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19 Dec 1994

Volume 65, Issue 25, pp. 3167-3289

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Mediation of strain from In0.36Ga0.64As layers through GaAs barriers in multiple quantum well structures

M. J. Ekenstedt, W. Q. Chen, T. G. Andersson, and J. Thordson

Appl. Phys. Lett. 65, 3242 (1994); http://dx.doi.org/10.1063/1.112425 (3 pages) | Cited 6 times

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The strain mediation in multiple quantum well structures consisting of In0.36Ga0.64As layers separated by GaAs barriers has been investigated by photoluminescence. Strain in layers grown by molecular beam epitaxy was evaluated by comparing the photoluminescence‐peak energies with calculated recombination energies in strained quantum wells using the effective‐mass Schrödinger equation. In structures consisting of two 40 Å thick In0.36Ga0.64As layers separated by a GaAs barrier, onset of relaxation is not observed until the barrier thickness is reduced below 100 Å. The corresponding value is 180 Å in a structure with two 50 Å thick In0.36Ga0.64As layers. Results also show that strain mediation increases with the number of strained In0.36Ga0.64As layers. In multiple quantum well structures with four 50 Å thick In0.36Ga0.64As layers, the barrier thickness required to stop strain mediation increases to 225 Å. In similar structures with eight and twenty 50 Å thick In0.36Ga0.64As layers this value is 275 Å. © 1994 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains
78.55.Cr III-V semiconductors

Novel low‐resistance ohmic contact to n‐type GaAs using Cu3Ge

M. O. Aboelfotoh, C. L. Lin, and J. M. Woodall

Appl. Phys. Lett. 65, 3245 (1994); http://dx.doi.org/10.1063/1.112426 (3 pages) | Cited 21 times

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We show that ϵ1‐Cu3Ge forms a low‐resistance ohmic contact to n‐type GaAs. The ϵ1‐Cu3Ge contact exhibits a planar and abrupt interface and contact resistivity of 6.5×10−7 Ω cm2 which is considerably lower than that reported for Ge/Pd and AuGeNi contacts on n‐type GaAs with similar doping concentrations (∼1×1017 cm−3). The contact is electrically stable during annealing at temperatures up to 450 °C. We also show that in the Ge/Cu/n‐type GaAs system, the contact remains ohmic over a wide range of Ge concentration that extends from 15 to 40 at. %. n‐channel GaAs metal–semiconductor field‐effect transistors using the ϵ1‐Cu3Ge ohmic contacts demonstrate a higher transconductance compared to devices with Ge/Pd and AuGeNi contacts. © 1994 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

InAlGaAs impact ionization rates in bulk, superlattice, and sawtooth band structures

Masayoshi Tsuji, Kikuo Makita, Isao Watanabe, and Kenko Taguchi

Appl. Phys. Lett. 65, 3248 (1994); http://dx.doi.org/10.1063/1.112427 (3 pages) | Cited 9 times

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Electron and hole impact ionization rates in bulk, superlattice, and sawtooth band structures consisting of an InAlGaAs system are determined from their photomultiplication characteristics. The impact ionization rate ratios are derived as 2.2, 3.0, and 3.6 for the bulk, superlattice and sawtooth structures, respectively, at an electric field of 470 kV/cm. The hole impact ionization rate in the InAlGaAs sawtooth structure is nearly equal to that of the InAlAs/InAlGaAs rectangular‐well superlattice. In contrast, the electron impact ionization rate in the sawtooth structure is larger than that in the superlattice. This difference is attributed to a lack of energy loss for electrons at the staircase band condition in the sawtooth structure. © 1994 American Institute of Physics.
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73.50.Fq High-field and nonlinear effects
73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)

Effect of main chain length in the exciton spectra of helical‐rod polysilanes as a model of a 5 Å wide quantum wire

Michiya Fujiki

Appl. Phys. Lett. 65, 3251 (1994); http://dx.doi.org/10.1063/1.112428 (3 pages) | Cited 15 times

