Showing papers in "Applied Physics Letters in 1981"
TL;DR: In this article, a novel passive mode-locking technique was proposed in which two synchronized counterpropagating pulses interact in a thin, saturable absorber to produce a short pulse.
Abstract: We report a novel passive mode‐locking technique in which two synchronized counterpropagating pulses interact in a thin, saturable absorber to produce a short pulse. Continuous stable trains of pulses shorter than 0.1 psec are obtained using a ring laser configuration.
794 citations
Abstract: Data are presented showing that Zn diffusion into an AlAs‐GaAs superlattice (41 Lz∼45‐A GaAs layers, 40 LB∼150‐A AlAs layers), or into AlxGa1−xAs‐GaAs quantum‐well heterostructures, increases the Al‐Ga interdiffusion at the heterointerfaces and creates, even at low temperature (<600 °C), uniform compositionally disordered AlxGa1−xAs. For the case of the superlattice, the diffusion‐induced disordering causes a change from direct‐gap AlAs‐GaAs (Eg∼1.61 eV) to indirect‐gap AlxGa1−xAs (x∼0.77, EgX∼2.08 eV).
563 citations
TL;DR: In this article, the backscattered light amplitude is measured from one end of a fiber as a function of optical frequency by tuning a HeNe laser over its linewidth.
Abstract: The backscattered light amplitude is measured from one end of a fiber as a function of optical frequency by tuning a HeNe laser over its linewidth. Fourier transform by a low‐frequency electronic spectrum analyzer then reveals the spatial distribution of scattering and of the fiber losses.
504 citations
TL;DR: In this paper, near-infrared optical absorption in undoped bulk GaAs ingots is shown to be due essentially to the presence of the main deep donor EL2, which is the first known method of quantitative determination of that level in semi-insulating material.
Abstract: Near‐infrared optical absorption in undoped bulk GaAs ingots is shown to be due essentially to the presence of the main deep donor EL2. Measurement of the corresponding absorption represents the first known method of quantitative determination of that level in semi‐insulating material. Furthermore, complete quenching of the corresponding absorption is shown to occur under high intensity illumination. This strong effect, reported for the first time, can be directly related to the existence of a metastable state for the level EL2 presenting a strong lattice relaxation.
399 citations
TL;DR: In this article, the authors showed that after intensive and long illumination of undoped a−Si:H samples, the dark ESR signal was considerably enhanced, and they concluded that the light-induced defects are single dangling bonds.
Abstract: After intensive and long illumination of undoped a‐Si:H samples the dark ESR signal is considerably enhanced. The g value of 2.0055 and the linewidth DHpp = 6–7 G leads to the conclusion that the light‐induced defects are single dangling bonds. They disappear again by thermal anneal at about 220 °C.
387 citations
IBM1
TL;DR: In this paper, a new model of Fermi-level pinning at the interfaces of compound semiconductor substrates and metallic or oxide overlayers was proposed, which assumes the standard Schottky picture of interface band alignment, but the interface phases involved are not the pure metal or oxide normally assumed by other models.
Abstract: The experimental observations of metallurgical interactions between compound semiconductor substrates and metallic or oxide overlayers have stimulated a new model of Fermi level ’’pinning’’ at these interfaces. This model assumes the standard Schottky picture of interface band alignment, but that the interface phases involved are not the pure metal or oxide normally assumed by other models. For both III‐V and II‐VI compounds, the barrier height to gold is found to correlate well with the anion work function, suggesting the interface phases are often anion rich. This correlation holds even for cases in which the ’’common anion rule’’ fails, and explains both successes and failures of this earlier model.
349 citations
TL;DR: In this paper, a passivation coating of W, or Pt, or both was used to prevent the rare earth from oxidation and Schottky-barrier heights of about 0.4 eV on n-Si and 0.7eV on p-Si were determined.
Abstract: Disilicide of rare‐earth metals (Dy, Er, Ho, and Gd) and Y have been formed by reacting the metallic film on both n‐ and p‐type silicons at around 350 °C for Schottky‐barrier height measurement using I‐V technique. A passivation coating of W, or Pt, or both was used to prevent the rare earth from oxidation. Schottky‐barrier heights of about 0.4 eV on n‐Si and 0.7 eV on p‐Si were determined.
326 citations
TL;DR: In this article, a hybrid rf/optical technique for studying sub-Doppler saturated absorption/dispersion resonances with excellent precision and symmetry is discussed, and a new level of accuracy for laser locking to an optical resonance is achieved.
Abstract: We discuss a refined, hybrid rf/optical technique for studying sub‐Doppler saturated absorption/dispersion resonances with excellent precision and symmetry. Sensitivity is limited mainly by fundamental noise in the signal. Resonance profiles obtained in I2 are in remarkable agreement with theory. The method promises a new level of accuracy for laser locking to an optical resonance.
319 citations
TL;DR: In this paper, a novel process for fabricating refractory sperconducting tunnel junctions is described, which is useful with both deposited and native oxide barriers, where the entire superconductor-barrier-superconductor sandwich is formed before the patterning of any layer.
Abstract: A novel process for fabricating refractory sperconducting tunnel junctions is described, which is useful with both deposited and native oxide barriers. The distinguishing feature of the method is that the entire superconductor‐barrier‐superconductor sandwich is formed before the patterning of any layer. Isolated Josephson junctions are then formed by anodizing through the upper electrode, while the devices themselves are protected by a photoresist mask. Using this process, Nb‐Si:H‐Nb junctions have been fabricated, whose product of critical current and subgap resistance exceeds 10 mV and whose critical current density varies by about 50% over a 2‐in. diameter wafer.
299 citations
TL;DR: In this paper, a piezoelectric ZnO sputtered onto a thin Si membrane supporting structure was used to excite a longitudinal bulk wave which reflects from the free surface of the film and membrane.
Abstract: This letter reports on a new and unique form of acoustic bulk wave resonator composed of a thin film of ZnO sputtered onto a thin Si membrane supporting structure. The piezoelectric ZnO is used to excite a longitudinal bulk wave which reflects from the free surface of the film and membrane. The structure thus forms an acoustical cavity which exhibits parallel and series electrical resonance responses at the ZnO film electrodes for both even and odd order modes. Fundamental resonant frequencies near 500 MHz have been achieved with parallel resonant Q’s over 9000. The temperature coefficient of resonant frequency was found to be −31 ppm for a Si to ZnO thickness ratio of six.
276 citations
TL;DR: In this article, it was shown that by modifying the layer structures of the conventional multiquantum well (MQW) lasers, extremely low Jth of 250 A/cm2 (averaged value) for broad-area Fabry-Perot diodes of 200×380 μm was obtained.
Abstract: It is shown that by modifying the layer structures of the conventional multiquantum well (MQW) lasers, extremely low Jth of 250 A/cm2 (averaged value) for broad‐area Fabry–Perot diodes of 200×380 μm was obtained. This was achieved as a result of utilizing the beneficial effects of the two‐dimensional nature of the confined carriers, the improved injection efficiency of the carriers into the GaAs wells, and an increased optical confinement factor in these modified MQW lasers. It was also determined that for low threshold operation the optimal AlAs composition x in the AlxGA1−xAs barrier layers is about 0.19 when GaAs wells are used and for barrier and well thicknesses ≳30 and 100 A, respectively.
TL;DR: In this paper, a clear valency electron controllability with substitutional impurity doping in the hydrogenated amorphous silicon carbide has been found, and a new type of a•SiC:H/a•Si:H heterojunction solar cell was developed.
Abstract: A clear valency electron controllability with substitutional impurity doping in the hydrogenated amorphous silicon carbide has been found. The amorphous silicon carbide is produced by the plasma decomposition of [SiH4(1−X)+CH4(X)] with the dopant gas of a B2H6 or PH3 system. Electrical and optical properties of doped amorphous SiC films are briefly demonstrated. Utilizing this a‐SiC:H as a wide‐band‐gap window material, we have developed a new type of a‐SiC:H/a‐Si:H heterojunction solar cell. A typical cell performance is Voc = 0.887 V, Jsc = 12.33 mA/cm2, fill factor = 0.653, and the conversion efficiency of 7.14% under AM‐1 illumination.
