Showing papers in "Applied Physics Letters in 1993"
TL;DR: In this article, the properties of a new family of metallic alloys which exhibit excellent glass forming ability are reported, where the critical cooling rate to retain the glassy phase is of the order of 10 K/s or less.
Abstract: We report on the properties of one example of a new family of metallic alloys which exhibit excellent glass forming ability. The critical cooling rate to retain the glassy phase is of the order of 10 K/s or less. Large samples in the form of rods ranging up to 14 mm in diameter have been prepared by casting in silica containers. The undercooled liquid alloy has been studied over a wide range of temperatures between the glass transition temperature and the thermodynamic melting point of the equilibrium crystalline alloy using scanning calorimetry. Crystallization of the material has been studied. Some characteristic properties of the new material are presented. The origins of exceptional glass forming ability of these new alloys are discussed.
2,305 citations
TL;DR: In this paper, a technique for patterning a self-assembled monolayer (SAM) on a gold substrate using an elastomer stamp was described, followed by selective etching in an aqueous, basic solution of cyanide ion and dissolved dioxygen (1M KOH, 0.1 M KCN).
Abstract: This letter describes a technique that can be used to produce well‐defined features of gold. The technique involves patterning of a self‐assembled monolayer (SAM) on a gold substrate using an elastomer stamp (fabricated either from a phenol‐formaldehyde polymer or polydimethylsiloxane), followed by selective etching in an aqueous, basic solution of cyanide ion and dissolved dioxygen (1M KOH, 0.1 M KCN). Electrically conductive structures of gold with dimensions as small as 1 μm have been produced using this procedure. Once a rubber stamp is fabricated, patterning and etching of gold substrates is straightforward. This method is convenient, does not require routine access to clean rooms and photolithographic equipment, and can be used to produce multiple copies of a pattern.
1,756 citations
TL;DR: In this paper, the 2D-3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum-sized dot structures.
Abstract: The 2D–3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum‐sized dot structures. Transmission electron micrographs reveal that when the growth of In0.5Ga0.5As is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of the InGaAs result. Size distributions indicate that these dots are ∼300 A in diameter and remarkably uniform to within 10% of this average size. The areal dot densities can be varied between 109 and 1011 cm−2. The uniformity of the dot sizes is explained by a mechanism based on reduction in adatom attachment probabilities due to strain. We unambiguously demonstrate photoluminescence at ∼1.2 eV from these islands by comparing samples with and without dots. The luminescent intensities of the dots are greater than or equal to those of the underlying reference quantum wells.
1,482 citations
TL;DR: In this article, the fabrication and characteristics of high efficiency thin-film CdS/CdTe heterojunction solar cells are described, and a high efficiency solar cell with an AM1.5 efficiency of 15.8% is reported.
Abstract: This letter describes the fabrication and characteristics of high‐efficiency thin‐film CdS/CdTe heterojunction solar cells. CdS films have been prepared by chemical bath deposition and p‐CdTe films have been deposited by close‐spaced sublimation. A CdS/CdTe solar cell of greater than 1 cm2 area with an AM1.5 efficiency of 15.8% is reported.
1,058 citations
TL;DR: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure as mentioned in this paper.
Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.
995 citations
TL;DR: In this article, the authors showed that by separating thin-film LEDs from their substrates (by epitaxial lift-off, for example), it is much easier for light to escape from the LED structure and thereby avoid absorption.
Abstract: There is a significant gap between the internal efficiency of light‐emitting diodes (LEDs) and their external efficiency. The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. We have found that by separating thin‐film LEDs from their substrates (by epitaxial lift‐off, for example), it is much easier for light to escape from the LED structure and thereby avoid absorption. Moreover, by nanotexturing the thin‐film surface using ‘‘natural lithography,’’ the light ray dynamics becomes chaotic, and the optical phase‐space distribution becomes ‘‘ergodic,’’ allowing even more of the light to find the escape cone. We have demonstrated 30% external efficiency in GaAs LEDs employing these principles.
993 citations
TL;DR: In this paper, a photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass.
