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21 Feb 2000

Volume 76, Issue 8, pp. 943-1075

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Bulk and surface recombination in InAs/AlAs0.16Sb0.84 3.45 μm light emitting diodes

M. J. Kane, G. Braithwaite, M. T. Emeny, D. Lee, T. Martin, and D. R. Wright

Appl. Phys. Lett. 76, 943 (2000); http://dx.doi.org/10.1063/1.125911 (3 pages) | Cited 18 times

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A study of the light generation efficiency of a series of InAs/AlAs0.16Sb0.84 light emitting diodes with p-type InAs active layers is reported. The bulk low-injection radiative efficiency of the p-type material is shown to be as high as 24% at a hole concentration of 1.5×1017 cm−3 but to decrease with increasing hole concentration in a manner consistent with the dominant low-injection nonradiative processes being Auger processes with two holes in their initial states and a total rate constant of 2×10−28 cm6 s−1. The maximum internal low-drive quantum efficiency achieved in the light emitting diodes is shown to be limited by interface recombination at the InAs/AlAs0.16Sb0.84 heterojunction and reabsorption in the active layer in addition to the bulk nonradiative processes in the InAs. A maximum value of ∼9% is achieved. © 2000 American Institute of Physics.  
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85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena

Blue emitting Sr2Ga2S5:Ce phosphor thin films grown by multisource deposition

Shinji Okamoto, Kastu Tanaka, and Youji Inoue

Appl. Phys. Lett. 76, 946 (2000); http://dx.doi.org/10.1063/1.125900 (3 pages) | Cited 7 times

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Blue emitting Sr2Ga2S5:Ce phosphor thin film has been first grown by multisource deposition. The evaporating source materials are Sr metal and Ga2S3 compound, and the dopant is CeCl3. This polycrystalline thin film shows the single orientation of (004). The SrS thin film is a buffer layer underneath the Sr2Ga2S5 thin film and is necessary for growth. The photoluminescence spectrum by excitation of the UV light at 290 nm is a broad band with two peaks at 443 and 484 nm, that is originated from 2D–4F5/2,7/2 transitions of Ce3+ ion. The emission is a saturated blue color and the Commission International de l’Eclairage chromaticity coordinates are x = 0.15 and y = 0.12. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
78.66.Nk Insulators

Saturation effects in Y2SiO5:Tb under low-voltage excitation

C. Stoffers, R. Y. Lee, J. Penczek, B. K. Wagner, and C. J. Summers

Appl. Phys. Lett. 76, 949 (2000); http://dx.doi.org/10.1063/1.125901 (3 pages) | Cited 7 times

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Low-voltage field emission device phosphors that are excited at high current densities often exhibit brightness saturation with increasing current. The physical processes responsible for saturation can be complex, with several mechanisms contributing, including ground state depletion and excited energy transfer. A two-level model, in conjunction with cathodoluminescence brightness and transient measurements, is used to show the influence of ground state depletion and thermal quenching on the saturation behavior of Y2SiO5:Tb under low-voltage excitation. © 2000 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence

Lightwave propagation through a 120° sharply bent single-line-defect photonic crystal waveguide

Masatoshi Tokushima, Hideo Kosaka, Akihisa Tomita, and Hirohito Yamada

Appl. Phys. Lett. 76, 952 (2000); http://dx.doi.org/10.1063/1.125902 (3 pages) | Cited 108 times

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We have demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC). Such propagation has not previously been experimentally confirmed. The photonic crystal was fabricated in a silicon-on-insulator (SOI) wafer with the top silicon layer of the wafer used as a core layer. A 877-μm-long single-line-defect waveguide was formed in the PC with a sharp 120° bend near the middle of the waveguide. A tapered-hemispherical-end fiber was coupled to the input end of the waveguide for the light input, and the output from the other end of the waveguide was directly observed by scanning its near-field profile with another tapered-hemispherical-end fiber. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Blue light generation in an external ring cavity using both cavity and grating feedback

