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Applied Physics Letters

Issue 21 • Date May 1991

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Displaying Results 1 - 25 of 44
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Spatial hole burning in Nd3+‐fiber lasers suppressed by push‐pull phase modulation

    Page(s): 2323 - 2325
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    Spatial hole burning causes rapid mode jumping and spectral broadening in free‐running long linear Nd3+‐fiber lasers. Phase modulators at either end of the resonator, operating in antiphase, provide active spatial averaging and permit stable single‐mode operation with a short‐term linewidth of ≊5 kHz at 1088 nm wavelength. View full abstract»

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  • High‐speed InGaAs/GaAs strained multiple quantum well lasers with low damping

    Page(s): 2326 - 2328
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    Strained In0.2Ga0.8As/GaAs multiple quantum well polyimide buried ridge waveguide lasers with 3 dB bandwidths of 20 GHz and K factors as low as 0.17 ns have been fabricated. This is the highest bandwidth and the lowest K factor reported to date for quantum well lasers in any material system or for lasers of the ridge waveguide geometry. View full abstract»

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  • Pulse shortening of a copper bromide laser by quenching of resonator transients

    Page(s): 2329 - 2330
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    Generation of single pulses from a copper bromide laser with 2 ns pulse width is described here. At 11 kHz the pulse repetition rate, the stability of the amplitude, and the pulse width of these pulses are excellent. Theoretical considerations of the pulse shortening are also shown to agree well with the experiment. View full abstract»

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  • Effect of waveguide uniformity on phase matching for frequency conversion in channel waveguides

    Page(s): 2331 - 2333
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    We have studied the effect of nonuniformity in graded index, channel waveguide dimensions on the phase‐matching condition for guided‐wave nonlinear frequency conversion. Both theoretical and experimental results using normalized waveguide parameters and quasi‐phase matching for second‐ harmonic generation in annealed proton‐exchanged LiNbO3 waveguides show the existence of an optimum waveguide design which is insensitive to inhomogeneities in the waveguide dimensions. Application of such a waveguide design using normalized approach can significantly relax the fabrication tolerance, leading to nonlinear guided‐wave devices with long interaction lengths and useful conversion efficiencies. View full abstract»

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  • Second‐harmonic generation transition in NaNb3O8 solid solutions

    Page(s): 2334 - 2335
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    An apparent transition between active and nonactive second‐harmonic generation (SHG) has been discovered in the NaNb3O8 solid solutions with the tetragonal tungsten bronze structure. No SHG was detected in 0.35Na2O:Nb2O5 solid solution crystal or its powder. Nevertheless, powder SHG with a magnitude comparable to KH2PO4 was observed when a small amount of Nb2O5 was added to the powder ground from the crystal and sintered again. Microcracks and ferroelectric domain boundaries have been observed in the crystal using transmission electron microscopy. The only difference between the lattice images of SHG active powder and non‐SHG active powder is the absence of microcracks and ferroelectric domain boundaries in the SHG active powder. Dielectric constant of the 0.35Na2O:Nb2O5 crystal is about 300 and δ is 0.003 for frequency from 120 kHz to 12 MHz. View full abstract»

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  • High‐speed modulation of strained‐layer InGaAs‐GaAs‐AlGaAs ridge waveguide multiple quantum well lasers

    Page(s): 2336 - 2338
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    Strained‐layer In0.35Ga0.65As‐GaAs‐AlGaAs graded index separate confinement heterostructure multiple quantum well lasers were grown by molecular beam epitaxy and processed as ridge waveguide structures. Devices with 3 μm×200 μm cavities have threshold currents of 18 mA (3000 A/cm2) and optical waveguide losses of 4.2 cm-1. The microwave modulation bandwidth of a 3 μm×200 μm device was determined to be 19.5 GHz, which exceeds the 15.5 GHz reported for multimode index‐guided devices, and is the highest direct modulation bandwidth reported for a quantum well laser. View full abstract»

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  • Enhanced and inhibited spontaneous emission in GaAs/AlGaAs vertical microcavity lasers with two kinds of quantum wells

