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27 Oct 1997

Volume 71, Issue 17, pp. 2409-2544

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High power mid-infrared interband cascade lasers based on type-II quantum wells

Rui Q. Yang, B. H. Yang, D. Zhang, C.-H. Lin, S. J. Murry, H. Wu, and S. S. Pei

Appl. Phys. Lett. 71, 2409 (1997); http://dx.doi.org/10.1063/1.120076 (3 pages) | Cited 58 times

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We report a high power mid-infrared interband cascade laser operating at temperatures up to 170 K. The threshold current densities of this laser are considerably lower than the previously reported values in cascade lasers. The structure was grown by molecular beam epitaxy on a GaSb substrate and comprises 23 periods of active regions separated by digitally graded multilayer injection regions. A peak optical output power of ∼ 0.5 W/facet and a slope of 211 mW/A per facet, corresponding to a differential external quantum efficiency of 131%, are observed at 80 K and at a wavelength of ∼ 3.9 μm. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors

Infrared filters using metallic photonic band gap structures on flexible substrates

Sandhya Gupta, Gary Tuttle, Mihail Sigalas, and Kai-Ming Ho

Appl. Phys. Lett. 71, 2412 (1997); http://dx.doi.org/10.1063/1.120077 (3 pages) | Cited 40 times

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Metallic photonic band gap (MPBG) filter structures operating at far infrared wavelengths have been designed, fabricated, and characterized. The MPBGs are multilayer metallic meshes imbedded in a flexible polyimide dielectric. Depending on the periodic pattern of the metal grids, the filters have either simple high-pass or more complex transmission characteristics. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and the interlayer separation. Optical transmission measurements on a high-pass structure show cutoff frequency of 3 THz and attenuation of more than 35 dB in the cutoff region, in good agreement with predicted results. Band-reject filters show similarly good attenuation and large fractional bandwidths. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure. © 1997 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

An iodine-doped polymer light-emitting diode

F. Huang, A. G. MacDiarmid, and B. R. Hsieh

Appl. Phys. Lett. 71, 2415 (1997); http://dx.doi.org/10.1063/1.120078 (3 pages) | Cited 56 times

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The performance of polymer light-emitting diodes (LEDs) having the configuration Al/MEH–PPV/ITO, where MEH–PPV=poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) has been improved by light iodine doping of the emissive MEH–PPV polymer layer whereby the turn-on voltage is reduced and the external quantum efficiency is increased by an order of magnitude. It differs from nondoped MEH–PPV LEDs in that light emission is observed in both forward and reverse bias modes. It is believed that the mobility of the I3− anions in the (MEH–PPV)x+y(I3)xy− species formed on doping the MEH–PPV compensate for injected charges at the electrodes, thus reducing the electron and hole injection barriers. © 1997 American Institute of Physics.  
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85.60.Jb Light-emitting devices
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds

Fabrication of waveguides in glasses by a poling procedure

W. Margulis and F. Laurell

Appl. Phys. Lett. 71, 2418 (1997); http://dx.doi.org/10.1063/1.120079 (3 pages) | Cited 11 times

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Single mode channel waveguides were fabricated in soda lime glass by poling the samples at 280 °C with 2.5 kV bias voltage. The refractive index of the glass was reduced by 1.5% due to the depletion of sodium ions, making possible the formation of waveguides in a depressed cladding configuration. © 1997 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ej Polarization and depolarization

Fabrication and superfluorescence of rare-earth chelate-doped graded index polymer optical fibers

Takeyuki Kobayashi, Shiro Nakatsuka, Takami Iwafuji, Ken Kuriki, Nana Imai, Takashi Nakamoto, Charles D. Claude, Keisuke Sasaki, Yasuhiro Koike, and Yoshi Okamoto

Appl. Phys. Lett. 71, 2421 (1997); http://dx.doi.org/10.1063/1.120080 (3 pages) | Cited 46 times

