Infrared laser (λ=3.2 μm) based on broken-gap type II heterojunctions with improved temperature characteristics

Laser structures based on broken-gap type II p-GaInAsSb/n-InGaAsSb heterojunctions in the active region are proposed and studied. Lasing at 3.2–3.4 μm has been obtained in the temperature range 77–195 K with a threshold current density of 400 A/cm² at 77 K and a characteristic temperature T₀=47 K. Pis’ma Zh. Tekh. Fiz. 23, 55–60 (February 26, 1997)     

Observation of a negative characteristic temperature for the threshold current of diode lasers for the 2.8 /gmm spectral range

A decrease in the lasing threshold with increasing temperature has been observed in InAs/InAsSbP laser heterostructures for the 2.7–2.9 μm spectral range at cryogenic temperatures (T=32–85 K). At temperatures below 50 K a negative characteristic temperature, T ₀=−70 K, was obtained for the threshold current. Characteristics of the temperature dependence of the threshold current and the laser output power were investigated. Pis#x2019;ma Zh. Tekh. Fiz. 23, 72–79 (November 26, 1997)     

p-GaSe-n-Ga2S3 heterojunctions

Epitaxial layers of n-Ga₂S₃ have been grown on p-GaSe single crystals annealed in sulfur vapor. The possibility of fabricating p-GaSe-n-Ga₂S₃ heterojunctions is demonstrated. Pis’ma Zh. Tekh. Fiz. 23, 22–24 (May 26, 1997)     

Application of a nuclear quadrupole resonance method to measure stress in a matrix-tracer system in composites

A quantitative correlation has been established between the shift of the nuclear quadrupole resonance frequency of the tracer and the stress in a matrix-tracer system in composites. Measurements are made of the ⁶³Cu resonance frequencies in samples of epoxy resin containing cuprous oxide powder. The stresses in the resin and their dependences on temperature and external pressure are determined. Pis’ma Zh. Tekh. Fiz. 23, 14–18 (April 12, 1997)     

Dependence of the empirical model parameters of the surface resistance of a high-temperature superconducting film on the parameters of the technological process

The dependence of the surface resistance on the substrate heater temperature has been investigated for the purpose of optimizing the conditions for preparing YBa₂Cu₃O_7−δ films. It is shown that the resistance R _sur is highly sensitive to the accuracy of maintaining the substrate holder temperature to minimize the surface resistance of the films and maximize the parameter γ, which determines the temperature-dependent curves σ(t) and λ_L(t). Pis’ma Zh. Tekh. Fiz. 23, 79–84 (August 12, 1997)     

Low temperature synthesis and magneto- electrical studies in Nd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> system

The system Nd_{1 − x}Pb_xMnO₃ with x ≤ 0.50 has been synthesized by citrate-gel route. All these samples have shown single phase structure with cubic symmetry. Magnetic and electrical behavior has been studied in the temperature range 4–300 K. The temperature dependent resistivity data shows that metal-semiconductor transitions occurs at temperature T_P∼ 166, 174 and 182 K for x = 0.30, 0.40 and 0.50 respectively. Under the field of 1 T, this transition shifts to higher temperature. These samples have shown maximum MR upto 40% under the field of 1 T at temperature lower than T_P. These results are supported by magnetic measurements over the observed temperature range. Resistivity data above T_P has been found to fit well with Tⁿ where n = −1/4 for x = 0.30 and n = −1/2 for x = 0.50 which is attributed to the variable range hopping of small polarons.     

Carrier transport in a diode base with locally nonuniform recombination properties

Nonuniformity of the recombination properties in the form of a layer of radiation defects is created in the base of a p ⁺−n diode. The change in the effective hole lifetime, measured by an injection-extraction method, is investigated and attributed to recombination in this layer. Pis’ma Zh. Tekh. Fiz. 23, 79–86 (May 12, 1997)     

Investigation of the thermal stability of picosecond gallium arsenide dynistor switches

The operation of GaAs n⁺-p-i-n ⁰-p ⁺ dynistor structures has been demonstrated experimentally under conditions of reversible avalanche breakdown at temperatures up to 200 °C with switching times remaining under 140 ps. A numerical simulation refined the influence of various parameters of the semiconductor on the temperature dependence of the switching characteristics. Pis’ma Zh. Tekh. Fiz. 24, 73–78 (August 12, 1998)     

Direct bonding of silicon wafers with a diffusion layer

The possibility of solid-phase direct bonding of silicon wafers having p ⁺-or n ⁺-type diffusion layers with a high surface dopant concentration has been demonstrated for the first time. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (March 26, 1998)     

Precipitation of mobile copper from Cu2−x Se samples under impact loading

It has been found that the rate of copper precipitation from samples of the superionic conductor copper selenide, Cu_2−x Se, exposed to impact loading is substantially higher than that under static pressure. This effect is attributed to the action of excess pressures and temperatures at crystal grain boundaries during the plastic deformation of the samples under impact. Pis’ma Zh. Tekh. Fiz. 23, 65–69 (March 12, 1997)     

Structural and electrical measurements of CdZnSe composite

TheI—Vcharacterization and the electrical resistivity of selenium rich Se₈₅Cd_15-xZn_x (x = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be poly crystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements ofI—V bdcharacteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 x 10⁸ Ωm and minimum 7.3 x 10⁵ Ωm and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.     

