductive YBaCuO detector in the measuring frequency band Δf=1–50 MHz and it has been shown that no bolometric detection regime exists at operating temperatures far below the superconducting transition. The time constant of the low-temperature inductive YBaCuO detector in the electronic regime is determined only by the electron-phonon interaction time in the nodal regions τ _e-ph ^d . The detector has the following limiting characteristics: when the operating temperature is reduced from 10 to 1K, the time constant τ _D varies between 10 and 100 ps and the sensitivity D* improves substantially from 10⁹ to 4×10¹² W⁻¹ cm Hz^1/2. Pis’ma Zh. Tekh. Fiz. 25, 14–19 (January 26, 1999)     

Preparation of thick YBa2Cu3O7−δ films by dc magnetron sputtering

High-temperature superconducting films up to 3.6 μm thick were obtained and their properties requisite for the development of microwave devices were investigated. It is shown that YBa₂Cu₃O_7−δ films of thickness exceeding 3–5λ _L may be obtained for use in the microwave range. Pis’ma Zh. Tekh. Fiz. 24, 89–94 (October 12, 1998)     

Microwave phase shifter with planar capacitors using strontium titanate films

A design of a microwave phase shifter based on a loaded microstrip line using planar SrTiO₃ capacitors as nonlinear elements is described. The microwave phase shifter (at T=300 K) demonstrated a continuous phase shift between 0 and ∼55 deg in the frequency range 8.6–9.0 GHz with a phase error not exceeding 5 deg. The quality parameter of the phase shifter in the operating frequency range was 110 deg/dB. Pis’ma Zh. Tekh. Fiz. 25, 78–83 (October 26, 1999)     

Electrical conduction in La<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>Er<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−α</Subscript> ceramics

Doubly doped LaErO₃ ceramics, La_0.9Ba_0.1Er_1−x Mg _x O_3−α (x = 0.05, 0.10, 0.15, 0.20), were synthesized by solid-state reaction method and characterized by X-ray diffraction (XRD). The samples have a single orthorhombic perovskite-type structure. The conduction behavior was investigated using various electrochemical methods including AC impedance spectroscopy, gas concentration cell, isotope effect of hydrogen, and hydrogen electrochemical permeation (pumping) in the temperature range of 500–1000 °C. The results indicated that specimens were pure ionic conductors under low oxygen partial pressure (about 10⁻⁷–10⁻²⁰ atm) and mixed conductors of proton, oxide ion, and electron hole under high oxygen partial pressure (about 10⁻⁵–1 atm). The pure ion conduction of the ceramics in hydrogen atmosphere was confirmed by electromotive force method of hydrogen concentration cell, and the observed emf values coincided well with the theoretical ones. The conductivity in H₂O–Ar atmosphere was higher than that in D₂O–Ar atmosphere, exhibiting an obvious isotope effect and proton conduction in water vapor containing atmosphere. It has been confirmed by electrochemical hydrogen permeation (hydrogen pumping) experiment that the ceramics were mainly proton conductors in hydrogen containing atmosphere. Whereas in dry oxygen-containing atmosphere, observed emf values of the oxygen concentration cell were far lower than the theoretical ones, indicating that the ceramics were mixed conductors of electron hole and oxide ion.     

Nonequilibrium processes in Hg1−x CdxTe n +−p junctions in a magnetic field

The results of measurements of the relaxation and current-voltage characteristics of Hg_{1− x} Cd_xTen ⁺−p junctions in a magnetic field are presented. It is shown that the lifetime of the nonequilibrium electrons in the p-type region undergoes an increase in a magnetic field, which can be associated with the heterogeneous distribution of defects from the junction boundary. The current-voltage characteristics in a magnetic field exhibit suppression of the diffusion component of the current and an increase in the contribution of the generation-recombination channel, as well as the appearance of shunting channels, which are associated with the influence of the surface. Pis’ma Zh. Tekh. Fiz. 23, 88–94 (October 26, 1997)     

Investigation of strained InxGa1−x As/InP quantum wells fabricated by metalorganic compound hydride epitaxy

An investigation was made of the possibility of using reduced-pressure MOC hydride epitaxy to fabricate highly strained (compressive stress) In_xGa_1−x As/In_0.53Ga_0.47As quantum wells on indium phosphide (100) substrates. The photoluminescence properties of these heterostructures were investigated. It was shown that these heterostructures are potentially useful for laser diodes emitting in the 1.5–2 μm range, which is important for environmental monitoring. Pis’ma Zh. Tekh. Fiz. 24, 46–51 (November 26, 1998)     

Formation of optoelectronic structures based on InAsSb/InAsSbP solid solutions

An etchant having the composition HCl/CrO₃ /HF/H₂O is proposed for fabricating optoelectronic devices (lasers, light-emitting diodes, and photodiodes) based on InAs solid solutions for the 3–5 μm spectral range. It is shown that the proposed etchant ensures isotropic rates of etching of InAs and GaInAsSb, InAsSPbP, and InAsSb solid solutions of varying composition. An example is given of the use of this etchant to produce high-power light-emitting diodes for the 3.3 μm spectral range. Pis’ma Zh. Tekh. Fiz. 24, 27–33 (August 12, 1998)     

Superluminescence in an AlGaAsSb/InGaAsSb/AlGaAsSb double heterostructure

Intense electroluminescence is observed for the first time in a AlGaAsSb/In_0.9Ga_0.1As_0.89Sb_0.21/AlGaAsSb double heterostructure in the 3–4 μm wavelength range at T=77 K. The structure was grown on a GaSb substrate by liquid-phase epitaxy. The photon energy at the maximum of the narrow emission band with a half-width of 9–10 eV is hv=387 meV which is 60 meV greater than the band gap of the narrow-gap InGaAsSb solid solution (E _g =326 meV). This behavior is attributed to the population inversion characteristics of the active region when an external bias is applied Pis’ma Zh. Tekh. Fiz. 23, 68–74 (May 12, 1997)     

Determination of electron transport coefficients in argon from ignition curves of rf and combined low-pressure discharges

Ignition curves of rf and combined (rf+static electric field) low-pressure discharges are used to determine the electron drift velocity V _dr in the range E/p≈70−2000 V/(cm·Torr) and the ratio of the longitudinal diffusion coefficient to the electron mobility D _L /μ _e in the range E/p≈ 1−2000 V/(cm·Torr). Pis’ma Zh. Tekh. Fiz. 24, 49–55 (April 26, 1998)     

Annealing of aluminum-silicon-dioxide-silicon structures after α-particle bombardment

An investigation is made of the isochronous annealing of Al-SiO₂-Si structures in the temperature range 20–450 °C after bombardment with α-particles from a Cm²⁴⁴ radioisotope source. In this temperature range it is observed that the positive charge in the insulator falls below the initial values. The hypothesis is put forward that this effect may be the result of defect formation and structural rearrangements near the Si/SiO₂ interphase boundary during irradiation and annealing. Pis’ma Zh. Tekh. Fiz. 25, 59–62 (August 26, 1999)