Thermal annealing behaviour on electrical properties of Pd/Ru Schottky contacts on n-type GaN

We have investigated the electrical properties of Pd/Ru Schottky contacts on n-GaN as a function of annealing temperature by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The Schottky barrier height of the as-deposited Pd/Ru contact is found to be 0.67 eV (I-V) and 0.79 eV (C-V), respectively. Measurements showed that the Schottky barrier height increased from 0.68 eV (I-V) and 0.80 eV (C-V) to 0.80 eV (I-V) and 0.96 eV (C-V) as the annealing temperature is varied from 200 °C to 300 °C. Upon annealing at 400 °C and 500 °C, the Schottky barrier height decreased to 0.73 eV (I-V) and 0.85 eV (C-V) and 0.72 eV (I-V) and 0.84 eV (C-V), respectively. It is noted that the barrier height further decreased to 0.59 eV (I-V) and 0.72 eV (C-V) when the contact is annealed at 600 °C. The change of Schottky barrier heights and ideality factors with annealing temperature may be due to the formation of interfacial compounds at the Ru/Pd/n-GaN interface. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2788

Bulk viscosity of spin-one color superconducting strange quark matter

The bulk viscosity in spin-one color-superconducting strange quark matter is calculated by taking into account the interplay between the nonleptonic and semi-leptonic week processes. In agreement with previous studies, it is found that the inclusion of the semi-leptonic processes may result in non-negligible corrections to the bulk viscosity in a narrow window of temperatures. The effect is generally more pronounced for pulsars with longer periods. Compared to the normal phase, however, this effect due to the semi-leptonic processes is less pronounced in spin-one color superconductors. Assuming that the critical temperature of the phase transition is much larger than 40 keV, the main effect of spin-one color superconductivity in a wide range of temperatures is an overall increase of the bulk viscosity with respect to the normal phase. The corresponding enhancement factor reaches up to about 9 in the polar and A-phases, about 25 in the planar phase and about 29 in the CSL phase. This factor is determined by the suppression of the nonleptonic rate in color-superconducting matter and, therefore, may be even larger if all quark quasiparticles happen to be gapped.Comment: 10 pages, 4 multi-panel figures, including one new in the final versio

Electrical Transport Characteristics and Deep Level Transient Spectroscopy of Ni/V/n-InP Schottky Barrier Diodes

We report on the temperature-dependent electrical characteristics and deep level transient spectroscopy (DLTS) of the Ni/V/n-InP Schottky diodes in the temperature range of 180-420 K. Current density - voltage (J-V) characteristics of these diodes have been analyzed on the basis of thermionic emission theory with Gaussian distribution model of barrier height. The calculated Schottky barrier height (bo) and ideality factor (n) of Ni/V Schottky contact is in the range of 0.39 eV and 2.36 at 180 K, and 0.69 eV and 1.27 at 420 K, respectively. It is observed that the zero-bias barrier height increases while ideality factor decreases with increasing temperature. A bo versus q/2kT plot is drawn to obtain evidence of a Gaussian distribution of the barrier heights, and values of = 0.95 eV and 0 = 128 eV for the mean barrier height and standard deviation. A modified Richardson plot gives (T=0)= 0.98 eV and Richardson constant (A*) = 7.068 A K – 2cm – 2. The discrepancy between Schottky barrier height (SBHs) estimated from J-V and C-V measurements is also discussed. Thus, it is concluded that the temperature dependence of J-V characteristics of the SBHs on n-InP can be explained on the basis of themionic emission mechanism with Gaussian distribution of the barrier heights. DLTS results showed that two deep levels are identified (E1 and E2) in as-grown sample having activation energies of 0.29 ± 0.01 and 0.69 ± 0.02 with capture cross-section 3.29 × 10 – 15 cm2 and 5.85 × 10 – 17 cm2 respectively. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2777

Electrical transport characteristics of Pd/V/N-InP Schottky diode from I-V-T and C-V-T measurements

The temperature dependence of current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Pd/V contacts on undoped n-type InP Schottky barrier diodes (SBDs) have been systematically investigated in the temperature range of 200-400 K. The transition metal palladium (Pd) is used as a second contact layer because it has high work function, it reacts with InP at low temperatures and improved contact morphology. The ideality factor (n) and zero-bias barrier height are found to be strongly temperature dependent and while the zero-bias barrier height Φbo (I-V) increases, the ideality factor n decreases with increasing temperature. The experimental values of BH and n for the devices are calculated as 0.48 eV (I-V), 0.85 eV (C-V) and 4.87 at 200 K, 0.65 eV (I-V), 0.69 (C-V) eV and 1.58 at 400 K respectively. The I-V characteristics are analyzed on the basis of thermionic emission (TE) theory and the assumption of Gaussian distribution of barrier heights due to barrier inhomogeneities that prevail at the metal-semiconductor interface. The zero-bias barrier height Φbo versus 1/2kT plot has been drawn to obtain the evidence of a Gaussian distribution of the heights and the values of φ=0.89 eV and σ0= 145 meV for the mean barrier height and standard deviation. The conventional Richardson plot exhibits non-linearity with activation energy of 0.53 eV and the Richardson constant value of 4.25 × 10– 6 Acm– 2 K– 2. From the C-V characteristics, measured at 1 MHz the capacitance was determined to increase with increasing temperature. C-V measurements have resulted in higher barrier heights than those obtained from I-V measurements. As a result, it can be concluded that the temperature dependent characteristic parameters for Pd/V/n-InP SBDs can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier heights. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2790

