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16 Mar 1998

Volume 72, Issue 11, pp. 1263-1400

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Suppressing self-induced frequency scanning of a phase conjugate diode laser array using counterbalance dispersion

Martin Løbel, Paul M. Petersen, and Per M. Johansen

Appl. Phys. Lett. 72, 1263 (1998); http://dx.doi.org/10.1063/1.120605 (3 pages) | Cited 9 times

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Experimental results show that angular dispersion strongly influences the self-induced frequency scanning of a multimode broad-area diode laser array coupled to a photorefractive self-pumped phase conjugate mirror. Prisms or a dispersive grating placed in the external cavity opposing the material frequency dispersion of the phase conjugate BaTiO3 crystal suppress the frequency scanning and stabilize the center wavelength and the output power. We show that the dispersion of the crystal is crucial for the mechanism of the frequency scanning. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Light emission from wavelength-tunable microcavities

H. Becker, R. H. Friend, and T. D. Wilkinson

Appl. Phys. Lett. 72, 1266 (1998); http://dx.doi.org/10.1063/1.121045 (3 pages) | Cited 15 times

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We report a novel microcavity design that allows the control in wavelength of the resonant modes of a microcavity operating in the visible spectrum. We have been able to shift the modes by up to 56 nm. The device is comprised of a thin film of a fluorescent semiconducting polymer combined with an electrically switchable liquid crystal layer, which are sandwiched between the two cavity mirrors. This structure serves as a tool for further experimental studies of the properties of microcavities and also has considerable technological potential, providing, for example, an efficient wavelength converter or tunable light source. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Very high power InGaAsP/InP distributed feedback lasers at 1550 nm wavelength

T. R. Chen, W. Hsin, and N. Bar-Chaim

Appl. Phys. Lett. 72, 1269 (1998); http://dx.doi.org/10.1063/1.121047 (3 pages) | Cited 9 times

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A continuous wave (cw) optical power of 108 mW was coupled into a polarization maintaining fiber from a high power distributed feed back (DFB) laser at 1550 nm wavelength. The laser also displays excellent high temperature performance, low noise, and narrow linewidth, which makes it very attractive for broadband supertrunking applications. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems
42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.60.Pk Continuous operation

GaSb–PbSe–GaSb double heterostructure midinfrared lasers

Z. Shi

Appl. Phys. Lett. 72, 1272 (1998); http://dx.doi.org/10.1063/1.121048 (3 pages) | Cited 2 times

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A GaSb/PbSe/GaSb double heterojunction laser structure is proposed. The advantages and feasibility of fabricating such lasers are discussed. Theoretical calculations show that the threshold gain for GaSb/PbSe lasers is much smaller than for traditional PbEuSe/PbSe lasers. Electrical confinement and heat dissipation is also significantly improved. The resulting much lower threshold currents and temperature difference between the active layer and heat sink should allow GaSb/PbSe lasers to operate in continuous wave mode above room temperature. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors

Linear and quadratic electro-optic coefficients of self-organized In0.4Ga0.6As/GaAs quantum dots

O. Qasaimeh, K. Kamath, P. Bhattacharya, and J. Phillips

Appl. Phys. Lett. 72, 1275 (1998); http://dx.doi.org/10.1063/1.121049 (3 pages) | Cited 23 times

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The electro-optic properties of self-organized In0.4Ga0.6As/GaAs quantum dots have been studied experimentally. Single-mode ridge waveguide structures were grown by molecular beam epitaxy with self-organized In0.4Ga0.6As/GaAs quantum dots in the guiding region. The measured linear and quadratic electro-optic coefficients are 2.58×10−11 m/V and 6.25×10−17 m2/V2, respectively, which are much higher than those obtained for bulk GaAs or quantum well structures. The measured transmission characteristics indicate that low-voltage amplitude modulators can be realized with quantum dot active regions. © 1998 American Institute of Physics.
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78.20.Jq Electro-optical effects
42.79.Hp Optical processors, correlators, and modulators
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

InGaAsP grown by He-plasma-assisted molecular beam epitaxy for 1.55 μm high speed photodetectors

Jin U. Kang, Michael Y. Frankel, Ronald D. Esman, D. A. Thompson, and B. J. Robinson

Appl. Phys. Lett. 72, 1278 (1998); http://dx.doi.org/10.1063/1.121046 (3 pages)

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Simple photoconductive optical detectors for 1.55 μm wavelength have been fabricated on InGaAsP grown by He-plasma assisted molecular beam epitaxy. Characterization of the photodetectors shows that their speed is determined by the free carrier trapping time, with a full width at half-maximum impulse response of approximately 6 ps. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Observation of self-starting phase-conjugate oscillation in a planar nematic liquid-crystal cell

Shu-Hsia Chen and Yuhren Shen

Appl. Phys. Lett. 72, 1281 (1998); http://dx.doi.org/10.1063/1.121050 (3 pages) | Cited 5 times

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We report the observation of self-starting optical phase-conjugate oscillation in a nematic liquid-crystal cell. A theoretical model based on the continuum theory of liquid crystals and optical theory of degenerate four-wave mixing is developed to explain the observed phenomena. © 1998 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
42.79.Kr Display devices, liquid-crystal devices

High-order azimuthal spatial modes of concentric-circle-grating surface-emitting semiconductor lasers

Craig Olson, Pamela L. Greene, Gary W. Wicks, Dennis G. Hall, and Steve Rishton

Appl. Phys. Lett. 72, 1284 (1998); http://dx.doi.org/10.1063/1.121051 (3 pages) | Cited 20 times