X. G. Sun, G. W. Switzer, and J. L. Carlsten

Appl. Phys. Lett. 76, 955 (2000); http://dx.doi.org/10.1063/1.125903 (3 pages) | Cited 6 times

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A simple scheme for the efficient frequency doubling of a Fabry–Perot diode laser in a bow tie ring cavity is described. By feeding back the ring cavity transmission into the laser after reflection off a grating, the diode laser operates in single mode and the frequency locks to the cavity resonance. Using a simple analytic form of the beam parameters for the ring cavity, the optimum cavity configuration is found for a high degree of mode matching between the diode output beam and the ring cavity. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings

Bipolar transport organic light emitting diodes with enhanced reliability by LiF doping

Vi-En Choong, Song Shi, Jay Curless, and Franky So

Appl. Phys. Lett. 76, 958 (2000); http://dx.doi.org/10.1063/1.125904 (3 pages) | Cited 21 times

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An electrode contact scheme based on the use of an organic LiF alloy is investigated. The performance of organic light emitting diodes (OLED) with this contact scheme in both heterojunction and bipolar transport/emitting layer (BTEL) OLED structures are compared with their counterparts with LiF buffer layers. The organic LiF contact scheme improved device reliability of BTEL OLEDs by 32% to 92 500 h while adversely affecting device reliability of heterojunction OLEDs. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.72.up Other materials

Peculiar noise properties of phonons generated by femtosecond laser pulses in antimony

O. V. Misochko, K. Kisoda, K. Sakai, and S. Nakashima

Appl. Phys. Lett. 76, 961 (2000); http://dx.doi.org/10.1063/1.125905 (3 pages) | Cited 11 times

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In femtosecond pump-probe experiments on antimony, we have detected coherent oscillations that exhibit phase-dependent noise. The Fourier transforms of the coherent amplitude and its variance show that the two fluctuate at different frequencies, suggesting that the phonons created in the pump-probe experiment are of a squeezed nature. © 2000 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Accurate determination of quasi-Fermi-level separation of semiconductor lasers

Linzhang Wu

Appl. Phys. Lett. 76, 964 (2000); http://dx.doi.org/10.1063/1.125906 (3 pages) | Cited 5 times

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For characterization of semiconductor lasers, quasi-Fermi-level separation is a critical parameter due to its relationship with carrier density and gain. Its determination should be made with accuracy within ±10 meV. In this letter, we report a simple technique to accurately measure the quasi-Fermi-level separation, photon energy at gain peak, and intrinsic optical loss for a given current. Through theoretical calculation and experimental results, we believe that the quasi-Fermi-level separation measured by our technique is accurate to ±0.5 meV. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.20.Nr Semiconductor compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
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Ductile quasicrystalline alloys

A. Inoue, T. Zhang, M. W. Chen, T. Sakurai, J. Saida, and M. Matsushita

Appl. Phys. Lett. 76, 967 (2000); http://dx.doi.org/10.1063/1.125907 (3 pages) | Cited 45 times

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See Also: RETRACTION

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An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.5−xNi10Mx (M=Ag, Pd, Au, or Pt; x = 5 and 10 at %) alloys. The volume fraction (Vf) of the I phase is about 85% for the 5% M alloy and nearly 100% for the 10% M alloy. The I phase changes to Zr2Cu+Zr2Ni+Zr2Al3 in a fully annealed state. Compressive fracture strength (σc,f) and fracture elongation (ϵc,f) of the 10% Pd cylinder with a diameter of 2 mm are respectively 1640 MPa and 2.2% for the glassy phase and increase to 1830 MPa and 3.1% for the I phase. The increase in σc,f is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in ϵc,f results from the localization effect of deformation into the glassy layer. The precipitation of the I phase implies that the glassy alloys include randomly oriented I configurations. The present work shows promise for the new class of high-strength nanoquasicrystalline materials. © 2000 American Institute of Physics.
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62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.44.Br Quasicrystals
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
64.75.-g Phase equilibria
61.46.-w Structure of nanoscale materials

