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The annealing of radiation-induced defects in carbon nanotube bundles below room temperature has been investigated experimentally. Significant feature of this study is that electron irradiation (with an energy 1 MeV and fluence up to 1016 el/cm2) was carried out at liquid helium temperature. A detailed analysis of the resistance change over a wide temperature range (7–300 K) enables us to prove partial annealing of irradiation-induced defects at moderate temperatures. It is shown that such an annealing follows a first-order reaction in whole investigated temperature range. While at temperatures below 40 K, annealing is nonactivation, tunneling process; at higher temperatures (100 − 300 K) it becomes activated, with activation energy of ~ 0.05 eV. The value of discovered activation energy is close to the migration energy of interstitial carbon atom in graphite. Probably, observed annealing of radiation-induced defects in carbon nanotube bundles is also caused by the migration of interstitial carbon atoms between single nanotubes below room temperature.

In situ measurements of the resistance changes of carbon nanotube bundles irradiated by 60Co γ-quanta at room temperature are presented. The peculiarity of our study consists in providing the sample irradiation in a hermetic cell filled with different gases at atmosphere pressure. Here we demonstrate the results for irradiation in hydrogen, deuterium, helium and argon media. The obtained dependences of the resistance change versus irradiation dose in vacuum are presented, too. We have developed a novel two-stage mechanism, which implies defect introduction by energetic intermediate particles that are gas atoms. Preliminary calculations for Compton electrons (0.85 MeV) and atmospheric gas pressure show the high efficiency of this two-stage mechanism in comparison to conventional one-stage mechanism. It is shown that the defect introduction rate in the developed two-stage mechanism is strongly dependent on the gas atomic mass and coincides well with our experimental results.

The effect of radioactive irradiation on H2 sorption by bundles of single-wall carbon nanotubes (SWNTs) has been investigated in various gas media. The samples were irradiated with γ-quanta (1.2 MeV) of 60Co ((1.5–1.7) × 107 rad) radiation at room temperature in deuterium, nitrogen, and oxygen atmosphere (P = 1 atm), and in a vacuum. The processes of H2 sorption and desorption in the SWNT bundles were investigated before and after irradiation in the temperature interval 12–1270 K. It is found that irradiation in a gas environment has a significant effect both on the low-temperature H2 sorption induced by the weak physical interaction, and the chemical H2 sorption by the SWNT bundles. A phenomenological model has been proposed to explain the defect generation in carbon nanotubes irradiated in gas media.

Experimental data on the electroreflectance spectra of γ-irradiated epitaxial GaN films on sapphire are reported. The irradiation doses are 105−2 × 106 rad. The theoretical electroreflectance spectra calculated on the basis of a model of three types of transitions are in agreement with experimental data with reasonable accuracy. The energies and broadenings of the transitions derived in the context of the model give grounds to infer that, in the GaN films, there are internal stresses dependent on the γ-irradiation dose.

The role of hot carriers in enhancing the radiation resistance of GaAs solar cells has been investigated. The laser-pulse induced, short-circuit current response method was used to study solar cell degradation caused by radiation damage. Samples were subject to radiation doses in the range 1×10 14 –4×10 16 electron cm −2 and then probed with laser pulses with 7 ns duration and 3.7 eV energy. We have developed a non-stationary theory of minority carrier flow in the active region of the solar cell. The theory allows a description of the temporal evolution of the short-circuit current and the dependence on irradiation dose. The model agrees well with experimental results using a single fitting parameter. This parameter is the carrier capture cross-section of radiation center E5 in the p-region emitter of the solar cell. The value of the cross-section was determined to be 0.1×10 −12 cm 2 from the results under non-stationary condition. This is seven times lower than that deduced from the current–voltage characteristics in the dark for a similar solar cell. The difference can be explained by a strong reduction of capture cross-section with increased carrier energy. Our results suggest that the observed cross-section reduction is caused by carrier accumulation at energies comparable with the optical phonon energy.

