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5 May 1997

Volume 70, Issue 18, pp. 2335-2481

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Photoluminescence and electroluminescence of ZnS:Cu nanocrystals in polymeric networks

Jinman Huang, Yi Yang, Shanhua Xue, Bai Yang, Shiyong Liu, and Jiacong Shen

Appl. Phys. Lett. 70, 2335 (1997); http://dx.doi.org/10.1063/1.118866 (3 pages) | Cited 87 times

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ZnS:Cu nanocrystals were synthesized in polymeric networks. X-ray photoemission spectroscopy and atomic absorption data show that the Zn and Cu ion mass contents were about 8.2% and 0.12%, respectively. The particle size of ZnS:Cu nanocrystals was about 3.0 nm, measured by UV-vis spectrum. Due to the quantum size effects, the band gap energy of ZnS nanocrystals was about 4.2 eV. Compared with the photoluminescence of ZnS which peaks at 390 nm, the photoemission of ZnS:Cu/polymer thin films was peaking at 415 nm because of Cu acting as luminescent centers. The ZnS:Cu/polymer was also used to fabricate light-emitting diode (LED), as the emitting layer of LED, the blue light of electroluminescence was observed at room temperature, and its turn-on voltage was less than 4 V. © 1997 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
61.46.-w Structure of nanoscale materials
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.60.Fi Electroluminescence
79.60.Jv Interfaces; heterostructures; nanostructures
78.40.Fy Semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
85.60.Jb Light-emitting devices

Titanium oxide/aluminum oxide multilayer reflectors for “water-window” wavelengths

Hiroshi Kumagai, Koichi Toyoda, Katsutaro Kobayashi, Minoru Obara, and Yasuhiro Iimura

Appl. Phys. Lett. 70, 2338 (1997); http://dx.doi.org/10.1063/1.118898 (3 pages) | Cited 24 times

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Twenty bilayers of titanium oxide and aluminum oxide with the layer-pair thickness of 4.43 nm on a silicon substrate were fabricated for novel multilayer reflectors at water-window wavelengths by an atomic layer deposition method of controlled growth with sequential surface chemical reactions. The high reflectance of over 30% at a wavelength of 2.734 nm and an incident angle of 71.8° from the normal incidence was demonstrated experimentally. The full width at half-maximum of the reflectances at 2.734 nm was 0.0381 nm, which corresponds to Δλ/λ=1.4%. © 1997 American Institute of Physics.
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07.85.-m X- and γ-ray instruments
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
07.60.Hv Refractometers and reflectometers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Nk Insulators

An efficient supersonic chemical oxygen–iodine laser operating without buffer gas and with simple nozzle geometry

D. Furman, B. D. Barmashenko, and S. Rosenwaks

Appl. Phys. Lett. 70, 2341 (1997); http://dx.doi.org/10.1063/1.118868 (3 pages) | Cited 9 times

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We report on an efficient supersonic chemical oxygen-iodine laser, energized by a jet-type singlet oxygen generator, operating without primary buffer gas and applying simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 177 W with chemical efficiency of 17% was obtained in a 5 cm gain length for Cl2 flow rate of 11 mmol/s. The power is almost unaffected by water vapor in the medium. © 1997 American Institute of Physics.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
78.60.Ps Chemiluminescence
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.40.Ki Supersonic and hypersonic flows
47.40.Hg Transonic flows
47.70.Fw Chemically reactive flows

Spontaneous emission factor of oxidized vertical-cavity surface-emitting lasers from the measured below-threshold cavity loss

J. H. Shin, Y. G. Ju, H. E. Shin, and Y. H. Lee

Appl. Phys. Lett. 70, 2344 (1997); http://dx.doi.org/10.1063/1.118869 (3 pages) | Cited 3 times

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A method to estimate the spontaneous emission factor β is proposed and applied to the 780 nm oxidized vertical-cavity surface-emitting lasers. The proportionality of the measured cavity loss multiplied by optical power to injected current is used. Our results agree better with theoretical calculations than those of conventional light-current curve fitting. The spontaneous emission factor of 0.0021 is obtained for a 2-μm-square device at room temperature. Since only the below-threshold information of cavity loss and output power are used in our method, the obtained β values are independent of any complex and unexpected above-threshold effects such as thermally induced mode-size contraction, as they should be. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.65.Mq Oxidation
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift

Resonant-cavity InGaAs/InAlGaAs/InP photodetector arrays for wavelength demultiplexing applications

S. Y. Hu, J. Ko, and L. A. Coldren

Appl. Phys. Lett. 70, 2347 (1997); http://dx.doi.org/10.1063/1.118870 (3 pages) | Cited 11 times

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Resonant-cavity photodetector arrays are demonstrated in the InGaAs/InAlAs/InP material system grown by solid-source molecular beam epitaxy. To reduce crosstalk between channels, these devices are designed with a high-Q cavity to obtain narrow-band photoresponse. In addition, a novel double-absorber design has been proposed and implemented to avoid position sensitivity related to the cavity standing wave and eliminate the need for in situ cavity-mode adjustment. Both Schottky and P-i-N diode structures are studied and compared. Eight element arrays with linearly distributed resonant wavelengths spanning over 30 nm are fabricated by using a three-level anodic oxidation process. An experimental channel rejection ratio of 14.5 dB at 4 nm away from the resonant peak has been achieved. © 1997 American Institute of Physics.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
85.60.Gz Photodetectors (including infrared and CCD detectors)

Excitonic luminescence up to room temperature in a ZnSe/MgS superlattice

Hiroyuki Nashiki, Ikuo Suemune, Hidekazu Kumano, Hideki Suzuki, Toshio Obinata, Katsuhiro Uesugi, and Jun’ichiro Nakahara

Appl. Phys. Lett. 70, 2350 (1997); http://dx.doi.org/10.1063/1.118867 (3 pages) | Cited 10 times

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Optical properties of a ZnSe/MgS superlattice (SL) were studied by reflection and photoluminescence (PL) spectroscopies. Excitonic structures were clearly observed in the reflection spectra up to room temperature, and the exciton absorption peak energy and linewidth were well coincident with the PL peak energy and linewidth. The origin of the lowest luminescence peak was indicated to be C1-HH1 exciton up to room temperature. The lineshape broadening due to longitudinal-optical-phonon scattering of excitons is much decreased in this SL compared to bulk ZnSe. © 1997 American Institute of Physics.
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78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
63.20.kk Phonon interactions with other quasiparticles

Photoluminescence in Si1−x−yGexCy alloys

J. D. Lorentzen, G. H. Loechelt, M. Meléndez-Lira, J. Menéndez, S. Sego, R. J. Culbertson, W. Windl, O. F. Sankey, A. E. Bair, and T. L. Alford

Appl. Phys. Lett. 70, 2353 (1997); http://dx.doi.org/10.1063/1.118871 (3 pages) | Cited 6 times

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We report photoluminescence from Si1−x−yGexCy films grown epitaxially on Si (100) by chemical vapor deposition. We observe significant energy shifts but no dramatic changes in the photoluminescence line shape caused by the presence of carbon. Using standard deformation potential theory to correct the epitaxial strain shifts, we conclude that the band gap of relaxed Si1−x−yGexCy alloys has a lower energy than the band gap of relaxed Si1−xGex with the same Si/Ge ratio. We propose an explanation of these results based on the assumption that carbon forms a resonant level within the conduction band of Si1−xGex. © 1997 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Quantum dot vertical-cavity surface-emitting laser with a dielectric aperture

D. L. Huffaker, O. Baklenov, L. A. Graham, B. G. Streetman, and D. G. Deppe

Appl. Phys. Lett. 70, 2356 (1997); http://dx.doi.org/10.1063/1.118872 (3 pages) | Cited 45 times

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Data are presented on an oxide-confined vertical-cavity surface-emitting laser that uses a quantum dot active region. The laser is grown by molecular beam epitaxy, with the quantum dot active region formed from a five monolayer deposition of In0.50Ga0.35Al0.15As. Lasing occurs at wavelengths corresponding to quantum dot transitions, with a room temperature pulsed threshold as low as 560 μA for a 7 μm diameter oxide aperture. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Single-mode vertical cavity surface emitting laser by graded-index lens spatial filtering

