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Showing papers in "Applied Physics Letters in 1985"


Journal ArticleDOI
TL;DR: In this article, the critical layer thickness for growth of GexSi1−x strained layers on Si substrates is calculated for 0≤x≤1.0.
Abstract: A calculation of the critical layer thickness hc for growth of GexSi1−x strained layers on Si substrates is presented for 0≤x≤1.0. The present results are obtained assuming misfit dislocation generation is determined solely by energy balance. This approach differs therefore from previous theories (e.g., Matthews et al.), in which the absence of mechanical equilibrium for grown‐in threading dislocations determines the onset of the generation of interfacial misfit dislocations. It is assumed that interfacial misfit dislocations will be generated when the areal strain energy density of the film exceeds the energy density associated with the formation of a screw dislocation at a distance from the free surface equal to the film thickness h. For films thicker than this critical value, screw (and edge) dislocations will be generated at the film/substrate interface. Values obtained for the critical thickness versus lattice mismatch are in excellent agreement with measurements of hc for GexSi1−x strained layers on...

1,584 citations


Journal ArticleDOI
TL;DR: In this paper, a dipole occurs between two envelope states of the conduction-band electron wave function, and is called a quantum well envelope state transition (QWEST).
Abstract: A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction‐band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65‐A‐thick‐ and 82‐A‐thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half‐maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low‐power optical digital logic.

902 citations


Journal ArticleDOI
TL;DR: In this article, the results of magnetic studies of thin film, periodic, Pd/Co layered structures with ultrathin cobalt (4-13 A) were presented and it was shown that films with Co thicknesses less than 8 A are easy to magnetize along a direction normal to the film surface.
Abstract: This letter presents the results of magnetic studies of thin film, periodic, Pd/Co layered structures with ultrathin cobalt (4–13 A). We show that films with Co thicknesses less than 8 A are easy to magnetize along a direction normal to the film surface. The best films have a saturation magnetization of about 500 emu/cm3 and a coercivity of 550 Oe, and thus they are candidates for a vertical magnetic recording medium. We attribute the perpendicular magnetic easy axis in these films to surface anisotropy at Pd/Co interfaces and strain in thin Co layers.

874 citations


Journal ArticleDOI
TL;DR: In this article, InAs/GaAs superlattices with ultra-thin InAs (few monolayer) were grown on GaAs substrates and the physical properties: x ray, transmission electron microscopy, and photoluminescence were used to characterize the different growth processes.
Abstract: InAs/GaAs superlattices with ultra‐thin InAs (few monolayer) were grown on GaAs substrates. Nucleation of InAs occurs in a two‐dimensional or a three‐dimensional way depending on the growth conditions. The physical properties: x ray, transmission electron microscopy, and photoluminescence were used to characterize the different growth processes.

801 citations


Journal ArticleDOI
TL;DR: In this article, a simple extension of the reflection high energy electron diffraction oscillation technique to vicinal surfaces provides a means of studying surface diffusion during molecular beam epitaxial growth, and some preliminary results for Ga diffusion during the growth of GaAs films with (001) 2×4 and 3×1 reconstructed surfaces are presented.
Abstract: A simple extension of the reflection high‐energy electron diffraction oscillation technique to vicinal surfaces provides a means of studying surface diffusion during molecular beam epitaxial growth. The basis of the method is described and some preliminary results for Ga diffusion during the growth of GaAs films with (001) 2×4 and 3×1 reconstructed surfaces are presented.

648 citations


Journal ArticleDOI
TL;DR: In this paper, a new method is described which produces fully dense, well aligned Nd•Fe•B magnets from rapidly quenched ribbons, achieved by hot pressing at ∼15 kpsi in argon at 700 °C, and a second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting).
Abstract: A new method is described which produces fully dense, well‐aligned Nd‐Fe‐B magnets from rapidly quenched ribbons Full density is achieved by hot pressing at ∼15 kpsi in argon at 700 °C A second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting) introduces a preferred magnetization direction parallel to the press direction Energy products of 40 MGOe (Br/Hci=135 kG/11 kOe) have been generated by this method

436 citations


Journal ArticleDOI
TL;DR: In this article, thermal wave detection and analysis can be performed, in a noncontact and highly sensitive manner, through the dependence of sample optical reflectance on temperature, which is demonstrated by an example of measuring the thickness of thin metal films.
Abstract: We show that thermal wave detection and analysis can be performed, in a noncontact and highly sensitive manner, through the dependence of sample optical reflectance on temperature. Applications to the study of microelectronic materials are illustrated by an example of measuring the thickness of thin metal films.