The influence of radiation exposure in hydrogen atmosphere on the radial thermal expansion of single-walled carbon nanotubes and on their sorption of hydrogen is studied. The irradiation was carried out with cobalt-60 γ-rays (with an energy of 1.2 MeV and an irradiation dose of 1.5·107 rad) in the normal hydrogen atmosphere under pressure 1 atm and at temperature of 300 K. The sorption and desorption of hydrogen by samples of nanotubes were investigated over the temperature range 15–1170 K before and after irradiation. It was found that the irradiation of carbon nanotubes (CNTs) in hydrogen atmosphere leads to considerable increasing an amount of hydrogen sorbed by the sample. The irradiation in hydrogen atmosphere resulted in increasing absolute values of radial thermal expansion of CNTs bundles over the temperature range investigated (2–120 K). The effects of hydrogen physically and chemically sorbed in bundles of CNTs on the radial thermal expansion of the irradiated samples were distinguished.

The results of experimental study of radiation resistance of GaAs-based solar cells are presented. The solar cells were irradiated by 1 MeV electrons at room temperature with the fluence up to 4 × 10 16 electrons cm - 2 . The radiation influence on the dark current and short-circuit current under illumination was investigated both experimentally and theoretically. It is shown that the radiation-produced electron traps E5 and hole traps H1 are responsible for irradiation-induced degradation of such solar cells. The radiation tolerance of the basic parameters (the short-circuit current, the output power) of GaAs solar cells is primarily determined by the radiation damage in p-regions.

The energy relaxation rate for hot electrons in AlGaN/GaN heterostructures was measured over the temperature range 4.2-300 K. Samples grown on sapphire and 4H-SiC substrates were studied. The most important result is that the hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. In the case of sapphire substrate, the dissipation can be described by the emission of optical phonons with an energy of 90 meV and relaxation time of 25 fs. In the case of SiC substrate, both activation energy and relaxation time exceed the values characteristic of the electron-LO-phonon dissipation process.

We report on experimental and theoretical studies of low and high field transport in AlGaN/GaN two-dimensional electron gas (2DEG). Magnetotransport of 2DEG created as a result of polarization effects at the heterointerface has been studied. The velocity-electric field characteristics extracted from pulsed current–voltage measurements in AlGaN/GaN heterostructures are in good agreement with transport calculations up to fields as high as 100 kV/cm.

Results of measurements of thermal conductivity κ of bulk GaN crystals in the temperature interval 4.2-300K are reported. Experiments were performed on three types of GaN material: (i) single, high-pressure grown GaN crystals showing highly n-type conductivity, (ii) on bulk Mg doped GaN crystals with slightly p-type conductivity, (iii) on homoepitaxial GaN layer grown by hydride vapour phase epitaxy (HVPE) on bulk GaN crystal. For the n-GaN crystals, the record thermal conductivity value κ max is equal to 1600 W/m x K at T max = 45K, and κ ≅ 230 W/m K at 300K. It is suggested that for this crystal and for T ≥ T max the contribution of Umklapp phonon scattering processes dominate in the heat transport processes. A heavily Mg doped crystal and HVPE GaN layer on bulk GaN show much lower thermal conductivity in the whole applied temperature region. The temperature dependence of κ shows the importance of point defects (impurities, vacancies) in determination of the thermal resistance of GaN bulk crystals.

Results of measurements of thermal conductivity of bulk GaN crystals in the temperature interval 4.2 – 300 K are reported. Experiments were performed on two types of single GaN crystals grown under high-pressure: highly conducting n-type sample and on a highly resistive sample compensated by magnesium doping. For n-GaN crystals, the highest thermal conductivity kmax is equal to 1600 W/m K at Tmax ¼ 45 K; and k . 220 W/m K at 300 K. Our analysis indicates that for the best n-GaN crystal and for T $ Tmax; the contribution of Umklapp phonon scattering processes dominate whereas for other samples scattering of phonons by point mass defects represents the main contribution. The dependence of kðTÞ is used to reveal possible mechanisms of thermal resistance of GaN crystals at temperatures Tmax: Our thermal conductivity measurements yields Debye’s temperature uD < 400 K: q 2003 Elsevier Ltd. All rights reserved.

