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6 Apr 1998

Volume 72, Issue 14, pp. 1667-1789

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The investigation of the relaxation processes in antiferroelectric liquid crystals by electro-optic spectroscopy

Yu. P. Panarin, O. Kalinovskaya, and J. K. Vij

Appl. Phys. Lett. 72, 1667 (1998); http://dx.doi.org/10.1063/1.121147 (3 pages) | Cited 32 times

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Electrooptic spectroscopy of an antiferroelectric liquid crystal is carried out over a range of frequencies from 1 Hz to 100 kHz. In the antiferroelectric SmCA phase two relaxation processes are found, one at the fundamental frequency of a mode and the second at twice the frequency of a different mode. A comparison of the results of the electro-optic spectroscopy with a theoretical study of the motion of the director of an antiferroelectric helix subject to a weak alternating field enables a determination of the origin of the relaxation processes in antiferroelectric phases. © 1998 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
78.20.Jq Electro-optical effects

Controlled spontaneous lifetime in microcavity confined InGaAlAs/GaAs quantum dots

L. A. Graham, D. L. Huffaker, Q. Deng, and D. G. Deppe

Appl. Phys. Lett. 72, 1670 (1998); http://dx.doi.org/10.1063/1.121148 (3 pages) | Cited 17 times

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Controlled spontaneous lifetimes are demonstrated in InGaAlAs/GaAs quantum dots confined in planar microcavities. Due to their independent and spectrally sharp light emission, the quantum dot emitters provide an excellent means for studying the spontaneous lifetime dependence on microcavity tuning, while maintaining experimental parameters such as temperature and pump intensity constant. The measured lifetime changes are compared with calculated results and show good agreement. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors

A low pressure mercury vapor resonance ionization image detector

O. I. Matveev, B. W. Smith, and J. D. Winefordner

Appl. Phys. Lett. 72, 1673 (1998); http://dx.doi.org/10.1063/1.121149 (3 pages) | Cited 5 times

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Narrow-band spectrally selective image detection based upon the resonance ionization of mercury atoms in a low pressure cell is described. Image dimensions and intensities were measured versus the wavelength of ionizing laser radiation and the dependence upon the voltage applied to electrodes was studied. The position sensitive image of the electron beam, created by two-step resonance photoionization of mercury, was studied when the detected laser beam was scanned spatially. A distorting influence of space charge due to positive mercury ions on the electron beam image was observed. Means of eliminating these distortions are discussed. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
32.80.Fb Photoionization of atoms and ions

Transmissive properties of Ag/MgF2 photonic band gaps

Mark J. Bloemer and Michael Scalora

Appl. Phys. Lett. 72, 1676 (1998); http://dx.doi.org/10.1063/1.121150 (3 pages) | Cited 100 times

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We present results of transmittance measurements on periodic layers of Ag/MgF2 at optical and microwave frequencies. These one-dimensional, photonic band gap materials exhibit transparency bands at optical frequencies and a huge stop band that extends throughout the near-IR to microwave frequencies and beyond. A unique feature of these metal/dielectric photonic band gap (MD–PBG) materials is that the overall transmittance in the pass band may increase as more periods are deposited. The center frequency, width, and sharpness of the pass bands are adjustable and generally depend on the thickness of the layers and the number of Ag/MgF2 periods. These simple periodic structures have applications as sensor and eye protection devices, heat reflecting windows, ultraviolet blocking films, and transparent electrodes for light emitting diodes and liquid crystal displays. © 1998 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.30.-j Infrared and Raman spectra
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Thermally stable high-gain photorefractive polymer composites based on a tri-functional chromophore

E. Hendrickx, J. Herlocker, J. L. Maldonado, S. R. Marder, B. Kippelen, A. Persoons, and N. Peyghambarian

Appl. Phys. Lett. 72, 1679 (1998); http://dx.doi.org/10.1063/1.121187 (3 pages) | Cited 26 times

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We report on the photorefractive properties of thermally stable polymer composites based on the dye 2, N, N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene. At an applied field of 50 V/μm, we have achieved a dynamic range of Δn = 8.5×10−3 and a net two-beam coupling gain of 202 cm−1. The diffraction efficiency peaks at an applied field of 28 V/μm, giving an external diffraction efficiency of 71%. © 1998 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
81.05.Qk Reinforced polymers and polymer-based composites
42.25.Fx Diffraction and scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Jq Electro-optical effects
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How good is the polarization selection rule for intersubband transitions?