Abstract: A photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass. A KrF excimer laser beam (249 nm) at normal incidence is modulated spatially by the phase mask grating. The diffracted light, which forms a periodic, high‐contrast intensity pattern with half the phase mask grating pitch, photoimprints a refractive index modulation into the core of photosensitive fiber placed behind, in proximity, and parallel, to the mask; the phase mask grating striations are oriented normal to the fiber axis. This method of fabricating in‐fiber Bragg gratings is flexible, simple to use, results in reduced mechanical sensitivity of the grating writing apparatus and is functional even with low spatial and temporal coherence laser sources.
953 citations
TL;DR: In this article, a novel method of fabricating a periodic domain structure with ideal laminar domains in LiNbO3 by applying an external field at room temperature is proposed.
Abstract: A novel method of fabricating a periodic domain structure with ideal laminar domains in LiNbO3 by applying an external field at room temperature is proposed. The method allows a high blue beam power of 20.7 mW and a high conversion efficiency of 600%/W cm2 to be obtained.
944 citations
TL;DR: The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene-vinylene), and buckminsterfullerene, C60, is reported in this paper.
Abstract: The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene‐vinylene), and buckminsterfullerene, C60, are reported. Rectification ratios in the current versus voltage characteristics exceed 104. When illuminated, the devices exhibit a large photoresponse as a result of photoinduced electron transfer across the heterojunction interface from the semiconducting polymer (donor) onto C60 (acceptor). The photodiode and photovoltaic responses are characterized. Photoinduced electron transfer across the donor‐accepted rectifying heterojunction offers potential for photodetector and for solar cell applications.
899 citations
TL;DR: In this article, the authors report the fabrication and dc characterization of a high electron mobility transistor (HEMT) based on a n−GaN−Al0.86N heterojunction.
Abstract: In this letter we report the fabrication and dc characterization of a high electron mobility transistor (HEMT) based on a n‐GaN‐Al0.14Ga0.86N heterojunction. The conduction in our low pressure metalorganic chemical vapor deposited heterostructure is dominated by two‐dimensional electron gas at the heterostructure interface. HEMT devices were fabricated on ion‐implant isolated mesas using Ti/Au for the source drain ohmic and TiW for the gate Schottky. For a device with a 4 μm gate length (10 μm channel opening, i.e., source‐drain separation), a transconductance of 28 mS/mm at 300 K and 46 mS/mm at 77 K was obtained at +0.5 V gate bias. Complete pinchoff was observed for a −6 V gate bias.
799 citations
TL;DR: In this paper, thermal treatment of a fluoroaluminosilicate glass codoped with Er3+•Yb3+ at a suitable temperature, microcrystallites were successfully precipitated in the glass matrix but little change was observed in the optical transmission spectra even around the ultraviolet edge, meanwhile the green upconversion luminescence due to the 4 S 3/2−4 I 15/2transition of Er3+, increased by a factor of ∼100 when a 097 μm laser diode(LD) (5 mW) was used for
Abstract: Through thermal treatment of a fluoroaluminosilicate glass codoped with Er3+‐Yb3+ at a suitable temperature, microcrystallites were successfully precipitated in the glass matrix but little change was observed in the optical transmission spectra even around the ultraviolet edge, meanwhile the green upconversion luminescence due to the 4 S 3/2‐4 I 15/2transition of Er3+ increased by a factor of ∼100 when a 097 μm laser diode(LD) (5 mW) was used for excitation The infrared to green or to red upconversion efficiencies for the vitroceramics are evaluated to be nearly 2 or 10 times as high as fluoride glasses, respectively Also higher mechanical and chemical stabilities and laser damage threshold over fluoride glasses or crystals are expected for the vitroceramics
TL;DR: In this article, a new detection scheme for atomic force microscopy (AFM) was proposed to yield atomic resolution images of conducting and nonconducting layered materials using a piezoresistive strain sensor embedded in the AFM cantilever.
Abstract: A new detection scheme for atomic force microscopy (AFM) is shown to yield atomic resolution images of conducting and nonconducting layered materials. This detection scheme uses a piezoresistive strain sensor embedded in the AFM cantilever. The cantilever is batch fabricated using standard silicon micromachining techniques. The deflection of the cantilever is measured directly from the resistance of the piezoresistive strain sensor without the need for external deflection sensing elements. Using this cantilever we achieved 0.1 Arms vertical resolution in a 10 Hz–1 kHz bandwidth.
TL;DR: In this article, a method to grow carbon microtubules with fullerene structure (buckytubes) has been identified, which consists of the catalytic decomposition of acetylene over iron particles at 700 °C.
