Showing papers in "Applied Physics Letters in 1987"
TL;DR: In this article, a double-layer structure of organic thin films was prepared by vapor deposition, and efficient injection of holes and electrons was provided from an indium-tinoxide anode and an alloyed Mg:Ag cathode.
Abstract: A novel electroluminescent device is constructed using organic materials as the emitting elements. The diode has a double‐layer structure of organic thin films, prepared by vapor deposition. Efficient injection of holes and electrons is provided from an indium‐tin‐oxide anode and an alloyed Mg:Ag cathode. Electron‐hole recombination and green electroluminescent emission are confined near the organic interface region. High external quantum efficiency (1% photon/electron), luminous efficiency (1.5 lm/W), and brightness (>1000 cd/m2) are achievable at a driving voltage below 10 V.
13,185 citations
TL;DR: In this paper, the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum was reported.
Abstract: We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.
1,122 citations
TL;DR: In this article, a force microscope is used to measure the magnetic force between a magnetized tip and the scanned surface, which shows promise for the high-resolution mapping of both static and dynamic magnetic fields.
Abstract: We describe a new method for imaging magnetic fields with 1000 A resolution. The technique is based on using a force microscope to measure the magnetic force between a magnetized tip and the scanned surface. The method shows promise for the high‐resolution mapping of both static and dynamic magnetic fields.
1,113 citations
TL;DR: In this paper, conditions for the selective lift-off of large area epitaxial AlxGa1−xAs films from the substrate wafers on which they were grown were discovered.
Abstract: We have discovered conditions for the selective lift‐off of large area epitaxial AlxGa1−xAs films from the substrate wafers on which they were grown. A 500‐A‐thick AlAs release layer is selectivity etched away, leaving behind a high‐quality epilayer and a reusable GaAs substrate. We have measured a selectivity of ≳107 between the release layer and Al0.4Ga0.6As. This process relies upon the creation of a favorable geometry for the outdiffusion of dissolved H2 gas from the etching zone.
895 citations
TL;DR: In this paper, a passivated nonradiative recombination center at the periphery of a GaAs/AlGaAs heterostructure bipolar transistor was proposed to increase the current gain of the device at low collector currents.
Abstract: With a simple chemical treatment we have passivated nonradiative recombination centers at the periphery of a GaAs/AlGaAs heterostructure bipolar transistor, resulting in a 60‐fold increase in the current gain of the device at low collector currents. This large enhancement in gain was achieved by spin coating thin films of Na2S9H2O onto the devices after their fabrication. We briefly discuss the passivation mechanism and the implications for other III‐V optoelectronic devices.
663 citations
TL;DR: In this paper, the influence of interface roughness on the mobility of two-dimensional electrons in modulation-doped AlAs/GaAs quantum wells was studied experimentally and theoretically.
Abstract: We study experimentally and theoretically the influence of interface roughness on the mobility of two‐dimensional electrons in modulation‐doped AlAs/GaAs quantum wells. It is shown that interface roughness scattering is the dominant scattering mechanism in thin quantum wells with a well thickness Lw<60 A, where electron mobilities are proportional to L6w, reaching 2×103 cm2/V s at Lw∼55 A. From detailed comparison between theory and experiment, it is determined that the ‘‘GaAs‐on‐AlAs’’ interface grown by molecular beam epitaxy has a roughness with the height of 3–5 A and a lateral size of 50–70 A.
600 citations
TL;DR: In this article, a 10.8 μm superlattice infrared detector based on doped quantum wells of GaAs/AlGaAs was proposed, which achieved a narrow bandwidth (10%) photosensitivity with a responsivity of 0.52 A/W and an estimated speed of 30 ps.
Abstract: We demonstrate a novel 10.8 μm superlattice infrared detector based on doped quantum wells of GaAs/AlGaAs. Intersubband resonance radiation excites an electron from the ground state into the first excited state, where it rapidly tunnels out producing a photocurrent. We achieve a narrow bandwidth (10%) photosensitivity with a responsivity of 0.52 A/W and an estimated speed of 30 ps.
