Y. Aiura

Photovoltaic effect observed in transparent p–n heterojunctions based on oxide semiconductors

Abstract Transparent p–n junctions composed of zinc oxide, copper-aluminum oxide and indium-tin oxide films were fabricated by pulsed laser deposition on glass substrates at temperatures as low as 400 °C. Diode characteristics in the current–voltage response and the photovoltaic effect were observed for the junctions fabricated. The photovoltaic junction had an optical transparency of more than 43% for the wavelengths λ>500 nm, and exhibited photovoltage as large as 80 mV when it was illuminated by a LED of λ≈470 nm. The properties of the photovoltaic transparent junction seemed to be degraded by the inadequate crystallinity of the copper-aluminum oxide layer. The ZnO/CuAlO/ITO/glass structure developed in this study has demonstrated a possible application of transparent solar cells.

Laser Based Angle-Resolved Photoemission, the Sudden Approximation, and Quasiparticle-Like Spectral Peaks in Bi2Sr2CaCu2O8+δ

A new low photon energy regime of angle resolved photoemission spectroscopy is accessed with lasers and used to study the superconductor Bi2Sr2CaCu2O8+delta. The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy - the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink and associated weight transfer are robust to a possible breakdown of the sudden approximation.

Structure and electronic states on reduced SrTiO3(110) surface observed by scanning tunneling microscopy and spectroscopy

The SrTiO3(110) surface, after annealing in ultrahigh vacuum (UHV) was observed by scanning tunneling microscopy/spectroscopy (STM/S). These observations were compared with the ultraviolet photoemission spectroscopy (UPS) and x‐ray photoemission spectroscopy (XPS) data previously reported. The surface, after annealing at 800 °C, is dominated by flat regions where tunneling spectra are of metallic character, in agreement with the UPS data that showed a clear cutoff at the Fermi energy, EF. After annealing above 1000 °C, step edges along [110] and rowlike structures along [001] with spacing ∼2.2 nm, close to 4√2a, are observed. The tunneling spectra showed an energy gap and an in‐gap state ∼1 eV below EF, both of which are similar to those reported on the SrTiO3(100) surface after annealing in UHV. After 20 cycles of annealing above 1000 °C, a new ordering with c(2×6) periodicity is observed on the terraces. The STM/S results are explained by formation of (100) and (010) microfacets in the course of anneal...

Doubling of the Bands in Overdoped Bi2Sr2CaCu2O8 + delta: Evidence for c-Axis Bilayer Coupling

We present high resolution angle resolved photoemission data of the bilayer superconductor Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) showing a clear doubling of the near E(F) bands. This splitting approaches zero along the (0,0)-->(pi,pi) nodal line and is not observed in single layer Bi(2)Sr(2)CuO(6+delta) (Bi2201), indicating that the splitting is due to the long sought after bilayer splitting effect. The splitting has a magnitude of approximately 75 meV near the middle of the zone, extrapolating to about 110 meV near the (pi,0) point. The existence of these two bands also helps to clear up the recent controversy concerning the topology of the Fermi surface.

Photoemission Study of the Metallic State of Lightly Electron-doped SrTiO3

Abstract The behavior of the metallic state of lightly electron-doped SrTiO3 has been studied using angle-integrated ultraviolet photoemission spectroscopy (UPS) and angle-resolved photoemission spectroscopy (ARPES). Two states in the bulk band gap of stoichiometric SrTiO3 are shown by doping electron carriers: a metallic state with a sharp Fermi cut-off and a broad state centered at ∼1.3 eV below the Fermi level. By slight oxygen exposure, the UPS spectra showed a rapid decrease in the spectral intensity of the metallic state followed by a sudden energy shift of the valence band. These changes are explained in terms of the band-bending effect due to the formation of a thick charge depletion layer when the adsorbed oxygen atoms attract the free electrons from the bulk to the surface. Normal-emission photoelectron spectra before the oxygen exposure showed that the spectral intensity of the metallic state is remarkably enhanced at the photon energy of 28 and 45 eV whereas its energy position is almost independent of the photon energy. Off-normal-emission spectra showed that the spectral intensity of the metallic state is drastically reduced with increasing emission angle. From a comparison between the calculated band structure and ARPES results, we conclude that the metallic state is qualitatively explained by the Fermi liquid behavior based on the band theory.

Effects of next-nearest-neighbor hopping of t' on the electronic structure of cuprate superconductors

Photoemission spectra of underdoped and lightly-doped Bi

Anisotropic Optical Spectra of α-Al2O3 Single Crystals in the Vacuum Ultraviolet Region. I. Spectra of Absorption Tail and Reflectivity

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Anisotropic Optical Spectra of α-Al 2O 3 Single Crystals in the Vacuum Ultraviolet Region. II. Spectra of Optical Constants

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BANDWIDTH CONTROL IN A PEROVSKITE-TYPE 3D1-CORRELATED METAL CA1-XSRXVO3. II. OPTICAL SPECTROSCOPY

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Optical Spectra of Y3Al5O12 (YAG) Single Crystals in the Vacuum Ultraviolet Region

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