Mapping the fluorescence yield on turbid media

Jianan Y. Qu, Zhijian Huang, and Jianwen Hua

Appl. Phys. Lett. 76, 970 (2000); http://dx.doi.org/10.1063/1.125908 (3 pages) | Cited 1 time

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In this letter, we introduce a combined polarization and fluorescence imaging technique for the measurement of fluorescence yield on the surface of turbid media. We use the cross-polarization method to reject the specular reflection and enhance the diffusive backscattering from the turbid media. It has been found that the ratio image of fluorescence versus cross-polarized reflection is not sensitive to the geometry of fluorescence excitation and illumination, and provides a map of fluorescence yield on the surface of imaged subject. The technique reported in this letter may potentially solve the problem for imaging of early cancers which usually start from the superficial layer of tissue and have the fluorescence yield lower than surrounding normal tissue. © 2000 American Institute of Physics.
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87.63.L- Visual imaging
87.50.wj Dosimetry/exposure assessment
87.19.X- Diseases

Photoluminescence spectra from δ-doped barrier layers in modulation-doped InAlAs/InGaAs field-effect transistor structures

Kazuo Watanabe and Haruki Yokoyama

Appl. Phys. Lett. 76, 973 (2000); http://dx.doi.org/10.1063/1.125909 (3 pages) | Cited 7 times

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The photoluminescence (PL) spectra from the Si δ-doped InAlAs barrier layers in modulation-doped InAlAs/InGaAs heterostructure field-effect transistor (HFET) structures with contact and recess-etch-stopper layers are investigated. A PL peak associated with the δ-doped layer (δ peak) is found. The δ-peak position shifts to shorter wavelength with increasing δ-doping concentration. The intensity reduction of the δ peak due to raising the temperature from 6 K is considerably slower than that of the exciton peak from the InAlAs buffer layer at about 8100 Å, to which confined electrons and holes probably contribute. As a result, the δ-peak overwhelms the exciton peak and becomes the main peak of the InAlAs PL at temperatures higher than 40 K. The δ peak is not detected from HFET structures without the contact and recess-etch-stopper layers. The δ peak is attributed to the recombination of electrons from the δ-doped layer and photogenerated holes confined in the upper side of the barrier layer. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
71.35.-y Excitons and related phenomena

Efficient n-type doping of diamond using surfactant-mediated epitaxial growth

Byung Deok Yu, Yoshiyuki Miyamoto, and Osamu Sugino

Appl. Phys. Lett. 76, 976 (2000); http://dx.doi.org/10.1063/1.125910 (3 pages) | Cited 15 times

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Fabrication of n-type diamond was studied by performing extensive first-principles total-energy calculations for a number of possible configurations during the epitaxial growth process. We find that spatially correlated codopant N–Al–N, which acts as a shallow donor in diamond, can be effectively formed by using a surfactant-based growth technique. This technique takes advantage of the difference in the growth modes of diamond which depend on surface species: incorporation of carbon into diamond crystal is promoted by surfactants (Al) but is locally prohibited by surface co-dopants (N–Al–N). Thus, the co-dopants are selectively buried in diamond. This approach provides a possible and very effective way to realize dense n-type doping of diamond which has not been possible using conventional techniques. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Refractive indices and absorption coefficients of MgxZn1−xO alloys

C. W. Teng, J. F. Muth, Ü. Özgür, M. J. Bergmann, H. O. Everitt, A. K. Sharma, C. Jin, and J. Narayan

Appl. Phys. Lett. 76, 979 (2000); http://dx.doi.org/10.1063/1.125912 (3 pages) | Cited 86 times

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Indices of refraction for MgxZn1−xO epitaxial films grown by pulsed-laser deposition on sapphire substrates with x up to 0.36 were determined in the range of wavelength 457–968 nm by analysis of optical transmission spectra and prism-coupled waveguide measurements. The dispersion follows the first-order Sellmeier dispersion equation. Absorption coefficients, exciton energy gaps, and binding energies of MgxZn1−xO alloys were determined by transmission spectroscopy. The excitonic absorption features were clearly visible at room temperature despite alloy broadening. These results provide important information for the design and modeling of ZnO/MgZnO heterostructure optoelectronic devices. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.15.Fg Pulsed laser ablation deposition

The elastic constants of single crystal β-Si3N4

R. Vogelgesang, M. Grimsditch, and J. S. Wallace

Appl. Phys. Lett. 76, 982 (2000); http://dx.doi.org/10.1063/1.125913 (3 pages) | Cited 39 times

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Using Brillouin scattering, we have determined the complete set of elastic constants of the technologically important β-Si3N4. Availability of single crystals has allowed us to measure all five independent cij, which (in units of GPa) are: c11 = 433(3), c33 = 574(3), c13 = 127(5), c44 = 108(2), c66 = 119(4), and c12 = c11−2c66 = 195(8), giving a bulk modulus of 259. Our values are compared with existing calculations and cij determined from nano-indentation results combined with empirical relations and trends in related materials. © 2000 American Institute of Physics.
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62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Epitaxial growth of AlN and Al0.5Ga0.5N layers on aluminum nitride substrates

L. J. Schowalter, Y. Shusterman, R. Wang, I. Bhat, G. Arunmozhi, and G. A. Slack

Appl. Phys. Lett. 76, 985 (2000); http://dx.doi.org/10.1063/1.125914 (3 pages) | Cited 21 times

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High quality epitaxial AlN and AlxGa1−xN layers have been grown by organo-metallic vapor-phase epitaxy on single crystal a-face AlN substrates. Here we report the characterization of these layers using Rutherford backscattering/ion channeling spectroscopy, atomic force microscopy, double crystal x-ray diffraction, and preliminary electrical results. Ion channeling along the [1120] axis gave a minimum yield of 1.5% for an AlN layer and 2.2% for an Al0.5Ga0.5N, indicating excellent crystal quality. A resistivity of 20 Ω cm and a mobility of 20 cm2/V s was measured in a Si-doped, 1-μm-thick Al0.5Ga0.5N grown epitaxially on the AlN substrates. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Effect of current crowding on vacancy diffusion and void formation in electromigration

K. N. Tu, C. C. Yeh, C. Y. Liu, and Chih Chen

Appl. Phys. Lett. 76, 988 (2000); http://dx.doi.org/10.1063/1.125915 (3 pages) | Cited 47 times

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In multilevel interconnects, current crowding occurs whenever the current changes direction, such as when passing through a via. We propose that in current crowding, the current-density gradient can exert a driving force strong enough to cause excess vacancies (point defects) to migrate from high to low current-density regions. This leads to void formation in the latter. This is a key feature of electromigration-induced damage in very large scale integrated interconnects. © 2000 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
66.30.Qa Electromigration
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Visible photonic band gap engineering in silicon nitride waveguides

M. C. Netti, M. D. B. Charlton, G. J. Parker, and J. J. Baumberg

Appl. Phys. Lett. 76, 991 (2000); http://dx.doi.org/10.1063/1.125916 (3 pages) | Cited 26 times

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We demonstrate experimentally the tuning of complete photonic band gaps in patterned silicon nitride waveguides. Transmission measurements were performed using an ultrabroadband high-brightness white light laser continuum, extracting extinction ratios as low as 10−4 in the gap regions. Angle-resolved measurements show the perfect alignment of the gap around the Γ-J direction. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.20.-e Optical properties of bulk materials and thin films

Self-assembled GaInNAs quantum dots for 1.3 and 1.55 μm emission on GaAs

M. Sopanen, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 76, 994 (2000); http://dx.doi.org/10.1063/1.125917 (3 pages) | Cited 97 times

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Ga0.3In0.7NxAs1−x (x ⩽ 0.04) and InNxAs1−x (x ⩽ 0.02) self-assembled quantum dots are fabricated on GaAs by gas-source molecular beam epitaxy. The effect of growth temperature on island density, island size, and optical properties is studied in detail. From a single layer of Ga0.3In0.7N0.04As0.96 dots embedded in GaAs, peak photoluminescence wavelength of up to 1.52 μm is detected at room temperature. Thus, the fabrication of 1.3 and 1.55 μm GaInNAs quantum dot lasers on GaAs becomes feasible. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
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.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.55.Px Semiconductor lasers; laser diodes

The initial stages of growth of CuPtB ordered Ga0.52In0.48P/GaAs and Ga0.47In0.53As/InP

Mark C. Hanna, Hyeonsik M. Cheong, and Angelo Mascarenhas

Appl. Phys. Lett. 76, 997 (2000); http://dx.doi.org/10.1063/1.125918 (3 pages) | Cited 5 times

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Atomic force microscopy and Raman spectroscopy were used to investigate the development of the surface morphology and ordering of Ga0.52In0.48P and Ga0.47In0.53As. A series of lattice-matched highly ordered Ga0.52In0.48P/GaAs and Ga0.47In0.53As/InP samples ranging in thickness from 2 to 50 nm were grown by low-pressure metalorganic vapor phase epitaxy on (001) direct and vicinal substrates. Raman spectroscopy provided direct evidence of CuPtB-type ordering in layers as thin as 10 nm for Ga0.52In0.48P and 5 nm for Ga0.47In0.53As. We find that the morphology of both Ga0.52In0.48P and Ga0.47In0.53As on (001)6B substrates consists of ridges with heights ranging from 2 to 10 nm, which are aligned predominately along the [110] direction. For Ga0.52In0.48P growth on (001) direct substrates, ridges similar to those obtained on 6B vicinal substrates form with no preferential orientation, while Ga0.47In0.53As growth on (001) direct substrates proceeds by a combination of two-dimensional-island and step-flow growth. The average roughness of the GaInP layers is approximately twice that of GaInAs layers. These findings suggest it may be difficult to produce abrupt large-area heterointerfaces in structures containing ordered Ga0.52In0.48P and Ga0.47In0.53As alloys. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films

K. Yamasaki, S. Juodkazis, M. Watanabe, H.-B. Sun, S. Matsuo, and H. Misawa

Appl. Phys. Lett. 76, 1000 (2000); http://dx.doi.org/10.1063/1.125919 (3 pages) | Cited 48 times

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We report the recording of a three-dimensional (3D) pattern in bulk polymethyl metacrylate (PMMA) films by microexplosion induced by a tightly focused (numerical aperture of oil-immersion objective was 1.3) single laser shot. Recording was done by picosecond (ps) single-pulse irradiation at 532 nm and by femtosecond at a 400 nm wavelength. The light-induced damage threshold of PMMA was found at ∼4 MW/cm2 for ps damaging. Readout of the 3D pattern was carried out by the recording of the transmission and the photoluminescence (PL) of bits. We demonstrate the possibility exciting PL of the optically damaged area inside the PMMA by one- and two-photon absorption. © 2000 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
78.55.Kz Solid organic materials
42.40.Ht Hologram recording and readout methods
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Nonlinear optical absorption in undoped and cerium-doped BaTiO3 thin films using Z-scan technique

W. F. Zhang, Y. B. Huang, M. S. Zhang, and Z. G. Liu

Appl. Phys. Lett. 76, 1003 (2000); http://dx.doi.org/10.1063/1.125920 (3 pages) | Cited 22 times