H. C. Liu, M. Buchanan, and Z. R. Wasilewski

Appl. Phys. Lett. 72, 1682 (1998); http://dx.doi.org/10.1063/1.121151 (3 pages) | Cited 45 times

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Using GaAs based quantum well infrared photodetectors (QWIPs) with either GaAs or InGaAs wells, we experimentally investigate the accuracy of the polarization selection rule for conduction band intersubband transitions. We employ a device structure and a light coupling geometry where the parasitic light scattering is negligible. The experiments imply that the selection rule is followed to an accuracy of 0.2% for a 8.1 μm QWIP with GaAs wells; this degrades to 3% for a 4.6 μm QWIP with In0.1Ga0.9As wells. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effect of external electric field on the growth of nanotubules

Anchal Srivastava, A. K. Srivastava, and O. N. Srivastava

Appl. Phys. Lett. 72, 1685 (1998); http://dx.doi.org/10.1063/1.121152 (3 pages) | Cited 4 times

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In the present investigation, we have studied the effect of electric field on the growth of carbon nanotubules. Different electric fields corresponding to 3, 6, 9, 15, and 21 V have been applied during the growth of the tubules. The estimate of the electric field corresponding to these voltages cannot be precisely evaluated in view of only approximately defined electrode dimensions. It has been observed that the application of electric field leads to the agglomerates (bundles) of nanotubules. The size, length, and alignment of these bundles varies with the strength of the applied electric field. The best results have been obtained with electric field corresponding to 6 V where the as-formed tubules are in parallel alignment and exist as bundles. As the electric field is increased, the alignment of tubules in the bundle becomes randomly oriented. The degree of randomness increases with increase of electric field after its optimum value corresponding to 6 V. The parallel alignment of the graphitic tubules is thought to result due to orientation of the tubule axis along the direction of the applied electric field corresponding to an optimum value (which for the present case is 6 V) of the impressed voltage. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Localized excitonic transitions in a ZnSe-Zn0.75Cd0.25Se double-superlattice grown by molecular beam epitaxy

Z. P. Guan, G. K. Kuang, E. Griebl, M. Kastner, and W. Gebhardt

Appl. Phys. Lett. 72, 1688 (1998); http://dx.doi.org/10.1063/1.121153 (3 pages) | Cited 2 times

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A group of well-defined exciton transitions from the localized states were observed in ZnSe-Zn0.75Cd0.25Se double-superlattice structure. The photoluminescence and photoreflectance have been employed to study the subband transitions at low temperatures. At 1.4 K, except the two ground states and two higher subbands of n = 1 light-hole and n = 2 heavy-hole excitonic transitions, other four peaks (A, B, C, and D) also were observed in wider-well superlattice. Those peaks were attributed to the excitonic transitions from n = 2 heavy-hole subband due to the fluctuation of well-barrier interface. Another localized excitonic transition from narrower-well superlattice appeared as increasing the modulated intensity in photoreflectance spectra. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Fz Weak or Anderson localization
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
78.20.-e Optical properties of bulk materials and thin films

Equation of state of wurtzitic boron nitride to 66 GPa

Vladimir L. Solozhenko, Daniel Häusermann, Mohamed Mezouar, and Martin Kunz

Appl. Phys. Lett. 72, 1691 (1998); http://dx.doi.org/10.1063/1.121186 (3 pages) | Cited 20 times