533 citations
TL;DR: In this paper, the crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y•Ba•Cu•O system using high-resolution neutron powder diffraction was determined.
Abstract: We have determined the crystal structure of the single‐phase stoichiometric high‐temperature superconductor in the Y‐Ba‐Cu‐O system using high‐resolution neutron powder diffraction. This compound has an orthorhombic structure with space group Pmmm and lattice constants a=3.8231 A, b=3.8864 A, and c=11.6807 A. The structure consists of ‘‘dimpled’’ CuO2 layers in the a‐b planes loosely bonded by one‐dimensional fencelike square‐planar CuO3 chains in the b‐c planes.
520 citations
TL;DR: In this paper, a model for the relaxation of an initially coherent metastable strained layer is developed, which is applied to relief of mismatch strain in the SiGe/Si(100) system, and good agreement with experimental data is found.
Abstract: An outstanding puzzle concerning strained‐layer semiconductors is that metastable structures can be grown in which exact coherence with the lattice is apparently conserved in layers much thicker than the equilibrium critical thickness. Using standard descriptions of dislocation dynamics and relaxation via plastic flow, a model for the relaxation of an initially coherent metastable strained layer is developed. This model is applied to relief of mismatch strain in the SiGe/Si(100) system, and good agreement with experimental data is found. Furthermore, the combined effect of relaxation kinetics and finite instrumental resolution on the observed critical thickness was calculated. The results successfully reproduce experimental data on metastable critical thickness in the SiGe/Si(100) system.
492 citations
TL;DR: In this article, a new process was proposed to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates.
Abstract: We report on a new process to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (106 A/cm2 at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, we have been able to pattern them in both the pre‐annealed and post‐annealed states using conventional positive photoresist technology.
411 citations
TL;DR: In this paper, single-crystal CoSi2 layers in silicon have been formed by high dose implantation of cobalt followed by annealing, and electrical transport measurements on the layers give values for the resistance ratios and superconducting critical temperatures that are better than the best films grown by conventional techniques.
Abstract: Buried single‐crystal CoSi2 layers in silicon have been formed by high dose implantation of cobalt followed by annealing. These layers grow in both the (100) and (111) orientations—those in (111) have better crystallinity, but those in (100) are of higher electrical quality. Electrical transport measurements on the layers give values for the resistance ratios and superconducting critical temperatures that are better than the best films grown by conventional techniques and comparable to bulk CoSi2.
TL;DR: In this paper, the first diode-laser (nominal 200mW 10-stripe laser diode) end-pump lasing of Nd:YVO4 was reported.
Abstract: We report on the first diode‐laser (nominal 200‐mW 10‐stripe laser diode) end‐pump lasing of Nd:YVO4. The lowest threshold (30 mW) and highest output power (120 mW) were observed from the Nd:YVO4 laser as compared to a similar Nd:YAG laser. Over 50% optical slope efficiency was obtained, the highest yet reported for diode pumping. This device performed at a 10% overall efficiency. Measurements over a 21‐nm range show the advantages of the Nd:YVO4 pump absorption band.
TL;DR: In this paper, the authors report measurements of the solid solid thermal boundary resistance Rbd, spanning the temperature range from 1 to 300 K, and find that Rbd is in agreement with the prediction of the acoustic mismatch model.
Abstract: We report measurements of the solid‐solid thermal boundary resistance Rbd, spanning the temperature range from 1 to 300 K Below 30 K, Rbd is found to be in agreement with the prediction of the acoustic mismatch model The influence of diffuse scattering at the interface is found to have a very minor influence on Rbd Above 30 K, Rbd decreases less rapidly with increasing temperature than predicted by the theory Phonon scattering in thin (∼30 A) disordered layers near the interface is shown to be a possible explanation Implications for heat removal from integrated circuits are discussed
TL;DR: In this article, the band-gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga 0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures.
