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13 Oct 1997

Volume 71, Issue 15, pp. 2061-2216

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Frictional imaging in a scanning near-field optical/atomic-force microscope by a thin step etched optical fiber probe

Hiroshi Muramatsu, Norio Chiba, and Masamichi Fujihira

Appl. Phys. Lett. 71, 2061 (1997); http://dx.doi.org/10.1063/1.120446 (3 pages) | Cited 13 times

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Use of a thin step etched optical fiber probe in a scanning near-field optical/atomic-force microscope (SNOM/AFM) produced frictional imaging. The probe was fabricated by the etching of an optical fiber to decrease its diameter and sharpen the tip end with a HF solution and by irradiating a CO2 laser beam to bend the tip. The spring constant of the thin probe is 100 times smaller than that of a conventional optical fiber probe, which allows the probe to be used as a contact AFM mode and in frictional imaging. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force microscopes
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
62.20.D- Elasticity
62.20.Qp Friction, tribology, and hardness

A highly efficient organic second-order nonlinear optical crystal based on a donor-acceptor substituted 4-nitrophenylhydrazone

Feng Pan, Man Shing Wong, Martin Bösch, Christian Bosshard, Urs Meier, and Peter Günter

Appl. Phys. Lett. 71, 2064 (1997); http://dx.doi.org/10.1063/1.119343 (3 pages) | Cited 4 times

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We present a novel organic crystal, 5-(methylthio)-thiophenecarboxaldehyde-4-nitrophenylhydrazone, with a large effective phase-matchable nonlinear optical coefficient, deff=29±3 pm/V at λ=1318 nm. Single crystals of dimensions up to 25×5×5 mm3 were grown. The large off-diagonal nonlinear optical coefficients can be explained with the two-dimensional geometry of the chromophores in the crystal lattice. Our crystal is ideally suited for optic parametric oscillation in the wavelength range from 1000 to 2500 nm. © 1997 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
42.70.Mp Nonlinear optical crystals

Photoluminescence properties of cubic GaN grown on GaAs(100) substrates by metalorganic vapor phase epitaxy

J. Wu, H. Yaguchi, K. Onabe, R. Ito, and Y. Shiraki

Appl. Phys. Lett. 71, 2067 (1997); http://dx.doi.org/10.1063/1.119344 (3 pages) | Cited 36 times

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Photoluminescence (PL) measurements were performed on cubic GaN films grown on GaAs(100) substrates by metalorganic vapor phase epitaxy. The cubic GaN films show a high optical quality that enables us to study the PL spectra in detail. From temperature and excitation intensity dependence, the emission lines at 3.274 and at 3.178 eV were assigned to the excitonic transition and the donor–acceptor pair transition, respectively. We also observed two additional emission lines at 3.088 and 3.056 eV. An excitonic emission at 3.216 eV with full width half maximum value as small as 73 meV was observed at 300 K. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

Third-order nonlinear optical properties of trans-dihydroxy-1,6,11,16-tetra(tert.butyl)porphyrazine germanium thin films

Hari Singh Nalwa, Michael Klaus Engel, Michael Hanack, and Georg Pawlowski

Appl. Phys. Lett. 71, 2070 (1997); http://dx.doi.org/10.1063/1.119386 (3 pages) | Cited 4 times

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Third-order nonlinear optical susceptibilities χ(3) of trans-dihydroxy-1,6,11,16-tetra-(tert.butyl) porphyrazine germanium [t-Bu4PazGe(OH)2] thin films measured by the third-harmonic generation technique are reported for the first time. The χ(3)(−3ω;ω,ω,ω) value as high as 1.3×10−11 esu was observed from a dominant three-photon resonance. The χ(3) values of porphyrazine germanium derivative are analogous to metallophthalocyanines and these results imply that axial substitution is beneficial for enhancing third-order optical nonlinearity. © 1997 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Measurements of the triplet state nonlinearity of C60 in toluene using a Z-scan technique with a nanosecond laser