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Helical polysilane rods were regarded as a soluble, polymeric model of a quantum wire with a ∼5 Å width. Spectral characteristics of the lowest exciton band of the helix located at ∼4 eV in isooctane at 20 °C were first measured as a function of a wire length varying from ∼35 Å to ∼3000 Å. Both the extinction coefficient and the circular dichroism coefficient were found to tend to increase linearly as the logarithm of the wire length increases, whereas the exciton energy and the spectral band width approached limiting values. © 1994 American Institute of Physics.
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71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
78.66.Qn Polymers; organic compounds

Electrical conductivity percolation in the (CdTe)1−xTex system

R. Ramírez‐Bon, F. J. Espinoza‐Beltrán, M. Pedroza‐Montero, F. Ruíz, J. González‐Hernández, O. Zelaya‐Angel, and F. Sánchez‐Sinencio

Appl. Phys. Lett. 65, 3254 (1994); http://dx.doi.org/10.1063/1.112429 (3 pages) | Cited 4 times

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The critical volume fraction for conductivity percolation in the di‐phasic system (CdTe)1−x Tex has been determined using atomic force microscopy. The onset for rapid increase in the electrical conductivity is found at a volume fraction of Te of about 0.4. According to previous theoretical calculations this value is characteristic of a system with two‐dimensional symmetry. It is also found that the Te phase grows in the form of columns, which explains the observed critical volume fraction value for percolation in the conductivity measurements. © 1994 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions

Panchromatic cathodoluminescence investigation of defects in CdTe bulk crystals and homoepitaxial layers

G. Salviati, P. Franzosi, M. Scaffardi, and S. Bernardi

Appl. Phys. Lett. 65, 3257 (1994); http://dx.doi.org/10.1063/1.113026 (3 pages) | Cited 2 times

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Scanning electron microscopy panchromatic cathodoluminescence has been used to investigate extended crystal defects in (111) CdTe bulk crystals and homoepitaxial layers grown by liquid phase epitaxy. Good defect images have been obtained by a very simple experimental setup using a Si photodiode at room temperature. The bulk crystals have been found to be affected by dislocations arranged in cellular structures, lineages roughly parallel to the [110] directions, [110] slip bands, and precipitates. The homoepitaxial layers exhibited dislocations, precipitates, and inclusions of growth solution. The wavy morphology typical of the layers grown by liquid phase epitaxy did not give rise to cathodoluminescence contrast. © 1994 American Institute of Physics.  
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence

Paramagnetic centers at and near the Si/SiOx interface in porous silicon

B. Pivac, B. Rakvin, and L. Pavesi

Appl. Phys. Lett. 65, 3260 (1994); http://dx.doi.org/10.1063/1.112430 (3 pages) | Cited 5 times

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Formation of paramagnetic centers in aged porous silicon samples is studied by electron paramagnetic resonance. Samples oxidized by aging in air at room temperature exhibit the Pb centers as dominant defects. These are formed at the interfaces between the Si nanocrystallites and the amorphous SiOx layer into which the nanocrystallites are embedded and which is formed during the aging. No other paramagnetic centers, such as the E′ center that is characteristic of thin SiO2 layers on Si, are observed. This finding is explained by the hydrogen passivation of E′ centers in oxygen‐rich porous structures and by the instability of the E′ center near the interface. The Pb center is stable after γ irradiation. © 1994 American Institute of Physics.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.80.Ed γ-ray effects
78.55.Hx Other solid inorganic materials

Temperature dependence of photoluminescence linewidth in modulation‐doped pseudomorphic high electron mobility transistor AlxGa1−xAs/InyGa1−yAs/GaAs structures

P. W. Yu, B. Jogai, T. J. Rogers, P. A. Martin, and J. M. Ballingall

Appl. Phys. Lett. 65, 3263 (1994); http://dx.doi.org/10.1063/1.112431 (3 pages) | Cited 19 times

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We report the temperature dependent characteristics of photoluminescence linewidth in terms of two‐dimensional electron gas sheet concentration for modulation δ‐doped AlxGa1−xAs/InyGa1−yAs/GaAs structures. The electron concentration is obtained using a self‐consistent solution of the coupled k⋅P Hamiltonian–Poisson equation. We find that only the full width at half maximum of the n=2 electron‐subband‐to‐n=1 hole subband transition is useful for characterizing high electron density at T=2–300 K. The importance of hole localization for correlating the electron density with photoluminescence linewidth is discussed. © 1994 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Separately contacted electron‐hole double layer in a GaAs/AlxGa1−xAs heterostructure