397 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the intrinsic RC delay of a single barrier limits the frequency of active oscillations to fmax = 1/(2πτ), where τ =eα−1(λ/c)exp(4πd/λ) with λ being the de Broglie wavelength of the tunneling electron, d the barrier thickness, e the dielectric permittivity, c the speed of light, and α≊1/137 the fine-structure constant.
Abstract: The speed of operation of negative differential resistance (NDR) devices based on resonant tunneling in a double‐barrier quantum‐well structure is considered. It is shown that the intrinsic RC delay of a single barrier limits the frequency of active oscillations to fmax =1/(2πτ), where τ=eα−1(λ/c)exp(4πd/λ) with λ being the de Broglie wavelength of the tunneling electron, d the barrier thickness, e the dielectric permittivity, c the speed of light, and α≊1/137 the fine‐structure constant. The relevance of this estimate to recent experimental results is discussed. An alternative mechanism for the NDR is proposed—not involving resonant tunneling. It should be observable in various single‐barrier structures in which tunneling occurs into a two‐dimensional system of states. In a double‐barrier structure, specially designed experiments are required to distinguish this effect from resonant tunneling.

395 citations


Journal ArticleDOI
TL;DR: In this article, the feasibility of producing erbium-doped silicon light-emitting diodes by molecular beam epitaxy is demonstrated, where the pn junctions are formed by growing an erbiam-dope p-type epitaxial silicon layer on an n-type silicon substrate.
Abstract: The feasibility of producing erbium‐doped silicon light‐emitting diodes by molecular beam epitaxy is demonstrated. The p‐n junctions are formed by growing an erbium‐doped p‐type epitaxial silicon layer on an n‐type silicon substrate. When the diodes are biased in the forward direction at 77 K they show an intense sharply structured electroluminescence spectrum at 1.54 μm. This luminescence is assigned to the internal 4f–4f transition 4I13/2→4I15/2 of Er3+ (4f11).

349 citations


Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate that deviations from 1/f noise behavior found in submicron silicon metaloxide-semiconductor field effect transistors operating at room temperature are the direct result of the decomposition of the 1/F spectrum into its constituent Lorentzian components.
Abstract: We demonstrate that deviations from 1/ f noise behavior found in submicron silicon metal‐oxide‐semiconductor field‐effect transistors operating at room temperature are the direct result of the decomposition of the 1/ f spectrum into its constituent Lorentzian components. In the time domain, these devices produce random telegraph signals due to localized and discrete modulations of the channel resistance caused by individual carrier trapping events.

283 citations


Journal ArticleDOI
TL;DR: In this article, the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy was measured using photocurrent spectroscopy.
Abstract: We have used photocurrent spectroscopy to measure the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy A dramatic lowering of the indirect band gap, relative to that of unstrained bulk Ge‐Si alloys, is observed Our results for 0≤x≤07 are in remarkably good agreement with recent calculations of the effects of misfit strain on the band edges of coherently strained Ge‐Si heterostructures At x=06, the gap is lower than that of pure Ge

Journal ArticleDOI
TL;DR: In this paper, the influence of the electron bombardment on the initial island density on the substrate surface and on the decomposition of the reactant gases (CH4 and H2) is discussed relating to the growth process of the films.
Abstract: Diamond thin films have been formed by the newly proposed electron assisted chemical vapor deposition on SiC with a high growth rate (3∼5 μm/h). The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the films is about 9000 kg/mm2. The influence of the electron bombardment on the initial island density on the substrate surface and on the decomposition of the reactant gases (CH4 and H2) is discussed relating to the growth process of the films.