Feng Li, Yinglin Song, Kun Yang, Shutian Liu, and Chunfei Li

Appl. Phys. Lett. 71, 2073 (1997); http://dx.doi.org/10.1063/1.119345 (3 pages) | Cited 6 times

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Triplet state nonlinearity of C60 in toluene is studied using the Z-scan technique with 8 ns, 532 nm pulses from a Q-switched Nd:YAG laser. Compared with the Z-scan results of C60 in toluene and iodine in toluene with proper concentration, the solvent instantaneous nonlinearity and the thermal nonlinearity resulting from the C60 intersystem crossing and excited state absorption are estimated. The real part of the C60 triplet state molecular polarizability is obtained. © 1997 American Institute of Physics.
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42.65.-k Nonlinear optics
36.40.Vz Optical properties of clusters
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.70.Dk Environmental and solvent effects

Design and performance of singular electric field terahertz photoconducting antennas

Y. Cai, I. Brener, J. Lopata, J. Wynn, L. Pfeiffer, and J. Federici

Appl. Phys. Lett. 71, 2076 (1997); http://dx.doi.org/10.1063/1.119346 (3 pages) | Cited 42 times

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We present new designs of more efficient terahertz (THz) radiation emitters and detectors enhanced by electric field singularities using sharp and laterally offset electrodes. We compare the performances of the terahertz emission and different polarization properties resulting from these structures. An average THz radiation power of 3 μW is achieved under 20 mW excitation, calibrated by free space electro-optic sampling. We also study the gap size dependence of the THz radiation, and find an absence of a positive electrode effect in the small gap limit. © 1997 American Institute of Physics.  
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84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices

Photoluminescence and far-infrared absorption in Si-doped self-organized InAs quantum dots

J. Phillips, K. Kamath, X. Zhou, N. Chervela, and P. Bhattacharya

Appl. Phys. Lett. 71, 2079 (1997); http://dx.doi.org/10.1063/1.119347 (3 pages) | Cited 37 times

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We report far-infrared absorption in directly doped self-organized InAs quantum dots. Photoluminescence spectra demonstrate a blue shift in peak intensity for increasing doping in the quantum dots. Far-infrared absorption measurements using a Fourier transform infrared spectrometer show absorption in the range of 13–18 μm for quantum dots with Al0.15Ga0.85As and GaAs as the barrier material. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Optical detection for scanning microdeformation microscopy

B. Cretin and P. Vairac

Appl. Phys. Lett. 71, 2082 (1997); http://dx.doi.org/10.1063/1.119348 (3 pages) | Cited 13 times

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Scanning microdeformation microscopy is a kind of ac contact force microscopy sensitive to the variations of the local elastic constants of the investigated material. In this letter a new optical interferometer designed for detecting the small displacement of the cantilever is reported. The setup is described and some applications of the laser probe to scanning microdeformation microscopy are demonstrated. © 1997 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.60.Ly Interferometers
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Manipulation of liquid crystal textures with a focused near infrared laser beam

Jun-ichi Hotta, Keiji Sasaki, and Hiroshi Masuhara

Appl. Phys. Lett. 71, 2085 (1997); http://dx.doi.org/10.1063/1.119349 (3 pages) | Cited 12 times

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Optical manipulation of disclinations and defects in liquid crystal films was demonstrated and discussed in terms of mass transfer induced by radiation pressure and of molecular rotation under the optical electric field. Orientation of liquid crystal molecules was controlled by changing the polarization direction of a focused cw laser beam. A disclination line could be deformed by moving the focal spot, just like drawing a bow. A point defect followed the laser beam so that it could be freely transported in the film. When two disclination points were optically manipulated to become fused, the defects disappeared immediately and did not return after switching off the laser. © 1997 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Jf Defects in liquid crystals
68.15.+e Liquid thin films
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Edge detection in phase-change optical data storage

