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4 Feb 2002

Volume 80, Issue 5, pp. 707-899

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Two-color quantum-well infrared photodetector with voltage tunable peaks

Amlan Majumdar, K. K. Choi, J. L. Reno, L. P. Rokhinson, and D. C. Tsui

Appl. Phys. Lett. 80, 707 (2002); http://dx.doi.org/10.1063/1.1447004 (3 pages) | Cited 15 times

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A two-color quantum-well infrared photodetector with voltage tunable detection peaks is demonstrated. It is based on electron transfer between two asymmetric coupled quantum wells under an applied bias. At 10 K, the peak detection wavelength is 7.5 μm for positive bias when the electrons reside in one of the wells, and switches to 8.8 μm at a large negative bias when the electrons are transferred to the other well. The electron activation behavior of dark current in this detector depends on both temperature and bias. We observed two distinctive activation energies under negative bias for two different temperature regimes and only one under positive bias. The voltage tunability of the detector and the activation energy are well explained by the calculated energy levels and oscillator strengths of intersubband transitions in the structure. © 2002 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
78.67.De Quantum wells
81.07.St Quantum wells

Ag photodoping into crystalline ZnSe

Hyun-Yong Lee, Joon-Suk Song, Hisao Makino, and Takafumi Yao

Appl. Phys. Lett. 80, 710 (2002); http://dx.doi.org/10.1063/1.1445464 (3 pages) | Cited 5 times

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We have investigated the possibility of Ag photodoping into crystalline (c-) ZnSe grown by molecular-beam epitaxy. A Ag/c-ZnSe sample was illuminated with a 325 nm HeCd laser at 10 K and its photoluminescence (PL) characteristics were measured in real time. Depending on the illumination time, there are considerable changes in the intensities of the deep-level peaks (2.059 and 2.345 eV) as well as the near-band-edge peak (2.798 eV). The emission band at 2.059 eV is almost independent of PL-excitation power, while the green luminescence band at 2.345 eV exhibits distinctly a power-dependent blueshift with increasing excitation power, which can be assigned as a donor-to-acceptor pair transition (AgiAgZn). In this letter, a model to explain Ag photodoping into c-ZnSe is proposed on the basis of the PL results. We believe that Ag, as an activator for luminescence, can be photodoped into c-ZnSe even though the extent and kinetics of the Ag doping are different from those of the amorphous chalcogenide. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.66.Hf II-VI semiconductors

Red electrophosphorescence from osmium complexes

Xuezhong Jiang, Alex K.-Y. Jen, Brenden Carlson, and Larry R. Dalton

Appl. Phys. Lett. 80, 713 (2002); http://dx.doi.org/10.1063/1.1445272 (3 pages) | Cited 27 times

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We report red electrophosphorescence from light-emitting diodes based on osmium (Os) complexes. Efficient red emission was achieved using an in situ polymerized tetraphenyldiaminobiphenyl-containing polymer as the hole-transporting layer and Os complexes doped blend of poly(N-vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole as the emitting layer. The emission peaks of the reported Os complexes, ranging from 620 to 650 nm, can be tuned by changing the structures of the ligands because the emission originates from triplet metal-to-ligand-charge-transfer excited state. The Os complexes trap both electrons and holes, which facilitates the direct recombination of holes and electrons on the complex sites. The peak external quantum efficiency and brightness achieved from the complexes were 0.82% and 970 cd/m2, respectively. The Commission Internationale de I’Eclairage chromaticity coordinates (x,y) for the best red emission from the complexes are (0.65, 0.33). © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

Optically written solid-state lasers with broadly tunable mode emission based on improved poly (2,5-dialkoxy-phenylene-vinylene)

G. Kranzelbinder, E. Toussaere, J. Zyss, A. Pogantsch, E. W. J. List, H. Tillmann, and H.-H. Hörhold

Appl. Phys. Lett. 80, 716 (2002); http://dx.doi.org/10.1063/1.1445473 (3 pages) | Cited 21 times

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We report an optical written distributed feedback (DFB) structure with broadly and continuously tunable mode emission (Δλ = 30 nm) based on polycondensation-type poly[2methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH–PPV). In a Lloyd-mirror configuration we realize first-order feedback by dynamic photoinduced in-plane gratings, which can also be imprinted permanently. This technique is a versatile fabrication tool for polymeric DFB laser structures while also providing an efficient method to probe the lasing performance of organic solid-state laser materials. Furthermore, features of the photoinduced absorption spectra of improved MEH–PPV indicate favorable material properties towards further homopolymer solid-state laser applications. © 2002 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.70.Jk Polymers and organics
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Fourier-transform photocurrent spectroscopy of microcrystalline silicon for solar cells

