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ABSTRACT: We investigated the luminescence properties of Eu-doped GaN (GaN:Eu) grown by atmospheric-pressure organometallic vapor phase epitaxy. The GaN:Eu exhibited radiant red emission due to the intra-4f shell transition of Eu3+ ions at room temperature. The intensity of the dominant peak was about 4 times higher than that in the sample grown at 10 kPa, even though the Eu concentration was only half that of the 10 kPa sample. This was mainly caused by the enhancement of the energy transfer from the GaN host to Eu ions. The enhanced energy transfer resulted in improved luminescence properties of a GaN:Eu light-emitting diode.
Applied Physics Letters 08/2010; 97(5):051113-051113-3. · 3.84 Impact Factor
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ABSTRACT: Modifications of direct transition energies by crystal lattice deformations were confirmed in β-FeSi2 epitaxial films on Si(111) substrates. With an increasing of annealing temperature (Ta), lattice constants of a-axis expanded, and those of b- and c-axis shrank, resulting in the volume reduction in −0.2%. In photoreflectance measurements, the direct transition energy at Y point in the Brillouin zone of β-FeSi2 ( ∼ 0.92 eV) was shifted to lower photon energy with the increase in Ta. These results revealed that the band-gap energy was modulated systematically by the lattice deformation, which suggests a possibility of band-gap engineering by the lattice deformation in β-FeSi2 epitaxial films on Si(111) substrates.
Applied Physics Letters 06/2009; 94(24):241907-241907-3. · 3.84 Impact Factor
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ABSTRACT: Carrier capturing in GaInP/Er,O-codoped GaAs (GaAs:Er,O)/GaInP laser diodes (LDs) was investigated by means of the threshold current density (J<sub> th </sub>) of laser emission. The Er-doped LDs showed laser emission of the GaAs band edge at room temperature, and its J<sub> th </sub> increases with the Er flow rate during the growth. In the dependence of J<sub> th </sub> on reciprocal cavity length, the effective gain factor of the LDs decreased by the codoping of Er and O. These results reveal that ultrafast capturing of injected carriers at an Er-related trap level is accomplished even in the stimulated emission region of GaAs. The fast capturing process allowed us to observe both the spontaneous intra- 4f -shell emission due to Er <sup>3+</sup> ions at 1.54 μ m and the stimulated emission at the GaAs band edge (∼840 nm ) in the Er-doped LDs.
Applied Physics Letters 01/2009; · 3.84 Impact Factor
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ABSTRACT: Er-related photoluminescence (PL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) grown by organometallic vapor phase epitaxy. The GaAs:Er,O which was slightly doped with Er exhibited both strong Er-related and band-edge luminescence. In the temperature dependence of the Er-related PL intensity, the intensity decreased with increasing temperature from 4.2 K to 30 K. The temperature region was quite coincident with the region where the Carbon-related PL intensity decreased. This behaviour implies the existence of a Carbon-related nonradiative process in GaAs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 06/2008; 5(9):2864 - 2866.
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ABSTRACT: Transition-metal (TM) doped zinc oxide (ZnO) films were grown by a developed plasma-enhanced chemical vapor deposition (PECVD) technique combined with RF sputtering. In the developed system, TMs such as Fe, Cr and Ni were doped into the ZnO films by RF sputtering with a stainless-steel electrode connected to a RF generator. X-ray diffraction (XRD) measurements revealed that the TM-doped ZnO films were successfully grown with c-axis orientation at 400 °C with RF power of 25 W. The doped TMs were segregated to the surface when the films were annealed at 700 °C in O2 ambient. After higher-temperature annealing at 800 °C, ZnO nanostructures with wire and tube shapes were formed by a catalytic influence of the segregated TMs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 06/2008; 5(9):3125 - 3127.
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ABSTRACT: Ultrafast carrier dynamics and terahertz radiation from Er,O-codoped GaAs (GaAs:Er,O) have been investigated by pump and probe reflectance and time-domain terahertz spectroscopy. In pump and probe reflectance measurements, GaAs:Er,O showed faster relaxation time (0.37–0.56 ps) of photoexcited carriers than undoped GaAs. In terahertz spectroscopy, the radiated terahertz amplitude decreased and the decay time of transient photocurrent became long with increasing Er concentration. The Er concentration dependence was understood by additional electron scattering due to the Er doping. The fast relaxation time and the terahertz radiation properties suggest new applications of GaAs:Er,O for the terahertz frequency region.
Applied Physics Letters 03/2008; 92(11):111115-111115-3. · 3.84 Impact Factor
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ABSTRACT: Dynamics of photo-excited carriers in Er,O-codoped GaAs have been systematically investigated by means of a pump and probe reflection technique. Time-resolved reflectivity exhibited an abrupt increase in amplitude, followed by a steep decrease to negative in less than 1 ps and then a gradual recovery. There were two components, fast and slow, in the recovery process. The fast recovery depended strongly on Er concentration and measurement temperature. The quantitative analysis indicated that the fast recovery corresponds to electron capture by a trap formed by Er and O codoping.
Physica B Condensed Matter · 1.06 Impact Factor