TL;DR: In this article, amorphous silicon indium tin oxide/n−i−p/stainless steel solar cells were tested for stability and showed a small initial drop to 5%, followed by a weak logarithmic decay that predicts only ∼20% further decrease in efficiency after 20 years in sunlight.
Abstract: Unencapsulated, amorphous silicon indium tin oxide/n‐i‐p/stainless‐steel solar cells were tested for stability. All cells have excellent shelf life. Changes occur during exposure to light, but can be controlled by the deposition conditions of the amorphous silicon. The changes are due to trapping and recombination of optically generated carriers in the i layer, and are reversibly annealed out above 175 °C. Preliminary life tests on two relatively stable cells showed a small initial drop to 5%, followed by a weak logarithmic decay that predicts only ∼20% further decrease in efficiency after 20 years in sunlight. Work is continuing on improving the efficiency and stability of these cells.
TL;DR: In this article, a novel effect, electro wetting, can be the basis of passive displays which switch reversibly from transparent to white, have fast response time (<1.0 ms), and can be operated with low voltages and low power consumption.
Abstract: We show that a novel effect, electro wetting, can be the basis of passive displays which (i) switch reversibly from transparent to white, (ii) have fast response time (<1.0 ms),and (iii) can be operated with low voltages (<1.0 V) and low power consumption (<1.0 mW/cm2). We derive the operating parameters and report experiments demonstrating the concept of electro‐wetting displays.
TL;DR: In this article, the most abrupt dielectric discontinuities between bulk and ambient (cleanest and/or smoothest surfaces) are determined by ellipsometry for single crystals of Si, Ge, and some III-V compounds.
Abstract: Chemical etching and cleaning procedures that produce the most abrupt dielectric discontinuities between bulk and ambient (cleanest and/or smoothest surfaces) are determined by ellipsometry for single crystals of Si, Ge, and some III‐V compounds. Differences among high‐symmetry orientations for Si and Ge indicate that preferential etching may be a factor in minimizing the amount of interface material left at a surface.
TL;DR: In this article, it is shown that the interface peak is due to trapping of holes at the silicon-silicon dioxide interface and the subsequent capture of injected electrons by the holes.
Abstract: In hole trapping and radiation damage in silicon dioxide, a characteristic interface‐state peak is present. It is shown by the present work that the interface peak is due to trapping of holes at the silicon‐silicon dioxide interface and the subsequent capture of injected electrons by the holes. It is postulated that dipolar complexes are formed, which give rise to electronic states at the interface. Similar dipoles may be responsible for neutral traps in the bulk of oxides after irradation.
TL;DR: The spectral width of GaAlAs single-mode diode lasers varied linearly with reciprocal output power at 300 K with a slope 50 times greater than that predicted by the SchawlowTownes expression without partial inversion.
Abstract: The spectral width of (GaAl)As cw single‐mode diode lasers varied linearly with reciprocal output power at 300 K with a slope 50 times greater than that predicted by the Schawlow‐Townes expression without partial inversion. While the spectral narrowing observed at 77 K for constant mode power is consistent with the predicted temperature dependence of the partial inversion contribution, the magnitude of the broadening can not completely be attributed to partial inversion.
TL;DR: In this paper, the structural perfection of these films has been explored by double crystal x-ray diffraction techniques, which reveal that films of ∼1 μm thick grown at 150 and 220°C are free of low-angle grain boundaries and are exactly lattice matched to the InSb substrate.
Abstract: Heteroepitaxial films on CdTe have been grown by molecular beam epitaxy (MBE) on InSb (001) orientation substrates at growth temperatures ≲220 °C. The structural perfection of these films has been explored by double crystal x‐ray diffraction techniques, which reveal that films of ∼1 μm thick grown at 150 and 220 °C are free of low‐angle grain boundaries and are exactly lattice matched to the InSb substrate. The lattice parameter mismatch is accommodated by misfit elastic strain.