M. Vanecek and A. Poruba

Appl. Phys. Lett. 80, 719 (2002); http://dx.doi.org/10.1063/1.1446207 (3 pages) | Cited 43 times

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The spectral dependence of the optical absorption coefficient in thin films of hydrogenated microcrystalline silicon is measured over nine orders of magnitude in the subgap, defect-connected region, and in the above-the-band gap region. Transmittance, reflectance, and constant photocurrent method measurements are combined with Fourier-transform photocurrent spectroscopy (FTPS). Results are analyzed and interpreted as due to electron transitions from defects or interband electron transitions, all having direct relevance to the thin-film microcrystalline silicon solar cell performance. FTPS is a fast and sensitive quantitative method for quality assessment of microcrystalline silicon absorber in solar cells and can be used for quality monitoring in solar cell production. © 2002 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
72.80.Cw Elemental semiconductors
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
84.60.Jt Photoelectric conversion

Observation of enhanced spontaneous emission coupling factor in nitride-based vertical-cavity surface-emitting laser

S. Kako, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 80, 722 (2002); http://dx.doi.org/10.1063/1.1430855 (3 pages) | Cited 15 times

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We demonstrate an enhancement of spontaneous emission coupling factor β in a nitride-based vertical-microcavity surface-emitting laser. The 2.5λ vertical microcavity, the quality factor of which reaches 740, is sandwiched between a nitride and an oxide distributed Bragg reflector. From input–output measurements and analyses of the rate equations, the β of the lasing mode at a wavelength of 396.1 nm is estimated to be 1.6×10−2. The estimated β can be well accounted for by a simple theoretical model. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.-p Quantum optics

Graded mixed-layer organic light-emitting devices

Anna B. Chwang, Raymond C. Kwong, and Julie J. Brown

Appl. Phys. Lett. 80, 725 (2002); http://dx.doi.org/10.1063/1.1446992 (3 pages) | Cited 69 times

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We describe the performance of graded, mixed-layer organic light- emitting devices (OLEDs). The devices are step graded from a mostly hole transporting layer (HTL) to a mostly electron transporting layer (ETL) from anode side to cathode side, respectively. Luminous efficiencies of >4.5 lm/W and 10 cd/A are obtained at 1000 cd/m2 for green, electrofluorescent, graded mixed OLEDs. These efficiencies are significantly higher than those of a uniformly mixed device, i.e., a device in which the HTL and ETL are uniformly mixed, but lower than those of a conventional heterostructure device employing the same dopant material. The operating lifetime of the graded mixed OLEDs, however, is much improved over the heterostructure device. The results of our work suggest that the graded mixed OLED device structure represents a path to achieving extended lifetimes with sufficient efficiency for flat panel display applications in which this parameter is critical to market acceptance. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems

Ga flux dependence of Er-doped GaN luminescent thin films

D. S. Lee and A. J. Steckl

Appl. Phys. Lett. 80, 728 (2002); http://dx.doi.org/10.1063/1.1447318 (3 pages) | Cited 15 times

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Er-doped GaN thin films have been grown on (111) Si substrates with various Ga fluxes in a radio frequency plasma molecular beam epitaxy system. Visible photoluminescence (PL) and electroluminescence (EL) emission at 537/558 nm and infrared (IR) PL emission at 1.5 μm from GaN:Er films exhibited strong dependence on the Ga flux. Both visible and IR PL and visible EL increase with the Ga flux up to the stoichiometric growth condition, as determined by growth rate saturation. Beyond this condition, all luminescence levels abruptly dropped to the detection limit with increasing Ga flux. The Er concentration, measured by secondary ion mass spectroscopy and Rutherford backscattering, decreases with increasing Ga flux under N-rich growth conditions and remains constant above the stoichiometric growth condition. X-ray diffraction indicated that the crystalline quality of the GaN:Er film was improved with increasing Ga flux up to stoichiometric growth condition and then saturated. Er ions in the films grown under N-rich conditions appear much more optically active than those in the films grown under Ga-rich conditions. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Holographic recording of fast phenomena