Barry J. Koch, James R. Leger, Anand Gopinath, Zhong Wang, and Robert A. Morgan

Appl. Phys. Lett. 70, 2359 (1997); http://dx.doi.org/10.1063/1.118873 (3 pages) | Cited 17 times

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4.5 mW of power in a single spatial mode has been obtained from a vertical cavity surface emitting laser (VCSEL) in an external cavity setup, using a graded index (GRIN) lens with a spatial filtering high reflecting aperture deposited on its endface. The spatial filter on the GRIN lens endface forces a larger single transverse mode in the VCSEL than is obtained without it. A brightness of 5.1×105 W/cm2 str is demonstrated, which is 91% of the maximum achievable. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Ry Gradient-index (GRIN) devices
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers

Transmission of pulsed CO2 laser beams through “opaque” liquids by a cavitation effect

A. German, D. Bunimovich, and A. Katzir

Appl. Phys. Lett. 70, 2362 (1997); http://dx.doi.org/10.1063/1.118874 (3 pages)

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The formation of a stationary cavity by a sequence of CO2 laser pulses was investigated in liquids of different viscosity and surface tension. Decreasing the surface tension of the liquid and increasing its viscosity increases the depth of the cavity and decreases the threshold energy needed for its formation. A theoretical model based on the Bernoulli–Stokes equation was developed. Good agreement between experimental and theoretical results was obtained. A method of reducing thermal damage, involving liquid layer effects during laser cutting of different materials, is proposed. © 1997 American Institute of Physics.
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42.62.Be Biological and medical applications
47.55.dp Cavitation and boiling
66.20.-d Viscosity of liquids; diffusive momentum transport

On the determination of internal optical mode loss of semiconductor lasers

P. M. Smowton and P. Blood

Appl. Phys. Lett. 70, 2365 (1997); http://dx.doi.org/10.1063/1.118875 (3 pages) | Cited 15 times

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Use is made of a numerical simulation of the light—current characteristic to examine the errors which may arise in the determination of the optical mode loss (αi) from the cavity length dependence of the external differential efficiency (ηextd). In particular, we focus on the effects of incomplete Fermi level pinning and carrier leakage, and show that αi can only be determined correctly if ηextd is determined under conditions where it is invariant both with current level and temperature. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Application of near-field optics to critical dimension metrology

S. J. Bukofsky, S. A. Selberg, R. D. Grober, and J. K. Trautman

Appl. Phys. Lett. 70, 2368 (1997); http://dx.doi.org/10.1063/1.118865 (3 pages) | Cited 2 times

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Scanned-probe microscopes often have difficulty measuring absolute lengths due to nonlinearities in the piezo elements used to scan the tip. We have developed a method which allows for calibrated scanning of a near-field optical aperture. This method allows for point-by-point correction for piezo nonlinearities such as hysteresis and creep by imaging the light emanating from a near-field probe onto a position-sensitive detector. We have used this principle to fabricate a microscope with 20 nm accuracy in tip position. With further improvements, we believe single nanometer accuracy is possible. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Optical superlattices—a strategy for designing phase-shift masks for photolithography at 248 and 193 nm: Application to AlN/CrN

P. F. Carcia, R. H. French, M. H. Reilly, M. F. Lemon, and D. J. Jones

Appl. Phys. Lett. 70, 2371 (1997); http://dx.doi.org/10.1063/1.118876 (3 pages) | Cited 7 times