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BaTiO3 and BaTiO3:Ce thin films with good surface morphology and tetragonal perovskite structure were fabricated on quartz substrates by pulsed-laser deposition technique at a deposition temperature of 750 °C. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties of the films were investigated using Z-scan method. The films display large nonlinear absorption effects. The two-photon absorption coefficients of the BaTiO3 and BaTiO3:Ce films were determined to be 51.7 and 59.3 cm/GW, respectively. All the results show that undoped and cerium-doped BaTiO3 ferroelectric thin films have potential applications in absorbing-type optical devices. © 2000 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
81.15.Fg Pulsed laser ablation deposition
78.30.Hv Other nonmetallic inorganics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Strongly enhanced Tb luminescence from titania xerogel solids mesoscopically confined in porous anodic alumina

N. V. Gaponenko, J. A. Davidson, B. Hamilton, P. Skeldon, G. E. Thompson, X. Zhou, and J. C. Pivin

Appl. Phys. Lett. 76, 1006 (2000); http://dx.doi.org/10.1063/1.125921 (3 pages) | Cited 28 times

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We report strongly enhanced Tb photoluminescence (PL) from a doped titania xerogel deposited on mesoporous anodic alumina. Transmission electron microscopy has confirmed the presence of the xerogel inside the pores of alumina films of up to several microns thickness. The optical bands attributed to 5D3→7Fi (i = 3,4,5), 5D4→7Fj (j=3,4,5,6) transitions of Tb3+, with a predominant band at 2.28 eV, are investigated between 6 and 300 K. At all temperatures, the Tb PL increases and the bands become narrower with an increase in the Tb concentration in the xerogel, the number of deposited layers employed and the thickness of the porous alumina film. © 2000 American Institute of Physics.
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78.55.Mb Porous materials
78.66.Nk Insulators
82.70.Gg Gels and sols
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Arsenic impurities in GaN

Chris G. Van de Walle and J. Neugebauer

Appl. Phys. Lett. 76, 1009 (2000); http://dx.doi.org/10.1063/1.125922 (3 pages) | Cited 36 times

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We present a comprehensive first-principles investigation of arsenic incorporation in GaN. Incorporation of As on the N site, which has previously been implicitly assumed, is favorable only under n-type conditions in a Ga-rich environment. Less Ga-rich conditions, and particularly p-type doping, strongly favor incorporation of As on the Ga site, where it behaves as a deep double donor. Arsenic thus acts as a compensating center, forming a real threat to acceptor doping of GaN and making p-type doping of GaAsN alloys impossible. The calculated donor levels for AsGa are consistent with luminescence lines around 2.6–2.7 eV in GaN intentionally doped with As. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors

Spatially localized dynamic properties of individual interfaces in semiconducting oxides

Bryan D. Huey and Dawn A. Bonnell

Appl. Phys. Lett. 76, 1012 (2000); http://dx.doi.org/10.1063/1.125923 (3 pages) | Cited 16 times

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Local electronic property variations at individual interfaces have been determined using scanning surface potential microscopy, a variant of atomic force microscopy in conjunction with locally applied electric fields. Micropatterning is used to isolate individual interfaces and position contacts so that biases can be controlled locally. Positional variations in the voltage dependent interface charge and density of states in polycrystalline zinc oxide are determined from surface potential imaging. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states

Valence band structure of cubic AlGaN/GaN superlattices

S. C. P. Rodrigues, L. M. R. Scolfaro, J. R. Leite, and G. M. Sipahi

Appl. Phys. Lett. 76, 1015 (2000); http://dx.doi.org/10.1063/1.125924 (3 pages) | Cited 14 times

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The influence of different material parameters, spin-orbit interaction, and strain effects on the valence band structure of cubic AlGaN/GaN superlattices is investigated. One-particle hole state calculations are carried out within the k⋅p theory by means of a full six-band Luttinger-Kohn Hamiltonian in a plane-wave representation. It is shown that the use of distinct values for the Luttinger parameters for the barrier and well regions leads to significant changes in the hole levels, particularly for large Al content. Spin-orbit interaction effects are responsible for strong nonparabolicities due to the light- and split-off-hole bands mixing. Besides, the hole levels are very sensitive to strain effects. Thus, it is demonstrated that these effects cannot be neglected in a realistic description of the valence band structure of these materials. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
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