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20 Mar 2000

Volume 76, Issue 12, pp. 1489-1630

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InGaN/GaN multi-quantum well distributed Bragg reflector laser diode

Jaehee Cho, S. Cho, B. J. Kim, S. Chae, C. Sone, O. H. Nam, J. W. Lee, Y. Park, and T. I. Kim

Appl. Phys. Lett. 76, 1489 (2000); http://dx.doi.org/10.1063/1.126072 (3 pages) | Cited 3 times

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An electrically injected InGaN/GaN-based distributed Bragg reflector (DBR) laser was demonstrated. Surface grating was formed on both sides of ridge waveguide by chemically assisted ion beam etching technique. The observed threshold current was 375 mA with threshold voltage of 15.1 V for 500×3 μm2 devices. The emission of the DBR laser occurred in a single longitudinal mode at a wavelength of 401.3 nm. The ratio of sidemode suppression was found to be more than 13 dB until a current injection of 1 A. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology

Self-aligned current aperture in native oxidized AlInAs buried heterostructure InGaAsP/InP distributed feedback laser

Zhi-jie Wang, Soo-jin Chua, Zi-ying Zhang, Fan Zhou, Jing-yuan Zhang, Xiao-jie Wang, Wei Wang, and Hong-liang Zhu

Appl. Phys. Lett. 76, 1492 (2000); http://dx.doi.org/10.1063/1.126073 (3 pages) | Cited 2 times

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A InGaAsP/InP self-aligned, native oxidized buried heterostructure (BH) distributed feedback (DFB) laser is proposed. It is as easy to process as the ridge waveguide DFB laser and has superior performance. The current aperture can be easily controlled without selective regrowth. The laser exhibits a low threshold of 5.0 mA with 36 dB side mode suppression ratio at the emission wavelength of 1.562 μm. It emits in a single lobe with full width at half maximum angles of 33.6° and 42.6° for the lateral and vertical fields, respectively. Its beam is more circular than that of the as-grown BH laser because the lower refractive index of oxide compared to the as-grown layer and results in a larger lateral optical confinement. Its characteristic temperature (T0) is 50 K at room temperature but increases in value at the higher temperature range. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Midinfrared emission from InGaN/GaN-based light-emitting diodes

Daniel Hofstetter, Jérôme Faist, and David P. Bour

Appl. Phys. Lett. 76, 1495 (2000); http://dx.doi.org/10.1063/1.126074 (3 pages) | Cited 4 times

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Midinfrared emission on violet, blue, and green InGaN light-emitting diodes has been measured between 85 and 300 K for various injection current densities. We found that the diode with the highest In composition in the active region had the shortest midinfrared emission wavelength and vice versa. With increasing In content, a significantly decreasing amount of TM polarization was observed in the midinfrared emission spectrum. This result suggests that the density of states in the higher-In content devices corresponds to a zero-dimensional electronic system rather than a two-dimensional electron gas. In contrast to this, the violet light-emitting diode exhibited a higher degree of TM polarization; similar to a red InGaP-based quantum-well device. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Ti:LiNbO3 waveguide polarizer with a Zn-doped overlayer prepared by liquid-phase epitaxy

Junichiro Ichikawa, Satoshi Uda, Kiyoshi Shimamura, Tsuguo Fukuda, Hirotoshi Nagata, and Junichiro Minowa

Appl. Phys. Lett. 76, 1498 (2000); http://dx.doi.org/10.1063/1.126075 (3 pages) | Cited 3 times

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Ti:LiNbO3 waveguide polarizers were obtained by an epitaxial growth of a Zn-doped LiNbO3 layer on the Ti:LiNbO3 waveguide. The film growth was carried out by a liquid-phase-epitaxy technique using a Li2O–V2O5 flux. Such an X-cut waveguide polarizer achieved a TE-mode (extraordinary ray) propagation with an extinction ratio over 30 dB at a light wavelength of 1.55 μm. This technique can be easily applied to Z- and Y-cut waveguide polarizers with TM- and TE-mode propagation, respectively. © 2000 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
42.79.Ci Filters, zone plates, and polarizers
42.79.Gn Optical waveguides and couplers