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This letter illustrates with AlN/CrN multilayers that optical superlattices, comprised of multilayers of a uv transmitting dielectric layer and a metallic layer, offer a systematic approach to design and fabricate partially transmitting, phase-shift masks for photolithography. From the measured optical constants of sputtered AlN/CrN multilayers, it was found that films had π-phase shift and tunable optical transmission between 5% and 15% at 365, 248, and 193 nm. We compared the optical properties of sputtered AlN/CrN multilayers to “ideal” superlattices, calculated from the measured optical properties of individual thick CrN and AlN layers, and to compositionally equivalent psuedobinary alloys of (AlN)1−x(CrN)x. Although optical properties for all three systems were nearly the same, which is attractive because it implies wide process lattitude, we found systematic differences that were attributed to their individual structures. A phase shift mask with 6% transmission at 365 nm was fabricated with a 1650-Å-thick (25 Å AlN+25 Å CrN) multilayer film. © 1997 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.-e Optical elements, devices, and systems

Single-mode and single-beam surface emission from visible red GaInP/AlGaInP laser diodes

P. O. Kellermann, A. Golshani, A. Köck, E. Gornik, H.-P. Gauggel, R. Winterhoff, and M. H. Pilkuhn

Appl. Phys. Lett. 70, 2374 (1997); http://dx.doi.org/10.1063/1.118877 (3 pages) | Cited 6 times

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Single-mode and single-beam surface emission (675–680 nm) has been achieved from visible red GaInP/AlGaInP laser diodes by applying the surface mode emission technique. The laser diodes emit a single beam via the surface with a beam divergence of 0.16° and show single-mode emission both in ac as well as in dc operation with a minimum spectral linewidth of 0.07 nm. The highest sidemode suppression achieved at present in ac operation is 19 dB. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Prediction of multiple-feature effects in plasma etching

Gyeong S. Hwang and Konstantinos P. Giapis

Appl. Phys. Lett. 70, 2377 (1997); http://dx.doi.org/10.1063/1.118878 (3 pages) | Cited 10 times

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Charging and topography evolution simulations during plasma etching of dense line-and-space patterns reveal that multiple-feature effects influence critically the etch profile characteristics of the various lines. By including neighboring lines, the simulation predicts a peculiar notching behavior, where the extent of notching varies with the location of the line. Feature-scale modeling can no longer be focused on individual features alone; “adjacency” effects are crucial for understanding and predicting the outcome of etching experiments at reduced device dimensions. © 1997 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.65.-y Plasma simulation

In situ observation of combustion to form TiN during ball milling Ti in nitrogen

Z.-H. Chin and T.-P. Perng

Appl. Phys. Lett. 70, 2380 (1997); http://dx.doi.org/10.1063/1.119084 (3 pages) | Cited 11 times

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Mechanical milling of Ti powder in nitrogen by a high-energy ball mill was performed. The pressure was monitored in situ. Initially, nitrogen was dissolved in Ti to form a solid solution. Under suitable conditions, when the nitrogen content had reached 32 at. %, the nitrogen pressure drastically dropped and instant formation of TiN took place. The TiN was formed by means of self-catalytic combustion, which was triggered by the high impact energy and the large clean surface of the fine Ti particles.© 1997 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Cy Elemental semiconductors
82.33.Vx Reactions in flames, combustion, and explosions

Onionlike structures and small nested fullerenes formation under electron irradiation of turbostratic BC2N

O. Stephan, Y. Bando, C. Dussarrat, K. Kurashima, T. Sasaki, T. Tamiya, and M. Akaishi

Appl. Phys. Lett. 70, 2383 (1997); http://dx.doi.org/10.1063/1.118879 (3 pages) | Cited 9 times

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Turbostratic BC2N samples were exposed to intense irradiation regimes in a high resolution electron microscope equipped with a field emission gun. Electron energy loss spectroscopy (EELS) analysis was used to check the sp2-bonding type and the composition of the starting materials. In highly crystalline areas, we observed a tendency for the basal planes to curl and form large “open” onionlike features. According to EELS quantification, no change of the composition occurs during their formation. Very occasionally, small nested fullerenes of less than 10 shells each with dimensions of the very internal shell close to that of a C60 were observed. These onions are thought to arise from the bending of a few basal planes of the planar starting material. © 1997 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.80.Fe Electron and positron radiation effects
81.05.ub Fullerenes and related materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Growth of TiSi2 from codeposited TiSix layers and interfacial layers