Abstract: A method to grow carbon microtubules with fullerene structure (buckytubes) has been identified. The method consists of the catalytic decomposition of acetylene over iron particles at 700 °C. Carbon microtubules of up to 50 μm in length are synthesized by this method. Electron diffraction and high resolution electron microscopy studies demonstrate that the structure of these microtubules corresponds to the helical structure recently reported by S. Iijima, Nature 354, 56(1991), prepared using an arc‐discharge evaporation method.
TL;DR: In this article, the output power was 90 μW and external quantum efficiency was as high as 0.15% at a forward current of 20 mA at room temperature with changes in the growth temperatures of an InGaN active layer between 820 and 800 °C.
Abstract: InGaN/GaN double‐heterostructure light‐emitting diodes were fabricated. The output power was 90 μW and the external quantum efficiency was as high as 0.15% at a forward current of 20 mA at room temperature. The peak wavelengths of the electroluminescence(EL) varied between 411 and 420 nm with changes in the growth temperatures of an InGaN active layer between 820 and 800 °C. The full widths at half maximum of EL were between 22 and 25 nm.
TL;DR: In this paper, the phase transformation mechanisms and the resulting microstructures of excimer laser-induced crystallization of amorphous Si films on SiO2 were investigated, and it was shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density.
Abstract: We have investigated the phase transformation mechanisms and the resulting microstructures of excimer laser‐induced crystallization of amorphous Si films on SiO2. It is shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density. It is found that at the transition between the two regimes, exceedingly large grain‐sized polycrystalline films can be obtained. We call this the super lateral growth phenomenon, and propose a model based on liquid‐phase regrowth from the residual solid seeds when near‐complete melting of the Si film occurs.
TL;DR: In this article, a nonlinear optical crystal Cesium triborate (CsB3O5, CBO) was discovered based on the anionic group theory, and the transparent range of CBO covers from 170 to 3000 nm.
Abstract: On the basis of the anionic group theory, a new nonlinear optical crystal cesium triborate, (CsB3O5, CBO) was discovered. Single crystals of CBO in centimeter size were grown from a stoichiometric melt. The transparent range of CBO covers from 170 to 3000 nm. The preliminary measurement of its second harmonic generation coefficient shows that its d14 is ∼0.468×d11 (β−BaB2O4). Its measured damage threshold is as high as 26 GW/cm2 at 1.053 μm, 1.0 ns.
TL;DR: In this paper, two-dimensional quantum well superlattices were used to separate the two bands and transform the material to an effective one-carrier system, and the effect of such an approach was investigated theoretically.
Abstract: Currently, the materials with the highest thermoelectric figure of merit (ZT) are one‐band materials. The presence of both electrons and holes lowers ZT, so two‐band materials such as semimetals are not useful thermoelectric materials. However, by preparing these materials in the form of two‐dimensional quantum‐well superlattices, it is possible to separate the two bands and transform the material to an effective one‐carrier system. We have investigated theoretically the effect of such an approach and our results indicate that a significant increase in ZT may be achieved. This result allows the possibility of using a new class of materials as thermoelectric refrigeration elements.
IBM1
TL;DR: In this article, the threshold voltage instabilities in nitride/oxide dual gate dielectric amorphous silicon (a•Si:H) thin-film transistors are investigated as a function of stress time, stress temperature, and stress bias.
Abstract: The threshold voltage instabilities in nitride/oxide dual gate dielectric hydrogenated amorphous silicon (a‐Si:H) thin‐film transistors are investigated as a function of stress time, stress temperature, and stress bias. The obtained results are explained with a multiple trapping model rather than weak bond breaking model. In our model, the injected carriers from the a‐Si:H channel first thermalize in a broad distribution of localized band‐tail states located at the a‐Si:H/aSiNx:H interface and in the a‐SiNx:H transitional layer close to the interface, then move to deeper energies in amorphous silicon nitride at longer stress times, larger stress electric fields, or higher stress temperatures. The obtained bias‐stress‐temperature induced threshold voltage shifts are accurately modeled with a stretched‐exponential stress time dependence where the stretched‐exponent β cannot be related to the β=TST/T0 but rather to β≂TST/T0*−β0 for TST≤80 °C; for TST≥80 °C, the β is stress temperature independent. We have al...