Abstract: The band‐gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures. Photoluminescence, Raman scattering spectroscopy, transmission electron microscopy, and impurity diffusion were used to investigate this functional relationship. Two pieces of evidence are shown which demonstrate that MOVPE Ga0.5In0.5P epitaxial layers with ‘‘abnormal’’ Eg∼1.85 eV and ‘‘normal’’ Eg∼1.9 eV correspond to an ordered and a random (Ga,In) distribution on column III sublattices, respectively. In an ordered state, a sequence of (110) planes...GaGaInInGaGaInIn...in the [110] direction is the most probable distribution.
TL;DR: In this article, the superconducting quantum interference devices (dc SQUIDs) were fabricated from thin films of the Superconducting Oxide YBa2Cu3Oy.
Abstract: We have fabricated superconducting quantum interference devices (dc SQUID’s) from thin films of the superconducting oxide YBa2Cu3Oy. The devices were made by first lithographically patterning an ion implant mask containing a 40 by 40 μm loop and two 17‐μm‐wide weak links over a ∼1‐μm‐thick oxide film. Ion implantation was then used to destroy the superconductivity in the film surrounding the device without actually removing material, resulting in a completely planar structure for the SQUID’s. The SQUID’s were operated in the temperature range from 4.2 to 68 K. The superconducting flux quantum was measured to be h/2e in these materials.
TL;DR: The superconductivity of YBa2Cu3O7 samples is greatly degraded by the interaction with water and humid air as discussed by the authors, which is probably due to the presence of nonequilibrium Cu3+ ions in this compound, but it should not preclude practical application of these materials since it should be possible to protect them with coatings of metal, glass, or plastic.
Abstract: We show that the superconducting YBa2Cu3O7 phase is highly sensitive to water and water vapor. This is probably due to the presence of nonequilibrium Cu3+ ions in this compound. In particular, the YBa2Cu3O7 phase decomposes in water to CuO, Ba(OH)2 and Y2BaCuO5 and evolves oxygen. Samples with a reduced oxygen content, e.g., YBa2Cu3O6.0, also decompose in an aqueous ambient. The superconductivity of YBa2Cu3O7 samples is greatly degraded by the interaction with water and humid air. This effect should not preclude practical application of these materials since it should be possible to protect them with coatings of metal, glass, or plastic.
TL;DR: In this paper, a collection mode near-field scanning optical microscopy was used to obtain super-resolution images of aluminum lines separated by 0.25 μm with peak edge sharpness of 0.07 μm.
Abstract: Super‐resolution imaging at optical wavelengths has been achieved with collection mode near‐field scanning optical microscopy. Reproducible images of 0.25‐μm aluminum lines separated by 0.25 μm have been generated with a peak edge sharpness of 0.07 μm. Images taken with differing probe sizes and at various heights demonstrate that the smallest resolvable features are roughly determined by the greater of the aperture size and the aperture to sample separation.
TL;DR: In this paper, a robust covalently bonded sulfide layer was proposed to explain the favorable electronic properties of GaAs/GaAs interfaces, and the surface recombination velocity at the interface between Na2S⋅9H2O and GaAs began to approach that of the nearly ideal AlGaAs/GAAs interface.
Abstract: We have discovered that a class of inorganic sulfides [Li2S, (NH4)2S, Na2S⋅9H2O, etc.] imparts excellent electronic properties to GaAs surfaces. The surface recombination velocity at the interface between Na2S⋅9H2O and GaAs begins to approach that of the nearly ideal AlGaAs/GaAs interface. We propose the formation of a robust covalently bonded sulfide layer to explain the favorable electronic quality of such interfaces.
TL;DR: In this article, the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices was measured, with 95% of the incident infrared energy being absorbed.
Abstract: We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.