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Rare-earth chelate-doped graded index (GI) polymer optical fibers (POF) are proposed and fabricated. The attenuation loss was measured to be 0.4 dB/m at 650 nm for a GI POF doped with 1 wt % of europium (Eu) chelate. Lifetime shortening and spectral narrowing verified the occurrence of superfluorescence at 614 nm in the Eu chelate-doped GI POF pumped with xenon flashlamps. The demonstration of superfluorescence shows that rare-earth chelate-doped GI POFs are appealing as optical amplifiers and superfluorescent sources in a variety of communication and sensor applications. © 1997 American Institute of Physics.
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42.81.Ht Gradient-index (GRIN) fiber devices
42.81.Dp Propagation, scattering, and losses; solitons
42.70.Jk Polymers and organics
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
78.45.+h Stimulated emission

Energy-gap narrowing in a current injected InGaN/AlGaN surface light emitting diode

G. Y. Zhao, G. Yu, T. Egawa, J. Watanabe, T. Jimbo, and M. Umeno

Appl. Phys. Lett. 71, 2424 (1997); http://dx.doi.org/10.1063/1.120081 (3 pages) | Cited 10 times

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The emission spectrum of a current injected InGaN/AlGaN surface emitting diode has been investigated. A clear redshift of the low energy edge with increasing injected current has been observed, and is attributed to the many body effects. The carrier density and band gap narrowing are obtained by fitting the line shape of the emission spectrum, using Landsberg model which includes many body effects. A redshift of around 92 meV of the low energy edge is obtained as injected current increases from 400 to 4000 mA. The band gap change can be described well in proportion to the 1/3 power of the carrier density, which is just suggested by the exchange energy of electron–electron, and hole–hole interactions. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices

Charge–carrier diffusion length in photorefractive crystals computed from the initial hologram phase shift

A. A. Freschi, P. M. Garcia, and J. Frejlich

Appl. Phys. Lett. 71, 2427 (1997); http://dx.doi.org/10.1063/1.120116 (3 pages) | Cited 8 times

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The phase shift between the pattern of light onto a photorefractive crystal and the resulting hologram at the very beginning of the recording process in two-wave mixing is analyzed and measured as a function of the applied electric field. These data allow one to compute the diffusion length of photoexcited charge carriers and to evaluate the actual electric field inside the crystal. A diffusion length of 0.14 μm is measured in a nominally undoped photorefractive Bi12TiO20 crystal using a 532 nm wavelength laser illumination, in agreement with results obtained from other methods. © 1997 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High power InAsSb/InPAsSb/InAs mid-infrared lasers

A. Rybaltowski, Y. Xiao, D. Wu, B. Lane, H. Yi, H. Feng, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 71, 2430 (1997); http://dx.doi.org/10.1063/1.120082 (3 pages) | Cited 9 times

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We demonstrate high-power InAsSb/InPAsSb laser bars (λ ≈ 3.2 μm) consisting of three 100-μm-wide laser stripes of 700 μm cavity length, with peak output power up to 3 W at 90 K, and far-fields for the direction perpendicular to the junction as narrow as 12° full width half maximum. Spectra and far-field patterns of the laser bars are shown to have excellent characteristics for a wide range of operating conditions, suggesting the possibility of even higher light power emission with good beam quality. Joule heating is shown to be the major factor limiting higher power operation. © 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

Pressure-dependent photoluminescence study of InxGa1−xN

W. Shan, J. J. Song, Z. C. Feng, M. Schurman, and R. A. Stall

Appl. Phys. Lett. 71, 2433 (1997); http://dx.doi.org/10.1063/1.120083 (3 pages) | Cited 17 times

