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3. Effect of n- and p-type Doping on Coherent Phonons in GaN

Author

Ishioka, Kunie, Kato, Keiko, Ohashi, Naoki, Haneda, Hajime, Kitajima, Masahiro, and Petek, Hrvoje

Subjects
Condensed Matter - Materials Science
Abstract

Effect of doping on the carrier-phonon interaction in wurtzite GaN is investigated by pump-probe reflectivity measurements using 3.1 eV light in near resonance with the fundamental band gap of 3.39 eV. Coherent modulations of the reflectivity due to the E2 and the A1(LO) modes, as well as the 2A1(LO) overtone are observed. Doping of acceptor and more so for donor atoms enhances the dephasing of the polar A1(LO) phonon via coupling with plasmons, with the effect of donors being stronger. Doping also enhances the relative amplitude of the coherent A1(LO) phonon with respect to that of the high-frequency E2 phonon, though it does not affect the relative intensity in Raman spectroscopic measurements. This enhanced coherent amplitude indicates that transient depletion field screening (TDFS), in addition to impulsive stimulated Raman scattering (ISRS), contribute to generation of the coherent polar phonons even for sub-band gap excitation. Because the TDFS mechanism requires photoexcitation of carriers, we argue that the interband transition is made possible at the surface with photon energies below the bulk band gap through the Franz-Keldysh effect.

Published
2013
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23. Diffusion properties of point defects in barium strontium titanate thin films

Author

Morito, Kentaro, Suzuki, Toshimasa, Kishi, Hiroshi, Sakaguchi, Isao, Ohashi, Naoki, and Haneda, Hajime

Subjects
Titanates -- Electric properties, Dielectric films -- Electric properties, Dielectric films -- Mechanical properties, Thin films -- Electric properties, Thin films -- Mechanical properties, Piezoelectricity -- Analysis, Business, Electronics, Electronics and electrical industries
Abstract

The influence of hydrogen atoms on the electrical behavior of (Ba,Sr)Ti[O.sub.3] (BST) thin film capacitors is examined. Findings reveal that an increase in the thermally incorporated hydrogen concentration in BST thin films results in electrical degradation.

Published
2007

28. Virtual structure in luminescence profile of zinc oxide films causing discrepancy in peak identification

Author

Yu-Guang Wang, Ohashi, Naoki, Ryoken, Haruki, and Haneda, Hajime

Subjects
Zinc oxide -- Optical properties, Photoluminescence -- Analysis, Interference (Light) -- Analysis, Dielectric films -- Optical properties, Thin films -- Optical properties, Physics
Abstract

The luminescence properties of zinc oxide (ZnO) films developed by pulsed laser deposition were examined by photoluminescence spectroscopy. The findings suggested that the existence of an interference effect in ZnO films was confirmed by systematically checking the variation in the photoluminescence spectra with film thickness.

Published
2006

34. Highly porous (TiO(sub 2)-SiO(sub 2)-TiO(sub 2))/Al(sub 2)O(sub 3)/TiO(sub 2) composite nanostructures on glass with enhanced photocatalysis fabricated by anodization and sol-gel process

Author

Chu, Song-Zhu, Inoue, Satoru, Awatsu, Satoshi, Wada, Kenji., Li, Di, and Haneda, Hajime.

Subjects
Catalysis -- Research, Titanium dioxide -- Electric properties, Metals -- Anodic oxidation, Metals -- Analysis, Chemicals, plastics and rubber industries
Abstract

The study aims three dimensional highly porus TiO(sub 2)-4%-SiO(sub 2)-1%-TiO(sub 2))/Al(sub 2)O(sub 3)/TiO(sub 2) composite nanostructures directly fixed on glass substrates were fabricated by anodization and sol-gel process. The photocatalytic performances of the resultant nanostructures were investigated by decomposing acetaldehyde gas under UV illumination.

Published
2003

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