Zhiwen Liu, Gregory J. Steckman, and Demetri Psaltis

Appl. Phys. Lett. 80, 731 (2002); http://dx.doi.org/10.1063/1.1446205 (3 pages) | Cited 13 times

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We report on a holographic method for recording fast events whose speed is limited by the laser pulse duration if the recording material has sufficient sensitivity to reliably record a frame of the fast event with a single pulse. The method we describe uses the angular selectivity of thick holograms to resolve frames that are recorded with adjacent pulses. Two specially designed cavities are used to generate the signal and reference pulse trains. We experimentally demonstrate the system by recording laser induced shock waves with a temporal resolution of 5.9 ns, limited by the pulse width of the Q-switched Nd:yttrium–aluminum–garnet laser used in the experiments. © 2002 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
06.60.Jn High-speed techniques (microsecond to femtosecond)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Evidence for bandedge lasing in a two-dimensional photonic bandgap polymer laser

N. Moll, R. F. Mahrt, C. Bauer, H. Giessen, B. Schnabel, E. B. Kley, and U. Scherf

Appl. Phys. Lett. 80, 734 (2002); http://dx.doi.org/10.1063/1.1446213 (3 pages) | Cited 22 times

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Optically pumped organic semiconductor lasers are fabricated by spincoating a thin film of a methyl-substituted ladder-type poly-(para-phenylene) onto a nanopatterned circular grating distributed Bragg reflector. Varying the period of the grating allows for tunability of the laser wavelength. Comparing the emission spectra below and above the threshold shows that the lasing is spectrally located at the bandedge of the Bragg dip. This is in excellent agreement with the calculated dispersion relation of the laser system. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
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Secondary electron emission in a mixed gas for application to the plasma display panel

Han S. Uhm, Eun H. Choi, and Jae Y. Lim

Appl. Phys. Lett. 80, 737 (2002); http://dx.doi.org/10.1063/1.1445470 (3 pages) | Cited 16 times

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The secondary electron emission from the surface of the MgO crystal is investigated for a mixed gas in connection with applications to the plasma display panel. The experimental data indicate that the coefficient γ of the secondary emission for the neon gas mixed with a small amount of xenon is almost the same as the coefficient for the xenon-only gas. This observation agrees very well with theoretical predictions. © 2002 American Institute of Physics.
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79.20.Hx Electron impact: secondary emission
52.75.-d Plasma devices
85.60.Pg Display systems
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Strain partitioning in coherent compliant heterostructures

D. Zubia, S. D. Hersee, and T. Khraishi

Appl. Phys. Lett. 80, 740 (2002); http://dx.doi.org/10.1063/1.1445803 (3 pages) | Cited 12 times

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A self-consistent set of equations describing strain partitioning in planar bilayers is developed using a typical definition of strain, the assumption of a coherent interface and a mechanical equilibrium criterion. This approach eliminates the need for the concepts of lattice mismatch and compatibility of deformation, leading to a general solution for the strains and in-plane lattice parameter in bilayer structures. Using the strain equations, the strain energies in the system are calculated as a function of the epilayer to substrate thickness ratio. It was found that for a given substrate thickness, the epilayer strain energy contains a maximum at a layer thickness ratio of ∼1. The peak epilayer strain energy is only ∼25% of the maximum possible in the system. A criterion based on energy considerations is proposed for determining whether to use the epilayer or substrate dislocation formation energy when calculating the epilayer critical thickness. This criterion is applied to the GexSi1−x/Si(100) material system and is manifested by a kink in the critical thickness versus substrate thickness curves. The kink is interpreted as a boundary identifying whether a threading dislocation will most favorably be injected into the substrate or epilayer when the critical thickness is exceeded. © 2002 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Lk Linear defects: dislocations, disclinations
62.20.F- Deformation and plasticity

Tetrahedral amorphous-carbon thin films for silicon-on-insulator application

Z. R. Song, Y. H. Yu, C. L. Li, S. C. Zou, F. M. Zhang, X. Wang, D. S. Shen, E. Z. Luo, B. Sundaravel, S. P. Wong, and I. H. Wilson

Appl. Phys. Lett. 80, 743 (2002); http://dx.doi.org/10.1063/1.1445472 (3 pages) | Cited 5 times