Chubing Peng, M. Mansuripur, W. M. Kim, and S. G. Kim

Appl. Phys. Lett. 71, 2088 (1997); http://dx.doi.org/10.1063/1.119350 (3 pages) | Cited 2 times

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A direct mark edge detection scheme for readout in phase-change optical disk systems is described. The medium for edge detetection must be optimized to have a 90° phase difference between the amorphous mark and the crystalline space. Theoretical analysis and numerical simulation have shown that the readout signal using mark edge detection is as good as that using conventional detection of reflectivity for long marks and superior for short marks. Noise level at the output of differential edge detection is lower than that at the output of conventional detection. We also show experimental results that confirm these predictions. © 1997 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps

Chemical vapor deposition of poly (p-phenylene vinylene) based light emitting diodes with low turn-on voltages

Kathleen M. Vaeth and Klavs F. Jensen

Appl. Phys. Lett. 71, 2091 (1997); http://dx.doi.org/10.1063/1.119351 (3 pages) | Cited 20 times

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We report fabrication of single layer poly (p-phenylene vinylene) (PPV) light emitting diodes with low turn-on voltages by chemical vapor deposition of dihalo p-xylenes. Devices made from dibromo p-xylene exhibit turn-on fields of 2×106 V/cm, which is in good agreement with solution processed PPV devices. Devices made from dichloro p-xylene, however, have significantly lower turn-on fields of 6.5×105 V/cm. The electroluminescent output of bilayer PPV/tris (8-hydroxyquinoline) aluminum devices made from the two monomers suggests that the chlorine based polymer may have improved electron transport characteristics compared to solution processed polymer, which is tentatively attributed to residual chlorine from the thermal conversion process. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.35.-x Polymers: properties; reactions; polymerization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Fi Electroluminescence

Z-scan measurements with Fourier analysis in ion-doped solids

C. R. Mendonça, L. Misoguti, and S. C. Zilio

Appl. Phys. Lett. 71, 2094 (1997); http://dx.doi.org/10.1063/1.119352 (3 pages) | Cited 6 times

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We report on the measurement of nonlinear refraction in ion-doped solids with a method that combines the single-beam Z-scan technique and a Fourier analysis of the transmittance time evolution. The laser beam is modulated at a frequency f and the Fourier components at f and 2f are shown to be related, respectively, to linear and nonlinear refractions. Their ratio is used to eliminate spurious linear effects as a way of increasing the sensitivity of the measurement. With this method we are able to measure nonlinear phase changes of a few tens of mrad, corresponding to wave front distortions smaller than λ/105. Moreover, the technique can discriminate nonlinear processes with different relaxation times. © 1997 American Institute of Physics.
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42.65.-k Nonlinear optics
78.20.Bh Theory, models, and numerical simulation

The effects of different interfacial environments on the optical nonlinearity of nanometer-sized CdO organosol

Xiaochun Wu, Rongyao Wang, Bingsuo Zou, Pengfei Wu, Li Wang, Jiren Xu, and Wei Huang

Appl. Phys. Lett. 71, 2097 (1997); http://dx.doi.org/10.1063/1.120424 (3 pages) | Cited 7 times

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The third-order optical nonlinearity χ(3) of nanometer-sized CdO with different interfacial environments has been measured using the Z-scan technique. The real and imaginary parts of χ(3) at 800 nm have been determined to be: −1.55×10−16 m2/W and 0.91 cm/GW for CdO–CTAB (cetyltrimethyl ammonium bromide) organosol, and −6.97×10−16 m2/W and 8.64 cm/GW for CdO–DBS (dodecylbenzene sulfonate) organosol. Origins of the optical nonlinearity and the effects of the interfacial conditions have been discussed. The optical Stark effect (OSE) and surface trapped states are the possible origins of the observed optical nonlinearity. The possible enhancement of optical nonlinearity of nanoparticles by intentional interfacial modification is suggested. © 1997 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
82.70.Gg Gels and sols
73.20.At Surface states, band structure, electron density of states
78.20.Jq Electro-optical effects