B. E. Kane, J. P. Eisenstein, W. Wegscheider, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 65, 3266 (1994); http://dx.doi.org/10.1063/1.112432 (3 pages) | Cited 29 times

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We describe a method for creating closely spaced parallel two‐dimensional electron and hole gases confined in 200 Å GaAs wells separated by a 200 Å wide AlxGa1−xAs barrier. Low‐temperature ohmic contacts are made to both the electrons and holes, whose densities are individually adjustable between 1010/cm2 to greater than 1011/cm2. © 1994 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Annealing induced refractive index and absorption changes of low‐temperature grown GaAs

S. U. Dankowski, P. Kiesel, B. Knüpfer, M. Kneissl, G. H. Döhler, U. D. Keil, D. R. Dykaar, and R. F. Kopf

Appl. Phys. Lett. 65, 3269 (1994); http://dx.doi.org/10.1063/1.112433 (3 pages) | Cited 7 times

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Large changes of the refractive index (Δn≊0.25) and absorption coefficient (Δα≊16 000 cm −1) of GaAs grown by molecular beam epitaxy (MBE) at low substrate temperature (LT‐GaAs) induced by annealing are reported. The refractive index difference between the LT‐GaAs layer and the GaAs substrate are determined from both, the amplitude of the Fabry–Pérot oscillations and the shift of their extrema towards shorter wavelengths yielding nearly the same results. With increasing anneal temperature the excess refractive index as well as the strong absorption at photon energies below the GaAs band gap (determined by transmission measurements) disappear around 700  °C. © 1994 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)

Electrical characterization of arsenic‐ion‐implanted semi‐insulating GaAs by current‐voltage measurement

Gong‐Ru Lin, Wen‐Chung Chen, C.‐S. Chang, and Ci‐Ling Pan

Appl. Phys. Lett. 65, 3272 (1994); http://dx.doi.org/10.1063/1.112434 (3 pages) | Cited 14 times

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The characteristics of an amorphous GaAs film by implanting dense arsenic ions into semi‐insulating GaAs substrate have been studied. The specific contact resistance of the sample at room temperature is found to be 1.1×10−1 Ω cm2. This indicates that the conduction‐band electron concentration is less than 1013 cm−3. The activation energy at temperature above 360 K and the density of states are, respectively, 0.6 eV and 1027 m−3 eV−1 as estimated from the slope of Arrhenius plot. Fitting of the Arrhenius plot also suggests that the carrier transport at metal/semiconductor junction of this material below 360 K is dominated by the variable‐range hopping conduction mechanism which depends on deep level defects. © 1994 American Institute of Physics.
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72.80.Ng Disordered solids
73.40.Cg Contact resistance, contact potential
73.25.+i Surface conductivity and carrier phenomena

Dynamic Wannier–Stark effect in semiconductor superlattices

J. B. Khurgin, S. J. Lee, and N. M. Lawandy

Appl. Phys. Lett. 65, 3275 (1994); http://dx.doi.org/10.1063/1.112435 (3 pages) | Cited 2 times

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A novel effect, consisting of optically induced effective mass change due to the change in the degree of localization in the semiconductor superlattices is theoretically investigated. Possible application as a nonabsorbing differential light detector/switch is considered. © 1994 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.-w Optical properties of specific thin films

Focused ion beam direct deposition of superconductive thin film

Shinji Nagamachi, Yasuhiro Yamakage, Masahiro Ueda, Hiromasa Maruno, Kei Shinada, Yoichi Fujiyama, Masatoshi Asari, and Junzo Ishikawa

Appl. Phys. Lett. 65, 3278 (1994); http://dx.doi.org/10.1063/1.112436 (3 pages) | Cited 9 times

