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The trivalent terbium ion (Tb3+) emits ultra-stable visible light consisting of blue, green, yellow, and red. Tb-doped semiconductors are candidates for novel full-color light sources in next-generation displays. Particularly, Tb-doped AlxGa1−xN (AlxGa1−xN:Tb) has attracted much attention for device applications. We present the luminescence properties of AlxGa1−xN:Tb grown by the organometallic vapor phase epitaxy. At 15 K, emission related to the 5D4–7FJ (J = 3, 4, 5, 6) transitions is observed for AlxGa1−xN:Tb with x ≥ 0.03. Thermal quenching of emission originating from the 5D4–7FJ transition is suppressed for higher Al compositions, and the luminescence is clearly observed at room temperature for AlxGa1−xN:Tb with x ≥ 0.06. The small thermal quenching is attributed to the enhanced excitation to the 5D4 level of Tb3+ ions via the 4f–5d transition and not due to the suppression of energy back-transfer paths in excited Tb3+ ions. Although additional emission originating from the 5D3–7FJ transitions is observed at 15 K for AlxGa1−xN:Tb with x ≥ 0.15, it is not observed at room temperature because the excitation to the 5D3 level via the 4f–5d transition is less efficient at high temperature. For Al0.15Ga0.85N:Tb, monochromatic green light is demonstrated using a SiO2/ZrO2 distributed Bragg reflector. [ABSTRACT FROM AUTHOR]

We report on the fabrication and optical characteristics of microdisk (MD) resonators with Er,O-codoped GaAs (GaAs:Er,O) as an active component. MD resonators based on GaAs:Er,O with different sidewall angles are fabricated by electron beam lithography followed by two different processes: dry and wet etching. Numerical simulations using a finite-difference time-domain method demonstrate an increase in the cavity quality (Q) factor of the MDs when sharpening the taper angle of the MDs. Micro-photoluminescence characterization of the MD resonators with excitation by a He–Ne laser reveals an 11.4-fold enhancement of Er-related luminescence and a cavity Q factor of 4.2 × 103. For the MD resonators with tapered sidewalls, further enhancement of Er luminescence and increased Q factor (>9.0 × 103) are observed. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) light with a wavelength of 650–950 nm is used for various biomedical applications. Although NIR emitters are typically based on GaAs-related materials, they contain toxic elements, and the emission wavelength can easily shift during the device operation due to temperature changes and current injection levels. On the other hand, Tm 3 + , which is one of the rare-earth ions, can generate ultra-stable NIR luminescence with a wavelength of ∼ 800 nm , based on 3 H 4 – 3 H 6 transitions in a 4f shell, and we have recently focused on Tm-doped GaN (GaN:Tm) based light-emitting diodes (LEDs) as novel NIR emitters. In this paper, we present a demonstration of a NIR-LED based on GaN:Tm grown by the organometallic vapor phase epitaxy method with optimized growth conditions and structures, where the parasitic reaction is well suppressed. NIR luminescence from the GaN:Tm-based LED is derived from 3 H 4 – 3 H 6 transitions of Tm 3 + ions and consists of three dominant peaks at 795, 806, and 814 nm. The turn-on voltage of the NIR-LED is ∼ 6.9 V, and it is significantly lower than the previously reported electroluminescent devices based on GaN:Tm with impact ionization processes. From a current dependence of the electroluminescence spectra and temperature-dependent photoluminescence for the NIR-LED, the peak shifts are determined to be < 7.6 pm/mA and ∼ 1.3 pm/K, respectively. [ABSTRACT FROM AUTHOR]