Role of extraordinary waves in uniform electron cyclotron resonance plasmas

Yoko Ueda and Yoshinobu Kawai

Appl. Phys. Lett. 71, 2100 (1997); http://dx.doi.org/10.1063/1.120416 (3 pages) | Cited 14 times

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The extraordinary wave (X wave) was found to contribute to the uniformity of an electron cyclotron resonance (ECR) plasma whose electron density is about 1–2×1017 m−3. The X wave propagated radially in the plasma both before and after the ECR point. The electron density jump occurred when the electron density was equal to the cutoff density of the X wave at the ECR point. Upon increasing the electron density, only the whistler wave propagated in a high density plasma of about 1018 m−3. © 1997 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.50.Gj Plasma heating by particle beams

Observation of body centered cubic Cu in Cu/Nb nanolayered composites

H. Kung, Y-C. Lu, A. J. Griffin, M. Nastasi, T. E. Mitchell, and J. D. Embury

Appl. Phys. Lett. 71, 2103 (1997); http://dx.doi.org/10.1063/1.119611 (3 pages) | Cited 23 times

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The deposition of thin alternating layers of Cu and Nb on Si(100) substrates has been studied by transmission electron microscopy as a function of layer thickness. For layer thickness above 25 Å, there is a strong texture orientation relationship with the close packed planes of fcc Cu parallel to close packed planes of bcc Nb, forming the so-called “Kurdjumov-Sachs” orientation relationship. However, at thicknesses of under 12 Å, the Cu is constrained to grow as a slightly distorted bcc structure. It is thought that, when it reaches a critical thickness between 12 and 20 Å, the bcc Cu loses coherency and transforms martensitically to the fcc phase, resulting in the observed Kurdjumov–Sachs orientation relationship. Electron energy loss spectroscopy observations indicate a difference of 2 eV in the L3 edge suggesting that the Fermi energy is lower in the constrained bcc form of Cu than in the equilibrium fcc structure. © 1997 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
79.20.Kz Other electron-impact emission phenomena

Mechanism for Si island retention in buried SiO2 layers formed by oxygen ion implantation

V. V. Afanas’ev, A. Stesmans, A. G. Revesz, and H. L. Hughes

Appl. Phys. Lett. 71, 2106 (1997); http://dx.doi.org/10.1063/1.119353 (3 pages) | Cited 2 times

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The density of silicon islands trapped in buried SiO2 layers produced by the implantation of oxygen into (001)Si substrates is monitored by atomic force microscopy for the oxygen dose range just above that required for continuous oxide formation. In addition to an exponential increase in the Si island density with oxygen dose, the regularly shaped remnants of an SiO2 phase with a reduced HF etch rate were found. The formation of this additional oxide phase as a result of enhanced internal pressure inside the Si crystal is proposed to account for the retention of Si islands in the buried oxide. © 1997 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.Cf Surface cleaning, etching, patterning

Thermal conductivity of isotopically enriched Si

W. S. Capinski, H. J. Maris, E. Bauser, I. Silier, M. Asen-Palmer, T. Ruf, M. Cardona, and E. Gmelin

Appl. Phys. Lett. 71, 2109 (1997); http://dx.doi.org/10.1063/1.119384 (3 pages) | Cited 67 times

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We have used an optical pump-and-probe technique to measure the temperature dependence of the thermal conductivity, κ(T), of isotopically pure Si. The sample was made from 99.7% 28Si by liquid phase epitaxy. Measurements were performed over the temperature range of 100–375 K. We found an increase in the thermal conductivity of isotopically pure Si, as compared to Si of natural isotopic abundance, throughout the entire temperature range. The results were theoretically reproduced by appropriately scaling the parameters used recently to fit the thermal conductivity of Ge samples with different isotopic compositions. A maximum in κ(T) of ∼ 4×104 W m−1 K−1 is predicted for 28Si at T ≃ 33 K. © 1997 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.Dv Thermal stability; thermal effects
78.47.-p Spectroscopy of solid state dynamics
78.66.Db Elemental semiconductors and insulators