Nanosecond transients in the electroluminescence from multilayer blue organic light-emitting devices based on 4,4′-bis(2,2′diphenyl vinyl)-1,1′-biphenyl

V. Savvate’ev, J. H. Friedl, L. Zou, J. Shinar, K. Christensen, W. Oldham, L. J. Rothberg, Z. Chen-Esterlit, and R. Kopelman

Appl. Phys. Lett. 76, 1501 (2000); http://dx.doi.org/10.1063/1.126076 (3 pages) | Cited 13 times

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Nanosecond electroluminescence (EL) overshoots observed when multilayer blue 4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl (DPVBi)-based organic light-emitting devices (OLEDs) are excited by rectangular voltage pulses are described. The overshoots occur at the voltage turn-off and exceed the cw brightness by up to an order of magnitude. Time-resolved images of the OLEDs demonstrate that the emission from most of the sample surface decays with a single time constant τ1 = 13±3 ns. This decay is attributed to recombination of charges which accumulate at the interface of the electron and hole transporting layers, possibly at intrinsic trapping sites. In areas of increased electron injection and EL, such as cathode edges and morphological defects, a second slower decay time 20 ns<τ2<1 μs is observed, apparently due to release of carriers from localized trap states in the organic/cathode interface. Only marginal variations in τ1 are found between bright and dim areas of the devices. At a bias of 10 V, the amplitude of the overshoot is found to peak at a pulse duration of ∼ 20 μs. Its behavior is believed to result from increased quenching of singlet excitons by the accumulated charges. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Simple model for calculating the ratio of the carrier capture and escape times in quantum-well lasers

B. Romero, J. Arias, I. Esquivias, and M. Cada

Appl. Phys. Lett. 76, 1504 (2000); http://dx.doi.org/10.1063/1.126077 (3 pages) | Cited 22 times

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We have developed a simple model for the carrier capture and escape processes in quantum-well (QW) lasers, which yields an analytical expression for the ratio of the carrier capture and escape times. It predicts a decrease in the escape time with injected carrier density due to the state filling effect. It also shows an exponential dependence of the escape time on the effective barrier height and on the inverse of the temperature. A comparison between experimental and calculated values for InGaAs/GaAs QW lasers is presented showing a good agreement. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Near-infrared to visible up-conversion in a forward-biased Schottky diode with a p-doped channel

J. S. Sandhu, A. P. Heberle, B. W. Alphenaar, and J. R. A. Cleaver

Appl. Phys. Lett. 76, 1507 (2000); http://dx.doi.org/10.1063/1.126078 (3 pages) | Cited 16 times

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Near-infrared radiation of wavelength 1.5 μm is up-converted to a visible wavelength of 818 nm by internal photoemission in a Schottky diode with a modulation p-doped channel. The near-infrared light incident upon the metal–semiconductor interface excites electrons from the metal into the semiconductor. The electrons then drift into the quantum well where they recombine radiatively, producing luminescence at the shorter wavelength of 818 nm. The intensity of the luminescence is strongly dependent on bias, and turns on at a forward bias of −0.7 V. © 2000 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
78.66.Fd III-V semiconductors
73.40.Ns Metal-nonmetal contacts
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Two-photon photocurrent imaging of vertical cavity surface emitting lasers

Chris Xu, Leo M. F. Chirovsky, W. S. Hobson, J. Lopata, Wayne H. Knox, John E. Cunningham, William Y. Jan, and L. A. D’Asaro

Appl. Phys. Lett. 76, 1510 (2000); http://dx.doi.org/10.1063/1.126079 (3 pages) | Cited 1 time

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We show that two-photon photocurrent imaging can be used to nondestructively study vertical cavity surface emitting lasers on a microscopic level. In particular, we study the aperture isolation created by shallow ion implantation. The combination of two-photon backside imaging and a probe station is ideal for internal and full wafer characterization. The required peak and average power levels for testing can be easily satisfied by available compact ultrafast laser sources, making the technique practical and user friendly. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Birefringence compensation in single solid-state rods