Galvanomagnetic properties of plastically deformed InSb single crystals

The dc Hall effect, dc conductivity and mobility have been studied on deformed and undeformed samples ofn-type InSb from liquid nitrogen temperature to room temperature. These studies have shown that the Hall coefficient values of deformed samples do not differ much from undeformed sample, but a considerable amount of change was observed in mobility, suggesting that equal number of donor and acceptor type dislocations are introduced during the deformation process. In addition the mobility variation of the deformed samples with temperature has shown a peak in 170–300°K range. The dislocation mobility (μ _D) is deduced from the observed mobilities of deformed and undeformed samples. The plotμ _D vs T has two regions, region 1 being independent of temperature and region 2 having a linear increase with temperature. Theβ factor obtained from region 2 is found to be almost equal to the one calculated from Dexter and Seitz model. The dislocation densities at room temperature are also calculated for the deformed samples using the above model.     

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)     

Life prediction of a Ni-base superalloy

Rene 80 samples were creep–rupture tested in air between 1144 and 1255 K at various stress levels. The mean stress exponent, n, and the mean activation energy for creep were calculated from the experimental results. The accelerated creep life of the alloy was evaluated by using iso-stress parametric equations and Monkman–Grant method.     

Electrical properties of Schottky diodes based on Carbazole

Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density versus voltage (J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region space charge limited conduction (SCLC) is observed. Number of states in the valence band (Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density (Nt) and activation energy are determined. The values of Nv and Nt are in the order 10²³ m⁻³ and 10²⁷ m⁻³ respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10⁻⁷ cm² V⁻¹ S⁻¹. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕb), diode ideality factor (n) and saturation current density (J₀) are determined. The value of n increases and ϕb decreases on annealing.     

Dynamic Remanent Vortices in Superfluid 3He-B

We investigate the decay of vortices in a rotating cylindrical sample of ³He-B, after rotation has been stopped. With decreasing temperature vortex annihilation slows down as the damping in vortex motion, the mutual friction dissipation α(T), decreases almost exponentially. Remanent vortices then survive for increasingly long periods, while they move towards annihilation in zero applied flow. After a waiting period Δt at zero flow, rotation is reapplied and the remnants evolve to rectilinear vortices. By counting these lines, we measure at temperatures above the transition to turbulence ∼0.6 T _c the number of remnants as a function of α(T) and Δt. At temperatures below the transition to turbulence T≲0.55 T _c, remnants expanding in applied flow become unstable and generate in a turbulent burst the equilibrium number of vortices. Here we measure the onset temperature T _on of turbulence as a function of Δt, applied flow velocity v=v _n−v _s, and length of sample L.     

Influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures

Results of an investigation of the influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures are presented for the first time. It is shown that nickel impurities in the silicon increase the total strain sensitivity n-Si〈Ni〉 structures. Pis’ma Zh. Tekh. Fiz. 23, 62–64 (May 12, 1997)     

Doping of Bi-Sr-Ca-Cu-O superconductors with Pb,Sn and Ag

Basic and substituted superconductors in the homologous series Bi₂Sr₂Ca _n−1Cu _n O_2n+4+y , Bi_2−x/2Sr_2−x/2L _x Ca _n−1Cu _n O_2n+4+y and Bi₂Sr_2−x L _x Ca _n−1Cu _n O_2n+4+y (L=Sn, Pb or Ag,x=0−0.4,n=2, 3 or 4) have been synthesized. All the prepared ceramic samples show superconducting behaviour with zero resistance atT _c=70 to 85 K. The compounds withn=3 or 4 showed onset temperature around 115K indicating involvement of a disproportionate solid-state reaction and formation of a two-phase system. The phase involving tin or lead oxides showed similar superconducting properties. Final rapid quenching of samples contributed to preservation of the high temperature equilibria with higher solubility of tin oxide in the quaternary system Bi-Sr-Ca-Cu-O. Silver was not soluble but precipitated in a colloidal form at interfaces between the crystalline grains.     

Influence of heat treatment conditions on the phase composition and superconducting properties of Bi1.6Pb0.4Sr1.98K0.02Ca2Cu3F0.8Oy ceramic

The influence of synthesis temperature and time on the properties and formation of superconducting phases in Bi_1.6Pb_0.4Sr_1.98K_0.02Ca₂Cu₃F_0.8O_y samples has been studied by x-ray phase analysis and by measuring the electrical resistance. It is found that the ratio of the 2223 and 2212 phases formed during synthesis at 845 °C for 240 h remains almost constant in the range 845–855 °C, regardless of the additional synthesis time. Synthesis at higher temperatures leads to breakdown of the 2223 phase and enhances the content of the 2212 phase and impurity phases. The highest values T _c(R=0)=112.8 K were obtained for samples synthesized at 845 °C for 240 h. Pis’ma Zh. Tekh. Fiz. 23, 30–34 (July 26, 1997)     

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)