Journal ArticleDOI
TL;DR: In this paper, the effects of silicon dopant type, resistivity, current density, and hydrofluoric acid concentration on the formation and properties of porous silicon were investigated using cross-section transmission electron microscopy.
Abstract: A systematic study is presented of the effects of silicon dopant type, resistivity, current density, and hydrofluoric acid concentration on the formation and properties of porous silicon. Cross‐section transmission electron microscopy revealed the presence of two distinct microstructures. The structure formed is determined by the doping level with the transition occurring near degeneracy. A model of the anodisation process is presented which is based on the semiconducting properties of the material and which explains the formation of the two different types of porous structure observed.

Journal ArticleDOI
TL;DR: In this article, a new technique, limited reaction processing (LRP), is introduced, in which radiant heating is used to provide rapid, precise changes in the temperature of a substrate to control surface reactions.
Abstract: We introduce a new technique, limited reaction processing, in which radiant heating is used to provide rapid, precise changes in the temperature of a substrate to control surface reactions. This process was used to fabricate thin layers of high quality epitaxial silicon. Abrupt transitions in doping concentration at the epitaxial layer/substrate interface were achieved for undoped films deposited on heavily doped substrates.

Journal ArticleDOI
TL;DR: In this paper, the authors show that hydrogen penetration depth into GaAs(Si) is inversely dependent on the Si concentration, and that the free-carrier concentration can be restored by heating at 420°C for less than 3 min.
Abstract: Hydrogen plasma exposure of n‐type GaAs(Si) at 250 °C results in a decrease of the free‐carrier concentration by several orders of magnitude. This neutralization effect has been demonstrated in silicon‐doped layers grown by molecular beam epitaxy or formed by annealed implants as well as in bulk material. The same effect is produced electrochemically (H3PO4 electrolyte), whereas helium plasma exposure has no effect, thus confirming the role of hydrogen insertion. The hydrogen penetration depth into GaAs(Si) is inversely dependent on the Si concentration. Recovery of the electrical activity follows first order dissociation kinetics with a dissociation energy of 2.1 eV. Complete restoration of free‐carrier concentration occurs by heating at 420 °C for less than 3 min. Extrapolated to low temperatures, these results imply many years of stability at 150 °C or below.

Journal ArticleDOI
TL;DR: Several models of boron neutralized by atomic hydrogen in silicon were tested by secondary ion mass spectrometer and infrared spectrometry as discussed by the authors, and it was shown that hydrogen concentration is comparable to that of Boron. Boron neutralization appears as a drop in free carrier absorption and as an increase in resistivity.
Abstract: Several models of boron neutralized by atomic hydrogen in silicon were tested by secondary ion mass spectrometry and infrared spectrometry. The hydrogen concentration is comparable to that of boron. Boron neutralization appears as a drop in free‐carrier absorption and as an increase in resistivity. A new infrared vibrational mode attributed to 〈111〉 vibrations of H tied to Si appears at 1875 cm−1.

Journal ArticleDOI
TL;DR: In this article, single amplified 40-fs optical pulses are compressed to 8-fs duration at a 5-kHz repetition rate using self-phase modulation in a singlemode optical fiber.
Abstract: Single amplified 40‐fs optical pulses are compressed to 8‐fs duration at a 5‐kHz repetition rate using self‐phase modulation in a single‐mode optical fiber.

Journal ArticleDOI
TL;DR: In this article, the growth and crystallinity of the silicon clusters were monitored by transmission electron microscopy and the minimum silicon crystal diameter was measured at 2.5 nm for both atmospheric and plasma-enhanced CVD films.
Abstract: Silicon‐rich SiO2 films of various compositions were deposited by atmospheric or plasma‐enhanced chemical vapor deposition (CVD) techniques. These films were annealed at various temperatures between 700 and 1100 °C. The growth and crystallinity of the silicon clusters were monitored by transmission electron microscopy. The growth of the silicon clusters was found to be diffusion controlled with an activation energy measured to a first approximation at 1.9 eV/atom for both atmospheric and plasma‐enhanced CVD films. A minimum annealing temperature of between 800 and 950 °C and a minimum amount of excess Si above SiO2 are required to form crystalline silicon particles in the films. The minimum silicon crystal diameter was measured at 2.5 nm.