The dopant distribution and surface and structural properties of Er- and Eu-doped GaN samples were investigated using atom probe tomography (APT) and atomic force microscopy (AFM). Erbium accumulation within host GaN threading dislocations was directly detected by APT allowing for the dislocations to be imaged in three dimensions. In addition, photoluminescence spectroscopy with high lateral resolution, by means of scanning near-field optical microscopy, was performed on Eu-doped GaN samples. By combining these results with AFM mappings of the same area, it was concluded that Eu3+ ions also accumulate at threading dislocations. Moreover, high-resolution surface profiles of both samples show that even dilute doping (<0.2%) of Eu and Er has a significant influence on the growth morphology of the GaN host material and the nature of the threading dislocations within it. Transmission electron microscopy techniques were used to show the influence of rare-earth incorporation on the growth of GaN lattice and the propagation of threading dislocations. [ABSTRACT FROM AUTHOR]

We report on the epitaxial growth and the optical properties of Tm,Yb-codoped ZnO (ZnO:Tm,Yb) thin films by sputtering-assisted metalorganic chemical vapor deposition. The characteristic light emission due to the intra-4f shell transitions of Tm3+ and Yb3+ ions in the ZnO host is observed at 4 K by using photoluminescence (PL) characterization. The time-resolved PL measurements on the Tm3+ and Yb3+ emission reveals that the carrier decay time of each ion can vary by changing the concentration of both Tm3+ and Yb3+ ions, which depends on a mixing ratio of Tm2O3 and Yb2O3 in a sputtering target. The energy transfer from Tm3+ to Yb3+ ions occurs in the sample with the high mixing ratio, and the reversed energy transfer process occurs with the lower mixing ratio. These results indicate that the concentration, and thus the carrier dynamics of Tm3+ and Yb3+ ions in the ZnO:Tm,Yb host, can be controlled by altering the mixing ratio of the sputter target and the frequency power. [ABSTRACT FROM AUTHOR]

We report on the growth and optical properties of Tm-doped AlGaN layers by organometallic vapor phase epitaxy (OMVPE). The morphological and optical properties of Tm-doped GaN (GaN:Tm) and Tm-doped AlGaN (AlGaN:Tm) were investigated by Nomarski differential interference contrast microscopy and photoluminescence (PL) characterization. Nomarski images reveal an increase of surface roughness upon doping Tm into both GaN and AlGaN layers. The PL characterization of GaN:Tm shows emission in the near-infrared range originating from intra-4f shell transitions of Tm3+ ions. In contrast, AlGaN:Tm also exhibits blue light emission from Tm3+ ions. In that case, the wider band gap of the AlGaN host allows energy transfer to higher states of the Tm3+ ions. With time-resolved PL measurements, we could distinguish three types of luminescent sites of Tm3+ in the AlGaN:Tm layer, having different decay times. Our results confirm that Tm ions can be doped into GaN and AlGaN by OMVPE, and show potential for the fabrication of novel high-color-purity blue light emitting diodes. [ABSTRACT FROM AUTHOR]

A systematic experimental study was performed on the Fano line shape exhibited by multilayer structures consisting of an Al layer, a SiO2 spacer layer, and an Al2O3 waveguide layer. In the structures studied, a sharp Fano resonance appears on the background of broad asymmetric resonance attributed to the excitation of a surface plasmon polariton at the Al/SiO2 interface. It is shown that the background asymmetric surface plasmon resonance can be well fitted to a single Fano function, and the sharp Fano line shape can be well fitted to a double Fano function expressed as a product of two single Fano functions. The results of measurements performed by varying the spacer layer thickness indicate that the width (Q factor) of the sharp Fano resonance decreases (increases) monotonously as the thickness increases. The Q factor achieved in the present study is as high as ~ 1500. A comparison with the results of electromagnetic calculations suggests that not only the spacer layer thickness but also the imaginary part of the dielectric constant of the waveguide layer plays an important role in the Fano line shape engineering. [ABSTRACT FROM AUTHOR]

The molecular beam epitaxy method is used to prepare (001)-oriented [Ni.sub.80][Fe.sub.20]/[Mn.sub.100-x][Pt.sub.x] and [Co.sub.90][Fe.sub.10]/[Mn.sub.100-x][Pt.sub.x] epitaxial bilayers. The uncompensated moment and torque curve were found to be dependent on the ratio of F/AF interfacial exchange coupling and the antiferromagnetic (AF) domain wall energy.