TL;DR: In this paper, the authors described the highest efficiency single junction thin-film cell reported to date with an active area efficiency of 14.8% with the cell structure n−ZnO/n−CdS/p−CuInSe2 deposited on a soda-lime glass substrate.
Abstract: An important milestone in the development of photovoltaic thin‐film solar cells is the achievement of 15% conversion efficiency. This letter describes the highest efficiency single junction thin‐film cell reported to date. An active area efficiency of 14.8% is obtained with the cell structure n‐ZnO/n‐CdS/p‐CuInSe2 deposited on a soda‐lime glass substrate. The current achievements are due to improved properties of the CuInSe2 layer and the heterojunctions compared to previously reported results. The rate and substrate temperature profiles used during the coevaporation process yield a relatively large‐grained material with very strong 〈112〉 orientation and low porosity. This results in reduced recombination rates, hence higher open circuit voltage and fill factor.
TL;DR: In this article, the authors measured internal and external quantum efficiencies of 99.7% and 72%, respectively, for photon number squeezed light, diode lasers, singlemode light-emitting-diodes, optical interconnects, and solar cells.
Abstract: Optically thin AlGaAs/GaAs/AlGaAs double heterostructures, (5000 A), are floated off their substrates by the epitaxial liftoff technique and mounted on various high reflectivity surfaces. From the absolute photoluminescence intensity, we measure internal and external quantum efficiencies of 99.7% and 72%, respectively. High spontaneous emission quantum efficiency, is important for photon number squeezed light, diode lasers, single‐mode light‐emitting‐diodes, optical interconnects, and solar cells.
TL;DR: In this article, an Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3 /SrRuOO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and 100) Si with an yttria stabilized zirconia buffer layer.
Abstract: Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.
TL;DR: In this article, a simple model quantum dot cell containing two electrons is analyzed as a candidate for quantum cellular automata implementations and the cell has eigenstates whose charge density is strongly aligned along one of two directions.
Abstract: A simple model quantum dot cell containing two electrons is analyzed as a candidate for quantum cellular automata implementations. The cell has eigenstates whose charge density is strongly aligned along one of two directions. In the presence of the electrostatic perturbation due to a neighboring cell, the ground state is nearly completely aligned (polarized) in one direction only. The polarization is a highly nonlinear function of the perturbing electrostatic fields and shows the strong bistable saturation important for cellular automation function.
TL;DR: In this article, the fabrication and characterization of a metal semiconductor field effect transistor (MESFET) based on single crystal GaN was reported and the GaN layer was deposited over sapphire substrate using low pressure metalorganic chemical vapor deposition.
Abstract: In this letter we report the fabrication and characterization of a metal semiconductor field effect transistor (MESFET) based on single crystal GaN. The GaN layer was deposited over sapphire substrate using low pressure metalorganic chemical vapor deposition. MESFET devices were fabricated on isolated mesas using TiAu for the source and drain ohmic contacts and silver for the gate Schottky. For devices with a gate length of 4 μm (channel opening, i.e., source to drain separation of 10 μm), a transconductance of 23 mS/mm was obtained at −1 V gate bias. Complete pinch‐off was observed for a gate potential of −12 V.
TL;DR: In this paper, perovskite template layers are grown between the YSZ buffer layer and the bottom LaSr•Co•O electrode for obtaining the required orientation of the subsequent layers.
Abstract: Ferroelectric Pb0.9La0.1Zr0.2Ti0.8O3 thin film capacitors with a symmetrical La‐Sr‐Co‐O top and bottom electrodes have been grown on [001] Si with yttria stabilized zirconia (YSZ) buffer layer. A layered perovskite ‘‘template’’ layer (200–300 A thick), grown between the YSZ buffer layer and the bottom La‐Sr‐Co‐O electrode, is critical for obtaining the required orientation of the subsequent layers. When compared to the capacitors grown with the Y‐Ba‐Cu‐O top and bottom electrodes, these structures possess two advantages: (i) the growth temperatures are lower by 60–150 °C; (ii) the capacitors show a larger remnant polarization ΔP (ΔP=switched polarization–nonswitched polarization), 25–30 μC/cm2, for an applied voltage of only 2 V (applied field of 70 kV/cm). The fatigue, retention, and aging characteristics of these new structures are excellent.
TL;DR: In this paper, the authors report measurements on the nature of aluminum and gold contacts to GaN and find a direct correlation between barrier height and work function of the metal, consistent with the strong ionic character of GaN.
Abstract: We report measurements on the nature of aluminum and gold contacts to GaN. The GaN films were deposited onto the R‐plane of sapphire substrates by molecular beam epitaxy and are autodoped n‐type. Metal contacts were deposited by evaporation and were patterned photolithographically. Current‐voltage characterization shows that the as‐deposited aluminum contacts are ohmic while the as‐deposited gold contacts are rectifying. The gold contacts become ohmic after annealing at 575 °C, a result attributed to gold diffusion. The specific contact resistivity of the ohmic aluminum and gold contacts were found by transfer length measurements to be of device quality (10−7–10−8 Ω m2). The results of these studies suggest a direct correlation between barrier height and work function of the metal, consistent with the strong ionic character of GaN.
TL;DR: In this article, it was shown that atomic hydrogen can simultaneously passivate and depassivate silicon dangling bonds at the Si(111)/SiO2 interface at room temperature via the reactions Pb+H0→PbH and PbH+H 0→Pbin+H2.
Abstract: Atomic hydrogen is found to simultaneously passivate and depassivate silicon dangling bonds at the Si(111)/SiO2 interface at room temperature via the reactions Pb+H0→PbH and PbH+H0→Pb+H2. The passivation reaction occurs more efficiently keeping the steady‐state Pb density at a low value of only 3–6×1011 cm−2 during atomic hydrogen exposure. This low Pb density can only account for a small fraction of the total number of interface states produced by atomic hydrogen.
TL;DR: In this paper, an electroluminescent device was fabricated using poly(Nvinylcarbazole) (PVK) as a hole-transporting emitter layer and a double layer of 1,2,4-triazole derivative (TAZ) and tris(8quinolinolato)aluminum(III) complex (Alq) as an electron transport layer.
Abstract: Electroluminescent devices were fabricated using poly(N‐vinylcarbazole) (PVK) as a hole‐transporting emitter layer and a double layer of 1,2,4‐triazole derivative (TAZ) and tris(8‐quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. A cell structure of glass substrate/indium‐tin‐oxide/PVK/TAZ/Alq/Mg:Ag was employed. In this cell structure, carrier injection from the electrodes to the PVK layer and concomitant electroluminescence from PVK were observed. Blue emission peaking at 410 nm and a luminance of 700 cd/m2 were achieved at a drive voltage of 14 V.
TL;DR: In this article, the authors provide a quantitative picture of the role of grading, by calculating the equilibrium distribution of dislocations and residual strain in such compositionally graded films, showing that in layers with graded strain, threads are subject to greater force and weaker pinning than in uniform layers, helping them to be swept to the edge of the sample.
Abstract: The performance of strained‐layer heterostructures is often limited by threading dislocations. Such defects can be reduced, and in some cases nearly eliminated, by growing a graded buffer layer. Here, we provide a quantitative picture of the role of grading, by calculating the equilibrium distribution of dislocations and residual strain in such compositionally graded films. In layers with graded strain, threading dislocations are subject to greater force and weaker pinning than in uniform layers, helping them to be swept to the edge of the sample.
TL;DR: In this article, a superconducting transition-edge microbridge biased at the center of its transition near 4.2 K was proposed for a mixer element for THz frequencies.
Abstract: We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition‐edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and a rf signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (<0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (if) response. The mixer offers ≊4 GHz if bandwidth, ≊80 Ω rf resistive impedance, good match to the if amplifier, and requires only 1–20 nW of local oscillator power. The upper rf frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double‐sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.
TL;DR: In this article, ordered diamond films have been deposited on single-crystal silicon substrates via an in situ carburization followed by biasenhanced nucleation, which is speculated to form an epitaxial SiC conversion layer.
Abstract: Ordered diamond films have been deposited on single‐crystal silicon substrates via an in situ carburization followed by bias‐enhanced nucleation. Textured diamond films with greater than 50% of the grains oriented D(100)//Si(100) and D〈110〉//Si〈110〉 were grown in both a horizontal and vertical microwave plasma chemical vapor deposition reactor. Separate diamond films from each of the two reactors were analyzed both by scanning electron microscopy and Raman spectroscopy. The in situ carburization is speculated to form an epitaxial SiC conversion layer, thus providing an economical alternative to obtaining epitaxial diamond films on single‐crystal SiC.