F. Turkoglu

Interferometer measurements of terahertz waves from Bi2Sr2CaCu2O8+d mesas

We fabricated rectangular mesa structures of superconducting Bi2Sr2CaCu2O8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R?T), current?voltage (I?V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06?mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54?THz was detected using the Michelson interferometric setup.

Emission of the THz waves from large area mesas of superconducting Bi2Sr2CaCu2O8+δ by the injection of spin polarized current

The effect of electromagnetic wave irradiation on the phase dynamics of intrinsic Josephson junctions in high temperature superconductors is investigated. We predict three novel effects by variation of the radiation amplitude and frequency: changing of the longitudinal plasma wavelength at parametric resonance; double resonance of the Josephson oscillations with radiation and longitudinal plasma wave; charging of superconducting layers in the current interval corresponding to the Shapiro step. The ”bump” structure in IVC recently observed experimentally is demonstrated. We also observe ragged Shapiro steps at double resonance.

Effect of substrate rotation speed and off-center deposition on the structural, optical, and electrical properties of AZO thin films fabricated by DC magnetron sputtering

In this study, aluminum-doped zinc oxide (AZO) thin films were deposited by DC magnetron sputtering at room temperature. The distance between the substrate and target axis, and substrate rotation speed were varied to get high quality AZO thin films. The influences of these deposition parameters on the structural, optical, and electrical properties of the fabricated films were investigated by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometry, and four-point probe techniques. The overall analysis revealed that both sample position and substrate rotation speed are effective in changing the optical, structural, and electrical properties of the AZO thin films. We further observed that stress in the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. An average transmittance above 85% in the visible range and a resistivity of 2.02 × 10−3 Ω cm were obtained for the AZO films.In this study, aluminum-doped zinc oxide (AZO) thin films were deposited by DC magnetron sputtering at room temperature. The distance between the substrate and target axis, and substrate rotation speed were varied to get high quality AZO thin films. The influences of these deposition parameters on the structural, optical, and electrical properties of the fabricated films were investigated by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometry, and four-point probe techniques. The overall analysis revealed that both sample position and substrate rotation speed are effective in changing the optical, structural, and electrical properties of the AZO thin films. We further observed that stress in the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. An average transmittance above 85% in the visible range and a resistivity of 2.02 × 10−3 Ω cm were obtained for the AZO films.

Inhomogenity of Micron-Sized Triple Terahertz Emitters Fabricated from Intrinsic Josephson Junctions in Single Crystal Bi2Sr2CaCu2O8+δ

The as-grown Bi2Sr2CaCu2O8+δ (Bi2212) crystals were heat-treated at various temperatures either in Argon atmosphere or in vacuum. Bi2212 triple mesa structures were fabricated by electron beam lithography and Ar ion beam etching processes. A set of samples has identical size (50 × 300 μm2) are vertically mounted in vacuum on the cold finger of an optical LHe continuous-flow cryostat and resistance versus temperature and current-voltage measurements achieved. We investigated and compared characteristics of three mesas which are on same chip and next to each other. By this way, we searched the crystal inhomogenity in triple mesa structures and studied how critical current density varies with the doping conditions.

Fabrication of double mesa structures by E-beam lithography from high temperature superconducting Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) for powerful terahertz emission

We work on a frequency tunable solid state device to meet the needs of continuous, coherent, powerful terahertz emission sources that fill practically important terahertz gap. High temperature superconducting (HTS) coherently oscillating Josephson junctions in Bi2Sr2CaCu2O8+δ (Bi2212) crystal make this approach very promising. Since doping dependence of Bi2212 is an important parameter, Bi2212 crystals are annealed in vacuum or purified argon gas flow at 425 °C. For further processing we pattern both single and double rectangular mesa structures by using electron beam lithography on the cleaved surface of the crystal. Resistance-temperature (R-T), and current-voltage behavior (I-V) measurements achieved.

Terahertz wave emission from layered superconductors: Interferometer measurements

Rectangular Bi2Sr2CaCu2O8+δ (Bi2212) mesa structures were fabricated on as-grown Bi2212 single crystal superconductors using standard photolithography and Ar ion beam etching techniques. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. Furthermore, in contrast to previous studies, the emission frequency was determined using interferometer set up instead of FTIR. The interference patterns were detected outside the cryostat after traveling long way through ambient space. The emission frequency calculated by Fourier transform of interference data is consistent with Josephson frequency-voltage relation.