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The strong effect of weak interband illumination on tunneling transport in doped GaAs/AlAs superlattices was found under conditions of electric domain formation. The photoresponse at voltages below the threshold one (before the domain formation) did not observe. The phenomenon is referred to strong carrier depletion inside the triangular high-field domain. The domain modes transformations under the illumination were also found. [ABSTRACT FROM AUTHOR]

Abstract—The tunneling electron transport in GaAs/AlAs and InAs/AlSb superlattices with electric domains at room temperature is studied. At voltages above the threshold for the formation of domains, a series of maxima on the current–voltage characteristics, almost equidistant in voltage, and current hysteresis during direct and reverse voltage sweeps were found. An explanation is proposed relating the origin of these maxima to tunnel transitions between quantum wells in a triangular domain, assisted by the emission of optical phonons, and hysteresis with a transition between modes with a moving and static domain. The large asymmetry of the transition times between domain modes was found. [ABSTRACT FROM AUTHOR]

The conductivity of epitaxial diamond films lightly doped with boron has been studied at strong electric fields up to ~5 × 105 V/ cm. It is shown that field ionization of boron acceptors in diamond at room temperature, because of the low concentration of free holes and the high binding energy of boron, occurs due to the Frenkel–Poole effect. [ABSTRACT FROM AUTHOR]

(m-i-p)-Structures with high-resistance epitaxial i-layers are fabricated on heavily doped p+-type substrates with platinum contacts. The structures are studied using several methods: optical and electron microscopy and luminescence, and electrophysical (C-V and I-V characteristics) methods and tested as detectors of ionizing radiation. It is shown that the (m-i-p)-structures are promising for development of several electronic devices (high-voltage diodes, detectors of ionizing radiation, and photovoltaic devices). [ABSTRACT FROM AUTHOR]

Electronic transport in short-period GaAs/AlAs superlattices with resonant cavities was studied at room temperature. The evolution of tunneling current at forward and backward bias sweep was investigated. The step-like decrease in current at some threshold voltage was referred to moving domain formation. The current hysteresis observed in current-voltage characteristics was explained by changes in electrical domain regimes. The series of maxima in the current-voltage characteristics was attributed to resonant tunneling of electrons through several barriers inside the domain. The change of threshold voltage for the domain formation at the change of the cavity parameters explained by the excitation of high-amplitude oscillations in the cavity which demonstrated the possibility to excite oscillations in the THz cavity by dynamical negative resistance of SLs with domains. [ABSTRACT FROM AUTHOR]

The series of almost voltage-periodic maxima found earlier in current–voltage characteristics of InAs/AlSb superlattices (SLs) at the voltage range of domain formation is studied. These oscillations are examined in InAs/AlSb SLs with different quantum well (QW) widths. It is found that the periodic changes of current in SLs with wide QW widths are caused by jumps of domain boundary between adjacent QWs. The considerably larger oscillation periods in narrow-QW SLs are supposed to be the result of considerable increase in the peak electric field inside the triangular domain which makes possible optical phonon-assisted tunneling between neighboring QWs. [ABSTRACT FROM AUTHOR]

A simplified theoretical description of electrical instability under thermal injection in multibarrier heterostructures is given in terms of internal positive feedback in each elementary unit of the hetero-object. In the simplest case, which is a sequence of equally high heterobarriers, a pair of neighboring wide- and narrow-gap layers is taken for an elementary unit. Analytical dependences of the current and voltage in the structure on the electron temperature at the injecting boundary of the heterobarrier and the respective bistable I- V characteristics are derived. A typical I- V characteristic with a clear-cut negative resistance region is demonstrated. It is taken in quasi-static electrical measurements made on 12-μm test multibarrier GaAs/AlGaAs mesas. [ABSTRACT FROM AUTHOR]