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Focused ion beam direct deposition of niobium has been developed as a technique for fabricating superconductive thin films. A Nb2+ ion beam extracted from a Nb10–Au50–Cu40 liquid metal ion source was accelerated to 40 keV, focused, deflected and finally decelerated to 50–1000 eV. The beam current density was 0.4–2 mA/cm2 and the minimum deposited linewidth was about 0.5 μm. The sticking probability of the Nb2+ ion beam and the critical temperature of deposited niobium films were measured. The deposition at different deposition rates and different residual gas pressure were performed. A clear relation was obtained between the critical temperature and the concentration of contaminations. This relation is consistent with the published relation for bulk niobium if it is assumed that the sticking probability of residual gas is 0.2. However, dependence of the critical temperature on ion energy was not observed. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Double resonant behavior of microstrip ring resonator in Tl‐based high Tc superconducting films

S. C. Wu, C. Y. Yeh, F. H. Chen, T. Y. Tseng, C. Wang, H. L. Chang, and H. J. Wang

Appl. Phys. Lett. 65, 3281 (1994); http://dx.doi.org/10.1063/1.112437 (3 pages) | Cited 3 times

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High Tc Tl–Ba–Ca–Cu–O superconducting thin films have been made by the dc magnetron sputtering followed by postannealing. In this study, a Tl‐based microstrip ring resonator was fabricated by using standard microelectronic photolithographic patterning and wet chemical etching. Experimental results indicated that these ring resonators exhibit the best unloaded Q of 3269 at its resonant frequency of 3.35 GHz and some other samples display the double resonant behavior at 77 K. The frequency difference of the double resonant peaks depends on the input microwave power, and the splitting is ascribed to spatial variations in the film microstructure. The physical properties of the films are about 1 μm thick, as high as 105 K transition temperature, and greater than 105 A/cm2 current density at zero magnetic field and 77 K. © 1994 American Institute of Physics.
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85.25.-j Superconducting devices
74.78.-w Superconducting films and low-dimensional structures
84.30.Le Amplifiers

Anisotropy and irreversibility line of iodine intercalated Bi2Sr2CaCu2O8+δ single crystals

J. Ricketts, R. Puzniak, C.‐J. Liu, G. D. Gu, N. Koshizuka, and H. Yamauchi

Appl. Phys. Lett. 65, 3284 (1994); http://dx.doi.org/10.1063/1.112438 (3 pages) | Cited 9 times

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A comparative study of the superconducting properties of pristine and stage 1 iodine intercalated Bi2Sr2CaCu2O8+δ single crystals is presented. We find the anisotropy of the penetration depth to be significantly reduced after intercalation. Specifically, the penetration depth perpendicular to the CuO2 planes is dramatically decreased, by about 60%. Reducing the anisotropy improves the position of the irreversibility line in the low field region where pinning is weak. However, in high fields the position of the irreversibility line is depressed. This can be explained by the influence of strong flux pinning. © 1994 American Institute of Physics.
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74.25.-q Properties of superconductors
74.72.-h Cuprate superconductors

Incommensuration in La‐modified antiferroelectric lead zirconate titanate ceramics

Z. Xu, Xunhu Dai, and Dwight Viehland

Appl. Phys. Lett. 65, 3287 (1994); http://dx.doi.org/10.1063/1.112441 (3 pages) | Cited 18 times

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Lanthanum‐modified lead zirconate titanate (PLZT) specimens with a La content of 2 at. % and a Zr/Ti ratio of 95/5 (PLZT 2/95/5) have been investigated by dielectric spectroscopy, Sawyer–Tower polarization (P‐E) measurements, and hot‐stage transmission electron microscopy (TEM). La ‘‘impurities’’ have been found to induce a 1/x〈110〉 incommensurate antiferroelectric structure at about 210 °C from a ferroelectric structure when cooled from above. The incommensurate structure was found to be stable below this temperature of the dielectric maximum, evolving slowly with decreasing temperature towards the commensurate antiferroelectric orthorhombic PZ structure. The incommensuration is believed to arise due to a competition between ‘‘broken’’ dipolar (ferroelectric) and sublattice (antiferroelectric) interactions. The ‘‘dirty’’ antiferroelectric Pb‐based system may be the first example of a proper incommensurately displacively modulated ferroelectric‐type material. © 1994 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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