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The application of a silicon-on-insulator substrate in a high-power integrated circuit is limited by the self-heating effect, caused by the poor thermal conductivity of the buried SiO2. We introduce tetrahedral amorphous-carbon thin films, formed by the filtered arc deposition method, as an alteration. We investigated the surface morphology, microstructure, and electrical properties of these films. The films deposited under a substrate bias of −200 V displayed outstanding surface topography (low surface roughness with the Rrms value under 0.5 nm) and excellent electrical property (breakdown field of 4.7 MV/cm). The film has a high content of sp3 bonds of carbon (87%) and low content of oxygen (<2%). © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.55.-a Thin film structure and morphology
77.22.Jp Dielectric breakdown and space-charge effects
81.05.U- Carbon/carbon-based materials

Constructing microstructures of poly- and nanocrystalline materials for numerical modeling and simulation

Dirk Gross and Mo Li

Appl. Phys. Lett. 80, 746 (2002); http://dx.doi.org/10.1063/1.1432448 (3 pages) | Cited 24 times

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A systematic method is developed for construction of microstructures of poly- and nanocrystalline materials for various numerical modeling and simulations. The automatic method uses as input the distribution functions of microstructure quantities such as the grain size or texture and, through a sequence of minimization procedures, obtains the desired microstructures. The digital samples generated using this method agree well with experimental samples in their topological, structural, and statistical properties. The application and impact of this method on atomistic and continuum simulation and modeling are discussed. © 2002 American Institute of Physics.
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61.72.-y Defects and impurities in crystals; microstructure
61.46.-w Structure of nanoscale materials
02.70.Ns Molecular dynamics and particle methods

Structure of recombination-induced stacking faults in high-voltage SiC p–n junctions

J. Q. Liu, M. Skowronski, C. Hallin, R. Söderholm, and H. Lendenmann

Appl. Phys. Lett. 80, 749 (2002); http://dx.doi.org/10.1063/1.1446212 (3 pages) | Cited 74 times

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The structure of stacking faults formed in forward-biased 4H- and 6H-SiC p–n− diodes was determined using conventional and high-resolution transmission electron microscopy. Typical fault densities were between 103 and 104 cm−1. All observed faults were isolated single-layer Shockley faults bound by partial dislocations with Burgers vector of a/3〈1–100〉-type. © 2001 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Polarized edge-incident photovoltage spectroscopy and reflectance characterization of a GaAs/GaAlAs vertical-cavity surface-emitting laser structure

J. S. Liang, S. D. Wang, Y. S. Huang, C. W. Tien, Y. M. Chang, C. W. Chen, N. Y. Li, D. Y. Lin, and Fred H. Pollak

Appl. Phys. Lett. 80, 752 (2002); http://dx.doi.org/10.1063/1.1445463 (3 pages) | Cited 6 times

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Polarized edge-incident photovoltage spectroscopy (EPVS) and normal-incident reflectance (NIR) studies are performed at room temperature on a bare as-grown wafer of GaAs/GaAlAs-based vertical-cavity surface-emitting laser (VCSEL) structure, designed for emitting at a wavelength near 850 nm. In addition to the interference features related to the properties of the mirrors stacks, in the NIR spectrum only the Fabry–Pérot cavity mode is clearly visible, while the polarized EPV spectra are used to identify the wavelength of fundamental and higher-order transitions from the quantum wells (QWs) in the active region. By comparing the experimental results with theoretical calculations, we are able to ascertain the Al composition, structure parameters, and material quality of the QWs in the VCSEL active regions. We demonstrate the potential of polarized EPVS for the contactless and nondestructive characterization of VCSELs at room temperature. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Influence of the barrier height on carrier recombination and transparency density in GaN-based laser structures

M. Vehse, P. Michler, I. Gösling, M. Röwe, J. Gutowski, S. Bader, A. Lell, G. Brüderl, and V. Härle

Appl. Phys. Lett. 80, 755 (2002); http://dx.doi.org/10.1063/1.1434305 (3 pages) | Cited 4 times

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Using temperature-dependent and gain measurements, we have examined the laser threshold density of (In,Ga)N/GaN/(Al,Ga)N laser structures with various well widths and different In contents in the active layer. Thermal activation energies, obtained by temperature-dependent photoluminescence measurements at low excitation densities, yield information on the nonradiative recombination channels and demonstrate the existence of two different activation processes. One of them may be related to thermal activation of localized carriers into quasifree states and subsequent nonradiative recombination. The other is attributed to thermal emission of carriers into the barriers. The influence of the barrier height is also reflected by the dependence of the threshold densities required on the temperature. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Defects induced in fused silica by high fluence ultraviolet laser pulses at 355 nm