Optimization of culture conditions of Streptomyces rochei (MTCC 10109) for the production of antimicrobial metabolites

Fermentation and culture conditions were studied in shaken-flask culture to induce the production of greater amounts of antimicrobial metabolites by Streptomyces rochei (10109). Antimicrobial metabolite production started after 48 h incubation and reached its optimum level at 20% inoculum size at 120 h, at which point the metabolites showed maximum antifungal and antibacterial activity against selected human pathogenic microorganisms (Candida albicans, Staphylococcus aureus and Escherichia coli). Optimal production occurred at pH 7.5 and temperature 32°C, with 2% glycerol and 1% peptone as the carbon and nitrogen sources respectively. The effects of adding sea water (optimum 30%) and NaCl (optimum 1%) were also evaluated.Keywords: human pathogen

The Stability of Strange Star Crusts and Strangelets

We construct strangelets, taking into account electrostatic effects, including Debye screening, and arbitrary surface tension sigma of the interface between vacuum and quark matter. We find that there is a critical surface tension sigma_crit below which large strangelets are unstable to fragmentation and below which quark star surfaces will fragment into a crystalline crust made of charged strangelets immersed in an electron gas. We derive a model-independent relationship between sigma_crit and two parameters that characterize any quark matter equation of state. For reasonable model equations of state, we find sigma_crit typically of order a few MeV/fm^2. If sigma <= sigma_crit, the size-distribution of strangelets in cosmic rays could feature a peak corresponding to the stable strangelets that we construct.Comment: 11 pages, LaTe

Meissner screening mass in two-flavor quark matter at nonzero temperature

We calculate the Meissner screening mass of gluons 4--7 in two-flavor quark matter at nonzero temperature. To this end, we study the effective potential of the 2SC/g2SC phases including a vector condensate $$and calculate the Meissner mass from the potential curvature with respect to$$. We find that the Meissner mass becomes real at the critical temperature which is about the half of the chemical potential mismatch. The phase diagram of the neutral two-flavor color superconductor is presented in the plane of temperature and coupling strength. We indicate the unstable region for gluons 4--7 on the phase diagram.Comment: 4 pages, 3 figures, minor revisions to text, version to appear in PR

Analytical and numerical evaluation of the Debye and Meissner masses in dense neutral three-flavor quark matter

We calculate the Debye and Meissner masses and investigate chromomagnetic instability associated with the gapless color superconducting phase changing the strange quark mass $M_s$ and the temperature $T$. Based on the analytical study, we develop a computational procedure to derive the screening masses numerically from curvatures of the thermodynamic potential. When the temperature is zero, from our numerical results for the Meissner masses, we find that instability occurs for $A_1$ and $A_2$ gluons entirely in the gapless color-flavor locked (gCFL) phase, while the Meissner masses are real for $A_4$, $A_5$, $A_6$, and $A_7$ until $M_s$ exceeds a certain value that is larger than the gCFL onset. We then handle mixing between color-diagonal gluons $A_3$, $A_8$, and photon $A_\gamma$, and clarify that, among three eigenvalues of the mass squared matrix, one remains positive, one is always zero because of an unbroken U(1)_\tilde{Q} symmetry, and one exhibits chromomagnetic instability in the gCFL region. We also examine the temperature effects that bring modifications into the Meissner masses. The instability found at large $M_s$ for $A_4$, $A_5$, $A_6$, and $A_7$ persists at finite $T$ into the $u$-quark color superconducting (uSC) phase which has $u$-$d$ and $s$-$u$ but no $d$-$s$ quark pairing and also into the two-flavor color superconducting (2SC) phase characterized by $u$-$d$ quark pairing only. The $A_1$ and $A_2$ instability also goes into the uSC phase, but the 2SC phase has no instability for $A_1$, $A_2$, and $A_3$. We map the unstable region for each gluon onto the phase diagram as a function of $M_s$ and $T$.Comment: 17 pages, 18 figure

Chromomagnetic instability in two-flavor quark matter at nonzero temperature

We calculate the effective potential of the 2SC/g2SC phases including vector condensates ($$and$$) and study the gluonic phase and the single plane-wave Larkin-Ovchinnikov-Fulde-Ferrell state at nonzero temperature. Our analysis is performed within the framework of the gauged Nambu--Jona-Lasinio model. We compute potential curvatures with respect to the vector condensates and investigate the temperature dependence of the Meissner masses squared of gluons of color 4--7 and 8 in the neutral 2SC/g2SC phases. The phase diagram is presented in the plane of temperature and coupling strength. The unstable regions for gluons 4--7 and 8 are mapped out on the phase diagram. We find that, apart from the case of strong coupling, the 2SC/g2SC phases at low temperatures are unstable against the vector condensation until the temperature reaches tens of MeV.Comment: 10 pages, 10 figures, revisions to text, published in Phys. Rev.