Room temperature current–voltage and noise measurements have been made before and after gamma irradiation on AlGaN/GaN high electron mobility transistors (HEMTs) grown on sapphire. The saturation current due to radiation-induced defects shows a nonlinear dependence on radiation dose. The deviation of the device parameters does not exceed 20% at highest radiation dose 109 Rad and the devices with larger gate lengths demonstrate a higher radiation hardness to the 60Co gamma rays. The noise spectra of devices after gamma irradiation follow the flicker noise (1/fγ) dependence with the exponent γ close to one. The Hooge parameter estimated for the HEMTs after gamma irradiation dose does not show a gate-bias dependence and increases by approximately three to five times at radiation dose 2 × 108 Rad. The analysis of noise spectra allowed to identify the major sources of noise generation in the investigated HEMT heterostructures.

Radiation effects are investigated in thin epitaxial films of the high-Tc superconductor (HTSC) YBa2Cu3O7−x irradiated by low doses of 1-MeV electrons. The maximum radiation dose (4×1016 electrons/cm2) is chosen from the condition that the defects formed as a result of electron–nucleus collisions cause a negligible lowering of the critical temperature of YBa2Cu3O7−x. Under this condition the main source of radiation effects in HTSC films can be processes involving excitation of the electronic subsystem of YBa2Cu3O7−x. When YBa2Cu3O7−x films are irradiated by doses of (1–4)×1016 electrons/cm2 their critical temperature Tc is observed to increase (in contrast to published reports of a decrease in Tc at irradiation doses greater than 1018 electrons/cm2) and then, after the irradiation has stopped, to relax over time to its original value. These effects are similar to those observed in the photoexcitation of the electronic subsystem of YBa2Cu3O7−x (photostimulated superconductivity). A decrease of the critica...

In presented study we investigate the influence of electron irradiation, with energy of incident electrons 1 MeV, on the electrical resistance of single-walled carbon nanotube bundles. Irradiation was performed at liquid helium temperature for the first time. To determine radiationinduced damages accumulation and its further thermal recovering, the samples resistance was in situ measured in wide temperature range (5 – 300 K). The results reveal radiation damage annealing at temperature ~ 200 K that we associate with formation of inter-tube links in the bundles.

Mechanisms of electron transport formation in 2D conducting channels of AlGaN/GaN heterostructures in extremely high electric fields at 4.2 K have been studied. Devices with a narrow constriction for the current flow demonstrate high-speed electron transport with an electron velocity of 6.8 × 107 cm/s. Such a velocity is more than two times higher than values reported for conventional semiconductors and about 15% smaller than the limit value predicted for GaN. Superior velocity is attained in the channel with considerable carrier reduction. The effect is related to a carrier runaway phenomenon. The results are in good agreement with theoretical predictions for GaN-based materials.

We report on the influence of low gamma irradiation (10^4 Gy) on the noise properties of individual carbon nanotube (CNT) field-effect transistors (FETs) with different gate configurations and two different dielectric layers, SiO2 and Al2O3. Before treatment, strong generation-recombination (GR) noise components are observed. These data are used to identify several charge traps related to dielectric layers of the FETs by determining their activation energy. Investigation of samples with a single SiO2 dielectric layer as well as with two dielectric layers allows us to separate traps for each of the two dielectric layers. We reveal that each charge trap level observed in the side gate operation splits into two levels in top gate operation due to a different potential profile along the CNT channel. After gamma irradiation, only reduced flicker noise is registered in the noise spectra, which indicates a decrease of the number of charge traps. The mobility, which is estimated to be larger than 2x10^4 cm2V-1s-1 at room temperature, decreases only slightly after radiation treatment demonstrating high radiation hardness of the CNTs. Finally, we study the influence of Schottky barriers at the metal-nanotube interface on the transport properties of FETs analyzing the behavior of the flicker noise component., 19 pages, 9 figures, 1 table, accepted for publication in "Nanotechnology" journal