R. Fluck, M. R. Hermann, and L. A. Hackel

Appl. Phys. Lett. 76, 1513 (2000); http://dx.doi.org/10.1063/1.126080 (3 pages) | Cited 8 times

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Various methods for compensating birefringence depolarization in solid-state rods are theoretically and experimentally analyzed and compared. Gaussian and flat top beam profiles are investigated. The efficiency in depolarization loss reduction using different techniques is discussed in terms of beam profile, rod fill factor, and thermal heat load. In Nd:yttrium–aluminum–garnet, the depolarization loss can be efficiently reduced below 5% with a compensating quarter-waveplate, up to 20 W heat load for a flat top beam and up to 70 W for a gaussian beam. © 2000 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.25.Lc Birefringence
78.20.Fm Birefringence

Room-temperature electroluminescence from electron-hole plasmas in the metal–oxide–silicon tunneling diodes

C. W. Liu, M. H. Lee, Miin-Jang Chen, I. C. Lin, and Ching-Fuh Lin

Appl. Phys. Lett. 76, 1516 (2000); http://dx.doi.org/10.1063/1.126081 (3 pages) | Cited 44 times

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An electron-hole plasma recombination model is used to fit the room-temperature electroluminescence from metal–oxide–silicon tunneling diodes. The relatively narrow line shape in the emission spectra can be understood by the quasi-Fermi level positions of electrons and holes, which both lie in the band gap. This model also gives a narrower band gap than that of bulk silicon. The surface band bending in the Si/oxide interface is responsible for this energy gap reduction. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
81.05.Cy Elemental semiconductors
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
71.20.Mq Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
73.20.At Surface states, band structure, electron density of states
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena

A cross-correlation spectroscopy in subterahertz region using an incoherent light source

O. Morikawa, M. Tonouchi, and M. Hangyo

Appl. Phys. Lett. 76, 1519 (2000); http://dx.doi.org/10.1063/1.126082 (3 pages) | Cited 19 times

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A subterahertz (sub-THz) spectroscopic system using a multimode laser diode and photoconductive antennas (PA) has been proposed. It employs a random fluctuation of the light intensity to produce the subterahertz radiation from the emitter PA and also to trigger the detector PA. The signal is obtained as the cross correlation between the sub-THz radiation amplitude and laser light intensity. The decrease in the amplitude and phase delay of the radiation due to transmission from a sample can be calculated from the signal in a broad spectral region of sub-THz. This system is applied to the measurement of the complex refractive indices of Si wafers. The obtained dispersion of the refractive indices is well explained by the Drude model. © 2000 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Db Elemental semiconductors and insulators
73.61.Cw Elemental semiconductors
78.30.Am Elemental semiconductors and insulators

Comparison of experimental and theoretical gain-current relations in GaInP quantum well lasers

P. M. Smowton, P. Blood, and W. W. Chow

Appl. Phys. Lett. 76, 1522 (2000); http://dx.doi.org/10.1063/1.126083 (3 pages) | Cited 8 times

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We compare the results of a microscopic laser theory with gain and recombination currents obtained from experimental spontaneous emission spectra. The calculated absorption spectrum is first matched to that measured on a laser, ensuring that the quasi-Fermi levels for the calculation and the experiment (spontaneous emission and gain) are directly related. This allows us to determine the inhomogeneous broadening in our experimental samples. The only other inputs to the theory are literature values of the bulk material parameters. We then estimate the nonradiative recombination current associated with the well and waveguide core from a comparison of measured and calculated recombination currents. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Voltage-controlled yellow or orange emission from GaN codoped with Er and Eu

D. S. Lee, J. Heikenfeld, R. Birkhahn, M. Garter, B. K. Lee, and A. J. Steckl

Appl. Phys. Lett. 76, 1525 (2000); http://dx.doi.org/10.1063/1.126084 (3 pages) | Cited 44 times

