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We investigate thermal emission from n-doped GaAs/AlGaAs quantum wells (QWs). Emission peaks with Lorentzian shapes (linewidth 11~19 meV) that reflect transitions between the first and second conduction subbands are observed in the mid-infrared range. It is demonstrated that the emission characteristics can be tuned by modifying the QW parameters. The peak emissivity is increased from 0.3 to 0.9 by modifying the doping density, and the peak wavelength is tuned from 6 to 10 μm by changing the well width. The obtained results are useful for the design of narrow-band thermal emitters. [ABSTRACT FROM AUTHOR]

We have recently reported the successful fabrication of bright single-photon sources based on Ag-embedded nanocone structures that incorporate InAs quantum dots. The source had a photon collection efficiency as high as 24.6%. Here, we show the results of various types of photonic characterizations of the Ag-embedded nanocone structures that confirm their versatility as regards a broad range of quantum optical applications. We measure the first-order autocorrelation function to evaluate the coherence time of emitted photons, and the second-order correlation function, which reveals the strong suppression of multiple photon generation. The high indistinguishability of emitted photons is shown by the Hong-Ou-Mandel-type two-photon interference. With quasi-resonant excitation, coherent population flopping is demonstrated through Rabi oscillations. Extremely high single-photon purity with a g(2)(0) value of 0.008 is achieved with π-pulse quasi-resonant excitation. [ABSTRACT FROM AUTHOR]

We investigated the magnetoconductivity Δσ(H)≡1/ρ(H)-1/ρ(0) in a wide range of magnetic fields for three-dimensional indium oxide films doped with zinc, tin, or gallium in the range of resistivity ρ(300K) between 4.1×10-6 Ωm and 1.7×10-3 Ωm. The weak localization theory was fitted to data for Δσ(H) at various temperatures in the range 2.0 K≤T≤50 K by the use of suitable characteristics Dτin(T) and Dτso, where D, τin, and τso are the electron diffusion constant, inelastic scattering time, and spin-orbit (s-o) scattering time, respectively. It was found that (i) for films with a large value of ρ, the sign of Δσ(H) changes from positive to negative with decreasing temperature as a precursor to an anti-weak localization effect; (ii) the ratio τso/τin decreases from ≈4000 to≈4.0 with increasing ρ; (iii) the strong ρ dependence of Dτso cannot be explained by the model with a constant atomic number Z in a formula τso∝1/Z4 proposed by Abrikozov and Gorkov Zh. Eksp. Teor. Fiz. 42, 1088 (1962); [Sov. Phys. JETP 15, 752 (1962)]. As a reason for this ρ dependence, we suggest that the s-o scattering changes with increasing ρ from light oxygen atoms to heavy atoms, i.e., indium, zinc, and gallium, because of the decrease in the number of oxygen vacancies acting as s-o scattering centers. [ABSTRACT FROM AUTHOR]

The creep behavior and elastic properties of cold-drawn poly(ethylene terephthalate) (PET) films, annealed in the range 60–240 °C have been investigated by means of microindentation testing. Two indentation methods have been used. The imaging method has been employed to examine the viscoplastic properties of the polymer materials while the depth-sensing method was used for the determination of Young's modulus values. The creep behavior (plastic flow) of cold-drawn PET is shown to be intimately correlated to the nanostructural changes occurring upon annealing. The observed decrease in the rate of creep, when the glassy material is annealed at 60 7°C, has been associated with the emerging smectic structure, which confers to the material a higher mechanical performance. The elastic properties of the smectic phase are found to be comparable to those of the glassy state. Young's modulus E values of the semicrystalline samples are discussed in light of the parallel model of crystalline and amorphous layers. E values are shown to depend on the crystalline lamellar thickness and the degree of crystallinity. Results suggest that Young's modulus values of the amorphous constrained regions within the crystals are higher than the E value of the fully amorphous material. [ABSTRACT FROM AUTHOR]

Presents information on a study which characterized residual strain, surface roughness and dislocations of alloy layers grown by molecular beam epitaxy on silicon(001) substrates. Experimental details; Results and discussion; Conclusions.