We report experimental results for the changes in conductivity of single-wall carbon nanotube bundles when irradiated by Co-60 gamma-rays in various environments. In the current study the samples investigated were irradiated in hermetic cells, either evacuated (0.1 Pa) or filled with hydrogen or deuterium at atmospheric pressure. In situ measurements of the resistance change as a function of irradiation dose at room temperature are presented. It was found that, for all irradiation conditions, the normalized resistance versus irradiation dose demonstrates a logarithmic behaviour. A phenomenological model for the observed dependence is derived. The current-voltage characteristics of the irradiated samples were measured in the temperature range from 4.5 to 300 K using short (10 ns) electric pulses, and the results demonstrate a scaling behaviour. This scaling occurs in the universal coordinates that correspond to the Tomonaga-Luttinger liquid concept. Our results confirm the existence of the Tomonaga-Luttinger liquid phase up to room temperature in carbon nanotubes after gamma-irradiation to a dose of 5 x10(7) rad in vacuum, 1 : 7 x 10(7) rad in hydrogen and 1 : 24 x 10(8) rad in deuterium.

Novel test structures fabricated on the basis of Si nanowires are the ultimate building blocks for future nanoelectronics and biological sensor applications. These structures have to be stable in operation. However, a great many factors influence stability, especially in a nanowire channel. In this contribution, we report on the transport and noise properties of nanowires with different channel lengths. We applied small-dose gamma irradiation treatment of the samples to obtain more stable operation of the test device structures. The structures under study were fabricated on the basis of SOI wafers using nanoimprint technology. High-quality nanowires were obtained by chemical wet etching with low defect density. In spite of relatively large lengths of the channels from 2µm to 22 µm, we found that normalized current noise spectral density decreases as a function of 1/(L2 ) in the samples with lengths below 7µm. Such dependence is characteristic of the contact contribution to the noise properties.At the same time, in relatively long samples the behavior was changed to 1/L dependence, demonstrating the priority of channel noise. The latter dependence was also registered for samples with small lengths after gamma irradiation, reflecting the improvement effect of the irradiation due to stress relaxation in the contact regions as well as increased stability of the structures and decreased scattering in the structure characteristics (Figure 1).An analysis of the random telegraph signal noise component, recorded for samples with small length before gamma treatment and reduced level after this treatment, confirms the obtained results. This demonstrates the positive effect of irradiation on the stability and reliability of the structure parameters.

We demonstrate field-effect transistors (FETs) fabricated on the basis of individual carbon nanotubes (CNTs) with top- and side-gate configurations using two different dielectric layers, SiO2 and Al2O3. Transport properties of the FETs are investigated using noise spectroscopy before and after low-dose gamma irradiation treatment (106 rad). A strong generation-recombination (GR) noise component observed before the treatment is used to identify several charge traps of two dielectric layers by their activation energy. In spite of reduced flicker noise level after gamma irradiation, the GR noise component almost disappears in the spectra after treatment. This indicates the reduction in the number of charge traps. We study the influence of the Schottky barriers at the metal-nanotube interface on the properties of FETs by analyzing the flicker noise component and identified the regime where the contact contribution is negligible and the conductivity is determined by the properties of CNT material.

In presented experimental study, the single-walled carbon nanotube bundles were irradiated by 60Co γ - quanta with energies 1.2 MeV in hydrogen and deuterium media at room temperature. Investigation of hydrogen sorption/desorption was carried out for irradiated and unirradiated samples in wide temperature range from 12 to 1273 K. Comparison of obtained results denotes that hydrogen adsorption capacity depends on gas environment used during γ - irradiation treatment. Moreover, this dependence is different in various temperature ranges. Irradiation in deuterium improves physisorption (below 65 K) up to 3.6 times. While irradiation in hydrogen medium improves chemsorption (above 673 K) up to 12.8 times in comparison with unirradiated sample. Single-walled carbon nanotubes are able to store hydrogen in temperatures from 70 to 500 K. Also, γ - irradiation in hydrogen and deuterium media enhance the amount of chemisorbed hydrogen even at gas loading pressure of 1 bar.