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The compressibility of wurtzitic boron nitride (wBN) taken in mixture with cubic BN has been measured at room temperature up to 66 GPa, using a diamond anvil cell and powder diffraction of synchrotron radiation. From the obtained pressure-volume relation for wBN the isothermal bulk modulus of B0 = 375±9 GPa and its first pressure derivative of dB0/dp = 4.9±0.7 have been calculated indicating that this phase has nearly the same compressibility as cBN (B0 = 377±4 GPa and dB0/dp = 4.1±0.2). Thermodynamic calculations using our findings on wBN equation of state have shown that wurtzitic boron nitride is metastable over the whole ranges of pressures and temperatures. © 1998 American Institute of Physics.
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64.30.-t Equations of state of specific substances
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Arsenic incorporation in HgCdTe grown by molecular beam epitaxy

P. S. Wijewarnasuriya and S. Sivananthan

Appl. Phys. Lett. 72, 1694 (1998); http://dx.doi.org/10.1063/1.121154 (3 pages) | Cited 22 times

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We report the results of in situ arsenic doping in HgCdTe layers grown by molecular beam epitaxy (MBE). Arsenic incorporation was carried out by two mechanisms called conventional doping and planar doping. The obtained results indicate that for both mechanisms, after Hg anneal, arsenic was successfully incorporated as an acceptor during the MBE growth. Secondary ion mass spectrometry and Hall-effect measurements before and after Hg annealing were used to characterize arsenic activity in the grown layers. Close to 100% acceptor doping efficiency with arsenic has been obtained on these MBE grown layers up to total arsenic concentrations of approximately 2×1018 cm−3, which is more than sufficient for a wide range of infrared devices. At much higher total arsenic concentrations, electrical activity falls off drastically as the doping level saturates. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.Cc Kinetics of defect formation and annealing

Local determination of the stacking sequence of layered materials

J. Fompeyrine, R. Berger, H. P. Lang, J. Perret, E. Mächler, Ch. Gerber, and J.-P. Locquet

Appl. Phys. Lett. 72, 1697 (1998); http://dx.doi.org/10.1063/1.121155 (3 pages) | Cited 21 times

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The ability to modify the stacking sequence of ultrathin films offers a unique way to change either the interaction strength or the doping, but demands a careful control of each atomic monolayer. Progress is hampered by the lack of a direct method that allows differentiation on a local scale between the various terminating layers of a crystal. Here, the combination of a vacuum annealing process and friction force microscopy reveals this local distinction on a SrTiO3 surface. Using the friction contrast, we find how the terminating layer of a single crystal profoundly influences the terrace edge structure. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
07.79.Lh Atomic force microscopes

Optical and electrical properties of aluminum oxide films deposited by spray pyrolysis

M. Aguilar-Frutis, M. Garcia, and C. Falcony

Appl. Phys. Lett. 72, 1700 (1998); http://dx.doi.org/10.1063/1.121156 (3 pages) | Cited 34 times

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The optical and electrical characteristics of spray pyrolysis deposited aluminum oxide films are reported. The films were deposited from a spraying solution of aluminum acetylacetonate in N,N-dimethylformamide using an ultrasonic mist generator on (100) Si substrates. The addition of water mist during the spraying deposition process resulted in an overall improvement of the films characteristics. The substrate temperature during deposition was in the 450–650 °C range. Deposition rates up to 90 Å/s were obtained depending on the spraying solution concentration and substrate temperature with an activation energy of the order of 31 kJ/mol. The optical energy band gap for these films was 5.63 eV and the refractive index at 630 nm up to 1.66 was measured by ellipsometry. The electrical characteristics of the films were determined from the capacitance and current versus voltage measurements of metal–oxide–semiconductor (MOS) structures incorporating them. A dielectric constant of 7.9, interface states density of the order of 1011×1/eV cm2 as well as breakdown fields higher than 5 MV/cm were determined in this way. © 1998 American Institute of Physics.
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78.66.Nk Insulators
77.55.-g Dielectric thin films
81.15.Rs Spray coating techniques
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
73.20.At Surface states, band structure, electron density of states

Hydrogen-decorated lattice defects in proton implanted GaN

Marcie G. Weinstein, C. Y. Song, Michael Stavola, S. J. Pearton, R. G. Wilson, R. J. Shul, K. P. Killeen, and M. J. Ludowise

Appl. Phys. Lett. 72, 1703 (1998); http://dx.doi.org/10.1063/1.121157 (3 pages) | Cited 22 times