TL;DR: InGaAs/InP quantum well layers grown by gas source molecular beam epitaxy have been used to fabricate quantum wires and boxes with transverse dimensions as small as ∼300 A.
Abstract: InGaAs/InP quantum well layers grown by gas source molecular beam epitaxy have been used to fabricate quantum wires and boxes with transverse dimensions as small as ∼300 A. These artificial structures exhibit intense low‐temperature photoluminescence and show exciton shifts of 8–14 meV expected of low dimensional confinement. Low surface recombination velocity characteristic of InP and its alloys should allow luminescence studies of features as small as ∼30 A under moderate excitation intensities.
TL;DR: In this article, the authors used a cross of double wires with an attached diamond stylus as a force sensor, and demonstrated the potential of atomic force microscopy (AFM) for studying both conducting and nonconducting surfaces.
Abstract: Images of graphite surfaces that are covered with oil reveal the hexagonal rings of carbon atoms. Images of a sodium chloride surface, protected from moisture by oil, exhibit a monoatomic step. Together, these images demonstrate the potential of atomic force microscopy (AFM) for studying both conducting and nonconducting surfaces, even surfaces covered with liquids. Our AFM uses a cross of double wires with an attached diamond stylus as a force sensor. The force constant is ≊40 N/m. The resonant frequency is ≊3 kHz. The lateral and vertical resolutions are 0.15 nm and 5 pm.
TL;DR: In this article, the authors observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field and applied these tunable transitions to high-speed infrared light modulators.
Abstract: We have observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field. Two samples consisting of 100 and 120 A GaAs quantum wells separated by 350 A AlGaAs barriers showed optical absorption peaks at 11.1 and 13.9 μm, respectively. In an electric field of 36 kV/cm, the 13.9 μm peak shifted to 13.7 μm and the 11.1 μm shifted to 11.0 μm, in good agreement with theoretical calculations. These tunable transitions can be applied to high‐speed infrared light modulators.
TL;DR: In this paper, a two-component Mossbauer spectrum of a nanocrystalline material is investigated, consisting of a crystalline component and an interfacial component, formed by the atoms located either in the crystals or in the interfacial regions between them.
Abstract: Nanocrystalline materials, which have been proposed to represent a new solid state structure, are investigated by Mossbauer spectroscopy. Nanocrystalline materials are polycrystals with a crystal size of typically 1–10 nm. These materials consist of two components of comparable volume fractions: a crystalline component and an interfacial component, formed by the atoms located either in the crystals or in the interfacial regions between them. As the atomic configurations of both components are different, two kinds of Mossbauer spectra are expected. Iron nanocrystalline material is found to exhibit a two‐component Mossbauer spectrum, consisting of a crystalline component and a second one with different Mossbauer parameters. The Mossbauer parameters of the second subspectrum are consistent with the model of the interfacial component of a nanocrystalline material.
TL;DR: In this paper, two microfabricated structures for the in situ measurement of mechanical properties of thin films, a suspended membrane, and an asymmetric released structure, were reported, and they yielded a residual tensile stress of 30 MPa and a Young's modulus of 3 GPa.
Abstract: Two microfabricated structures for the in situ measurement of mechanical properties of thin films, a suspended membrane, and an asymmetric ‘‘released structure,’’ are reported. For a polyimide film on silicon dioxide, the membrane measurements yield a residual tensile stress of 30 MPa and a Young’s modulus of 3 GPa. The released structures measure the ratio of residual stress to Young’s modulus, and yield 0.011 at strains comparable to the suspended membranes, and 0.015 at larger strains. The ultimate strain as measured by both structures is approximately 4%.
TL;DR: In this article, the thermal properties of AlAs/GaAs superlattices were measured with the ac calorimetric method and it was found that the thermal diffusivity and thermal conductivity of the AlAs and GaAs super-lattice are larger than those of AlGaAs alloy due to the suppression of alloy scattering in the super lattice.