We have constructed a cylindrical cavity resonator with a hybrid coupler where circularly polarized microwaves can be irradiated to a sample. The polarity of the microwave can be switched by changing the input ports of the hybrid coupler. The cavity resonator is small enough to be mounted on a cryostat which enables us to change the sample temperature in a wide range. To demonstrate the performance of the cavity resonator mounted on a cryostat, Yttrium Iron Garnet (YIG) was used as a test sample. We succeeded in selectively exciting left and right circularly polarized modes with high polarization (>80%). We also evaluated the susceptibility tensor of YIG in the cryostat. The technique presented here would offer a new direction in the fields of spintronics and quantum information. [ABSTRACT FROM AUTHOR]

We theoretically and experimentally demonstrate dynamic, all-linear time-reversal of infrared light in planar optical circuits for the first time. We propose that the oscillatory motion of the light stored in cavities can be time-reversed by fast nonadiabatic tuning of the frequency of eigenmodes of a coupled cavity system and experimentally demonstrate it using a system consisting of distant high-Q-factor two-dimensional photonic crystal cavities between which effective direct couplings are formed via line-defect waveguides. We also analyze the loss and methods to reduce the loss, as well as a theory that expands our system to realize general time-reversal operation for any input light. [ABSTRACT FROM AUTHOR]

Presents a study which deposited hydrogenated amorphous silicon carbide (α-SiC:H) films with a radio frequency plasma-enhanced chemical vapor deposition (PECVD) system which utilizes a direct current electric field applied independently of the inductively coupled radio frequency field. Diagram of the field-enhanced PECVD; Method used in fabricating heterojunction alpha-SiC:H/c-Si diodes; Growth of the a-SiC:H films.

The temperature dependence of the electrical resistance (R-T) and the current-voltage (I-V) characteristics has been measured and analyzed in a 40 nm thick Ti thin film, which is used as a transition edge sensor (TES). The analyses of the I-V characteristics with the vortex-antivortex pair dissociation model indicate the possible existence of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional superconducting Ti thin films. We investigated the noise due to the vortices' flow in TESs. The values of the current noise spectral density in the TESs were estimated by employing the vortex dynamics caused by the BKT transition in the Ti thin films. The estimated values of the current noise spectral density induced by the vortices' flow were in respectable agreement with the values of excess noise experimentally observed in the TESs with Ti/Au bilayer. [ABSTRACT FROM AUTHOR]

Metallic nanocavities have been actively studied for realizing nanolasers with low threshold. Presence of resonance modes with high cavity Q values is the indication of low internal loss that leads to low threshold lasing. However, cavity Q values observed in metallic nanocavities below lasing threshold remain low at present on the order of 100 to 500. We study the possibility to realize higher resonance Q values with a metallic nanocavity. For probing purpose of cavity modes we propose to employ broad mid-gap-state optical emission of n-type GaAs. With this method we report the observation of a resonance mode with the high Q value of 3800 at room temperature with the metallic nanocavity. The cavity mode is identified as a whispering-gallery mode with finite-element-method simulation. [ABSTRACT FROM AUTHOR]

The ion-induced-bending (IIB) phenomenon was applied for fabricating a field-emitter array (FEA). The IIB method can form a vertical-thin-film (VTF) structure with micron-order height and a high aspect ratio from a thin film. Accordingly, it only needs small quantities of material and uses no specialized equipment. As a result of the optimization of the IIB phenomenon, the apex radius of the VTF was decreased by decreasing the film thickness. The material dependence of the IIB method was investigated, and the authors found that the molybdenum film gives the largest bending angle of the three refractory metals tested. An emission current of 10 μA from the Mo-VTF emitter with 1000 tips was obtained at relatively low extraction voltage. Then thus conclude that IIB is a very promising method for fabricating a FEA. [ABSTRACT FROM AUTHOR]

We report a lateral oxide-confinement layer for InP-based devices using lattice-matched AlGaAsSb. The confinement-layer-induced excess loss at different widths was extracted after de-embedding the losses due to carrier diffusion, nonradiative recombination, and changes in internal injection efficiency. The results show that AlGaAsSb oxide acts as an excellent confinement layer, and shows no excess loss down to a width of 4 µm. [ABSTRACT FROM AUTHOR]