Inelastic nuclear resonant scattering with sub-meV energy resolution

T. S. Toellner, M. Y. Hu, W. Sturhahn, K. Quast, and E. E. Alp

Appl. Phys. Lett. 71, 2112 (1997); http://dx.doi.org/10.1063/1.120448 (3 pages) | Cited 21 times

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With an undulator-based synchrotron source and a tunable x-ray monochromator, we produce an x-ray beam with a flux of 4×108 photons/s in an energy bandwidth of 920±110 μeV (ΔE/E ≈ 6.2×10−8) at a photon energy of 14.4 keV. The tunability of the monochromator allows for a measurement of lattice excitations in α-Fe using the technique of inelastic nuclear resonant scattering from 57Fe. The phonon density-of-states are extracted from the measurement and compared to the calculated phonon density-of-states derived from neutron-scattering measurements. © 1997 American Institute of Physics.
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61.05.cf X-ray scattering (including small-angle scattering)
07.85.Qe Synchrotron radiation instrumentation
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

High resolution positron-annihilation spectroscopy with a new positron microprobe

H. Greif, M. Haaks, U. Holzwarth, U. Männig, M. Tongbhoyai, T. Wider, K. Maier, J. Bihr, and B. Huber

Appl. Phys. Lett. 71, 2115 (1997); http://dx.doi.org/10.1063/1.120451 (3 pages) | Cited 20 times

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In cooperation with Zeiss/LEO GmbH, a monoenergetic positron source has been integrated in the electron optical system of a scanning electron microscope by help of a magnetic prism. The electron optics serves both to image the specimen with electrons and to form a positron microbeam that allows local positron-annihilation measurements with a resolution in the micron range. The fatigue damage profile along the cross section of a copper plate after a three-point bending test has been investigated. The obtained S-parameter profile coincides well with the expected fatigue damage distribution. © 1997 American Institute of Physics.
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78.70.Bj Positron annihilation
07.77.Ka Charged-particle beam sources and detectors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Polarization-dependent, laser-induced anisotropic photocrystallization of some amorphous chalcogenide films

V. Lyubin, M. Klebanov, M. Mitkova, and T. Petkova

Appl. Phys. Lett. 71, 2118 (1997); http://dx.doi.org/10.1063/1.119354 (3 pages) | Cited 17 times

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We report the observation of the influence of light polarization on the photocrystallization process and on the properties of crystallized films. Irradiation with linearly polarized He–Ne laser light results in the preparation of polycrystalline films with strong optical anisotropy (dichroism), the sign of which is determined by the direction of the electrical vector of light. The results obtained allow one to select from previously proposed mechanisms of photocrystallization. Large values of photoinduced dichroism in the films studied can be interesting for different applications of photoinduced anisotropy. © 1997 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.-a Thin film structure and morphology
61.43.Fs Glasses
61.82.Fk Semiconductors
78.20.Fm Birefringence
78.66.Jg Amorphous semiconductors; glasses

Influence of interstitial copper on diffusion length and lifetime of minority carriers in p-type silicon

A. A. Istratov, C. Flink, H. Hieslmair, T. Heiser, and E. R. Weber

Appl. Phys. Lett. 71, 2121 (1997); http://dx.doi.org/10.1063/1.119355 (3 pages) | Cited 23 times

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Though copper can be quenched interstitially in p-type silicon, it precipitates completely within 10–15 h at room temperature. The decay of concentration of interstitial copper in p-Si was monitored by capacitance–voltage characteristics (C–V) and surface photovoltage (SPV). It is shown that the time constant of change of minority carrier diffusion length, as measured by SPV, correlates well with the precipitation of interstitial copper. The capture cross section of interstitial copper is estimated to be in the range 10−15–10−17 cm2. It is shown that interstitial copper is far less deleterious than iron and can limit the diffusion length of commercial p-Si wafers only if its concentration is above 1013 cm−3. However, copper precipitates may be detrimental to lifetime even for much lower copper concentrations. © 1997 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
64.75.-g Phase equilibria
73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects

The determination of activation energy in quantum wells

Jinli Ding and Raphael Tsu

Appl. Phys. Lett. 71, 2124 (1997); http://dx.doi.org/10.1063/1.119356 (3 pages) | Cited 7 times

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The use of an Arrhenius plot of the temperature dependent current-voltage at some appropriate voltage leads to a temperature and voltage dependent activation energy, which is shown to be identical to the average energy carried by the electrons in flowing between the contacts separated by a quantum well structure. An optimal temperature range is limited by the highest temperature the system can tolerate without deleterious effects. The effective barrier height determined in a limited voltage range V ⩽ 2(E1−Ef)/e is equal to the ground state energy E1, of the quantum well structure. © 1997 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.Gk Tunneling

Single variant ordering in GaInAs/InP

R. Wirth, H. Seitz, M. Geiger, F. Scholz, A. Hangleiter, A. Mühe, and F. Phillipp

Appl. Phys. Lett. 71, 2127 (1997); http://dx.doi.org/10.1063/1.119357 (3 pages) | Cited 9 times

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Spontaneously ordered Ga0.47In0.53As grown on substrates with the (001) surface tilted 4° towards {111}B are studied using spectroscopic methods as well as x-ray diffraction, transmission electron diffraction and dark-field transmission electron microscopy. The single variant ordering is proved by the absence of one class of the ordering induced ½{111}B superlattice spots in transmission electron diffraction patterns as well as by the tilted polarization of the photoluminescence emerging from the samples cleaved edge. The temperature dependence of the luminescence peak position shows an anomalous behavior at low temperatures and a strong dependence of the peak position on the excitation power. From low temperature absorption measurements, we find a band gap reduction of 37 meV and a valence band splitting of 13.2 meV. © 1997 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.05.J- Electron diffraction and scattering
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds

Large excited state Stokes shift in crescent-shaped AlGaAs/GaAs quantum wires

Xue-Lun Wang, Mutsuo Ogura, Hirofumi Matsuhata, and Ali Hamoudi

Appl. Phys. Lett. 71, 2130 (1997); http://dx.doi.org/10.1063/1.119358 (3 pages) | Cited 19 times

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The Stokes shifts of the ground and the excited states in a crescent-shaped AlGaAs/GaAs quantum wire (QWR) are investigated using photoluminescence (PL) and PL excitation spectroscopy. The first excited electron to heavy-hole transition showed a Stokes shift (∼17 meV) considerably larger than that of ground state-related transitions (∼4 meV). This is a quite different phenomenon than that observed in two dimensional quantum well structures, and can be explained by the spatial separation of wave functions with different confinement energies in crescent-shaped QWRs. © 1997 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

Correlation of two diamagnetic bands of the magnetic circular dichroism of the optical absorption with EL20 in GaAs

K. H. Wietzke, F. K. Koschnick, and K. Krambrock

Appl. Phys. Lett. 71, 2133 (1997); http://dx.doi.org/10.1063/1.119359 (3 pages) | Cited 2 times

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In a previous investigation, a diamagnetic band of the magnetic circular dichroism of the optical absorption (MCDA) in semi-insulating GaAs centered at 1.19 eV was observed and attributed to the neutral diamagnetic charge state of EL2, EL20. In this letter, we show a direct correlation between the signal intensities of two diamagnetic MCDA bands located at 0.93 and 1.19 eV and the concentration of neutral diamagnetic EL20 centers in different GaAs samples. A calibration factor is presented for the absolute MCDA intensities. This opens up the possibility of measuring the concentrations of EL20 and EL2+ using the same technique. © 1997 American Institute of Physics.
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78.20.Ls Magneto-optical effects
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors
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