Abstract: Thermal properties of semiconductor superlattices have been investigated for the first time. The thermal properties of AlAs/GaAs superlattices were measured with the ac calorimetric method. It is found that the thermal diffusivity and thermal conductivity of the AlAs/GaAs superlattices are larger than those of the AlGaAs alloy due to the suppression of alloy scattering in the superlattice. However, the thermal diffusivity and thermal conductivity decrease with a decrease in the superlattice period and seem to approach those of the Al0.5Ga0.5As alloy in the limit of short‐period superlattices.
TL;DR: In this paper, the authors report preliminary success in the fabrication of fine-wire, composite superconductors consisting of a high-conductivity normal metal shell such as Ag or Cu/Ni/Au and a superconducting core of Ba2YCu3O7 oxide.
Abstract: Commercially useful, bulk superconductors typically require stabilization using a normal metal cladding for reasons of electrical, thermal, and mechanical protection and, in general, need to be drawn into fine fibers and wound into a magnet configuration. The recent discovery of high‐TC superconductor materials such as Ba2YCu3O7 stimulated worldwide interest in the subject, however, with much concern about fabricability of such brittle ceramic materials into desirable fine wire geometry. In this letter, we report preliminary success in the fabrication of fine‐wire, composite superconductors consisting of a high‐conductivity normal metal shell such as Ag or Cu/Ni/Au and a superconducting core of Ba2YCu3O7 oxide. The wire is would into a coil, and then heat treated to produce the desired chemistry in a dense structure. The resistivity of the composite wire is measured to be zero at ≊90 K (in zero field) with a zero‐field critical density of ≊175 A/cm2. Microscopy and x‐ray analysis show that the superconduc...
TL;DR: In this article, the formation of metal-containing amorphous hydrogenated carbon films (a•C:H) in a reactive sputtering process was reported and the layers were prepared at room temperature using various metals of different concentrations.
Abstract: The formation of metal‐containing amorphous hydrogenated carbon films (a‐C:H) in a reactive sputtering process is reported. The layers were prepared at room temperature using various metals of different concentrations. According to tribological measurements the layers exhibit small friction values and an extremely low abrasive wear rate. The electrical conductivity depends on the metal concentration and could be varied over many orders of magnitude.
TL;DR: In this paper, a diamond thin film has been formed by dc plasma chemical vapor deposition with a high growth rate (∼20 μm/h) without surface scratching by diamond or c-BN powder.
Abstract: Diamond thin films have been formed by dc plasma chemical vapor deposition with a high growth rate (∼20 μm/h). The diamond has been grown from methane (CH4) and hydrogen (H2) mixed gases on Si and α‐Al2O3 substrates at a pressure of 200 Torr without surface scratching by diamond or c‐BN powder. The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the film is the same as that of natural diamond (∼10 000 kg/mm2). The influence of the dc discharge in a low vacuum (∼200 Torr) on diamond synthesis will be discussed briefly.
TL;DR: In this article, a high frequency shift of the main Raman peak is observed with increasing photon energy, interpreted in terms of scattering from π-bonded carbon clusters which is resonantly enhanced for incident photon energies approaching the π−π* resonance.
Abstract: Resonant Raman spectroscopy has been used to study amorphous hydrogenated carbon films. For films containing both sp2 and sp3 bonded carbon a well‐defined high‐frequency shift of the main Raman peak is observed with increasing exciting photon energy. This shift is interpreted in terms of scattering from π‐bonded carbon clusters which is resonantly enhanced for incident photon energies approaching the π–π* resonance.
TL;DR: In this article, the first demonstration of a nonlinear coupler switch capable of substantially complete all-optical switching at sub-picosecond rates with no light-induced thermal effects is presented.
Abstract: We report the first demonstration of a nonlinear coupler switch capable of substantially complete all‐optical switching at subpicosecond rates with no light‐induced thermal effects.