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Several vibrational bands were observed near 3100 cm−1 in GaN that had been implanted with hydrogen at room temperature and subsequently annealed. Our results indicate that these bands are due to nitrogen-dangling-bond defects created by the implantation that are decorated by hydrogen. The frequencies are close to those predicted recently for VGa–Hn complexes, leading us to tentatively assign the new lines to VGa defects decorated with different numbers of H atoms. © 1998 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology

A model of bonding and band-forming for oxides and nitrides

Chang Q. Sun

Appl. Phys. Lett. 72, 1706 (1998); http://dx.doi.org/10.1063/1.121158 (3 pages) | Cited 24 times

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Correlation between chemical bonds, energy bands, and the corresponding properties of oxides and nitrides is established. It is proposed that an oxygen or nitrogen atom can hybridize and form a tetrahedron with its four neighbors through bonding orbitals and nonbonding lone pairs. As a result, the energy states of the host material are modified with four additional features, namely, sp3-hybrid bonding, nonbonding (lone pair), antibonding (dipole), and hole states. Therefore, oxygen and nitrogen possess the special ability of not only enlarging the band gap by hole production but also adding an antibonding subband above the Fermi level. © 1998 American Institute of Physics.
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61.50.Lt Crystal binding; cohesive energy
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
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Boron segregation in As-implanted Si caused by electric field and transient enhanced diffusion

R. D. Chang, P. S. Choi, D. L. Kwong, D. Wristers, and P. K. Chu

Appl. Phys. Lett. 72, 1709 (1998); http://dx.doi.org/10.1063/1.121159 (3 pages) | Cited 5 times

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Boron segregation in an implanted arsenic profile in Si during annealing was investigated under various annealing conditions. It was found that both the implant damage created by arsenic implantation and arsenic deactivation enhance the diffusion of the embedded boron layer toward the shallow As implanted profile. The segregation phenomenon was observed in both 650 °C furnace annealed (FA) and 1000 °C rapid thermally annealed (RTA) samples. For the 650 °C FA sample, the boron segregation peak was located at the junction formed by implanted As, where residual dislocation loops at the original amorphous/crystalline (a/c) interface were also observed. However, no a/c interface dislocation loops were found to be present for the RTA samples. Additional anomalous boron segregation was observed for the 1000 °C RTA+750 °C FA samples. The additional boron segregation is not correlated with defect layers. It is, therefore, concluded that the anomalous boron segregation is caused by the electric field resulting from the formation of a p-n junction. © 1998 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
68.35.Fx Diffusion; interface formation
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Coherent-to-incoherent transition in surfactant mediated growth of InAs quantum dots

B. R. A. Neves, M. S. Andrade, W. N. Rodrigues, G. A. M. Sáfar, M. V. B. Moreira, and A. G. de Oliveira

Appl. Phys. Lett. 72, 1712 (1998); http://dx.doi.org/10.1063/1.121160 (3 pages) | Cited 14 times

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In this letter, we present an atomic force microscopy study of a series of Te-mediated InAs/GaAs samples with InAs coverage ranging from 1.5 to 3 monolayers. We were able to directly identify the growth mode transition and the mechanism of relaxed island formation. At the limit of coherent growth mode, strained quantum dots aggregate, forming twin quantum dots (TQDs), which are structures of two, or more, dots virtually bonded together, separated by less than 3 nm. The onset of the incoherent mode is then unambiguously characterized by the coalescence of individual TQDs forming initially small, and then larger, relaxed islands. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Preservation of atomic flatness at SiO2/Si(111) interfaces during thermal oxidation in a furnace

Noriyuki Miyata, Heiji Watanabe, and Masakazu Ichikawa

Appl. Phys. Lett. 72, 1715 (1998); http://dx.doi.org/10.1063/1.121161 (3 pages) | Cited 13 times