The excellent soft magnetic properties of amorphous (a-) CoFeSiB films make it suited for use in the yoke of granular-in-gap sensors, but only if their thermal stability can be improved. To this end, this study investigated the effects of adding small amounts of other metals on the magnetic and structural properties of a-CoFeSiB films. It was found that adding metals with relatively large atomic radii is an effective way to increase thermal stability, with both Ta and Hf showing good thermal stability after annealing at temperatures of 473 to 573 K. Indeed, a -(CoFeSiB)96.2Hf3.8 film was found to maintain its initial coercivity of 0.2 Oe without very little decrease in magnetization after annealing at 623 K. Furthermore, even after annealing at 673K a -(CoFeSiB)93.0Hf7.0 film still had a relatively low coercivity of approximately 0.5 Oe. [ABSTRACT FROM AUTHOR]

We found an anomalous Eu-related luminescence peak in the temperature dependence of photoluminescence (PL) spectra in Eu-doped gallium nitride (GaN:Eu) grown by organometallic vapor phase epitaxy. Its PL intensity increased with increasing temperature and reached a maximum around 140 K, while the main peak intensities decreased monotonically in this region. Timeresolved PL measurements (TR-PL) revealed a delayed increase of PL intensity after the laser pulse. An analysis of the characteristics hereof indicated that the mechanism behind this afterglow is thermally activated and its transfer efficiency is dependent on the excitation intensity. We developed a model that explains these results, where excitation of the Eu ions associated to this peak takes place via two different carrier traps. [ABSTRACT FROM AUTHOR]

The nature of Eu incorporation and resulting luminescence efficiency in GaN has been extensively investigated. By performing a comparative study on GaN:Eu samples grown under a variety of controlled conditions, and using a variety of experimental techniques, the configuration of the majority site has been concluded to contain a nitrogen vacancy (VN). The nitrogen vacancy can appear in two symmetries, which has a profound impact on the luminescence and magnetic properties of the sample. The structure of the minority site has also been identified. We propose that, for both sites, the excitation efficiency of the red Eu emission is improved by the presence of donor-acceptor pairs in the close vicinity of the Eu. [ABSTRACT FROM AUTHOR]

Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7K

(001)-oriented Ni80Fe20/Mn100-xPtx and Co90Fe10/Mn100-xPtx epitaxial bilayers were prepared using the molecular beam epitaxy method. Their exchange anisotropies were measured using a torque magnetometer, while their interfacial Mn uncompensated moments were measured by means of x-ray magnetic circular dichroism. The bilayers exhibited both one- and fourfold components in their anisotropy torque curves, which are difficult to explain using a simple model assuming the coherent rotation of ferromagnetic (F) and antiferromagnetic (AF) spins. Uncompensated Mn moments were confirmed to exist in the Mn100-xPtx layer due to exchange coupling with the adjacent F layer, and the Mn moment of CoFe/Mn100-xPtx was found to be larger than that of NiFe/Mn100-xPtx. In order to understand the experimental results, we extended the Mauri et al. [J. Appl. Phys. 62, 3047 (1987)] domain wall model by assuming cubic anisotropy in the AF and four AF domains whose interfacial moments are oriented along the principal axis of (001)-oriented Mn–Pt. The model predicted the uncompensated AF moment resulting from the domain wall formed in the AF layer and well reproduced the coexistence of one- and fourfold anisotropies in the in-plane torque curves. The uncompensated moment and torque curve were found to be dependent on the ratio of F/AF interfacial exchange coupling and the AF domain wall energy. By changing the ratio, it was possible to reproduce exchange anisotropy for various systems, such as NiFe/MnPt, NiFe/MnIr, and CoFe/MnPt. [ABSTRACT FROM AUTHOR]

Tensile components for films deposited by rf sputtering are increased by incremental deposition of Co layers due to a difference between the lattice constants of Co and Pd. Studies using atomic force microscope show that the increase in tensile components increases the total film thickness and the surface roughness.