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Orange and yellow-colored light emission has been achieved at room temperature in the same elecroluminescent device (ELD) made on GaN thin films codoped with Er and Eu. The GaN film was grown by molecular-beam epitaxy on Si (111) substrates using solid sources for Ga, Er and Eu and a plasma source for N2. Simple Schottky devices were fabricated on the GaN films using indium–tin oxide (ITO) transparent electrodes. ELD spectra show that the yellow and orange colors result from the combination of green emission from Er (537, 558 nm) and red emission from Eu (621 nm). A color change was observed with applied bias, producing yellow at higher bias (−100 V) and orange at lower bias (−70 V). We have fabricated both relatively small (∼250 μm) and large (1.45 mm) ELDs. Parameters for the chromaticity diagram were calculated to be x=0.382, y=0.605 for the yellow emission and x=0.467, y=0.523 for the orange emission. This work shows the possibility of achieving any intermediate color in the spectrum from green to red by adjusting the concentration of Er and Eu in GaN. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Mercury depletion as a way of changing the emission spectrum of a fluorescent lamp

L. P. Bakker and G. M. W. Kroesen

Appl. Phys. Lett. 76, 1528 (2000); http://dx.doi.org/10.1063/1.126085 (3 pages) | Cited 7 times

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We present a promising option for changing the emission spectrum of a fluorescent lamp. In a neon/mercury discharge, neon radiation is produced when the mercury density is sufficiently low. Under certain discharge conditions, radial cathaphoresis causes depletion of mercury atoms in the center of the plasma. This effect is especially well pronounced at high electrical currents and low mercury pressures. We measured the color temperature of a fluorescent lamp containing a neon/mercury discharge at several mercury pressures and currents. The color temperature of this lamp varied from 4000 to 2100 K. We also performed ultraviolet absorption measurements. From these measurements, we obtained the mercury atom density profile in the discharge. A significant decrease of the mercury density in the center of the plasma is indeed observed under certain discharge conditions. © 2000 American Institute of Physics.
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52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
42.72.Bj Visible and ultraviolet sources

Magnetic-field-dependent plasma composition of a pulsed arc in a high-vacuum ambient

Jochen M. Schneider, André Anders, Björgvin Hjörvarsson, and Lars Hultman

Appl. Phys. Lett. 76, 1531 (2000); http://dx.doi.org/10.1063/1.126086 (3 pages) | Cited 13 times

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The effect of a magnetic field on the plasma composition of a pulsed Au plasma stream in a high-vacuum ambient is described. The plasma was formed with a pulsed vacuum-arc-plasma source, and the time-resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. Plasma impurities due to ionization of nonmetallic species (H+, O+, and N+) were found to be below the detection limit in the absence of a magnetic field. However, in the presence of a magnetic field (0.4 T), the contribution of ionized nonmetal species to the plasma composition was up to 0.22 atomic ratio. These results are characteristic of plasma-based techniques where magnetic fields are employed in a high-vacuum ambient. In effect, the impurity incorporation during thin-film growth pertains to the present findings. © 2000 American Institute of Physics.
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52.25.Vy Impurities in plasmas
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
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Brittle-ductile relaxation kinetics of strained AlGaN/GaN heterostructures

S. J. Hearne, J. Han, S. R. Lee, J. A. Floro, D. M. Follstaedt, E. Chason, and I. S. T. Tsong

Appl. Phys. Lett. 76, 1534 (2000); http://dx.doi.org/10.1063/1.126087 (3 pages) | Cited 48 times

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We have directly measured the stress evolution during metal-organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to determine directly a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained AlxGa1−xN grown on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation. © 2000 American Institute of Physics.
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62.20.M- Structural failure of materials
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Effects of surface resonance state on the plasmon resonance absorption of Ag nanoparticles embedded in partially oxidized amorphous Si matrix

L. Yang, G. H. Li, and L. D. Zhang

Appl. Phys. Lett. 76, 1537 (2000); http://dx.doi.org/10.1063/1.126088 (3 pages) | Cited 36 times

