Effect of interface traps on Debye thickness semiconductor films

The presence of the boundary interface trapping states and their role in determining the properties of Debye thickness thin semiconductor films, are demonstrated experimentally, using PbTe films deposited on mica. These charged states could not be observed earlier and be studied directly, because of the screening by the relatively high carrier density of the ordinary PbTe. Thin, Debye length thickness, PbTe films with a high concentration of interface trapping centers, possess an extraordinary high resistance. In this case the thermostimulated capacitor discharge method can be successfully applied to determine the energy of these levels, their carrier capture cross-sections and their donor- or acceptor-like character. The experimental results and theoretical calculations are discussed.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Pyroelectric effect induced by the built-in field of the p-n junction in the quantum paraelectric PbTe: experimental study

We report here the first observation of a pyroelectric effect in a nonpolar semiconductor. This effect originates in the temperature-dependent electric dipole of the PbTe p-n junction. The junction was illuminated by a chopped CO(2) laser beam, and periodic and single-pulse pyroelectric signals were observed and measured as a function of temperature, reverse bias voltage, and chopper frequency. The measured pyroelectric coefficient is approximately 10(-3) microC/cm(2) K in the region of 40-80 K. The theoretical model describes quantitatively all experimental features. The time evolution of the temperature inside the junction region was reconstructed.     

Experimental and theoretical investigation of the pyroelectric effect of the p-n junction in a paraelectric non-polar semiconductor

We describe here the first comprehensive investigation of a pyroelectric response of a p-n junction in a non-polar paraelectric semiconductor. The pyroelectric effect is generated by the, temperature dependent, built-in electrical dipole moment. High quality PbTe p-n junctions have been prepared specifically for this experiment. The pyroelectric effect was excited by a continuous CO₂ laser beam, modulated by a mechanical chopper. The shape and amplitude of the periodic and single-pulse pyroelectric signals were studied as a function of temperature (10-130 K), reverse bias voltage (up to −500 mV) and chopping frequency (4-2000 Hz). The pyroelectric coefficient is ≈10⁻³ μC/cm²K in the temperature region 40-80 K. The developed theoretical model quantitatively describes all the experimental features of the observed pyroelectric effect. The time evolution of the temperature within the p-n junction was reconstructed.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Antioxidative properties of lactoferrin from bovine colostrum before and after its lyophilization

The effect of lactoferrin (LF) derived from native, frozen and lyophilized bovine colostrum on the intensity of free-radical processes in model systems has been investigated. It was shown that LF, not depending on the source of its obtaining, is an efficient iron chelator and decreases intensity of peroxidative processes. It was established, that antioxidative properties of LF from lyophilized colostrum have remained unchanged within 12 months of dry colostrum storage under proper conditions.