TL;DR: In this article, high conductivity films of zinc oxide have been prepared by reactive rf magnetron sputtering from an oxide target, and a second low power discharge at the substrate is used to initiate growth of the highly conducting material on room-temperature substrates.
Abstract: Highly conductive films of zinc oxide have been prepared by reactive rf magnetron sputtering from an oxide target. Film conductivities ranging from ∼10−8 Ω−1 cm−1 to 5×102 Ω−1 cm−1 can be obtained depending on the sputter conditions. Films with sheet resistivities of 85 Ω/⧠ showed little absorption and ∼90% transmission between λ = 4000→8000 A. A second low power discharge at the substrate is used to initiate growth of the highly conducting material on room‐temperature substrates. Thus, during the deposition of insultating ZnO, turning on this second discharge causes the deposition to ’’switch’’ from low conductivity to high conductivity material. This is of particular interest in the fabrication of semiconductor‐insulator‐semiconductor solar cells where precise control over the thickness of the insulating layer is necessary and where a highly transparent and conductive window‐junction layer is required.
TL;DR: In this article, the Hall resistance of the two-dimensional electron gas in GaAs•AlxGa1−xAs heterostructures was observed at 4.2 K and at magnetic fields as low as 4.6 T.
Abstract: Quantization of the Hall resistance of the two‐dimensional electron gas in GaAs‐AlxGa1−xAs heterostructures is observed at 4.2 K and at magnetic fields as low as 4.2 T. This demonstrates its practical use as a primary resistance standard.
TL;DR: In this article, a subpicosecond laser has been used to trigger a GaAs photoconductive switch driving a dipole antenna, and the microwave transient produced was measured with a correlation technique to have a FWHM of less than 3 psec.
Abstract: A subpicosecond laser has been used to trigger a GaAs photoconductive switch driving a dipole antenna. The microwave transient produced was measured with a correlation technique to have a FWHM of less than 3 psec. This technique was also used in a contactless measurement of the 250‐psec lifetime of a GaAs sample.
TL;DR: In this article, high-quality epitaxial layers of GaAs have been grown in a molecular beam system using AsH3 as the arsenic source, achieving peak electron mobilities of over 130,000 cm2/V
Abstract: High‐quality epitaxial layers of GaAs have been grown in a molecular beam epitaxial system using AsH3 as the arsenic source. Peak electron mobilities of over 130 000 cm2/V sec and 77‐K mobilities as high as 110 000 cm2/V sec have been observed in a 5‐μm‐thick GaAs layer with a carrier concentration of 2.4×1014 cm−3. These layers were grown on Cr‐doped semi‐insulating GaAs substrates. Initial results indicate that As1 may be the preferred specie for the growth of high‐purity GaAs.
TL;DR: In this article, a heterostructure semiconductor laser with a graded-index waveguide and separate carrier and optical confinements prepared by molecular beam epitaxy is discussed, and it is shown that only when the active layer thickness is ≲700 A a significantly lower Jth is obtained by employing the symmetric laser structure instead of the regular double heterostructures.
Abstract: A heterostructure semiconductor laser with graded‐index waveguide and separate carrier and optical confinements prepared by molecular beam epitaxy is discussed. These lasers have very low broad‐area threshold current densities Jth 500 A/cm2 and support narrow beams of Gaussian distribution with far‐field half‐power full‐width in the direction perpendicular to the junction plane ϑ⊥ ∼20°–30°. It is also shown that only when the active layer thickness is ≲700 A a significantly lower Jth is obtained by employing the symmetric laser structure instead of the regular double heterostructure.
TL;DR: In this article, a general trend of increasing defect density with atomic weight of the inert gas is observed, and the observation that high deposition rates can be achieved concurrently with low defect densities when helium is used as a deluent.
