Semiconducting Region Research Articles

Patterning of thin-film high-T/sub c/ circuits by the laser-writing method

The authors report studies on a laser-based 2-D patterning technique that implements a focused beam from a continuous-wave (CW) Ar-ion laser to locally heat up an epitaxial Y-Ba-Cu-O film in a controlled (oxygen-rich or oxygen-poor) atmosphere. It is shown that the laser-writing method enables a reproducible fabrication in the same film of oxygen-depleted (semiconducting) regions next to enriched ones (superconducting), in a manner similar to n- and p-type diffusion regions in semiconductors. A number of test structures, laser-written in initially oxygen-rich or oxygen-poor films deposited on MgO, SrTiO/sub 3/, and LaAlO/sub 3/ single crystals, have been measured. The best, very homogeneous superconducting (oxygen-rich) circuits were patterned in oxygen-depleted YBCO deposited in the LaAlO/sub 3/ substrates. The structures exhibited a 0.5-K-wide superconducting transition, T/sub c0/=89.5 K, and J/sub c/ above 10/sup 5/ A/cm/sup 2/. >

Zero-bias anomalies in high-Tc-superconductor tunnel junctions.

The zero-bias conductance peak that is often found in the tunneling characteristics of high-temperature-superconductor (HTS) junctions is analyzed in the framework of the Anderson-Appelbaum model for electron magnetic interaction. We have found that when the anomaly develops at T>T c , its temperature behavior is determined by the superconducting properties of the HTS, while, when it develops at T<T c , the presence of normal or semiconducting surface regions can be supposed. A giant resistance peak seems to indicate interdiffusion of the counterelectrode into the base material

Transport investigation of HgTeCdTe single and multiple quantum wells

We compare and contrast the magneto-transport properties of HgTeCdTe single quantum wells, multiple quantum wells, and superlattices. In agreement with theory, electron mass broadening is observed in the superlattices but not in the single or multiple quantum wells. We also observe for the first time a second semiconducting region in thick-well structures which was recently predicted theoretically.

The Madelung Energy in Copper-Oxide-Based Ceramics

The Madelung energy in the (Y, Ca)(Ba, La) 2 Cu 3 O 6+δ system has been calculated in order to find the distribution of hole carriers among sites. We regard the compoundas a superconductor, when the lowest-energy distribution is such that holes enter sites in CuO 2 sheets, whereas we regard it as a semiconductor, when no holes enter sites in the CuO 2 sheets. Based on this criterion, we find a phase diagram, where the superconducting region is separated from the semi-conducting region by a boundary. A good agreement with the experimental finding by Tokura et al . is obtained, when account is taken of the ordering of exygen vacancies in the basal plane of Fig. 1 in the text. It is found that for some compounds with small δ(∼0.25), holes are spontaneously produced in CuO 2 sheets, so that the compounds may be a superconductor although their nominal hole content is zero.

Amplification of Bleustein–Gulyaev waves in cadmium sulfide

The propagation of Bleustein–Gulyaev waves in the presence of a dc electric field in the vacuum baked piezoelectric semiconducting crystals of class 6 has been studied theoretically. By solving the partial differential equations representing the electron–acoustic wave interaction in the piezoelectric semiconducting region, and the Laplace’s equation in the vacuum region separately and fulfilling the relevant boundary conditions, we obtain an expression for the amplification coefficient. The effects of carrier diffusion, resistivity, and carrier drift velocity on the amplification coefficient have been studied based on numerical calculations for the semiconducting CdS sample. It has been observed that, compared to Rayleigh waves, the Bleustein–Gulyaev waves give a much higher amplification.

Anomalous magnetoresistance in 1T-TaS 2

Transverse magnetoresistance of 1T-TaS 2 was measured in magnetic fields up to 100 kOe in the semiconductive region corresponding to the commensurate charge density wave (CDW) state.

Structure independent properties of expanded crystalline mercury

The band structure of expanded crystalline mercury has been calculated in the density range 14.6-5 g cm-3 for three different crystal structures, bcc, fcc, and rhombohedral structure. A simple local pseudopotential calculation scheme has been used in a few symmetry points of the Brillouin zone. The main results of our calculations, more or less independent of the chosen structure, are: a normal metallic region 14.6 g cm-3> rho >11 g cm-3, a real band gap starting at about 8.5 g cm-3 and a semiconducting region 8 g cm-3> rho >5 g cm-3. A comparison with experimental data for expanded liquid mercury has been made.

High pressure effect on the electrical properties of NiS 2

A semiconductor-metal transition in the electrical resistance of NiS 2, which has been suggested to be a Mott transition, is observed with decreasing temperature under pressure up to 44 kbar. The transition temperature increases with pressure with a slope of dT dP = 6 ± 1 K/kbar . The activation energy in a semiconducting region is found to decrease with increasing pressure and to vanish at about 46 kbar. The critical pressure and temperature are predicted to be 46 ± 2 kbar and 350 ± 20 K.