High-power blue-violet laser diodes with aspect ratio as low as 2.3 and threshold current down to 33 mA have been realized. The relationship between threshold current and optical confinement factor was investigated in order to minimize the beam divergence angle perpendicular to the junction plane (θ[sub ⊥]). θ[sub ⊥] was found to decrease with reduction of the optical confinement factor, whereas threshold current density increased. A new layer structure, in which a p-typed cladding layer was located next to an AlGaN electron blocking layer, and a GaInN guiding layer was inserted between the active and the AlGaN electron blocking layer, was effective for obtaining small θ[sub ⊥] while maintaining low threshold current. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An improvement of an all-optical modulation scheme that utilizes an intersubband transition is proposed and investigated in connection with intersubband carrier relaxation dynamics. N-doped GaAs/AlGaAs quantum wells are pumped by an ultrashort (∼120 fs) intersubband-resonant pulse and probed by an interband-resonant white-light continuum. Ultrafast modulation speed of ∼0.4 ps is demonstrated, which is faster than that of the previous scheme by as much as a factor of 10. It is found that a large part of the carriers, which are excited from the first conduction subband to the second conduction subband, transfer to unknown trapping states at a relaxation time that is comparable to that of the pump–pulse duration. The existence of the carrier relaxation path via L valley subbands is strongly suggested as the cause. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Y-Ba-Cu-O films were deposited on Al-coated Si substrates by the plasma-spray method. The Al buffer layer appears to be effective in yielding crack-free adhesive Y-Ba-Cu-O films. Resistance measurements indicate that the films exhibit a superconducting phase below 90 K. Results of x-ray microanalysis and x-ray photoelectron spectroscopy confirm that the Al buffer forms an Al2O3 layer and prevents precipitation of Cu at the film/substrate interface. [ABSTRACT FROM AUTHOR]

Reports on the development of high-strength, high-conductivity copper-silver alloys for high-field pulsed magnet use. Repetition of the intermediate heat treatment; Display of a tensile strength by the optimized Cu-16 at.% Ag alloy wire.

A picosecond-range all-optical modulation based on the nonlinear interaction between interband- and intersubband-resonant light in GaAs/AlGaAs multiple quantum wells was demonstrated. A free electron laser (FEL) with a very short pulse width (<10 ps) was used for the intersubband excitation. The dependence of the modulation depth on the wavelength of the intersubband-resonant light was investigated by utilizing the wide tunability of the FEL. The result is in good agreement with the intersubband absorption spectrum of the multiple quantum wells measured by FT-IR spectroscopy, which indicates that the observed modulation is indeed based on the intersubband transition induced by the FEL. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High photon-extraction efficiency is strongly required for a practical single-photon source. We succeed in fabricating metal (sliver)-embedded nanocone structure incorporating an InAs quantum dot. Efficient photon emission of ∼200 000 photons per second is detected and single-photon emission is demonstrated using autocorrelation measurements. The photon-extraction efficiency as high as 24.6% is obtained from the structure. [ABSTRACT FROM AUTHOR]

We have developed a technique to align a two-dimensional photonic-crystal nanocavity (PCNC) with an indium arsenide/gallium arsenide self-assembled quantum dot (QD), using microscopic photoluminescence (μ-PL) spectroscopy to image a wafer with a low-density of QDs and pre-formed positioning marks. Individual QD emission wavelengths were evaluated from μ-PL spectra, and positions relative to the marks were determined. The wavelength detuning between the QD-emission peak and the PCNC resonant frequency was < 4 nm, and the alignment standard deviation was < 50 nm. The emission peaks of a single QD and a PCNC aligned by this technique showed anti-crossing, implying high accuracy. [ABSTRACT FROM AUTHOR]

We have investigated the dependence of crystallographic tilt and defect distribution on mask material in metalorganic chemical vapor deposition grown GaN layers formed utilizing an epitaxial lateral overgrowth (ELO) technique using x-ray diffraction and transmission electron microscopy. Crystallographic tilt in the ELO GaN layer was suppressed by changing the mask material from electron beam (EB)-evaporated SiO[sub 2] to plasma enhanced chemical vapor deposition (PECVD) grown SiO[sub 2] and PECVD SiN[sub x]. Defect distribution also changes in accordance with mask materials. By depositing a thin PECVD SiN[sub x] layer on the PECVD SiO[sub 2] mask, the crystalline quality of the ELO layer changes from that used with the SiO[sub 2] mask to that used with the SiN[sub x] mask. These results suggest that the interface between the ELO GaN layer and the mask has a significant effect on crystallographic tilt and defect distribution. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Modulation of interband-resonant light (∼800 nm) by intersubband-resonant light (5-7 μm) was investigated in n-doped AlGaAs/GaAs multiple quantum wells by a two-color femtosecond pump-probe technique. Modulation with a recovery time of ∼1 ps is observed in a plainer-type modulation device at room temperature. The modulation of interband absorption coefficient is ∼1000 cm-1 when the energy density of the intersubband light pulse is ∼4 fJ/μm2. The modulation efficiency indicates that 99% modulation can be achieved with a control pulse energy of ∼1 pJ when a conventional waveguide-type device structure is utilized. The mechanism which determines the modulation speed is discussed in terms of carrier relaxation process. It is shown that the modulation speed is mainly determined by the inter- and intrasubband relaxation times, where the latter is influenced by hot phonon effects. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]