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Nanocomposite films consisting of nanosized Ag particles embedded in partially oxidized amorphous Si matrices were prepared by radio frequency cosputtering deposition. Subsequent heat treatment at different temperatures ranging from 200 to 500 °C and its effects on the optical absorption of the films were investigated by spectrometry in the wavelength ranging from 200 to 1200 nm. “Surface resonance state” is introduced to discuss the broadening, blue-shift, and intensity decrease of the plasmon resonance absorption peak with decreasing Ag particle size. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.40.Kc Metals, semimetals, and alloys

Photoluminescence of CdSe nanocrystallites embedded in BaTiO3 matrix

Ji Zhou, Longtu Li, Zhilun Gui, S. Buddhudu, and Yan Zhou

Appl. Phys. Lett. 76, 1540 (2000); http://dx.doi.org/10.1063/1.126089 (3 pages) | Cited 18 times

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This letter reports the photoluminescence properties of CdSe quantum dots (QDs) embedded in a ferroelectric BaTiO3 matrix. The main emission from the samples has been assigned to the band–edge transition of QDs. With an increase in the heat treatment temperature, the emission peak has been shifted to a longer wavelength. This shift has been attributed due to the dielectric environment effects of the matrix on the electronic structure of the QDs. The dependences of the peak position on the heat-treatment temperature and dot size are found in agreement with the theoretical simulation results reported previously. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.-w Structure of nanoscale materials

Self-enhancement in the electroluminescence of a near-infrared ionic dye

Hiroyuki Suzuki

Appl. Phys. Lett. 76, 1543 (2000); http://dx.doi.org/10.1063/1.126090 (3 pages) | Cited 25 times

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This letter reports self-enhancement behavior observed in the near-infrared electroluminescence (EL) of an ionic dye, 2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methylbenzothiazolium perchlorate doped in poly(N-vinylcarbazole). The EL intensity measured under a constant current, and therefore, the external EL quantum efficiency (ϕex), increases with time both when the EL is generated continuously in a constant current mode and kept in a no-bias field, whereas it decreases in a reverse-bias field. With an enhancement factor of about 80 under a constant current of 0.1 mA/cm2, ϕex reaches the 1% photons/electron level. I conclude that the behavior originates from the enhanced electron and hole injection caused by the alignment of the doped ionic dye molecules along the bias field. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Recombination dynamics of carriers in an InGaN/AlGaN single-quantum-well light-emitting diode under reverse-bias voltages

Hiromitsu Kudo, Hiroki Ishibashi, Ruisheng Zheng, Yoichi Yamada, and Tsunemasa Taguchi

Appl. Phys. Lett. 76, 1546 (2000); http://dx.doi.org/10.1063/1.126091 (3 pages) | Cited 7 times

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The radiative recombination process of the blue emission band in an InGaN single-quantum-well light-emitting diode has extensively been investigated by means of the dependence of an external electric field on photoluminescence and time-resolved photoluminescence spectra. Two emission (higher and lower) components separated by about 40 meV are found in the emission band on the condition of reverse bias at 77 K. It is also found that the luminescence intensity decreases dramatically with increasing reverse-bias voltage at room temperature. The model based on field ionization of excitons cannot explain the present experimental phenomena. It is, therefore, suggested that the free-carrier recombination process is dominant at room temperature. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Relationship between optical properties and crystallinity of nanometer Y2O3:Eu phosphor

T. Igarashi, M. Ihara, T. Kusunoki, K. Ohno, T. Isobe, and M. Senna

Appl. Phys. Lett. 76, 1549 (2000); http://dx.doi.org/10.1063/1.126092 (3 pages) | Cited 95 times

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Y2O3-doped Eu3+ (Y2O3:Eu) nanometer particles (NPs) were synthesized via a chemical route. The particle size estimated by x-ray diffractometry and transmission electron microscopy was about 61 nm. Two photoluminescence peaks were observed at 582 and 587 nm, being attributed to the transition of 5D0→7F1a of Eu3+ in the S6 and C2 symmetry sites of Y2O3, respectively. The intensity ratio of the photoluminescence peaks at 582 nm to at 587 nm was larger for NPs than for micrometer particles (MPs). The excitation peak of NPs due to the charge-transfer band shifted toward the high-energy side as compared with that of MPs. According to x-ray diffractometry, the lattice distortion and the lattice constant were larger for NPs than for MPs, showing the restructure at the near surface and the increase in ionicity of the Eu–O bond with decreasing particle size. This explains the blueshift in the excitation peak. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.66.Fn Inorganic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.50.Lt Crystal binding; cohesive energy