M. A. Stevens-Kalceff, A. Stesmans, and Joe Wong

Appl. Phys. Lett. 80, 758 (2002); http://dx.doi.org/10.1063/1.1446203 (3 pages) | Cited 20 times

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Point defects induced at the exit surface of optical-grade fused silica by high power (>30 J/cm2) 355 nm laser pulses have been investigated to elucidate the nature of laser damage in optics for use at high peak powers (>2 GW/cm2). Six defects have been identified. Eγ′ and E74′ defects were identified using electron spin resonance spectroscopy. The nonbridging oxygen hole center, a self-trapped exciton, an oxygen-deficient center, and interstitial O2 were identified and spatially resolved in the damage craters using cathodoluminescence microanalysis. The defects are associated with the laser generated shock waves and/or thermal explosion. © 2002 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
78.60.Hk Cathodoluminescence, ionoluminescence
76.30.Mi Color centers and other defects
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
62.50.-p High-pressure effects in solids and liquids

Direct determination of atomic structure in multiple quantum wells InGaN/GaN

K. Watanabe, Jer-Ren Yang, N. Nakanishi, K. Inoke, and M. Shiojiri

Appl. Phys. Lett. 80, 761 (2002); http://dx.doi.org/10.1063/1.1433916 (2 pages) | Cited 17 times

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We present an analysis of a homogeneous cellular interface between ultrathin InGaN and GaN layers in a high-resolution high-angle annular dark field scanning transmission electron microscopy image processed by the deconvolution technique. The method provides high-quality atomic-resolved images uniquely from the experimental images without preassumed models and image simulations. The processed image, then, shows definitely the position of interface between InGaN and GaN layers at atomic scale and an evidence of coherent epitaxial growth. © 2002 American Institute of Physics.
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68.65.Cd Superlattices
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
68.65.Fg Quantum wells

Screening beneficial dopants to Cu interconnects by modeling

Chun-Li Liu

Appl. Phys. Lett. 80, 763 (2002); http://dx.doi.org/10.1063/1.1445471 (3 pages) | Cited 1 time

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We present the results of first-principles simulations of dopant segregation to grain boundaries (GBs), dopant bulk diffusion, dopant and Cu self-diffusion at the GB, and the effect of the presence of a dopant on Cu diffusion at the GB for advanced Cu alloy interconnects. Several dopants that inhibit Cu GB diffusion were identified. Two primary mechanisms were found, namely, dopant blocking and dopant dragging. Early experimental results have confirmed model predictions for one of the several dopants (carbon) identified so far. The mean time to failure has increased more than 60% with a carbon concentration in Cu as low as 0.01 at. % and the resulting resistivity increase can be controlled below 15% compared to undoped Cu. © 2002 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Ry Impurity doping, diffusion and ion implantation technology
66.30.J- Diffusion of impurities
64.75.-g Phase equilibria
61.72.Mm Grain and twin boundaries
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Lattice-matched, epitaxial, silicon-insulating lanthanum yttrium oxide heterostructures

Supratik Guha, Nestor A. Bojarczuk, and Vijay Narayanan

Appl. Phys. Lett. 80, 766 (2002); http://dx.doi.org/10.1063/1.1445465 (3 pages) | Cited 31 times

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We demonstrate a ternary (LaxY1−x)2O3 thin-film oxide that can be grown epitaxially on Si(111) substrates with a lattice constant that can be matched to twice the lattice constant of silicon. We further show that silicon can then be deposited epitaxially (though with a high defect density) on this oxide such that epitaxial silicon/oxide/silicon structures may be grown. We discuss the microstructural relationships and the growth modes for the oxide on silicon and silicon on oxide growths. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
73.40.Ty Semiconductor-insulator-semiconductor structures
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators

Phase separation suppression in InGaN epitaxial layers due to biaxial strain

A. Tabata, L. K. Teles, L. M. R. Scolfaro, J. R. Leite, A. Kharchenko, T. Frey, D. J. As, D. Schikora, K. Lischka, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 80, 769 (2002); http://dx.doi.org/10.1063/1.1436270 (3 pages) | Cited 50 times

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Phase separation suppression due to external biaxial strain is observed in InxGa1−xN alloy layers by Raman scattering spectroscopy. The effect is taking place in thin epitaxial layers pseudomorphically grown by molecular-beam epitaxy on unstrained GaN(001) buffers. Ab initio calculations carried out for the alloy free energy predict and Raman measurements confirm that biaxial strain suppress the formation of phase-separated In-rich quantum dots in the InxGa1−xN layers. Since quantum dots are effective radiative recombination centers in InGaN, we conclude that strain quenches an important channel of light emission in optoelectronic devices based on pseudobinary group-III nitride semiconductors. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.Nq Composition and phase identification
78.66.Fd III-V semiconductors
64.75.-g Phase equilibria
65.20.-w Thermal properties of liquids
65.40.G- Other thermodynamical quantities
68.65.Hb Quantum dots (patterned in quantum wells)
78.30.Fs III-V and II-VI semiconductors

Phase separation in Nd60−xYxFe30Al10 melt-spun ribbons

Z. G. Sun, W. Löser, J. Eckert, K.-H. Müller, and L. Schultz

Appl. Phys. Lett. 80, 772 (2002); http://dx.doi.org/10.1063/1.1447324 (3 pages) | Cited 14 times

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The structure of melt-spun Nd60−xYxFe30Al10 (x = 0, 10, and 30) ribbons has been investigated by x-ray diffraction, isochronal differential scanning calorimetry (DSC), isothermal DSC, and thermomagnetic measurements. Precipitation of nanocrystalline Nd embedded in an amorphous matrix is found upon quenching. The amorphous phase further separates into Fe-rich regions and Fe-depleted regions. The growth of Nd nanocrystals upon annealing was identified by the characteristic isothermal calorimetric signal. The Fe-depleted amorphous phase crystallizes at 580 K, while the Fe-rich amorphous phase crystallizes at about 740, 779, and 750 K for x = 0, 10, and 30, respectively. Phase separation in the amorphous matrix is also revealed by the thermomagnetic measurements, which show ferromagnetic transitions at about 60 and 480 K. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
75.50.Bb Fe and its alloys
61.46.-w Structure of nanoscale materials
61.43.Dq Amorphous semiconductors, metals, and alloys
81.30.Mh Solid-phase precipitation
81.40.Gh Other heat and thermomechanical treatments
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Energy dispersive x-ray diffractometry as a tool alternative to differential scanning calorimetry for investigating polymer phase transitions

V. Rossi-Albertini, A. Isopo, R. Caminiti, and U. Tentolini

Appl. Phys. Lett. 80, 775 (2002); http://dx.doi.org/10.1063/1.1447317 (3 pages) | Cited 2 times

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Recently, a technique based on energy dispersive x-ray diffraction has been proposed to follow the polymer phase transitions. However, the potentialities of this method were not clear, as well as the experimental conditions in which it is more convenient than differential scanning calorimetry, generally used for the same purpose. In the present letter, the answer to this question is provided. It is shown that the two methods are complementary, rather than equivalent, the heating rate being the relevant parameter to establish which is preferable. The demonstration of this statement is given through the observation of the complex thermal properties of a reference sample studied in both ways at progressively lower heating rates. The connection between such unusual application of x-ray diffraction and the differential scanning calorimetry is discussed in terms of the two possible definitions of entropy. © 2002 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
61.05.cp X-ray diffraction
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.70.K- Solid-solid transitions
64.70.D- Solid-liquid transitions

Electron energy-loss spectroscopy characterization of the boron p-like density of states in MgB2

X. Kong, Y. Q. Wang, H. Li, X. F. Duan, R. C. Yu, S. C. Li, F. Y. Li, and C. Q. Jin

Appl. Phys. Lett. 80, 778 (2002); http://dx.doi.org/10.1063/1.1446986 (3 pages) | Cited 6 times

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The microstructure and boron K-edge fine structure in MgB2 produced under high pressure are studied using high-resolution transmission electron microscopy and electron energy-loss spectroscopy in a transmission electron microscope. A pre-peak located at 188 eV in the boron K-edge energy-loss near edge structure (ELNES) provides a direct evidence for the existence of a high and unfilled p-like density of states (DOS) across the Fermi level. The σ(px+py) states dominate in this unfilled p-like DOS. The theoretical simulation results of the ELNES using the linearized augmented plane wave method can explain the experimental spectrum very well. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Jb Electronic structure (photoemission, etc.)
79.20.Uv Electron energy loss spectroscopy
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