Journal ArticleDOI
TL;DR: In this article, the crystal orientation dependence of n− and p−type Si doping in molecular beam epitaxial GaAs was investigated and high electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes were demonstrated for the first time.
Abstract: Results on crystal orientation dependence of n‐ and p‐type Si doping in molecular beam epitaxial GaAs are presented. High electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes are demonstrated for the first time. The doping results should prove useful for various transistor structures and complementary circuits. Also, due to the differences in the band structure for different orientations, quantum well heterostructures are likely to exhibit many interesting phenomena which are strongly orientation dependent.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of the Nd2(Fe1−xCox)14B system were investigated to improve the thermal properties of Nd•Fe•B magnets.
Abstract: We have investigated the magnetic properties of the Nd2(Fe1−xCox)14B system to improve the thermal properties of the Nd‐Fe‐B magnets. Nd2(Fe1−xCox)14B exists in the tetragonal form in the entire range of 0≤x≤1. In this system, the replacement of Fe by Co significantly increases the Curie temperature. The room‐temperature magnetization of Nd2(Fe1−xCox)14B has its maximum value at x=0.1. However, because of the decrease in the anisotropy energy and the saturation magnetization by further substitution of Co for Fe, a reasonable substitution range of Co is suggested to be x<0.2 in the sintered Nd‐Fe‐B magnet. In this range of Co, we have succeeded in improving the reversible temperature coefficient of the remanence for the Nd‐Fe‐B magnets.

Journal ArticleDOI
TL;DR: In this paper, the authors characterized various InxGa1−xAs/GaAs strained-layer superlattices by Hall effect, ion beam channeling, and photoluminescence measurements in order to evaluate their crystalline quality Structural characteristics (eg, layer strains and thicknesses) were obtained from channeling or xray diffraction studies.
Abstract: Various InxGa1−xAs/GaAs strained‐layer superlattices have been characterized by Hall effect, ion beam channeling, and photoluminescence measurements in order to evaluate their crystalline quality Structural characteristics (eg, layer strains and thicknesses) were obtained from channeling or x‐ray diffraction studies The structures had strains in the alloy layers of 05–27% Critical layer thicknesses for degradation of sample quality are in good agreement with the theoretical expression proposed by J W Matthews and A E Blakeslee [J Cryst Growth 27, 118 (1974)] Our results provide important information for design of strained‐layer devices

Journal ArticleDOI
TL;DR: In this paper, it was shown that the current collected by a p−n junction in presence of a unit point generation of carriers at a point P is the same (apart from the dimensions) as the excess minority carrier density at P due to a unit density at the junction edge.
Abstract: It is shown that the current collected by a p‐n junction in presence of a unit point generation of carriers at a point P is the same (apart from the dimensions) as the excess minority‐carrier density at P due to a unit density of carriers at the junction edge. Use of this reciprocity relation may simplify the calculation of beam induced currents in semiconductor devices. The practical meaning of this property is illustrated in the case of a light‐emitting diode containing defects.

Journal ArticleDOI
TL;DR: In this paper, the time dependence of photoluminescence due to carrier recombination and the gratings created by degenerate four-wave mixing were measured in semiconductor-doped color filter glasses.
Abstract: The time dependence of both the photoluminescence due to carrier recombination and the gratings created by degenerate four‐wave mixing were measured in semiconductor‐doped color‐filter glasses. Values ranging from 80 to less than 16 ps (laser pulse width limited) are measured in several different samples at various excitation levels. A slower mechanism, believed to be thermal in nature, is also observed with a lifetime in excess of 9 ns.

Journal ArticleDOI
TL;DR: In this paper, the performance of SIPOS-crystalline silicon-SIPOS double heterostructure solar cells was investigated, and it was shown that these solar cells can be much more efficient than had been suspected.
Abstract: For maximal performance solar cells should resemble semiconductor lasers, i.e., they should be constructed in the form of a double heterostructure. We have found rather good performance in SIPOS‐crystalline silicon‐SIPOS double heterostructure solar cells, where SIPOS≡SiOx. The processing of these solar cells gives insights into the truly outstanding performance of the n+‐SIPOS: p‐Si heterojunction which has a forward saturation current coefficient J0=10−14 A/cm2, or equivalently an ‘‘emitter Gummel number’’ Ge=3.3×1015 s/cm4. This suggests that crystalline silicon solar cells can be much more efficient than had been suspected.