    Page(s): 2339 - 2341
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    We investigate enhanced and inhibited spontaneous emission effects in a vertical λ‐microcavity structure having two kinds of quantum wells (QWs) with the thicknesses of 76 and 114 Å, measuring both photoluminescence intensity and carrier lifetime. The 76 and 114 Å QWs are placed at the maximum and at the nodes of the emitted standing wave in the microcavity, respectively. When the λ‐microcavity mode is tuned to the quantized band‐gap energy of the 76 Å QWs (enhanced condition), the PL intensity is enhanced compared with the case that the cavity mode is tuned to the quantized band‐gap energy of the 114 Å QWs (inhibited condition). In addition, the increase of the carrier lifetime is also observed under the inhibited condition. These results demonstrate existence of enhanced and inhibited spontaneous emission effects in the microcavity structures. View full abstract»

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  • Optically controlled surface‐emitting lasers

    Page(s): 2342 - 2344
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    Vertical cavity surface‐emitting lasers are integrated with GaAs/AlGaAs heterojunction phototransistors to yield optically controlled lasers. The two‐terminal device operates in several modes: As an amplifier with a large signal, external optical gain of 5, as in optical logic gate, and as an optically or electrically triggerable latch. The optical AND gate has an output on‐to‐off ratio of 10:1. Although the device has no optical feedback, latching is achieved with appropriate biasing through impact ionization. The device structure is advantageous for forming large two‐dimensional arrays for optical signal processing. View full abstract»

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  • Anomaly in Cp/Cv: A possible signature of a liquid‐glass transition

    Page(s): 2345 - 2347
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    Brillouin scattering from two classic glass‐forming materials, ZnCl2 and glycerol, reveals a maximum in the ratio (γ) of specific heats Cp and Cv as a function of temperature. We propose that the temperature at which the maximum in γ occurs in our materials may be indicative of a ‘‘liquid‐like’’ to ‘‘solid‐like’’ transformation. As such it may be a convenient thermodynamic signature of a ‘glass’ transition. View full abstract»

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  • Defect reduction in GexSi1-x epitaxy by rapid thermal processing chemical vapor deposition using a low‐temperature in situ preclean and a Si buffer layer

    Page(s): 2348 - 2350
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    For chamber base pressure ≊5×10-4 mbar in a rapid thermal processing chemical vapor deposition system, a 900 °C H2 prebake for 60 s results in relatively high defect densities in the GexSi1-x epitaxial layer due to surface damage caused by the H2 prebake. We have demonstrated that a very low thermal budget in situ preclean (800 °C/15 s) can reduce the defect densities. In addition, the use of a Si buffer layer grown at 1000 °C for 60 s prior to the GexSi1-x growth is capable of significantly reducing defect densities. View full abstract»

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  • Raman analysis of Si/Ge strained‐layer superlattices under hydrostatic pressure

    Page(s): 2351 - 2353
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    Raman scattering was used to study optical phonons in a Si12Ge4 strained‐layer superlattice on c‐Si(001) that was subjected to hydrostatic pressure at room temperature. The change of phonon frequency with pressure, dω/dP, for the principal quasi‐confined LO mode in the Ge layers, is found to be significantly smaller than that for bulk crystalline Ge. This difference is shown to be due to the tuning of biaxial strain in the Ge layers and the pressure response of the confined mode as hydrostatic pressure is varied. Both strain and confinement make comparable contributions to dω/dP for the Ge layers in the superlattice examined here. View full abstract»

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  • Characterization of the early stages of electromigration at grain boundary triple junctions

    Page(s): 2354 - 2356
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    The formation and growth of holes and hillocks at grain boundary triple junctions in thin‐film conductors of gold on gallium arsenide and thin‐film conductors of aluminum‐1 wt. % silicon on (oxidized) silicon during the early stages of electromigration have been investigated through measurement of fractional change of electrical resistance ΔR/R and microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor ΔY, which defines the degree of cumulative flux divergence and, consequently, the degree of susceptibility to formation and growth of holes or hillocks. Resultant holes are characterized by a shape factor  f, which defines the degree of noncircularity and, consequently, relates fractional change of hole area to ΔR/R. Estimates of the upper limit for ΔY and the average value of  f  are in good agreement with measured values of ΔR/R and consistent with observed microstructure. View full abstract»

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  • Reduced dislocation density in Ge/Si epilayers