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We present the results of pressure-dependent photoluminescence (PL) studies of single-crystal InxGa1−xN (0 ⩽ x<0.15) films grown on top of thick GaN epitaxial layers by metalorganic chemical vapor deposition with sapphire as substrates. PL measurements were performed at 10 K as a function of applied hydrostatic pressure using the diamond-anvil-cell technique. The luminescence emissions from the InxGa1−xN epifilms were found to shift linearly toward higher energy with increasing pressure. By examining the pressure dependence of the PL spectra, the pressure coefficients for the emission structures associated with the direct band gap of InxGa1−xN were determined. The values of the pressure coefficients were found to be 3.9×10−3 eV/kbar for In0.08Ga0.92N and 3.5×10−3 eV/kbar for In0.14Ga0.86N. © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
62.50.-p High-pressure effects in solids and liquids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Multivariable dependence of modulation spectroscopy in semiconductor superlattices

T. P. Pearsall and A. DiVergilio

Appl. Phys. Lett. 71, 2436 (1997); http://dx.doi.org/10.1063/1.120084 (3 pages)

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The modulation spectrum of semiconductor superlattices is shown to be a sensitive function of photon wavelength and local energy band-bending in the superlattice structure. The added dependence leads directly to the concept of a modulation spectroscopy surface for heterostructures as opposed to a simple plot in two dimensions of amplitude as a function of photon energy. The implications of these results for the use of modulation spectroscopy methods such as contactless photoreflectance spectroscopy, where the band bending cannot be controlled, are discussed. © 1997 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Jq Electro-optical effects

Band gap bowing and refractive index spectra of polycrystalline AlxIn1−xN films deposited by sputtering

T. Peng, J. Piprek, G. Qiu, J. O. Olowolafe, K. M. Unruh, C. P. Swann, and E. F. Schubert

Appl. Phys. Lett. 71, 2439 (1997); http://dx.doi.org/10.1063/1.120112 (3 pages) | Cited 47 times

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The AlGaInN semiconductor system is currently of high interest for applications in blue light emitting devices. AlInN is a prospective material for lattice matched confinement layers. We measure the refractive index as well as the band gap across the entire compositional range of high-quality polycrystalline AlInN samples. Strong band gap bowing is observed. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors

Direct writing of silicon gratings with highly coherent ultraviolet laser

Chung-Yen Chao, Cheng-Yen Chen, Chee-Wee Liu, Yih Chang, and C. C. Yang

Appl. Phys. Lett. 71, 2442 (1997); http://dx.doi.org/10.1063/1.120447 (3 pages) | Cited 7 times

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Silicon gratings with periods from 180 to 550 nm were fabricated with a laser ablation technique in which the interference fringe from an intense and coherent ultraviolet laser at 266 nm directly melted silicon surface. The scanning electron microscopy and atomic force microscopy pictures showed that the corrugations were in quite good quality with the depth as large as 70 nm. The measurement of grating period dependence on temperature showed that rapid thermal annealing could release the thermal strains, which were built during the melting and cooling process in laser ablation, and make the grating period variation more regular. Also, with an air gap between the sample and prism surfaces, the fabricated gratings had weaker thermal strains and more regular temperature dependencies. All the measurement results of temperature dependence were consistent with theoretical predictions. © 1997 American Institute of Physics.
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42.79.Dj Gratings
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.-b Surface treatments
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
87.64.Dz Scanning tunneling and atomic force microscopy
07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
42.86.+b Optical workshop techniques

Pulsed laser deposition of Cu:Al2O3 nanocrystal thin films with high third-order optical susceptibility

J. M. Ballesteros, R. Serna, J. Solís, C. N. Afonso, A. K. Petford-Long, D. H. Osborne, and R. F. Haglund

Appl. Phys. Lett. 71, 2445 (1997); http://dx.doi.org/10.1063/1.120117 (3 pages) | Cited 65 times