Abstract: Electrical, optical, and structural characterization of hydrogenated amorphous silicon films plasma‐deposited from mixtures of SiH4 with different inert‐gas diluents reveals substantial differences in a number of properties. A general trend of increasing defect density with atomic weight of the inert gas is observed. Of specific interest to device applications is the observation that high deposition rates can be achieved concurrently with low defect densities when helium is used as a deluent.
TL;DR: In this article, the disilicides of rare earth metals (Gd, Dy, Ho, Er, plus Y and La) were studied by using x-ray diffraction and ion backscattering spectrometry.
Abstract: Reactions between Si and thin films of rare‐earth metals (Gd, Dy, Ho, Er, plus Y and La) in the temperature range of 275–900 °C have been studied by using x‐ray diffraction and ion backscattering spectrometry. The disilicides of these metals are apparently the first phase to form, forming rapidly within a narrow temperature range (325–400 °C), and are stable up to 900 °C. The growth does not follow a layered growth mode.
TL;DR: In this article, the authors reported energy conversion efficiency as high as 5.96% on polycrystalline transparent magnesium Zn3P2 diodes, 0.7 cm2 in area, tested under simulated AM1 illumination.
Abstract: Energy conversion efficiencies as high as 5.96% are reported on polycrystalline transparent magnesium Zn3P2 diodes, 0.7 cm2 in area, tested under simulated AM1 illumination. The transparent Mg films with low sheet resistivities are obtained by dc sputtering. The effective minority‐carrier diffusion length in Zn3P2 is estimated from spectral response measurements and correlates well with the measured short‐circuit current. Loss analysis of the present cells shows a practical upper limit of 9% in conversion efficiency.
TL;DR: In this article, the Schottky barrier height to p-type silicon was estimated to be 0.4 eV, which corresponds to the band gap of silicon, based on forward I/V and photoresponse measurements.
Abstract: Some rare‐earth elements, Tb, Er, Yb (including Y) and some of their respective silicides were found to make ohmic contacts to n‐type silicon. Forward I/V and photoresponse measurements give values of about 0.7 eV for the Schottky‐barrier height to p‐type silicon. The sum of this value and of the experimentally estimated barrier height to n‐type silicon, 0.4 eV, corresponds to the band gap of silicon.
TL;DR: In this article, the authors used ion implantation to control the carrier lifetime in silicon-on-sapphire (SOS) films and found that the carrier mobility was at least an order of magnitude higher than amorphous silicon materials with similar relaxation times.
Abstract: Radiation damage caused by ion implantation is used to control the carrier lifetime in silicon‐on‐sapphire (SOS) films. Photoconductivity measurements show the relaxation time changes by several orders of magnitude and can be as short as 8 ps. The carrier mobility is found to be at least an order of magnitude higher than amorphous silicon materials with similar relaxation times. A photodetector is described that demonstrates the high‐speed capability of these high‐defect‐density films.
TL;DR: In this paper, the authors studied the effect of pulse energy on the melting and resolidification of a silicon crystal wafer, and provided evidence that thermalization time for a dense carrier plasma and the lattice is shorter than 10−11 s.
Abstract: Ultrafast melting and resolidification on a (111) sufarce of a silicon crystal wafer, induced by 20‐ps pulses at 532‐nm wavelength, is accompanied by the emission of charged particles. This emission is studied as a function of pulse energy, in combination with time‐resolved reflectivity changes and post‐annealing morphology. The data provide evidence that thermalization time for a dense carrier plasma and the lattice is shorter than 10−11 s.
TL;DR: In this article, a short description of electro-optical effects observed in a DF phase of disk-like molecules is given, and the existence of dielectric and electrohydrodynamic instabilities are pointed out.
Abstract: The aim of this letter is to give a short description of some electro‐optical effects which are observed in a DF phase of disklike molecules. We point out the existence of dielectric and electrohydrodynamic instabilities. The last one is the experimental evidence of the interesting situation of an anisotropic liquid with ea≳0σa<0 in the homeotropic configuration. These electro‐optic effects can be useful in display applications of the discotic phases.