Journal ArticleDOI
TL;DR: In this paper, a method for compressing optical pulses at any wavelength in an optical fiber is described, which uses the negative dispersion property of permanent phase gratings created within the fiber.
Abstract: A method is described for compressing optical pulses at any wavelength in an optical fiber. It uses the negative dispersion property of permanent phase gratings created within the fiber. No external grating pair is required.

Journal ArticleDOI
TL;DR: The structure and properties of thin amorphous carbon films are critically dependent upon the preparation conditions as mentioned in this paper, and it is shown that structural trade-offs prevent the formation of so-called "amorphous diamond", a material with simultaneous extreme hardness and wide optical band gap.
Abstract: The structure and properties of thin amorphous carbon films are critically dependent upon the preparation conditions. Hydrogenated amorphous carbon films, prepared by both ion beam sputtering and glow discharge techniques, have been investigated by solid‐state 13C magic angle spinning nuclear magnetic resonance measurements of the sp2 and sp3 bonding sites. Film hardness and density correlate with the incorporated hydrogen, whereas the optical band gap is controlled by the fraction of tetrahedral (sp3) versus graphitic (sp2) bonding. It is shown that structural trade‐offs prevent the formation of so‐called amorphous diamond, i.e., a material with simultaneous extreme hardness and wide optical band gap.

Journal ArticleDOI
TL;DR: In this article, the optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature.
Abstract: The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation‐doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction‐band offset of 60% of the band‐gap discontinuity. For modulation‐doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two‐dimensional electron gas.

Journal ArticleDOI
TL;DR: In this article, it was shown that photo-etching of n-WSe2 leads to a large improvement in its photoresponse, achieving conversion efficiencies in excess of 14% in polyiodide solution under simulated solar light.
Abstract: It is shown that careful photoetching of n‐WSe2 leads to a large improvement in its photoresponse. Conversion efficiencies in excess of 14% were obtained in polyiodide solution under simulated solar light. A significant red shift in the photocurrent spectrum is observed after photoetching as well as hexagonal etch pits which reduce the reflectivity of the surface.

Journal ArticleDOI
TL;DR: In this paper, the compositional dependence of the band gap energy was determined and the free and bound exciton lines for x = 0 and 1 and only broadened bound excititon peaks for other compositions were quantitatively explained based on compositional fluctuations of the cations.
Abstract: Photoluminescence (PL) experiments were carried out at 300 and 12 K to investigate the electro‐optical properties of Cd1−xZnxTe grown by molecular beam epitaxy on GaAs substrates. The compositional dependence of the band‐gap energy was determined. It has a quadratic dependence on x. The near band edge PL spectra at 12 K show free and bound exciton lines for x=0 and 1 and only broadened bound exciton peaks for other compositions. The bound exciton broadenings are quantitatively explained based on the compositional fluctuations of the cations. The PL line shapes give indications of the high quality of the layers.

Journal ArticleDOI
TL;DR: In this article, the spectral and temporal dependence of the material's third order nonlinear optical susceptibility χ(3) was measured for the wavelength range from 9×10−9 esu at 6515 A to 5× 10−10 esu in 7015 A.
Abstract: Degenerate four‐wave mixing of tunable dye laser pulses in good optical quality single crystal platelets of poly bis(p‐toluene sulfonate) of 2, 4‐hexadiyne‐1, 6 diol (PTS) polydiacetylene was used to measure the spectral and temporal dependence of the material’s third order nonlinear optical susceptibility χ(3). For the wavelength range measured ‖χ(3)‖ varied from 9×10−9 esu at 6515 A to 5×10−10 esu at 7015 A. The material’s response time was determined to be less than the optical pulse width (≂6 ps) over this wavelength range.