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Nanocomposite films comprising metal Cu nanocrystals embedded in an Al2O3 matrix were deposited by alternating pulsed laser ablation from metallic Cu and ceramic Al2O3 targets. The films were grown in vacuum on glass substrates held at room temperature. The as-grown films contain 4 nm Cu nanocrystals in an amorphous Al2O3 matrix, with a total thickness of 190 nm. The films show a substantial third-order susceptibility with an electronic nonlinear refractive index of (2.93±1.08)⋅10−10 cm2 W−1 and a nonlinear saturation of −(2.34±0.18)⋅10−5 cm W−1. © 1997 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
42.65.An Optical susceptibility, hyperpolarizability
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Fg Pulsed laser ablation deposition
78.66.Jg Amorphous semiconductors; glasses
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

SiGe quantum dots prepared on an ordered mesoporous silica coated Si substrate

Y. S. Tang, S. Cai, G. Jin, J. Duan, K. L. Wang, H. M. Soyez, and B. S. Dunn

Appl. Phys. Lett. 71, 2448 (1997); http://dx.doi.org/10.1063/1.120085 (3 pages) | Cited 23 times

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This letter reports a new way of preparing wafer sized SiGe quantum dots on an ordered mesoporous sol gel silica coated Si. It was found from x-ray diffraction that very good regular layers of mesoscopic sized SiGe quantum dots can be formed in the silica. Initial low temperature photoluminescence measurements show much improved light emission of the buried dots. This technique is a potential low cost method for producing quantum dot arrays. © 1997 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
78.55.Hx Other solid inorganic materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Suppression of silicide formation in Ta/Si system by ion-beam-assisted deposition

Joon Seop Kwak, Hong Koo Baik, Jong-Hoon Kim, and Sung-Man Lee

Appl. Phys. Lett. 71, 2451 (1997); http://dx.doi.org/10.1063/1.120086 (3 pages) | Cited 10 times

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In order to increase the failure temperature of a Ta diffusion barrier for Cu, the suppression of silicide formation in a Ta/Si system by ion-beam-assisted deposition of Ta film was investigated. When the Ta layer was deposited without ion bombardment, the reaction between Ta and Si started at 600 °C. In the case where the Ta film was prepared with concurrent ion bombardment, however, the silicide formation was retarded up to 700 °C. The suppression of Ta silicide formation can be attributed to a densification of grain boundaries in the Ta film by ion bombardment, followed by a reduction of the chemical driving force for the initial stage of silicide formation. The Ta diffusion barrier deposited by ion-beam-assisted deposition effectively suppressed the reaction between Si and Cu layers up to 650 °C for 30 min. © 1997 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
85.40.Ls Metallization, contacts, interconnects; device isolation

Network morphology of polymer stabilized liquid crystals

I. Dierking, L. L. Kosbar, A. Afzali-Ardakani, A. C. Lowe, and G. A. Held

Appl. Phys. Lett. 71, 2454 (1997); http://dx.doi.org/10.1063/1.120087 (3 pages) | Cited 34 times

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Monomer solubility is identified as the primary factor determining network morphology in polymer stabilized cholesteric liquid crystal textures. Poorly soluble monomers form coarse structures composed of discrete, oblong grains, whereas soluble monomers yield smooth, continuous polymer networks. A crossover from smooth to grainy structure is observed as a function of monomer concentration. The grainy structure results from precipitation polymerization and the observed behavior is well described by the Flory–Huggins theory of polymer solubility. © 1997 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
64.70.M- Transitions in liquid crystals

Temperature dependence of excitonic energy in isolated Se chains formed in channels of AlPO4-5 crystals

H. D. Sun, Z. K. Tang, W. M. Zhao, and George K. L. Wong

Appl. Phys. Lett. 71, 2457 (1997); http://dx.doi.org/10.1063/1.120113 (3 pages) | Cited 11 times

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Optical absorption spectra of Se chains formed in channels of AlPO4-5 (AFI) crystals are measured in the temperature range from 80 to 298 K. The excitonic energy of the isolated Se chains is observed to shift to lower energy linearly with increasing temperatures, in sharp contrast to the positive temperature coefficient in trigonal-Se crystal. The marked change in the temperature behavior of the excitonic energy is attributed to the greatly diminished interchain interaction in Se–AFI as well as the weakening of the electron-optical-phonon coupling in a low-dimensional system. © 1997 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.38.-k Polarons and electron-phonon interactions