    Page(s): 2357 - 2359
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    Mismatched epilayers, for which the coherency strain has been relieved by misfit dislocation introduction, typically exhibit high epithreading dislocation densities. When the misfit is substantial, as for Ge or GaAs grown by molecular beam epitaxy onto (001) Si substrates, the density is regularly over 109 cm-2. We have grown Ge on Si (111) and (001) with epithreading dislocation densities in the 106 cm-2 range by use of chemical vapor deposition. This is because longer, and thus fewer, misfit dislocations appear for strain relief. Potential explanations for this are postulated. The most likely reason is that thermally activated dislocation glide is much faster at chemical vapor deposition growth temperatures. View full abstract»

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  • Amorphization processes in self‐ion‐implanted Si: Dose dependence

    Page(s): 2360 - 2362
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    The structural transformation in self‐ion‐implanted Si has been investigated using Raman spectroscopy and Rutherford backscattering spectrometry. The crystal Si Raman peak at 520 cm-1 decreased, broadened, and shifted toward lower wave numbers as the 100 keV Si+ dose was increased from 0.8 to 8.5×1014 cm-2. These peak shifts can be attributed to uniaxial lattice expansion in the direction normal to the Si surface and they are substantially larger than those predicted in uniaxially strained crystal Si. The results suggest that accumulated defects generated by ion bombardment not only expand the crystal Si lattice but also reduce the force constant which in turn increases plasticity and finally gives rise to amorphization of the Si lattice. View full abstract»

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  • Al‐Ga monolayer lateral growth observed in situ by scanning electron microscopy

    Page(s): 2363 - 2365
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    The characteristics of an Al‐Ga top layer on AlGaAs and GaAs surfaces during alternate supply molecular beam epitaxy (MBE) growth are studied by in situ observation using a MBE scanning electron microscope (SEM) hybrid system. It is found that an Al‐Ga alloy top layer has a pseudo‐self‐limiting nature. It is also found that the migration distance of Al‐Ga atoms on an Al‐Ga alloy top layer is as large as 10 μm. By utilizing these characteristics, a μm‐scale Al‐Ga monolayer lateral growth process is realized, and the lateral growth rate, about 1 μm/s, is observed. Comparison of this growth with migration‐enhanced epitaxy is discussed. View full abstract»

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  • Occupancy of the DX center in n‐Al0.32Ga0.68As under uniaxial stress

    Page(s): 2366 - 2368
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    We have used the deep level transient spectroscopy signal height as a function of applied stress data and the statistics of the occupancy of the DX center to obtain the stress dependence of the thermal binding energy of the neutral DX center, EDX. We find that EDX decreases with about the same rate for uniaxial stresses along 〈100〉 and 〈111〉 directions. Our results confirm that the DX center is a highly localized center as proposed by Chadi and Chang and disagree with the model assuming the DX center being an effective mass state of the doping impurity associated with the L band. View full abstract»

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  • Quantum molecular dynamics treatment for the electronic relaxation of high‐density plasmas in two‐dimensional structures

    Page(s): 2369 - 2371
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    We examine effects of the exchange interaction on the thermalization dynamics of high‐density photogenerated plasmas in quantum wells. A technique for simulating the transient dynamics is presented which combines the conventional Ensemble Monte Carlo method for the carrier‐phonon scattering, with a molecular dynamics scheme for treating the many‐body contributions to the long‐range Coulomb potentials. Account is taken of the exchange‐energy interactions in keeping with the exclusion principle and the Fermi nature of the system. Our results indicate that the exchange corrections slow the cooling of the photogenerated plasma at carrier densities above 1012 cm-2. The effect is due primarily to a weakening of the direct Colomb force, and demonstrates that calculations based on simple carrier–carrier scattering alone would underestimate thermalization time constants. View full abstract»

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  • In situ patterning of contamination resists in metalorganic chemical vapor deposition for fabrication of quantum wires

    Page(s): 2372 - 2374
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    We demonstrated a novel selective growth technology for the fabrication of quantum microstructures utilizing in situ patterning of contamination resist in the metalorganic chemical vapor deposition system. The results indicate that a GaAs quasi‐quantum wire structure, as narrow as 700 nm, can be successfully fabricated, showing that this technique may be applied to fabrication technologies for quantum microstructures. View full abstract»