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SiO2/Si(111) interfaces formed by a furnace oxidation are studied by a scanning reflection electron microscopy (SREM). SREM observation indicates that the initial atomic steps on a Si(111) surface are preserved at the SiO2/Si interface and the interfacial steps do not move laterally even after 48-nm-thick oxidation. A profile analysis of reflection high-energy electron diffraction shows that the SiO2/Si interface consists of islands which have a diameter of about 5 nm and monolayer depth. Our results indicate that the layer-by-layer oxidation caused by two-dimensional island nucleation proceeds under furnace oxidation. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Controlling threading dislocation densities in Ge on Si using graded SiGe layers and chemical-mechanical polishing

M. T. Currie, S. B. Samavedam, T. A. Langdo, C. W. Leitz, and E. A. Fitzgerald

Appl. Phys. Lett. 72, 1718 (1998); http://dx.doi.org/10.1063/1.121162 (3 pages) | Cited 179 times

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A method of controlling threading dislocation densities in Ge on Si involving graded SiGe layers and chemical-mechanical polishing (CMP) is presented. This method has allowed us to grow a relaxed graded buffer to 100% Ge without the increase in threading dislocation density normally observed in thick graded structures. This sample has been characterized by transmission electron microscopy, etch-pit density, atomic force microscopy, Nomarski optical microscopy, and triple-axis x-ray diffraction. Compared to other relaxed graded buffers in which CMP was not implemented, this sample exhibits improvements in threading dislocation density and surface roughness. We have also made process modifications in order to eliminate particles due to gas-phase nucleation and cracks due to thermal mismatch strain. We have achieved relaxed Ge on Si with a threading dislocation density of 2.1×106 cm−2, and we expect that further process refinements will lead to lower threading dislocation densities on the order of bulk Ge substrates. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.72.Lk Linear defects: dislocations, disclinations
81.65.Ps Polishing, grinding, surface finishing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.Cf Surface cleaning, etching, patterning
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Electrical and physical characterization of deuterium sinter on submicron devices

H. C. Mogul, L. Cong, R. M. Wallace, P. J. Chen, T. A. Rost, and K. Harvey

Appl. Phys. Lett. 72, 1721 (1998); http://dx.doi.org/10.1063/1.121163 (3 pages) | Cited 14 times

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The impact of a deuterium (D2) sinter under two different annealing conditions, 450 °C/60 min and 450 °C/90 min, was studied and compared to the traditional forming gas (FG) sinter. Channel hot carrier (CHC) measurements indicated that while the D2 sinter for 60 min improves the lifetime of the devices by 10× over the FG sinter, an additional increase in the D2 anneal time actually has a negative impact on lifetime. DC current–voltage measurements also showed that samples sintered in D2 ambient for 60 min were the least prone to degradation under stress. Gated diode results showed no appreciable amount of difference in the initial interface state density among the different samples. Secondary ion mass spectroscopy indicated that neither poly nor salicide appears to be a complete barrier to D2 diffusion. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
66.30.J- Diffusion of impurities
72.20.Ht High-field and nonlinear effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Cn Elemental semiconductors

Temperature dependence of large positive magnetoresistance in hybrid ferromagnetic/semiconductor devices

N. Overend, A. Nogaret, B. L. Gallagher, P. C. Main, M. Henini, C. H. Marrows, M. A. Howson, and S. P. Beaumont

Appl. Phys. Lett. 72, 1724 (1998); http://dx.doi.org/10.1063/1.121164 (3 pages) | Cited 34 times

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We investigate a new type of magnetoresistance (MR) in which the resistivity of a near-surface two-dimensional electron gas is controlled by the magnetization of a submicron ferromagnetic grating defined on the surface of the device. We observe an increase in resistance of up to ∼ 1500% at a temperature of 4 K and ∼ 1% at 300 K. The magnitude and temperature dependence of the MR are well accounted for by a semiclassical theory. Optimization of device parameters is expected to increase considerably the magnitude of the room temperature MR. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
75.47.De Giant magnetoresistance
73.61.At Metal and metallic alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Strain variations in InGaAsP/InGaP superlattices studied by scanning probe microscopy

Huajie Chen, R. M. Feenstra, R. S. Goldman, C. Silfvenius, and G. Landgren

Appl. Phys. Lett. 72, 1727 (1998); http://dx.doi.org/10.1063/1.121165 (3 pages) | Cited 22 times