Texture analysis of indium films grown on GaAs(100) by molecular beam epitaxy

J. Kečkéš, B. Ortner, Š. Németh, B. Grietens, and G. Borghs

Appl. Phys. Lett. 71, 2460 (1997); http://dx.doi.org/10.1063/1.120088 (3 pages)

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X-ray diffraction texture analysis is employed to study heteroepitaxial layers of indium grown on GaAs(100) surfaces by molecular beam epitaxy. The results document the epitaxial relationships In{101}∥GaAs{111} and In〈100〉∥GaAs〈110〉. Furthermore, an In{101} plane is oriented nearly parallel to another GaAs{111} plane, with angular deviation less than 3.9°. Due to the symmetry of the zincblende structure, for each GaAs(111) plane, In crystallites are detected in three equivalent positions. The growth of In layers was strongly influenced by the polar character of the GaAs structure, because indium was found to grow preferably on {111}A planes. © 1997 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Studies of density and surface roughness of ultrathin amorphous carbon films with regards to thickness with x-ray reflectometry and spectroscopic ellipsometry

S. Logothetidis and G. Stergioudis

Appl. Phys. Lett. 71, 2463 (1997); http://dx.doi.org/10.1063/1.120089 (3 pages) | Cited 26 times

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Specular x-ray reflectivity (XRR) measurements were used to study the density and surface roughness of ultrathin hydrogen-free amorphous carbon films deposited by sputtering, of thickness varying from 25 to 325 Å. The film thickness and surface roughness obtained from XRR measurements are in good agreement with that found by spectroscopic ellipsometry (SE) and atomic force microscopy. The results for the film composition obtained from SE and XRR are supported by stress measurements. Films (especially those with thickness below 100 Å) deposited with positive substrate bias voltage were found to exhibit a reduction in density, sp3 C–C bonding, and internal compressive stresses and an increase in surface roughness by increasing film thickness. © 1997 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
68.60.Bs Mechanical and acoustical properties
61.43.Er Other amorphous solids

Titanium thin film growth on small and large misfit substrates

M. Huth and C. P. Flynn

Appl. Phys. Lett. 71, 2466 (1997); http://dx.doi.org/10.1063/1.120090 (3 pages) | Cited 10 times

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The influence of lattice misfit on the growth of Ti (0001) is investigated in the limit of small negative (−1%) and large positive (+6.8%) misfit by choosing MgO (111) and Al2O3 (0001) as substrate materials. Reflection high energy electron diffraction imaging and intensity measurements during growth reveal two-dimensional nucleation of islands on MgO, in contrast to three-dimensional nucleation on Al2O3. X-ray analysis of 30-nm-thick films on MgO shows a two-component line shape in transverse scans of the (0002) and (0004) reflections, pointing to a high degree of structural coherence in the weak disorder limit. The surface morphology of films grown on MgO depends strongly on the substrate temperature during growth. © 1997 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)

Organic electroluminescence cells based on thin films deposited by ultraviolet laser ablation

N. Matsumoto, H. Shima, T. Fujii, and F. Kannari

Appl. Phys. Lett. 71, 2469 (1997); http://dx.doi.org/10.1063/1.120114 (3 pages) | Cited 10 times

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Organic thin films of copper-phthalocyanine (CuPc) and aluminum tris-8-hydroxyquinline (Alq3) were fabricated via KrF laser ablation. In spite of poor crystallinity exhibited in the reconstructed organic films, the CuPc film still works as a hole-transport layer in electroluminescence cells based on the CuPc and Alq3 layers. Electroluminescence at ∼ 500 nm was obtained with a low initiation voltage of ∼ 12 V. There is no significant difference in electroluminescence performance for devices fabricated via laser ablation and thermal evaporation. Emission at ∼ 600 nm caused by energy transfer from Alq3 to 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) is also observed from a DCM-doped Alq3 emission layer. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Hd Other semiconductors
81.15.Fg Pulsed laser ablation deposition