Structures of nitridated layers on sapphire studied by x-ray reflectivity and diffraction

Ki-Sung Kim, Seon-Hyo Kim, and Dong-Ryul Lee

Appl. Phys. Lett. 76, 1552 (2000); http://dx.doi.org/10.1063/1.126093 (3 pages) | Cited 6 times

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A nitridated layer of c-plane sapphire was studied by using synchrotron x-ray reflectivity and diffraction measurements. The nitridation of the sapphire surface produced an epitaxial AlN layer with a low mosaicity (1 arcmin) normal to the surface. The nitridation temperature determined the limiting thickness for the nitridated layer. Excessive nitridation beyond the limiting thickness caused strain relaxation by a reduction of lateral domain size and an increase in lateral mosaicity. Therefore, the nitridated layer with compressive strain may provide better nucleation sites for the subsequent GaN overlayer growth than the strain-relaxed one. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
78.20.-e Optical properties of bulk materials and thin films

Experimental measurements of the strength of metals approaching the theoretical limit predicted by the equation of state

E. Moshe, S. Eliezer, Z. Henis, M. Werdiger, E. Dekel, Y. Horovitz, S. Maman, I. B. Goldberg, and D. Eliezer

Appl. Phys. Lett. 76, 1555 (2000); http://dx.doi.org/10.1063/1.126094 (3 pages) | Cited 28 times

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The approach to the ultimate strength of metals is determined experimentally. The ultimate strength of metals was calculated using a realistic wide-range equation of state. The strength of metals was measured using shock waves created in aluminum and copper foils with a short- (20–100 ps) pulse high-power laser. The strength of the materials was determined from the free-surface-velocity time history, which was measured with an optically recording velocity interferometer system. The strain rates in these experiments were in the range (1.5–5)×108 s−1. © 2000 American Institute of Physics.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
79.20.Ds Laser-beam impact phenomena
62.20.-x Mechanical properties of solids
81.40.Gh Other heat and thermomechanical treatments

Adatom condensation and quantum dot sizes in InGaAs/GaAs (001)

R. Leon, J. Wellman, X. Z. Liao, J. Zou, and D. J. H. Cockayne

Appl. Phys. Lett. 76, 1558 (2000); http://dx.doi.org/10.1063/1.126095 (3 pages) | Cited 11 times

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The sizes and concentrations of capped and surface InGaAs/GaAs quantum dots (QDs) grown under the same conditions have been investigated. Comparisons obtained with transmission electron microscopy and scanning probe microscopy imaging show a significant enlargement in the sizes of surface QDs compared with capped QDs. This discrepancy in dot dimensions increases with decreasing island surface densities and can be partially explained by thermal adatom condensation during sample cooling. These findings suggest a technique to estimate adatom concentrations and their migration lengths in strained heteroepitaxy. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.35.Fx Diffusion; interface formation
61.46.-w Structure of nanoscale materials

Bandgap closure of a flattened semiconductor carbon nanotube: A first-principles study

Mário S. C. Mazzoni and H. Chacham

Appl. Phys. Lett. 76, 1561 (2000); http://dx.doi.org/10.1063/1.126096 (3 pages) | Cited 41 times

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We investigate, through first-principles calculations, the effects of a flattening distortion on the electronic properties of a semiconductor carbon nanotube. The flattening causes a progressive reduction of the band gap from 0.92 eV to zero. The band-overlap insulator-metal transition occurs for an interlayer distance of 4.6 Å. Supposing that the flattening of the nanotube can be produced by a force applied by a scanning microscope tip, we estimate that the force per unit length of the nanotube that is necessary to reach the insulator-metal transition is 7.4 N/m. © 2000 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
71.30.+h Metal-insulator transitions and other electronic transitions
71.15.-m Methods of electronic structure calculations
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