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Strain-compensated InGaAsP/InGaP superlattices are studied in cross section by atomic force microscopy and scanning tunneling microscopy. Undulations in the morphology of the {110} cross-sectional faces are observed, and are attributed to elastic relaxation of this surface due to underlying strain arising from thickness and compositional variations of the superlattice layers. Finite element computations are used to extract a quantitative measure of the strain variation. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.-x Mechanical properties of solids
68.35.Gy Mechanical properties; surface strains

Phase separation in InGaN/GaN multiple quantum wells

M. D. McCluskey, L. T. Romano, B. S. Krusor, D. P. Bour, N. M. Johnson, and S. Brennan

Appl. Phys. Lett. 72, 1730 (1998); http://dx.doi.org/10.1063/1.121166 (3 pages) | Cited 97 times

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Evidence is presented for phase separation in In0.27Ga0.73N/GaN multiple quantum wells. After annealing for 40 h at a temperature of 950 °C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of In-rich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase. A diffraction peak corresponding to an In-rich phase is also present in the annealed material. Nanoscale In-rich InGaN precipitates are observed by transmission electron microscopy and energy dispersive x-ray chemical analysis. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
64.75.-g Phase equilibria
78.66.Fd III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.40.Fy Semiconductors

Acoustically driven bound exciton lifetimes in CdS crystals

O. A. Korotchenkov and T. Goto

Appl. Phys. Lett. 72, 1733 (1998); http://dx.doi.org/10.1063/1.121167 (3 pages) | Cited 1 time

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The exciton lifetime has been found to be repeatedly tuned by a MHz frequency acoustic driving without degradation of the optical properties of CdS crystals. The increase in the lifetime, up to 5%, followed by its ∼20% decrease has been detected with increasing driving amplitude. The lifetime increase can now be understood as due to reduction in the electron-hole wave function overlap in electric fields generated by the driving. The decrease in the recombination lifetime is ascribed to a widening of the potential well trapping the exciton due to variations in the local-crystal environment at acoustic driving. © 1998 American Institute of Physics.
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71.35.Ee Electron-hole drops and electron-hole plasma
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Intense photoluminescence from self-assembling InGaN quantum dots artificially fabricated on AlGaN surfaces

Hideki Hirayama, Satoru Tanaka, Peter Ramvall, and Yoshinobu Aoyagi

Appl. Phys. Lett. 72, 1736 (1998); http://dx.doi.org/10.1063/1.121168 (3 pages) | Cited 57 times

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We demonstrate photoluminescence (PL) from self-assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metalorganic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition to three-dimensional nanoscale island formation by using “antisurfactant” silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be ∼ 10 nm and ∼ 5 nm, respectively, by an atomic-force microscope (AFM). Indium mole fraction of InxGa1−xN QDs is controlled from x = ∼ 0.22 to ∼ 0.52 by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, from the temperature dependence of the PL-peak energy, we convincingly show that the PL emission actually comes from the InGaN QDs. © 1998 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Inhomogeneous strain in individual quantum dots probed by transport measurements

C. D. Akyüz, A. Zaslavsky, L. B. Freund, D. A. Syphers, and T. O. Sedgwick

Appl. Phys. Lett. 72, 1739 (1998); http://dx.doi.org/10.1063/1.121169 (3 pages) | Cited 9 times

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Resonant tunneling measurements are used to probe the inhomogeneous strain in individual SiGe quantum dots. Current–voltage characteristics of strained Si/SiGe resonant tunneling diodes of diameter D ⩽ 0.25 μm exhibit additional fine quasi-periodic structure in the resonant peaks. The fine structure is consistent with lateral quantization in the SiGe quantum well due to in-plane confining potentials arising from inhomogeneous strain, which we calculate by finite element techniques for various D. Quenching of the fine structure by a magnetic field is consistent with the effective length scale of the strain-induced potential. © 1998 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Le Other inorganic semiconductors
73.23.-b Electronic transport in mesoscopic systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Cw Elemental semiconductors
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