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  • Electrical properties of GaAs/GaN/GaAs semiconductor‐insulator‐semiconductor structures

    Page(s): 2375 - 2377
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    We report on the current‐voltage (IV) characteristics of GaAs/GaN/GaAs semiconductor‐insulator‐semiconductor structures as a function of temperature. IV measurements show a strong temperature dependence indicating a thermal distribution of carriers flowing over a barrier. From these data we deduce an effective conduction band barrier of 0.9 eV between GaAs and GaN. View full abstract»

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  • p‐type doping of InP and Ga0.47In0.53As using diethylzinc during metalorganic molecular beam epitaxy

    Page(s): 2378 - 2380
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    Diethylzinc (DEZn) was used as a p‐type dopant source during metalorganic molecular beam epitaxy of Ga0.47In0.53As and InP. The incorporation efficiency of the Zn was less than 10-3. However, doping levels from p=1×1017 to 3×1019 cm-3 were obtained at growth temperatures of 485–510 °C. Measurements with secondary‐ion mass spectrometry indicated negligible diffusion of Zn in the Ga0.47In0.53As at these doping levels and growth temperatures. The DEZn was used to dope the p‐type InP cladding layer of broad‐area separate confinement multiquantum well (SCH‐MQW) lasers. Threshold current densities as low as 600 A/cm2 were achieved in nonoptimized structures. View full abstract»

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  • Fabrication of photodiode arrays by molecular assembly technique

    Page(s): 2381 - 2383
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    Mixed monolayers of 5‐(4‐N‐decylpyridinium)‐10,15,20‐tri‐p‐tolyl porphyrin (PyP) and arachidic acid (AA) were prepared on a water surface as a precursor for organized arrays of photodiodes. By compression and expansion of the films, PyP self‐assembled to form nearly circular domains with their size dependent on the molar ratio of PyP and AA. These structures were successfully incorporated into Schottky‐type cells, and their photoelectric properties were studied on the domain level by illumination of a focused light with a diameter of 20 μm. The short‐circuit photocurrents showed large fluctuations depending on the position of illumination, which reveals that the PyP domains function as photodiode arrays. View full abstract»

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  • Low‐pressure growth of ZnTe by Ar laser‐assisted metalorganic vapor phase epitaxy

    Page(s): 2384 - 2386
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    The effect of Ar laser irradiation upon ZnTe homoepitaxial growth has been investigated in low‐pressure metalorganic vapor phase epitaxy. Dimethylzinc and diethyltelluride were used as source materials. The growth rate of the ZnTe layer was greatly enhanced by irradiating vertically onto the (100) substrate. Photoluminescence measurements revealed that the quality of the layer is improved by the irradiation. Diethyltelluride is effectively decomposed on the surface by the irradiation. View full abstract»

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  • Improved electronic properties of GaAs surfaces stabilized with phosphorus

    Page(s): 2387 - 2389
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    We report on a new passivation procedure of the GaAs surface based on a thermal treatment under a PH3 overpressure. This treatment results, by As/P exchange, in the formation of a thin superficial GaP layer which prevents the formation of an arsenic oxide, as observed by x‐ray photoelectron spectroscopy analysis. Subsequent increase of the photoluminescence signal indicates improved electronic properties of GaAs surfaces as a result of this passivation procedure. View full abstract»

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  • Native‐oxide coupled‐stripe AlyGa1-yAs‐GaAs‐InxGa1-xAs quantum well heterostructure lasers

    Page(s): 2390 - 2392
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    Data are presented on a high‐performance native‐oxide coupled‐stripe AlyGa1-yAs‐GaAs‐InxGa1-xAs quantum well heterostructure laser realized by the recently introduced simple process of ‘‘wet’’ oxidation (H2O vapor+N2,≳400 °C, 3 h) of the upper AlyGa1-yAs confining layer. If the native oxide between active stripes (ten 5 μm stripes on 10 μm centers) is brought into closer proximity with the waveguide and quantum well region (i.e., from 0.53 to 0.4 μm), the 10‐stripe laser operates decoupled because of increased (coupling) absorption losses and some index guiding. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory