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31 Dec 1990

Volume 57, Issue 27, pp. 2873-2961

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Extremely low threshold current AlGaAs buried‐heterostructure quantum well lasers grown by liquid phase epitaxy

Zh. I. Alferov, V. M. Andreyev, A. Z. Mereutza, A. V. Syrbu, and V. P. Yakovlev

Appl. Phys. Lett. 57, 2873 (1990); http://dx.doi.org/10.1063/1.103762 (3 pages) | Cited 8 times

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Data are presented on AlGaAs single quantum well buried‐heterostructure lasers grown by two‐step liquid phase epitaxy (LPE). The base laser structures were grown by low‐temperature LPE in the temperature interval of 600–400 °C. Broad‐area threshold current densities of 300 A/cm2 were measured for 1‐mm‐long lasers. The buried heterostructure was formed in the second LPE process including in situ selective mesa melt etching. Threshold currents of 1.3 mA in a continuous regime were obtained for uncoated lasers having 125‐μm‐long cavities.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Permanent grating induced by nonlinear absorption in polysilane films

H. Nakano, Y. Ishida, T. Yanagawa, and N. Matsumoto

Appl. Phys. Lett. 57, 2876 (1990); http://dx.doi.org/10.1063/1.103763 (3 pages) | Cited 2 times

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The optical grating memory effect in polysilane film is investigated. A refractive index grating is formed within a few minutes by using visible light near room temperature. The grating formation time is dominated by the peak intensity of the pumping beams, and its dependence on the wavelength of the pumping beams corresponds to the two‐photon absorption spectrum. The grating formation mechanism is explained as the result of the chain scission induced by two‐photon absorption.
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78.66.Qn Polymers; organic compounds
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Vb Optical storage systems, optical disks

Small‐angle neutron scattering study of semiconductor microcrystallites in optical glasses

Vittorio Degiorgio, GianPiero Banfi, Giancarlo Righini, and Adrian Rennie

Appl. Phys. Lett. 57, 2879 (1990); http://dx.doi.org/10.1063/1.103764 (3 pages) | Cited 16 times

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The structure of semiconductor‐doped glasses is studied by small‐angle neutron scattering. We derive the average size of the microcrystals, and we give information on the spatial distribution of the microcrystals. A new aspect emerging from our data is the existence of a depletion region that during nucleation and growth each crystal creates around itself.
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42.70.Ce Glasses, quartz
61.05.fg Neutron scattering (including small-angle scattering)
61.43.Fs Glasses
61.43.-j Disordered solids
61.44.Br Quasicrystals

Frequency stability and reproducibility of optically pumped far‐infrared lasers

Richard L. Crownover, Henry O. Everitt, Frank C. De Lucia, and David D. Skatrud

Appl. Phys. Lett. 57, 2882 (1990); http://dx.doi.org/10.1063/1.103765 (3 pages) | Cited 2 times

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Direct measurements of the gain profile of optically pumped far‐infrared lasers show that large shifts in the laser frequency can be caused by the absorption from thermal molecules on the laser transition. The absorption shifting greatly exacerbates pump frequency deviations, resulting in an extreme sensitivity to pump offsets and drifts. This pressure‐dependent shifting mechanism is not present in transversely pumped lasers, which explains their superior frequency reproducibility compared to longitudinally pumped lasers, and reconciles two apparently conflicting results regarding laser stability.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
33.80.Be Level crossing and optical pumping
33.70.Jg Line and band widths, shapes, and shifts
34.50.Ez Rotational and vibrational energy transfer

Room‐temperature exciton absorption in (Zn,Cd)Se/ZnSe quantum wells at blue‐green wavelengths

J. Ding, N. Pelekanos, A. V. Nurmikko, H. Luo, N. Samarth, and J. K. Furdyna

Appl. Phys. Lett. 57, 2885 (1990); http://dx.doi.org/10.1063/1.103766 (3 pages) | Cited 61 times

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Excitonic absorption has been investigated in multiple quantum wells of (Zn,Cd)Se/ZnSe in an effort to increase the electron‐hole Coulomb interaction. Well‐defined absorption peaks for the n=1 heavy hole exciton are observed at room temperature showing evidence for a reduced exciton‐optical phonon scattering rate.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
63.20.kk Phonon interactions with other quasiparticles

Femtosecond gain dynamics and saturation behavior in InGaAsP multiple quantum well optical amplifiers

K. L. Hall, Y. Lai, E. P. Ippen, G. Eisenstein, and U. Koren

Appl. Phys. Lett. 57, 2888 (1990); http://dx.doi.org/10.1063/1.103767 (3 pages) | Cited 28 times

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Femtosecond pump‐probe experiments on InGaAs/InGaAsP multiple quantum well optical amplifiers reveal ultrafast dynamics that are similar to, but quantitatively different from, those observed in bulk amplifiers. Pulse energy saturation of the amplifier gain is also studied using 150 fs and 20 ps pulses and is found to be pulsewidth dependent. The measured saturation energies are 200 fJ and 6 pJ, respectively.
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78.47.-p Spectroscopy of solid state dynamics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Molecular beam epitaxy grown PbEuSeTe buried‐heterostructure lasers with continuous wave operation at 195 K

Z. Feit, D. Kostyk, R. J. Woods, and P. Mak

Appl. Phys. Lett. 57, 2891 (1990); http://dx.doi.org/10.1063/1.103768 (3 pages) | Cited 8 times

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Lattice‐matched buried‐heterostructure (BH) PbEuSeTe lasers were fabricated using a two‐stage molecular beam epitaxy growth procedure. Lasers with 4‐μm‐wide and 0.6‐μm‐thick buried PbTe and Pb0.9976Eu0.0024Se0.0034Te0.9966 active layers were grown. Record continuous wave (cw) operating temperatures of 195 and 183 K were measured for BH diode lasers with binary PbTe active layer, and quaternary PbEuSeTe (0.22 at. % Eu) active layer compositions, respectively. For PbTe active layer BH lasers, threshold currents of 3.2 mA (80 K) and 36.2 mA (140 K) were measured in cw operation mode. For Pb0.9976Eu0.0024Se0.0034Te0.9966 BH active layer lasers, threshold currents of 2.9 mA (80 K) and 23.4 mA (140 K) were measured in cw operation mode.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

ZnSe/ZnSe0.92S0.08/GaAs single‐crystal waveguides as visible modulators

M. H. Jupina, E. M. Garmire, N. Shibata, and S. Zembutsu

Appl. Phys. Lett. 57, 2894 (1990); http://dx.doi.org/10.1063/1.103769 (3 pages) | Cited 11 times

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Electro‐optic and electroabsorptive modulations have been demonstrated in Schottky barriers in epitaxial ZnSe waveguides with cladding layers of ZnSeS grown single crystal on GaAs substrates. Using an argon laser we demonstrate guided‐wave electro‐optic modulation with voltages which are predicted by bulk ZnSe electro‐optic coefficients. With a 3 mm sample, half‐wave modulation was observed at 4 V per micron electrode separation. Electroabsorption with 9.2 dB modulation in a 0.6‐mm‐long sample was observed at 488 nm. With surface electrodes, rectification within the Schottky barrier made possible a unique rectified optical modulation.
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42.82.-m Integrated optics
42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects

Optoelectronic generation of time‐division multiplexed ultrafast bit stream on a coplanar waveguide

C. Shu, X.‐C. Zhang, E. S. Yang, and D. H. Auston

Appl. Phys. Lett. 57, 2897 (1990); http://dx.doi.org/10.1063/1.103745 (2 pages) | Cited 5 times

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We have developed a technique to generate a two‐dimensional array of optical beams with equal intensities and a constant sequential time delay from a mode‐locked laser. A light modulator was used to code the spatially separated beams, which were then multiplexed to form a serial pulse string. With the multiplexed beam focused on a picosecond photoconductor, an ultrafast electrical signal was generated.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
78.20.Jq Electro-optical effects
85.60.-q Optoelectronic devices

Optical switching of quantum interference through exchange interactions between coherent electron waves and photoexcited virtual excitons

M. Yamanishi, Y. Osaka, K. Yamatani, and S. Agou

Appl. Phys. Lett. 57, 2899 (1990); http://dx.doi.org/10.1063/1.103746 (3 pages) | Cited 1 time

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Proposed and analyzed is an ultrafast modulation scheme for electron quantum interference based on exchange interactions between coherent electron waves and photoexcited virtual excitons in quantum wire interferometers.
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42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps
71.35.-y Excitons and related phenomena
74.20.-z Theories and models of superconducting state

Optical channel waveguide fabrication based on electron beam irradiation of silica

S. J. Madden, Mino Green, and D. Barbier

Appl. Phys. Lett. 57, 2902 (1990); http://dx.doi.org/10.1063/1.103747 (2 pages) | Cited 3 times

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The bombardment of silica by low‐energy electrons induces compaction and an increase in refractive index. We have used this phenomenon, combined with photolithographic processing, to make channel waveguides in silica, most of which are monomode, with a depth of 2–7 μm, and peak index variation between 10−3 and 10−2. Channel waveguide widths down to 2 μm have been fabricated on fused silica plates and on silica layers grown on silicon by plasma‐enhanced chemical vapor deposition (PECVD) methods. The lowest measured linear losses at 633 nm were 0.3 db/cm in PECVD silica and 1.9 db/cm in the fused silica plates, although much lower losses are anticipated in the latter material. Using this method we have fabricated 3 dB directional couplers in both materials.
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42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
42.82.-m Integrated optics
61.80.Fe Electron and positron radiation effects

Low‐threshold disorder‐defined buried‐heterostructure AlxGa1−xAs‐GaAs quantum well lasers by open‐tube rapid thermal annealing

T. A. Richard, J. S. Major, F. A. Kish, N. Holonyak, S. C. Smith, and R. D. Burnham

Appl. Phys. Lett. 57, 2904 (1990); http://dx.doi.org/10.1063/1.103748 (3 pages) | Cited 3 times

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AlxGa1−xAs‐GaAs single stripe quantum well heterostructure (QWH) lasers fabricated via Si impurity‐induced layer disordering (IILD) in an As‐free open tube rapid thermal annealing furnace are reported. The Si IILD, with good surface morphology, is obtained using a Si/Si3N4 source layer with the QWH wafer in face‐to‐face contact with a GaAs substrate during the anneal (13 min, 1000 °C). Continuous wave (cw) 300 K operation of the lasers with uncoated facets has produced output powers as high as 25 mW/facet with threshold currents as low as 7 mA. The devices operate single mode at a wavelength of 812 nm and have high differential quantum efficiencies of ∼44%, with some as high as 57%.
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42.55.Px Semiconductor lasers; laser diodes
66.30.J- Diffusion of impurities
68.35.Fx Diffusion; interface formation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Visible mechanism of liquid crystals on graphite under scanning tunneling microscopy

H. Nejoh

Appl. Phys. Lett. 57, 2907 (1990); http://dx.doi.org/10.1063/1.103749 (3 pages) | Cited 13 times

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Liquid crystals on graphite have been observed by scanning tunneling microscopy. Although an isolated 4‐n‐octyl‐4′‐cyanobiphenyl (8CB) molecule shows a wide 11 eV energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), its image could be obtained by tunneling bias around 800 mV far below this energy gap. The fact that 8CB with a large energy gap could be imaged was confirmed by a spectroscopic measurement. This LC molecule visualizing mechanism is interpreted from one viewpoint as the result of energy level shift possibly caused by molecule‐substrate interaction and from another viewpoint as the result of periodic molecules forming an energy band.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
31.15.A- Ab initio calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Instability of partially disordered carbon‐doped AlGaAs/GaAs superlattices

I. Szafranek, J. S. Major, B. T. Cunningham, L. J. Guido, N. Holonyak, and G. E. Stillman

Appl. Phys. Lett. 57, 2910 (1990); http://dx.doi.org/10.1063/1.103750 (3 pages) | Cited 8 times

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Superlattices of Al0.3Ga0.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CCl4 were annealed for 24 h at 825 °C under a variety of ambient and surface encapsulation conditions. Pronounced changes in photoluminescence from the annealed superlattices with storage time at room temperature, as opposed to an excellent reproducibility of that from the as‐grown, not annealed samples, are reported. These changes may be indicative of degraded thermal stability of the annealed superlattice crystals due to high‐temperature‐induced lattice defects. The systematic failure to fabricate buried‐heterostructure quantum well lasers via impurity‐induced layer disordering in similarly doped AlGaAs/GaAs crystals, which may be related to the same effect, is also discussed.
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66.30.J- Diffusion of impurities
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Laser‐assisted deposition of nanometer structures using a scanning tunneling microscope

S.‐T. Yau, D. Saltz, and M. H. Nayfeh

Appl. Phys. Lett. 57, 2913 (1990); http://dx.doi.org/10.1063/1.103728 (3 pages) | Cited 12 times

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Nanometer‐scale deposits as small as 1 nm have been made on graphite surfaces using laser‐induced multiphoton fragmentation and ionization of trimethylaluminum (TMA) molecules in the tunneling junction of a scanning tunneling microscope. Laser radiation generates ions, which are guided to the surface by the electric field between the tip and the surface. The resolution of this technique is limited by the extent of the field in the tunneling junction.
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85.40.Hp Lithography, masks and pattern transfer
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Quantized resistance in in‐plane gated narrow constriction fabricated by wet etching

Y. Takagaki, K. Gamo, S. Namba, S. Takaoka, and K. Murase

Appl. Phys. Lett. 57, 2916 (1990); http://dx.doi.org/10.1063/1.103729 (3 pages) | Cited 12 times

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A narrow in‐plane gated constriction is defined by technique employing electron beam lithography and wet chemical etching. Two‐dimensional electron gas beside the narrow channel is used to control the number of occupied subbands in the constriction. A ballistic transport through the point contact is manifested by the observation of successive resistance steps when the subbands are depopulated.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Cg Contact resistance, contact potential
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Mechanisms for the emission of visible light from GaAs field‐effect transistors

Hans P. Zappe and Donat J. As

Appl. Phys. Lett. 57, 2919 (1990); http://dx.doi.org/10.1063/1.103730 (3 pages) | Cited 12 times

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The emission of visible light from GaAs metal‐semiconductor field‐effect transistors under high electric field conditions is studied in detail in order to learn more about the luminescence mechanism. The electroluminescence spectrum is examined for energies both greater and less than the energy gap. It is seen that the form of the subgap spectrum can be explained by a Bremsstrahlung mechanism. However, the prominence of a voltage‐dependent band‐gap peak indicates that recombination processes also contribute to visible photon emission. A strongly polarized component of electroluminescence further substantiates the existence of radiative elastic collisions (Bremsstrahlung) and may provide insights into the scattering behavior of electrons in the channel.  
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72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
78.60.Fi Electroluminescence
85.30.Tv Field effect devices

Forbidden Auger process in strained InGaSb/AlGaSb quantum wells

Y. Jiang, M. C. Teich, and W. I. Wang

Appl. Phys. Lett. 57, 2922 (1990); http://dx.doi.org/10.1063/1.103731 (3 pages) | Cited 16 times

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Carrier loss due to Auger recombination has been known to be the major factor limiting the performance of long‐wavelength semiconductor lasers. We show for the first time that the dominant Auger process in InGaSb/AlGaSb and InGaAs/InP strained quantum well structures can be suppressed because of the conversation of energy and crystal momentum with the sufficient reduction of the in‐plane heavy hole masses. As a result, low‐threshold currents and good temperature performance can be achieved in strained quantum well semiconductor lasers. An analytic expression for the in‐plane effective hole masses in a strained quantum well is derived and used to calculate the hole masses of InGaSb/AlGaSb strained quantum wells.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes

Quantum and classical lifetimes in a Ga0.49In0.51P/GaAs heterojunction

S. Ben Amor, L. Dmowski, J. C. Portal, K. P. Martin, R. J. Higgins, and M. Razeghi

Appl. Phys. Lett. 57, 2925 (1990); http://dx.doi.org/10.1063/1.103732 (3 pages) | Cited 7 times

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We report a study of the subband structure of Ga0.49In0.51P/GaAs heterojunctions. High‐field (0<B<20 T) magnetotransport measurements were performed at low temperatures (4.2 K) under hydrostatic pressure (P<12 kbar). The strong persistent photoconductivity effect in this system allowed us to tune the two‐dimensional electron gas (2DEG) density (N2D) with short light bursts from a red electroluminescent diode. The pressure dependence of N2D shows that in contrast with other systems, pressure effects on the band discontinuity and the effective mass are responsible for the observed density dependence. Both single particle (quantum) and scattering (classical) lifetimes were measured. The ratio of the classical‐to‐quantum lifetimes was large (≊10) at ambient pressure and confirmed the dominant role of scattering by remote ionized impurities. After illumination, the ratio quickly decreases with increasing 2DEG density. However when pressure is applied, this ratio decreases with decreasing N2D, giving evidence of a pressure‐induced misfit strain at the interface that modifies the dominant scattering mechanisms.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Hydrogen passivation of Si δ‐doped GaAs grown by molecular beam epitaxy

V. Swaminathan, M. T. Asom, G. Livescu, M. Geva, F. A. Stevie, S. J. Pearton, and J. Lopata

Appl. Phys. Lett. 57, 2928 (1990); http://dx.doi.org/10.1063/1.103733 (3 pages) | Cited 2 times

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Hydrogen passivation of Si δ‐doped GaAs grown by molecular beam epitaxy is studied. Just as in uniformily Si‐doped GaAs, exposure of the δ‐doped material to a low frequency (30 kHz) hydrogen plasma at 250 °C for 30 min deactivates the Si donors in the δ spikes. For samples with Si doping of (1–6)×1018 cm−3, carrier concentration in the spikes decreased by nearly three orders of magnitude following hydrogenation. Secondary‐ion mass spectrometric analysis of deuterated samples confirmed trapping of deuterium in the Si‐doped spikes. Consistent with the deactivation of Si donors following hydrogenation, changes were observed in the near‐band edge luminescence spectrum at 4.2 K, which showed in the hydrogenated sample the absence of Burstein–Moss shift that was observed in the as‐grown sample. This hydrogen‐induced passivation of Si donors in the δ spikes can be of benefit in selectively deactivating donor atoms in device applications, and also provide a method for tailoring the hydrogen distribution in an epitaxial structure.
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81.65.-b Surface treatments
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.40.Tv Optical and dielectric properties related to treatment conditions
85.40.Ls Metallization, contacts, interconnects; device isolation

Effect of nucleation mechanism on planar defects in InAs on Si (100)

C.‐H. Choi, L. Hultman, R. Ai, and S. A. Barnett

Appl. Phys. Lett. 57, 2931 (1990); http://dx.doi.org/10.1063/1.103734 (3 pages) | Cited 6 times

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Suppression of three‐dimensional (3D) island nucleation during growth of InAs on Si (100), achieved by using very low energy, high‐flux Ar ion irradiation, reduced planar defect densities. For 13 eV ion irradiation, 3D islands nucleated after ∼2 monolayers (ML) of deposition, similar to conventional molecular beam epitaxy. High‐resolution transmission electron microscopy studies of nominally 18‐ML‐thick films showed 3D InAs islands with {111} facets. A high density of {111} twins and stacking faults was observed adjacent to many of the {111} facets. Most of these defects propagated into the film upon further growth. When nucleation was carried out with 28 eV ion irradiation, flat InAs films were observed for thicknesses up to ∼10 ML. The 3D islands that nucleated at higher thicknesses were flatter with less faceting than in the 13 eV case. The density of planar defects in the initial nucleation layer and in thicker InAs films was reduced when 3D island nucleation was suppressed. These results indicate that planar defects formed directly on the {111} facets of the 3D islands.
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68.35.Rh Phase transitions and critical phenomena
68.35.Fx Diffusion; interface formation
68.35.Ja Surface and interface dynamics and vibrations
64.60.Q- Nucleation

Surface Fermi‐level changes in n‐type GaAs determined from Hall‐effect measurements

W. R. Miller and G. E. Stillman

Appl. Phys. Lett. 57, 2934 (1990); http://dx.doi.org/10.1063/1.103735 (3 pages) | Cited 4 times

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Changes in the surface Fermi‐level position in n‐type epitaxial GaAs samples are determined by Hall‐effect measurements of the corresponding changes in the sheet concentrations and theoretical calculations of the surface depletion thickness. The changes are induced and reversed repeatedly by alternating wet chemical treatments in hydrogen peroxide and ammonium hydroxide. This is the first known use of hydrogen peroxide to restore the surface Fermi level to near its starting value and demonstrate the repeated variation of the surface Fermi level by ammonium hydroxide. The results agree with the predictions of the advanced unified defect model and with published reports of increased band bending on n‐type material, rather than with conflicting reports of decreased band bending. The results also indicate that problems may exist with other techniques used to measure surface‐ potential changes.
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71.55.Eq III-V semiconductors
73.20.At Surface states, band structure, electron density of states
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors

High performance AlGaInP visible light‐emitting diodes

C. P. Kuo, R. M. Fletcher, T. D. Osentowski, M. C. Lardizabal, M. G. Craford, and V. M. Robbins

Appl. Phys. Lett. 57, 2937 (1990); http://dx.doi.org/10.1063/1.103736 (3 pages) | Cited 72 times

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The performance of surface‐emitting visible AlGaInP light‐emitting diodes (LEDs) is described. The devices have external quantum efficiencies greater than 2% and luminous efficiencies of 20 lm/A in the yellow (590 nm) spectral region. This performance is roughly ten times better than existing yellow LEDs and is comparable to the highest performance red AlGaAs LEDs currently available. The devices also perform favorably compared to existing devices in the orange and green spectral regions. Low‐pressure organometallic vapor phase epitaxy (OMVPE) is used to grow the epitaxial layers. The devices consist of a double heterostructure with an AlGaInP active region grown on a GaAs substrate.
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85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Critical current density of Bi‐Pb‐Ca‐Sr‐Cu‐O high Tc superconductors via rapidly quenched glass precursors

Masahiro Tatsumisago, Shinzo Tsuboi, Noboru Tohge, and Tsutomu Minami

Appl. Phys. Lett. 57, 2940 (1990); http://dx.doi.org/10.1063/1.104204 (2 pages) | Cited 2 times

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Two‐ and three‐step heat treatment processes of Bi1.6Pb0.4Ca2Sr2Cu3Ox rapidly quenched precursor glasses were examined to produce dense high Tc superconducting glass ceramics with a high critical current density Jc. The heat treatment at around the glass transition, which was expected to accelerate the nucleation rate, contributed to enhance the Jc values. The maximum Jc value of 1800 A cm−2 was obtained through the three‐step heat treatment performed firstly at 350 °C, for 1 h, then at 700 °C for 1 h, and finally at 855 °C for 20 h.
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74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
81.40.Rs Electrical and magnetic properties related to treatment conditions

Amplitude dependence of magnetic stiffness in bulk high‐temperature superconductors

S. A. Basinger, J. R. Hull, and T. M. Mulcahy

Appl. Phys. Lett. 57, 2942 (1990); http://dx.doi.org/10.1063/1.104205 (3 pages) | Cited 27 times

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Magnetic stiffness has been measured in several vibratory systems composed of a permanent magnet elastically suspended above a stationary high‐temperature superconductor at 77 K. For Y‐Ba‐Cu‐O, Ag/Y‐Ba‐Cu‐O, (Pb‐Bi)‐Sr‐Ca‐Cu‐O, and Tl‐Ba‐Ca‐Cu‐O sintered disks, both the vertical and horizontal magnetic stiffnesses increase strongly as the magnet’s oscillation decays, down to amplitudes of 1 μm. Vertical stiffness is about twice as strong as horizontal stiffness, and both are much stronger than the gradient of the levitation force for large monotonic changes in magnet height over the superconductor. These results are not deducible from contemporary magnetization measurements, and elastic pinning of flux lines are believed to contribute significantly to the stiffness.
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74.70.-b Superconducting materials other than cuprates
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
07.55.-w Magnetic instruments and components
74.25.-q Properties of superconductors
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