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12 Jun 2000

Volume 76, Issue 24, pp. 3501-3655

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Coherent terahertz emission from optically pumped intersubband plasmons in parabolic quantum wells

R. Bratschitsch, T. Müller, R. Kersting, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 76, 3501 (2000); http://dx.doi.org/10.1063/1.126687 (3 pages) | Cited 6 times

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We report on few-cycle terahertz (THz) emission from modulation-doped parabolic quantum wells. The quantum wells are optically excited by near-infrared femtosecond laser pulses. The observed THz emission corresponds to the intersubband plasmon of the parabolic quantum well. The emission frequency is independent of the number of optically generated carriers. We identify the excitation mechanism of the intersubband plasmon and hence THz emission to be ultrafast field screening. This mechanism allows for an optically driven THz emission from a completely symmetric nanostructure, in contrast to quantum beats which require a broken symmetry for their excitation. © 2000 American Institute of Physics.
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78.70.Gq Microwave and radio-frequency interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Fd III-V semiconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals

Yoshinobu Maeda and Yoichi Matsuoka

Appl. Phys. Lett. 76, 3504 (2000); http://dx.doi.org/10.1063/1.126688 (3 pages)

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All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals were demonstrated using a feedback ring resonator and an erbium-doped fiber amplifier. The output modulation degree depends on the dosage of erbium and the amplifier gain. The maximum value was 83% when the input modulation degree was 55%. The inverted output signal was amplified by approximately ten times as large as the input signal. The output modulation degree increased abruptly at an amplifier gain of more than 25 dB when it has feedback. The device was characterized by the property that optical signals for 1.53 μm light can be inverted and amplified. © 2000 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
85.70.Ge Ferrite and garnet devices

Dynamics of amplified spontaneous emission in InAs/GaAs quantum dots

C. Lingk, G. von Plessen, J. Feldmann, K. Stock, M. Arzberger, G. Böhm, M.-C. Amann, and G. Abstreiter

Appl. Phys. Lett. 76, 3507 (2000); http://dx.doi.org/10.1063/1.126689 (3 pages) | Cited 11 times

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We investigate the dynamics of amplified spontaneous emission (ASE) in self-assembled InAs/GaAs quantum dots, using pulsed optical excitation of an edge-emitting sample at room temperature. A material gain of 1.5×104 cm−1 is determined for 800 nm excitation with 1.5 μJ/cm2 pulses. Using photoluminescence up-conversion, we show that increases in both electron–hole pair density and photon density in the excited stripe cause a significant decrease in the decay time from 2.2 ns, corresponding to spontaneous emission, to about 0.9 ns, corresponding to stimulated emission or ASE. A carrier capture time of 10 ps limits the onset of the ASE process for short stripe lengths. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.45.+h Stimulated emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Self-assembled ErAs islands in GaAs for optical-heterodyne THz generation

C. Kadow, A. W. Jackson, A. C. Gossard, S. Matsuura, and G. A. Blake

Appl. Phys. Lett. 76, 3510 (2000); http://dx.doi.org/10.1063/1.126690 (3 pages) | Cited 21 times

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We report photomixer devices fabricated on a material consisting of self-assembled ErAs islands in GaAs, which is grown by molecular beam epitaxy. The devices perform comparably and provide an alternative to those made from low-temperature-grown GaAs. The photomixer’s frequency response demonstrates that the material is a photoconductor with subpicosecond response time, in agreement with time-resolved differential reflectance measurements. The material also provides the other needed properties such as high photocarrier mobility and high breakdown field, which exceeds 2×105 V/cm. The maximum output power before device failure at frequencies of 1 THz was of order 0.1 μW. This material has the potential to allow engineering of key photomixer properties such as the response time and dark resistance. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
77.22.Jp Dielectric breakdown and space-charge effects

Photoluminescence of ZnS:Mn embedded in three-dimensional photonic crystals of submicron polymer spheres

Ji Zhou, Y. Zhou, S. Buddhudu, S. L. Ng, Y. L. Lam, and C. H. Kam

Appl. Phys. Lett. 76, 3513 (2000); http://dx.doi.org/10.1063/1.126691 (3 pages) | Cited 44 times

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ZnS:Mn has been in-filled in photonic crystals of submicron polymer spheres. The effect of the photonic band gap on the photoluminescence (PL) properties of ZnS:Mn has been investigated. Because of the overlap of the transmission dip of the photonic crystal and the photoluminescence band of ZnS:Mn, both suppression and enhancement in the PL of the phosphor have been observed. A strong dependence of the fluorescence lifetime on the emission wavelength in the range of the stop band has been found. This strong dependence is believed to arise from the very low photon density of state within the stop band of the ZnS:Mn in-filled photonic crystal as result of a high dielectric contrast between ZnS:Mn and the polystyrene spheres. © 2000 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics

Structure and morphology of polymer-stabilized cholesteric diffraction gratings

S. W. Kang, S. Sprunt, and L. C. Chien

Appl. Phys. Lett. 76, 3516 (2000); http://dx.doi.org/10.1063/1.126692 (3 pages) | Cited 24 times

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We report a study of polymer network morphology in planar diffraction gratings formed from polymer-stabilized cholesteric liquid crystals. Photopolymerizing a mesogenic monomer yields a regular sawtooth morphology, composed of polymer sheets running at an acute angle between thick, uniformly aligned bundles which reside on the opposing substrates. To explain this morphology and evidence of two grating vectors in the diffraction pattern, we propose a model for the liquid-crystal director where out-of-phase twists at the surfaces gear into an interior twist, which has half the period of the surface twist, via splay distortions running between the substrates. The morphology also changes significantly when a nonmesogenic monomer is substituted or when selectively polarized states of UV radiation are used to cure the polymer. © 2000 American Institute of Physics.
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42.79.Dj Gratings
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.25.H- Macromolecular and polymers solutions; polymer melts

Optically pumped InAs quantum dot microdisk lasers

H. Cao, J. Y. Xu, W. H. Xiang, Y. Ma, S.-H. Chang, S. T. Ho, and G. S. Solomon

Appl. Phys. Lett. 76, 3519 (2000); http://dx.doi.org/10.1063/1.126693 (3 pages) | Cited 57 times

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We have achieved lasing in InAs quantum dot embedded GaAs microdisks under optical pumping. Above the lasing threshold, a drastic increase of emission intensity is accompanied by a decrease of the spectral linewidth of the whispering gallery modes. The laser light is linearly polarized. The polarization direction is parallel to the disk plane. The wide gain spectrum of quantum dots allows simultaneous lasing in several whispering gallery modes of a microdisk. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers

Tetravalent tin complex with high electron affinity for electroluminescent applications

X. T. Tao, M. Shimomura, H. Suzuki, S. Miyata, and H. Sasabe

Appl. Phys. Lett. 76, 3522 (2000); http://dx.doi.org/10.1063/1.126694 (3 pages) | Cited 2 times

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We report the synthesis and electroluminescent properties of the organometallic complex diphenyltin bis-hydroxyquinoline (Sph2q2). The complex was prepared by the reaction of diphenyltin dichloride with 8-hydroxyquinoline and shows an absorption cutoff wavelength of 460 nm and bright photoluminescence with a peak wavelength at 508 nm. The ionization potential of Sph2q2 was determined to be ∼6.0 eV by photoemission apparatus, and the electron affinity is estimated to be 3.3 eV. Sph2q2 was used as an emitting and electron injection layer in bilayer devices. The electroluminescence (EL) properties and charge injection properties of Sph2q2 are characterized. Sph2q2 is easily soluble in common organic solvents and further modification of its properties is possible. The results indicate that tetravalent tin complexes are potential emitting and charge injection materials for EL applications. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
85.60.Jb Light-emitting devices

Electro-optic polymer modulators for 1.55 μm wavelength using phenyltetraene bridged chromophore in polycarbonate

Min-Cheol Oh, Hua Zhang, Attila Szep, Vadim Chuyanov, William H. Steier, Cheng Zhang, Larry R. Dalton, Hernan Erlig, Boris Tsap, and Harold R. Fetterman

Appl. Phys. Lett. 76, 3525 (2000); http://dx.doi.org/10.1063/1.126695 (3 pages) | Cited 24 times

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Electro-optic polymer modulators operating at 1550 nm are demonstrated based on a nonlinear optical polymer of a phenyltetraene bridged chromophore in polycarbonate. It has a large electro-optic coefficient (r33 = 55 pm/V at 1550 nm), good thermal stability (90 °C), and low loss (1.7 dB/cm). A thin protective layer was used in the fabrication of ridge waveguides on the nonlinear polymer. We measured Vπ of 2.4 and 3.7 V at 1300 and 1550 nm, respectively. The chip loss of the modulator at both wavelengths was 5 dB, not including fiber coupling losses. © 2000 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Jq Electro-optical effects

Solution of the dark state problem in antiferroelectric liquid crystal displays

Koen D’havé, Per Rudquist, Sven T. Lagerwall, Herman Pauwels, Witold Drzewinski, and Roman Dabrowski

Appl. Phys. Lett. 76, 3528 (2000); http://dx.doi.org/10.1063/1.126696 (3 pages) | Cited 72 times

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So far, it has proven impossible to achieve an acceptable dark state between crossed polarizers for antiferroelectric liquid crystals (AFLCs), which otherwise would have an enormous potential for electro-optic applications, in particular for high-resolution full color displays. The reason lies in static and dynamic spatial fluctuations of the optic axis. As both have intrinsic causes it is not likely that the problem is ever going to be solved by improvement in alignment and addressing methods. We show that if the directors in alternating layers are orthogonal to each other, the AFLC acquires new optical properties such that the problem is eliminated, and a dark state extinction is achieved which is only limited by the quality of the polarizers. After having synthesized such a material, we have been able to demonstrate the predicted unique electro-optical properties of this new class of AFLC materials. © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
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Towards ordered arrays of magnetic semiconductor quantum wires

Limei Chen, Peter J. Klar, Wolfram Heimbrodt, Felix Brieler, and Michael Fröba

Appl. Phys. Lett. 76, 3531 (2000); http://dx.doi.org/10.1063/1.126697 (3 pages) | Cited 27 times

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The diluted magnetic semiconductor (Cd, Mn)S has been incorporated into ordered wire-like pores of hexagonal mesoporous silica. X-ray and Raman spectra reveal the wurtzite structure of the incorporated material. Photoluminescence and photoluminescence excitation spectra of the (Cd, Mn)S-wire samples show clearly the optical transitions within the half-filled Mn 3d shell, typical for Mn incorporated in a II–VI host material. The blueshift of the absorption edge of (Cd, Mn)S-wire samples compared to reference crystalline and powder samples of the same Mn content is due to quantum confinement in the nanowires. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
78.66.Hf II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors

Strain relief via trench formation in Ge/Si(100) islands

S. A. Chaparro, Y. Zhang, and Jeff Drucker

Appl. Phys. Lett. 76, 3534 (2000); http://dx.doi.org/10.1063/1.126698 (3 pages) | Cited 56 times

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Trenches formed at Ge/Si(100) island bases become an effective strain-relief mechanism at high growth temperatures. Trenches result from diffusion of the most highly strained material to regions of lower strain. The trench depth self-limits, scaling linearly with island diameter. A simple atomistic model of island elasticity indicates that this self-limiting behavior is of kinetic rather than energetic origin. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
81.05.Cy Elemental semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Tuning of conduction intersublevel absorption wavelengths in (In, Ga)As/GaAs quantum-dot nanostructures

Dong Pan, Elias Towe, Steve Kennerly, and Mei-Ying Kong

Appl. Phys. Lett. 76, 3537 (2000); http://dx.doi.org/10.1063/1.126699 (3 pages) | Cited 3 times

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We demonstrate that by increasing the amount of (In, Ga)As deposit in a quantum dot layer, the intersublevel absorption wavelength for (In, Ga)As/GaAs quantum-dot infrared photodetectors can be blue-shifted from 15 to 10 μm while the photoluminescence peak is red-shifted. We directly compare the measured energy spacing between intersublevels obtained from infrared absorption spectroscopy with those obtained from photoluminescence spectroscopy. We find that the intersublevel energy spacing determined from absorption measurements is much larger than that obtained from the photoluminescence measurements. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Carrier and light trapping in graded quantum-well laser structures

G. Aichmayr, M. D. Martín, H. van der Meulen, C. Pascual, L. Viña, J. M. Calleja, F. Schafer, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 76, 3540 (2000); http://dx.doi.org/10.1063/1.126700 (3 pages) | Cited 1 time

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We investigated the carrier and light trapping in GaInAs/AlGaAs single-quantum-well laser structures by means of time-resolved photoluminescence and Raman spectroscopy. The influence of the shape and depth of the confinement potential and of the cavity geometry was studied by using different AlGaAs/GaAs short-period superlattices as barriers. Our results show that grading the optical cavity improves considerably both carrier and light trapping in the quantum well, and that the trapping efficiency is enhanced by increasing the graded confining potential. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
78.47.-p Spectroscopy of solid state dynamics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Nanoscale InGaAs concave disks fabricated by heterogeneous droplet epitaxy

Takaaki Mano, Katsuyuki Watanabe, Shiro Tsukamoto, Nobuyuki Koguchi, Hiroshi Fujioka, Masaharu Oshima, Chae-Deok Lee, Jae-Young Leem, Hwack Joo Lee, and Sam Kyu Noh

Appl. Phys. Lett. 76, 3543 (2000); http://dx.doi.org/10.1063/1.126701 (3 pages) | Cited 28 times

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The detailed cross-sectional structure of InGaAs quantum dots fabricated by a heterogeneous droplet epitaxy method was investigated by means of cross-sectional transmission electron microscopy observation. It was confirmed that concave disks without any dislocations or wetting layer were formed at the upper part of the flat surface. This result was consistent with the change of photoluminescence intensity and peak position. The sizes of the disks were estimated to be 30 and 12 nm in lateral and vertical directions, respectively. From this estimation, the occurrence of a phase-separation effect is suggested. © 2000 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
64.75.-g Phase equilibria
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Substitutional carbon incorporation during Si1−x−yGexCy growth on Si(100) by molecular-beam epitaxy: Dependence on germanium and carbon

J. P. Liu and H. J. Osten

Appl. Phys. Lett. 76, 3546 (2000); http://dx.doi.org/10.1063/1.126702 (3 pages) | Cited 8 times

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We present results on the kinetics of substitutional carbon incorporation during growth of Si1−x−yGexCy alloys on silicon (100) using solid-source molecular-beam epitaxy. Substitutional carbon concentration decreases with increasing germanium content for samples grown at 400 °C with the same carbon flux and growth rate. The reduction in substitutional carbon concentration is small at low carbon flux, increasing significantly at higher carbon fluxes. The results indicate that the effect of either Ge or C concentration can dominate the substitutional C incorporation, depending on the total C concentration range. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.up Other materials
81.05.Hd Other semiconductors

Exciton spectra of ZnO epitaxial layers on lattice-matched substrates grown with laser-molecular-beam epitaxy

T. Makino, C. H. Chia, N. T. Tuan, Y. Segawa, M. Kawasaki, A. Ohtomo, K. Tamura, and H. Koinuma

Appl. Phys. Lett. 76, 3549 (2000); http://dx.doi.org/10.1063/1.126703 (3 pages) | Cited 108 times

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Optical properties in undoped-ZnO epilayers grown by the laser-molecular-beam epitaxy method on lattice-matched ScAlMgO4 substrates were investigated. The absorption spectrum at 5 K has two sharp peaks, both of which are attributed to resonances of A and B excitons, which reflect a small nonradiative damping constant of excitons as well as high film crystallinity accomplished by the virtue of lattice matching. The coupling strengths of exciton-acoustic phonon and of exciton–longitudinal-optical phonon were directly determined from the temperature dependence of exciton absorption spectra independently for A and B excitons, which are close in energy and obey the same selection rule for each other. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.kk Phonon interactions with other quasiparticles

Strain relaxation mechanism for hydrogen-implanted Si1−xGex/Si(100) heterostructures

H. Trinkaus, B. Holländer, St. Rongen, S. Mantl, H.-J. Herzog, J. Kuchenbecker, and T. Hackbarth

Appl. Phys. Lett. 76, 3552 (2000); http://dx.doi.org/10.1063/1.126704 (3 pages) | Cited 50 times

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A mechanism of strain relief of H+ ion implanted and annealed pseudomorphic Si1−xGex/Si(100) heterostructures grown by molecular beam epitaxy is proposed and analyzed. Complete strain relaxation was obtained at temperatures as low as 800 °C and the samples appeared free of threading dislocations within the SiGe layer to the limit of transmission electron microscopy analysis. In our model, H filled nanocracks are assumed to generate dislocation loops, which glide to the interface where they form strain relieving misfit segments. On the basis of this assumption, the conditions for efficient strain relaxation are discussed. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.uf Ge and Si
68.60.Bs Mechanical and acoustical properties

Patterned growth of individual and multiple vertically aligned carbon nanofibers

V. I. Merkulov, D. H. Lowndes, Y. Y. Wei, G. Eres, and E. Voelkl

Appl. Phys. Lett. 76, 3555 (2000); http://dx.doi.org/10.1063/1.126705 (3 pages) | Cited 196 times

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The results of studies of patterned growth of vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots of various diameters and Ni lines with variable widths and shapes were fabricated using electron beam lithography and evaporation, and served for catalytic growth of VACNFs whose structure was determined by high resolution transmission electron microscopy. It is found that upon plasma pre-etching and heating up to 600–700 °C, thin films of Ni break into droplets which initiate the growth of VACNFs. Above a critical dot size multiple droplets are formed, and consequently multiple VACNFs grow from a single evaporated dot. For dot sizes smaller than the critical size only one droplet is formed, resulting in a single VACNF. In the case of a patterned line, the growth mechanism is similar to that from a dot. VACNFs grow along the line, and above a critical linewidth multiple VACNFs are produced across the line. The mechanism of the formation of single and multiple catalyst droplets and subsequently of VACNFs is discussed. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Formation of icosahedral quasicrystalline phase in Zr70Ni10M20(M=Pd, Au, Pt) ternary metallic glasses

J. Saida, M. Matsushita, C. Li, and A. Inoue

Appl. Phys. Lett. 76, 3558 (2000); http://dx.doi.org/10.1063/1.126706 (3 pages) | Cited 57 times

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An icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary metallic glasses with two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase are 687 K for Pd, 754 K for Au and 783 K for Pt at a heating rate of 0.67 K s−1. The size of the icosahedral particles is in the range of 5–20 nm. The second crystallization reaction results in the formation of Zr2Ni+Zr2Pd and Zr2Ni+ZrPt phases in the Zr–Ni–Pd and Zr–Ni–Pt alloys, respectively, and Zr3Au phase in the Zr–Ni–Au alloy through a single exothermic reaction. The formation of nanoscale icosahedral phase indicates the possibility that icosahedral short-range order exists in the glassy state. © 2000 American Institute of Physics.
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61.44.Br Quasicrystals
61.43.Fs Glasses
64.70.K- Solid-solid transitions
81.30.Mh Solid-phase precipitation
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Initial oxynitridation of a Si(001)-2×1 surface by NO

Noriyuki Miyata, Heiji Watanabe, and Masakazu Ichikawa

Appl. Phys. Lett. 76, 3561 (2000); http://dx.doi.org/10.1063/1.126707 (3 pages) | Cited 10 times

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We investigated the initial oxynitridation of an atomically flat Si(001)-2×1 surfaces by NO. The first oxynitridation, in which NO reacts with the first Si layer on the Si(001)-2×1 surface, takes place in a layer-by-layer manner caused by two-dimensional nucleation. However, further oxynitridation for the second Si layer proceeds in a three-dimensional manner in which the atomic-scale roughness at the oxynitride/Si interface increases. In addition, it was found that N is incorporated as N ≡ Si3, even though the oxynitride is ultrathin. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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Micromechanical cantilever magnetometer with an integrated two-dimensional electron system

M. P. Schwarz, D. Grundler, I. Meinel, Ch. Heyn, and D. Heitmann

Appl. Phys. Lett. 76, 3564 (2000); http://dx.doi.org/10.1063/1.126708 (3 pages) | Cited 36 times

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We have realized a micromechanical cantilever magnetometer with an integrated two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure grown by molecular-beam epitaxy (MBE). The cantilever was defined by lithography and wet-etched selectively to a MBE-grown stop layer. We reach a sensitivity of 10−13 J/T, which enables us to study the de Haas–van Alphen effect in a 2DES of only 0.04 cm2 area. We demonstrate that, at low temperature, the oscillation amplitude at even filling factors is enhanced by a factor of up to 1.8 with respect to the single-particle value. © 2000 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.10.Cm Micromechanical devices and systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.43.-f Quantum Hall effects
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Er–carrier interaction and its effects on the Er3+ luminescence of erbium-doped Si/SiO2 superlattices

Jung H. Shin, Ji-Hong Jhe, Se-Young Seo, Yong Ho Ha, and Dae Won Moon

Appl. Phys. Lett. 76, 3567 (2000); http://dx.doi.org/10.1063/1.126740 (3 pages) | Cited 13 times

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The Er–carrier interaction and its effects on the Er3+ photoluminescence properties of erbium-doped Si/SiO2 superlattices are investigated. The interaction between the erbium atoms and the electronic carriers was controlled by doping erbium into the SiO2 layers only and by depositing buffer layers of pure SiO2 between the erbium-doped SiO2 layers and the Si layers. We demonstrate that by controlling the erbium-carrier interaction, a three orders of the magnitude enhancement of the Er3+ luminescence intensity and a nearly complete suppression of the temperature-induced quenching of Er3+ luminescence can be achieved while still allowing the Er3+ ions to be excited by the carriers. We identify the asymmetry between the dominant carrier-mediated excitation and the de-excitation paths of Er3+ ions as the possible cause for the observed effects. © 2000 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

Positively charged defects associated with self-assembled quantum dot formation

A. E. Belyaev, S. T. Stoddart, P. M. Martin, P. C. Main, L. Eaves, and M. Henini

Appl. Phys. Lett. 76, 3570 (2000); http://dx.doi.org/10.1063/1.126709 (3 pages) | Cited 4 times

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Capacitance measurements are used to investigate a series of single-barrier n-i-n GaAs/AlAs/GaAs heterostructures incorporating a layer of self-assembled InAs quantum dots into the AlAs barrier. They reveal a low-density, excess positive charge in the AlAs barrier which we attribute to defects associated with quantum dot formation. The quantity of positive charge is proportional to the amount of AlAs deposited on top of the dots. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.61.Ey III-V semiconductors

Surface segregation determination by epitaxy temperature steps

E. Kasper and M. Oehme

Appl. Phys. Lett. 76, 3573 (2000); http://dx.doi.org/10.1063/1.126710 (3 pages) | Cited 1 time

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A method for determination of surface segregation during molecular-beam epitaxy is proposed. At constant beam fluxes, the temperature is switched which causes a segregation-dependent doping profile. The segregation ratio is extracted from the integrated profile avoiding problems with limited depth resolution in the nanometer regime. The method was tested with boron segregation on (100) silicon (T = 500–700 °C). A clear proof of the concentration dependence of the boron segregation is given. At 600 °C, the segregation ratio rs decreases from 55 to 12 nm when the doping level is increased from 3.5×1018 to 7.5×1019 cm−3. © 2000 American Institute of Physics.
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64.75.-g Phase equilibria
81.05.Cy Elemental semiconductors
68.55.Nq Composition and phase identification
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.S- Impurities in crystals
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