R. T. Tung, K. Fujii, K. Kikuta, S. Chikaki, and T. Kikkawa

Appl. Phys. Lett. 70, 2386 (1997); http://dx.doi.org/10.1063/1.118880 (3 pages) | Cited 12 times

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The silicide formation characteristics from composition profiles created on Si by codepositions was investigated. It was shown that a thin interfacial amorphous TiSix layer, with x ∼ 0.5–1, deposited between Si and the Ti film led to a significant reduction in the observed C49→C54 TiSi2 transformation temperature. The presence of the amorphous interfacial TiSix layer slowed down the initial silicidation rate, but promoted the nucleation of the final C54 TiSi2 phase. Predeposition and preannealing were also found to facilitate the growth of C54 TiSi2, as was growth from codeposited full TiSix layers with Ti-rich compositions. The efficacy of the (interfacial) TiSix layer was demonstrated for different temperature ramp rates and for a variety of substrates including undoped α-Si, preamorphized n+-Si, and preamorphized p+-Si. But this effect was found to be absent on single crystal Si. Possible mechanisms of the observed effects were discussed. © 1997 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
73.40.Ns Metal-nonmetal contacts
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.35.Fx Diffusion; interface formation
64.70.K- Solid-solid transitions
61.72.Cc Kinetics of defect formation and annealing

Microscopic chemical state identification of a silicon-carbide fiber by soft x-ray photoabsorption spectroscopy

Qing Ma, Richard A. Rosenberg, Changyoung Kim, Jostein Grepstad, and Piero Pianetta

Appl. Phys. Lett. 70, 2389 (1997); http://dx.doi.org/10.1063/1.118881 (3 pages) | Cited 2 times

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Chemical states of a 140 μm silicon carbide fiber are determined by soft x-ray photo-absorption spectroscopy, using a magnetic projection photoelectron microscope, performed on the surface obtained by fracturing. The spectrum of the carbon core of the fiber has prominent π∗ and σ∗ resonance peaks and is very similar to that measured on highly oriented pyrolitic graphite, indicating a graphitic nature of the carbon core. The spectrum of the silicon carbide coating of the fiber reveals similar features to those of single-crystal silicon carbide, indicating that this coating is in the crystalline or polycrystalline phase. © 1997 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Effect of nonhydrostaticity on the pressure induced phase transformation of rhombohedral boron nitride

T. Taniguchi, T. Sato, W. Utsumi, T. Kikegawa, and O. Shimomura

Appl. Phys. Lett. 70, 2392 (1997); http://dx.doi.org/10.1063/1.118882 (3 pages) | Cited 6 times

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An in situ x-ray diffraction study of room-temperature compression of rhombohedral boron nitride (rBN) was performed up to 10 GPa. Although no phase transformation of rBN was observed in a liquid pressure transmitting medium, the structure of rBN changed to become disordered within the layered stacking sequence at less than 1 GPa with the solid-state pressure transmitting medium. Further transformation to the wurtzite structure (wBN) was observed at 6 GPa and was unquenchable upon the release of pressure at room temperature. The orientation relationship of the phase transformation of rBN to wBN was compared with that of hexagonal BN to wBN. © 1997 American Institute of Physics.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.05.cp X-ray diffraction
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Optical absorption and light-induced charge transport of Fe2+ in BaTiO3

A. Mazur, O. F. Schirmer, and S. Mendricks

Appl. Phys. Lett. 70, 2395 (1997); http://dx.doi.org/10.1063/1.118883 (3 pages) | Cited 11 times

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Iron doped barium titanate was grown and reduced at various temperatures. Using optical absorption and electron paramagnetic resonance (photo-EPR) simultaneously, a wide absorption band at ∼ 2.1 eV due to Fe2+ is established. The light-induced charge transport between Fe2+/3+ and shallow Ti4+/3+−VO is identified, showing a two-center type response at low and one-center type response at room temperature. © 1997 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.40.Ha Other nonmetallic inorganics

Structural study of InAs quantum boxes grown by molecular beam epitaxy on a (001) GaAs-on-Si substrate

D. Lacombe, A. Ponchet, J.-M. Gérard, and O. Cabrol

Appl. Phys. Lett. 70, 2398 (1997); http://dx.doi.org/10.1063/1.118863 (3 pages) | Cited 3 times

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InAs quantum boxes have been obtained by molecular beam epitaxy on a GaAs-on-Si substrate using the strained-induced 2D–3D transition. The boxes are examined by transmission electron microscopy and compared with those obtained under the same growth conditions on a GaAs substrate. Although there exist 107 dislocations per cm2 in the GaAs-on-Si substrate, high quality coherent strained islands are observed with a density slightly higher than on GaAs substrate. The behavior of the threading dislocations originating from the Si–GaAs interface when they cross the island plane is also investigated. Although some dislocations are bent in the island plane, the island distribution is apparently not affected by the vicinity of a threading dislocation. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Phonon properties and microstructure of annealed LiTaO3:Nd

X. L. Wu, X. M. Bao, S. S. Jiang, D. Feng, and S. Tong

Appl. Phys. Lett. 70, 2401 (1997); http://dx.doi.org/10.1063/1.118884 (3 pages) | Cited 4 times

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Phonon properties and microstructure of annealed Nd-doped LiTaO3 (LT:Nd) were examined by means of Raman scattering and infrared spectra. Raman spectra show the splitting of A1(TO) mode at 204 cm−1 and the appearance of an additional shoulder peak at ∼208 cm−1, indicating that the homogeneous distribution of Nd ions leads to the structural recovery of partial oxygen octahedra centered with Li and Ta ions, but the microstructural deviation from original LT trigonal system still exists. The enhancement of E(TO) mode intensities and the reduction of A1(TO) mode intensities in the A1+E symmetry spectrum are mainly attributed to the microstructural deviation of LT:Nd and the changed photorefractive effect due to annealing. Infrared spectra in the OH stretching region suggest that the changed photorefractive effect arises from the displacements of positive ions along the optical z axis. © 1997 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.72.Cc Kinetics of defect formation and annealing

Influence of Zr/Ti ratios on the deformation in the hysteresis loop of Pb(Zr,Ti)O3 thin film capacitors

Eun Gu Lee, Dirk J. Wouters, Geert Willems, and Herman E. Maes

Appl. Phys. Lett. 70, 2404 (1997); http://dx.doi.org/10.1063/1.118885 (3 pages) | Cited 16 times

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Electric field shift and deformation in the polarization-electric field characteristics of Pb(Zr,Ti)O3 (PZT) thin film capacitors with various Zr/Ti ratios have been studied as a function of the annealing temperature after patterning the top sputter-deposited Pt electrode using reactive ion etch with Ar gas. A large field shift and a constriction in the hysteresis loops are observed, particularly in low Zr/Ti PZT films annealed below 400 °C. A strong blocking layer effect in unannealed capacitor is found to be related to the internal field caused by trapped charges near electrodes. As the Zr/Ti ratio decreases, the field shift increases and the annealing temperature at which the internal field disappears also increases. © 1997 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.Dj Domain structure; hysteresis

Valence band discontinuity at a cubic GaN/GaAs heterojunction measured by synchrotron-radiation photoemission spectroscopy

S. A. Ding, S. R. Barman, K. Horn, H. Yang, B. Yang, O. Brandt, and K. Ploog

Appl. Phys. Lett. 70, 2407 (1997); http://dx.doi.org/10.1063/1.118886 (3 pages) | Cited 26 times

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The valence band discontinuity of the n-type cubic GaN/GaAs heterojunction is measured by means of angle-resolved photoemission spectroscopy using synchrotron radiation. High quality cubic GaN films are grown on GaAs(100) substrates by nitrogen plasma-assisted molecular beam epitaxy, and the valence band discontinuity is determined by a combination of core and valence level spectra. A value of ΔEV=(1.84±0.1) eV across the GaN/GaAs heterojunction is obtained, which means that the discontinuity in the conduction bands at this interface is very small, such that a vertical contact scheme may be realized for GaN/GaAs heterojunctions.© 1997 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Nr Semiconductor compounds
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