Dislocation density reduction via lateral epitaxy in selectively grown GaN structures

Tsvetanka S. Zheleva, Ok-Hyun Nam, Michael D. Bremser, and Robert F. Davis

Appl. Phys. Lett. 71, 2472 (1997); http://dx.doi.org/10.1063/1.120091 (3 pages) | Cited 181 times

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The microstructure and the lateral epitaxy mechanism of formation of homoepitaxially and selectively grown GaN structures within windows in SiO2 masks have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy. The structures were produced by organometallic vapor phase epitaxy for field emission studies. A GaN layer underlying the SiO2 mask provided the crystallographic template for the initial vertical growth of the GaN hexagonal pyramids or striped pattern. The SiO2 film provided an amorphous stage on which lateral growth of the GaN occurred and possibly very limited compliancy in terms of atomic arrangement during the lateral growth and in the accommodation of the mismatch in the coefficients of thermal expansion during cooling. Observations with TEM show a substantial reduction in the dislocation density in the areas of lateral growth of the GaN deposited on the SiO2 mask. In many of these areas no dislocations were observed. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
65.40.De Thermal expansion; thermomechanical effects

Work-hardening effects in the lattice relaxation of single layer heterostructures

D. González, D. Araújo, G. Aragón, and R. García

Appl. Phys. Lett. 71, 2475 (1997); http://dx.doi.org/10.1063/1.120092 (3 pages) | Cited 3 times

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A modelization of the strain relaxation in single heteroepitaxial layers is presented in this letter. The calculations consider the energetic variations of the heteroepitaxial structure when introducing one new dislocation into the existing interfacial array of fixed misfit dislocations without continuous readjustment of the spacing array. The interaction energy of the new dislocation with both lattice mismatch and dislocation array is shown to be the limiting factor that controls the mechanism of strain relaxation at the saturation stage of relaxation. The model is shown to be in good agreement with the lattice relaxation behavior of previously published strain/thickness data. © 1997 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effect of electronic corrections on the thickness dependence of thin oxide reliability

G. B. Alers, A. S. Oates, D. Monroe, K. S. Krisch, and B. E. Weir

Appl. Phys. Lett. 71, 2478 (1997); http://dx.doi.org/10.1063/1.120093 (3 pages) | Cited 5 times

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The thickness dependence of constant voltage lifetime tests are compared for ultrathin oxides in the range of 50–125 Å. An apparent factor of 100 enhancement in the lifetime of 50 Å oxides relative to the 125 Å oxides is observed at a fixed electric field when the field in the oxide is calculated using the physical thickness of the oxide as determined by ellipsometry. When corrections are made for the distribution of electrons at the silicon interface including depletion in the silicon and quantum-mechanical screening effects then this apparent enhancement is reduced and all oxides have similar lifetimes at a fixed field. Such a rescaling of oxide reliability demonstrates the importance of accurate determination of electric field and oxide voltage in thin oxides and that oxide reliability is not significantly affected by thickness down to 50 Å, depending only on field. We compare different techniques for determining the effective thickness using current-voltage or capacitance-voltage (C-V) curves. We show that accurate estimates of the electric field can be obtained from integration of the C-V relation of the capacitor. When electric fields are calculated using C-V curves, a consistent set of extrapolation parameters can be obtained for all thicknesses. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects

High spatial resolution spectroscopy of a single V-shaped quantum wire

J. Bellessa, V. Voliotis, R. Grousson, X. L. Wang, M. Ogura, and H. Matsuhata

Appl. Phys. Lett. 71, 2481 (1997); http://dx.doi.org/10.1063/1.120094 (3 pages) | Cited 35 times

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We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 μm2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum wells. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.20.Fz Weak or Anderson localization
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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