The transport properties of Si nanowire (NW) structures fabricated on the basis of silicon on insulator (SOI) wafers were studied using noise spectroscopy before and after treatment with small doses of gamma radiation. The total resistance obtained from the I-V characteristics of Si NW structures scaled perfectly with length. Normalized flicker noise demonstrated 1/L2 dependence, which is a characteristic of dominant noise contribution from near-contact regions. The behavior changed to 1/L dependence after a small dose (1×104 Gy) of gamma radiation treatment. Comparison of the random telegraph signal (RTS) noise parameters in the samples with small lengths before and after the treatment revealed a decrease in RTS amplitude and a shift to a lower frequency range after gamma irradiation. These results confirmed that the main changes in the samples were related to strain relaxation near-contact regions. In addition, such treatment resulted in a considerable decrease in the scattering data of device parameters.

We report on experimental studies of high-field electron transport in AlGaN/GaN two-dimensional electron gas. The velocity-electric field characteristics are extracted from 10 to 30 ns pulsed current-voltage measurements for 4.2 and 300 K. An electron drift velocity as high as 1.7x10(7) cm/s was obtained in the fields 150 kV/cm. Estimates of thermal budget of the system show that overheating of the electrons exceeds 1700 K at highest electric fields achieved in the experiment. (C) 2004 American Institute of Physics.

The conductivity of bundles of carbon single-walled nanotubes with metallic conductivity (metallic nanotubes) is investigated over the wide temperature range 4.2-330 K and electrical fields up to 50 V. The usage of short electrical pulses of the duration of 10 ns allowed to avoid an influence of a self-heating of the investigated structures on current-voltage characteristics. It is shown that the temperature dependence of conductivity is described by the power function G proportional to T(alpha). At helium temperatures the asymptotic dependence of current on applied voltage is close to J proportional to V(1+alpha) with alpha = 0.45. From comparison of the obtained results of measurements with calculations, it is shown that the conductivity of nanotube bundles is well described within the theory of the Luttinger-liquid conductivity for one-dimensional conductors. The self-heating of the carbon nanotube bundles was observed in the case of measurements in the regime of dc current. A method for determination of the self-heating temperature of nanotube bundles as a function of an applied electrical field is proposed. The power dependence of the self-heating temperature on voltage T proportional to V(p) with the exponent p = 2.1 was observed above some threshold voltage in the temperature range 4.2-200 K. Above 200 K the exponent decreased down to p = 1.35. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3662331] Simultaneous publication in Fizika Nizkikh Temperatur, volume 37, issue 8, pages 892-902 (2011).

In recent years, considerable attention has been focused on studies on the influence of gamma radiation treatments on the performance of semiconductor materials and devices, which are very important for spacecraft applications. Among the different objects studied, carbon-nanotube-based (CNT) structures are considered promising due to their unique properties. There are a number of publications concerning their microwave applications. For example, a single-electron transistor can be used as a highly sensitive electrometer based on the sequential tunneling of electrons in the Coulomb blockade regime [1]. In this article, the authors reported on their investigation of radio-frequency single-electron transistor (rf-SET) operation of single-walled CNT quantum dots in the strong tunneling regime. They reached a charge sensitivity of 2.3×10−6e/Hz1/2 over a bandwidth of 85 MHz at a temperature of 4.2K and a carrier frequency of 754.2 MHz. These results indicate a gain-bandwidth product of 3.7×1013 Hz(3/2)/e, which is one order of magnitude better than for conventional rf-SETs.

Single-walled carbon nanotube field-effect transistors (CNT-FETs) were characterized before and after gamma radiation treatment using noise spectroscopy. The results obtained demonstrate that in long channel CNT-FETs with a length of 10 mu m the contribution of contact regions can be neglected. Moreover, radiation treatment with doses of 1x10(6) and 2x10(6) rad allows a considerable decrease parallel to the nanotube parasitic conductivity and even the shift region with maximal conductivity to the voltage range of nearly zero gate voltage that improves the working point of the FETs. The Hooge parameters obtained before and after gamma radiation treatment with a dose of 1x10(6) rad are found to be about 5x10(-3). The parameters are comparable with typical values for conventional semiconductors.

I–U characteristics of n-Ge:Sb samples with impurity concentrations of Nd = 2 × 1016 cm−3 are of S-shape at the temperature of liquid He. The depth of the NDC-region increases with lowering the temperature and with application of uniaxial stress along the 〈111〉 direction. This fact is explained within the framework of the “three-level” mechanism of the impurity breakdown. Nonequilibrium ballistic phonons ionise excited states of impurity atoms abundantly populated in pre-breakdown fields, and cause the development of breakdown, that approves the model discussed. [Russian Text Ingore].

The propagation of beams of acoustic phonons generated by photoexcitation in a single highly conductive n-type gallium nitride crystal with the c-axis perpendicular to the surface was studied. Diffusive propagation of phonon beams was observed. Estimations of contributions of two main kinds of phonon scatterers, i.e. Ga vacancies and free carriers, show that the latter are responsible for the forming of the diffusive pulses. This conclusion is supported by the results of comparison of propagation of phonon pulses in specimen with the bare surface and with the condensed 4He film on it.

The effect of a small dose of gamma irradiation on transport characteristics of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures was investigated. It is shown that the carrier concentration remains practically unchanged after an irradiation dose of 10(6) rad, while the 2DEG mobility exhibits a considerable increase. The results are explained within a model that takes into account the relaxation of elastic strains and structural-impurity ordering occurring in the barrier layer under irradiation. (C) 2008 American Institute of Physics.

The maximal value of thermal conductivity \kappa_{max} of the perfect wurzite GaN crystal containing isotopes of natural abundance is estimated. Our upper limit of \kappa=4800 W/Km at T_{max}=32 K is smaller than calculated by Liu and Balandin \kappa=6000 W/Km and higher than obtained by Slack et al \kappa=3750 W/Km. The phenomenological dependence \kappa \propto T^{-1.43} obtained by Mion et al for the temperature interval 300-450 K is extended to 200-300K. For temperatures higher than T_max the best fitting of our experimental data to Callaway's formula is obtained for Grueneisen's constant equal to \gamma = 1.35., Comment: 7 pages, 3 figures

Here we report the results of an experimental study of the thermal conductivity of GaN crystals doped by oxygen with concentrations of 4 × 1016, 2.6 × 1018 and 1.1 × 1020 cm−3, carried out in the temperature interval 7–318 K. We observed the highest thermal conductivity ever reported for GaN, 269 Wm–1 K–1 at 300 K, in the sample with the lowest oxygen content. This result is explained by the renormalization of GaN elastic constants, caused by the effect of spontaneous polarization. Results were analyzed using the Callaway model. The contribution of phonon scattering by free carriers in doped GaN crystals was considered for the first time. We show that free electrons reduce the thermal conductivity by up to 32%–42% at 300 K for a sample with a 1.1 × 1020 cm−3 of oxygen concentration.

We report on lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range 20-300 K and by the adiabatic method in the range 5-70 K. We fit the experimental data using two temperatures model. The best fit with the accuracy of 3 % was obtained for the temperature independent Debye's temperature $\theta_{\rm D}=365$ {\rm K} and Einstein's temperature $\theta_{\rm E}=880$ {\rm K}. We relate these temperatures to the function of density of states. Using our results for heat conduction coefficient, we established in temperature range 10-100 K the explicit dependence of the phonon mean free path on temperature $\it{l}_{\rm ph}\propto T^{-2}$. Above 100 K, there is the evidence of contribution of the Umklapp processes which limit phonon free path at high temepratures. For phonons with energy $k_{\rm B}\times 300 $ {\rm K} the mean free path is of the order 100 {\rm nm}, Comment: 5 pages, 4 figures

Experimental results on high electric field transport of 2DEG in GaN/AlGaN heterostructures are presented. Used time resolution of 0.1ns allows observing new peculiarities in the high field current flow that are shown and discussed.

In this paper, we presented results of steady state and pulse measurement of AlGaN/GaN heterostructures up to ultra high electric fields accompanied by low frequency noise measurements. Hot electron relaxation process were analysed. The contact resistance was measured in low field (ohmic) region and taken into account when calculating the average electric field. The velocity-field characteristics in AlGaN/GaN heterostructures obtained by measurement of the current-voltage characteristics. The spectra of the normalised current noise for different values of electric field E measured at T=300 K for the device with channel length of 25 /spl mu/m and width of 100 /spl mu/m is studied through experimental results.

A superconducting metallic film bolometer in contact with thermal bath of temperature T 0 , is biased by a (i) constant current I b , or by (ii) the constant voltage U b . The absorption of the time-dependent power of a phonon beam W(t) elevates temperature of the film to T(t) > To. The thermal contact of the bolometer with the environment is characterized by the thermal conductance G, and it depends on [T n (t) - T n 0] (n = 4-6). For both above methods of bias, we derive ordinary nonautonomous nonlinear differential equations of the first order. These equations are numerically solved. The knowledge of W(t) allows one to calculate (i) U b (t) or (ii) I b (t). The inverse problem of calculation of W(t) from known (i) U b (t) or (ii) I b (t) is also solved. Using W(t) calculated in computer experiments, we obtained the bolometer signal, and compared it with results of real experiments performed on GaAs in which I b is fixed, and U is measured. Comparison of calculated results with results obtained for the linearized model shows that the nonlinearity is essential for the correct description of metallic superconducting film bolometer response.

Effect of small dose gamma-irradiation on electrical characteristics of AlGaN/GaN high electron mobility transistors has been investigated. Decreasing of the leakage current and its noise has been registered after dose of 1×106 Rad. As-grown heterostructures used in further for the device fabrication have been examined after the same radiation treatment. The small dose radiation results are explained within a model that takes into account relaxation of elastic strains and structural-impurity ordering occurring in the barrier layer under irradiation.

The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent with theoretical prediction.

High-quality Si nanowire field effect transistors (FETs) were fabricated using thermal nanoimprint and chemical wet etching technologies. FET structures of different lengths demonstrate high carrier mobility with values of about 750 cm2/Vs and low volume densities of active traps in the dielectric layers of 5 × 1017 cm−3 eV−1. We investigated the transport properties of these n-type channel structures using low-frequency noise spectroscopy before and after gamma radiation treatment. Before gamma irradiation, FET structures with lengths of less than 4 μm exhibited noise from contact regions with 1/(L2) dependence for the relative 1/f noise. After gamma radiation, the spectra reflected the priority of channel noise with 1/L dependence for all samples. The transport characteristics show that the fabricated nanowire FETs improved scalability, decreased parameter scattering, and increased stability after treatment. The results demonstrate that these nanowire FETs are promising for nanoelectronic and biosensor applications due to the cost-efficient technology and advanced performance of FETs with improved stability and reliability.

High-quality silicon nanowire (NW) field-effect transistors (FETs) were designed and fabricated. Features of transport and modulation phenomena of the structures were studied using a number of techniques, including noise spectroscopy. Using the 1/f noise component level, the values of the volume trap densities in gate dielectric are estimated to be around 1 × 1017 cm−3 eV−1. This result proves high quality of the investigated structures. Analysis of Lorentzian noise components of NW samples is used to characterize single trap and its parameters. A strong modulation of carrier concentration in the conducting channel under influence of even single carrier capture event has been revealed. Possibility of fine tuning of the transport properties of the sample with low-dose gamma irradiation has been shown. The gamma radiation treatment of the NW samples was applied as an effective technique to confirm the strong influence of trap charges on conductivity behavior in the channel of NW FETs. The results demonstrate that the modulation effects at the nanoscale enable effective changing of the channel conductivity by single capture events and thus are promising for future information technologies and ultra-sensitive single-molecular sensor applications.

We have measured thermal conductivity, κ, in the wide temperature range 4– 300 K of GaN bulk single crystals grown by high-pressure, high-temperature synthesis. Obtained results ( 1600 W/Km at 45 K ) are the highest κ values reported on GaN material. At the room temperature κ is about 210 W/Km . The contributions to the GaN thermal resistance of Umklapp process, mass point defects as well as phonon scattering on dislocations and sample boundary are discussed.

We propose and demonstrate a coding-decoding procedure as an important step to realize one more Si-based photonic device. Low-fluence (

A number of experiments uses optically excited electron system of the crystal as a source of nonequilibrium phonons. Wide set of these was carried out on GaAs (see [1,2]). The frequencies of the initial acoustic phonons, generated by excited carriers or via fast intermediate stage of optical phonon creation, are up to the boundary acoustic ones. The propagation of these phonons has a complicated character, as they have short mean free paths due both to isotope scattering and anharmonic processes. Thus, there is a problem to calculate the time shapes of registered phonon pulses.

The conductance and the current-voltage characteristics of metallic single wall carbon nanotube bundles have been measured between 4.2 and 330 K using 10–30 ns electric pulses to avoid overheating. The current-voltage characteristics at different temperatures collapse to a single curve when plotted in the specific coordinates following from the Tomonaga–Luttinger (T–L) liquid concept. Direct evidence is obtained for the existence of a T–L liquid phase up to 190 K and the system shows a transition between the T–L liquid state and a Mott insulating phase below 25 K.

The propagation of acoustic phonons in GaAs generated by laser radiation of a clean as well as Au coated surface are experimentally investigated in dependence on the crystallographic orientation. The angular dependence of the T1 phonon spectrum is confirmed by comparison with the calculated focussing factor. Besides the ballistic motion of modes of L, T1, and T2 polarization a further peak is observed in the time of flight spectra, which is interpreted by repeated conversion and decay processes of high-frequency phonons leading to T2 modes with a frequency low enough for ballistic motion. [Russian Text Ignored]

Currently, there is a great interest in in situ superconducting materials in which the dispersive superconducting current paths in a normal matrix are created by physical-chemical processes that occur naturally in certain alloys, rather than by the more common “forced” method, which is used in multifilamentary composite materials.

In this work we present steady-state characteristics and low-frequency noise spectra of AlGaN/GaN based high electron mobility transistors (HEMTs) exposed to gamma ray radiation. The devices with a variety of gate length (150-350 nm) and width (100-400 νm) were irradiated by 60Co gamma rays with doses in the range of 104-109 Rad and flux of 102 Rad/s. Dose dependencies of basic operating parameters of the transistors, such as saturation current (Isat), transconductance (gm), channel conductance (gc), and threshold voltage (VT) are analysed. Our study show that visible changes of above mentioned parameters are observed under relatively small doses (105 Rad) and strongly depend on the HEMT's topology. The transconductance decreases and threshold voltage becomes more negative for all devices while deviation of these parameters from its initial values does not exceed 20% at highest irradiation dose. At the same time variation of the channel conductance as well as saturation current depends to a high extent on the gate voltage (Vg). At |Vg| < |Vcr|, both Isat and gc show a reversal proportional to the cumulative dosage of radiation. However, at |Vg| > |Vcr|, drain saturation current and channel conductance increase with the cumulative dosage of radiation. The effect is more pronounced in short-length-gate devices.

This is a study of the low temperature kinetics of the sorption and subsequent desorption of 3He, 4He, H2, D2, Ne, and N2 by bundles of single-wall carbon nanotubes with closed ends (c-SWNT). The characteristic times of the sorption and desorption processes are the same to within the experimental error. Annealing a sample of bundles at 500 °C greatly reduces the characteristic times and changes their temperature dependences. The effect of annealing decreased with increasing molecular weight of the dissolved gas. At temperatures below 16 K the sorption times for 3He, 4He, H2, and D2 depends weakly on temperature, which suggests a tunnel character of the sorption for these impurities by nanotube bundles. The effect of γ-irradiation of nanotube bundles on the sorption and desorption of hydrogen is qualitatively similar to the effect of annealing.