Through mathematical modeling of the conductivity of multibarrier heterostructures, the steady-state current-voltage characteristics, the S-shaped behavior of which is indicative of electrical instability, are obtained. To study its dynamic parameters, an analytical model of instability is developed using known approximations of the physics of semiconductor devices. In the steady-state case, the model yields an S-shaped current-voltage characteristic close to numerical simulation results. This fact is considered as confirmation of the adequacy of the developed analytical model. In the small-signal case, the latter is generalized to the situation with harmonic electrical perturbation. The resulting formula for the frequency dependence of the small-signal impedance indicates the possibility of dynamic-resistance negativity up to terahertz frequencies. A clear physical interpretation of the instability in terms of positive feedback in the unit cell of the multibarrier heterostructures under study is proposed. The results of measurements of the quasi-stead-state current-voltage characteristics of fabricated test multibarrier GaAs/AlGaAs structures with a pronounced portion of negative differential resistance are also presented. [ABSTRACT FROM AUTHOR]

In contrast to the abundance of systems-oriented approaches describing changes on the transcriptome or proteome level, relatively few studies have employed the metabolome. The goal of the presented research was to identify as many intracellular metabolites as possible in a Spiroplasma melliferum extract by flow injection time-of-flight mass spectrometry. The Mollicutes class bacterium S. melliferum is a member of a unique category of bacteria that have in common the absence of a cell wall, a reduced genome, and simplified metabolic pathways. Metabolite identification was confirmed by fragmentation of previously detected ions by target mass spectrometry. The selected liquid chromatography approach, hydrophilic interaction chromatography with amino and silica columns, effectively separates highly polar cellular metabolites prior to their detection on a high accuracy mass spectrometer in positive and negative acquisition mode for each column. Here we present reliable measurement of 76 metabolites, including components of sugar, amino acid, and nucleotide metabolism. We have identified about a third of the possible intracellular S. melliferum metabolites predicted by genome annotation. [ABSTRACT FROM AUTHOR]

The miniband conductivity in short-period GaAs/AlAs superlattices with a terahertz cavity has been studied. A stepwise decrease in the current caused by the formation of the electrical domains has been observed in current-voltage characteristics at a certain threshold voltage. It has been found that this threshold voltage changes considerably under the variation of the cavity parameters. The shift of the threshold has been explained by the excitation of high-amplitude oscillations in the cavity. [ABSTRACT FROM AUTHOR]

Results of an electrooptical study of a water solution of carbon nanotubes obtained using the catalytic method are presented. It is shown that nanotubes, which anisotropically absorb light, are oriented in an electric field and create a pronounced linear electric dichroism due to light absorption, rather than light scattering (as in the case of colloids with particles with sizes close to that of nanotubes). An analysis of the relaxation dependences of the electric dichroism shows that nanotubes deform, which are oriented in the electric field; in this case, the deformation sublinearly depends on the field amplitude and reaches a limiting value. The relaxation dependence of the field-induced dichroism agrees with the autocorrelation function of depolarized light scattered perpendicular to the incident light flux. [ABSTRACT FROM AUTHOR]

The stimulated emission spectrum of uniaxially strained p-Ge is presented. The energy spectrum of the states of a shallow acceptor in Ge under uniaxial compression is calculated. The threshold pressure at which the acceptor state split off from the ground state becomes resonant is found. The pressure dependence of the width of this resonant level is calculated. The stimulated emission lines are identified. In particular, it is shown that the principal emission peak corresponds to the transition of holes from the resonant 1s(1s[sub r]) state to the local p[sub ±1] state. The probabilities of optical transitions are calculated. A mechanism of population inversion due to the intense resonant scattering of hot holes with an energy corresponding to the position of the 1s[sub r] level is proposed. © 1999 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Vertical transport in short-period InAs/AlSb superlattices with type-II heterojunctions is studied at room temperature. It is found that negative differential conductivity appears in the miniband-conduction mode upon the overlapping of quantum-confined states in a periodic system of quantum wells. In the nonresonant-tunneling mode, equidistant peaks appear on the current-voltage characteristic of these superlattices. These peaks are attributed to the influence of the optical cavity on optical electron transitions in quantum wells (Purcell effect). [ABSTRACT FROM AUTHOR]

Far-infrared radiation from hot holes in Ge under streaming conditions is investigated. Stimulated emission is observed from uniaxially compressed samples without magnetic field. The existence of inversion is due to a strain splitting of the light and heavy hole bands. [ABSTRACT FROM AUTHOR]