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We report the emission properties of concentric-circle-grating, surface-emitting (CCGSE), distributed-feedback semiconductor lasers oscillating in single high-order azimuthal spatial modes. The evolution of the spatial profile of the beam emitted by such lasers with increasing excitation depends upon the spatial gain distribution and the depth of the circular waveguide grating. The polarization of the high-order spatial modes is predominantly radial. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems
42.79.Dj Gratings

Thermal equilibrium of Ge-related defects in a GeO2-SiO2 glass

Masahide Takahashi, Takumi Fujiwara, Taiji Kawachi, and Akira J. Ikushima

Appl. Phys. Lett. 72, 1287 (1998); http://dx.doi.org/10.1063/1.121052 (3 pages) | Cited 9 times

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In a 15.7 GeO2⋅84.3 SiO2 glass prepared by a vapor axial deposition method, optical absorptions at 4.92 and 5.08 eV were observed from 300 to 600 K. The results were then compared with electron spin resonance (ESR) measurement using the same samples. The absorption at 4.92 eV was found to increase with increasing temperature, while the optical absorption at 5.08 eV decreased with increasing temperature. These changes of optical absorption indicate that the concentration of neutral oxygen monovacancy is reduced at higher temperatures. The changes were quite reversible with the temperature. Concentration of Ge E′ center, estimated from ESR, increased with increasing temperature, which is in contrast with the decrease of neutral oxygen monovacancy. The present result strongly suggests the thermal equilibrium reaction between neutral oxygen monovacancy and Ge E′ center. © 1998 American Institute of Physics.
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78.40.Pg Disordered solids
61.43.Fs Glasses
76.30.Mi Color centers and other defects

Liquid crystal display with wide viewing angle

Bau-Jy Liang, Shu-Hsia Chen, and Y. F. Wang

Appl. Phys. Lett. 72, 1290 (1998); http://dx.doi.org/10.1063/1.121053 (3 pages) | Cited 6 times

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A conic-cylindrical-cavities liquid crystal (conic CCLC) cell is developed for wide-viewing-angle displays. This conic-CCLC cell has been successfully manufactured and inquired. This display has a superwide viewing angle of over ±70° in both the horizontal and vertical directions under the condition of no gray-scale inversion. The enhancement of viewing angle is believed to result from the director symmetric alignment in the conic-CCLC. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
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Asymmetric microtrenching during inductively coupled plasma oxide etching in the presence of a weak magnetic field

Marc Schaepkens and Gottlieb S. Oehrlein

Appl. Phys. Lett. 72, 1293 (1998); http://dx.doi.org/10.1063/1.121068 (3 pages) | Cited 38 times

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When fabricating microscopic features in SiO2 layers using low pressure, high-density fluorocarbon plasmas, microtrenching has commonly been observed. Microtrenching has been explained either as due to ion scattering from sloped sidewalls or negative charging of the sidewalls by electrons, and the influence of the associated electric field on ion trajectories. In this work, we show that a weak magnetic field produces a significant asymmetry in microtrenching. Our results demonstrate unambiguously that electron-based sidewall charging is to a significant extent responsible for microtrenching, and, more generally, that differential charging is an important effect in microstructure fabrication using high-density plasmas. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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Electromigration-induced stress in aluminum conductor lines measured by x-ray microdiffraction

P.-C. Wang, G. S. Cargill, I. C. Noyan, and C.-K. Hu

Appl. Phys. Lett. 72, 1296 (1998); http://dx.doi.org/10.1063/1.120604 (3 pages) | Cited 68 times

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Electromigration-induced stress distributions in 200 μm long, 10 μm wide aluminum conductor lines in 1.5 μm SiO2 passivation layers have been investigated in real time using synchrotron-based white-beam x-ray microdiffraction. The results show that a steady-state linear stress gradient along the length of the line developed within the first few hours of electromigration and that the stress gradient could be manipulated by controlling the magnitude and the direction of the current flow. From the current density dependence of the steady-state stress gradient, the effective valence Z∗ was determined to be 1.6 at 260 °C. From the time dependence of the transient-state stress gradient, the effective grain boundary diffusion coefficient Deff was estimated to be 8.2×10−11 cm2/s at 260 °C using Korhonen’s stress evolution model [M. A. Korhonen, P. Bo̸rgesen, K. N. Tu, and C.-Y. Li, J. Appl. Phys. 73, 3790 (1993)]. Both Z∗ and Deff values are in good agreement with the previously reported values. © 1998 American Institute of Physics.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
68.60.Bs Mechanical and acoustical properties
73.61.At Metal and metallic alloys
81.65.Rv Passivation
61.72.Mm Grain and twin boundaries
81.05.Bx Metals, semimetals, and alloys

Fabrication and evaluation of a localized plasmon resonance probe for near-field optical microscopy/spectroscopy

M. Ashino and M. Ohtsu

Appl. Phys. Lett. 72, 1299 (1998); http://dx.doi.org/10.1063/1.121031 (3 pages) | Cited 22 times

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A technique that excites a localized plasmon on the apex of probe for near-field optical microscope and spectroscope is presented. Vapor deposition and heating of several tens nm thick gold films on 1 nm thick germanium-covered tapered optical fiber probe make highly adherent and smooth overlayers. A “tunneling-photon-mode” experimental system combined with a dye laser is used to excite a localized plasmon. The enhancement of near-field intensity was measured varying incident photon energies with its maximum occurring at 2.11 eV. This local field enhancement could be estimated to generate only in the close proximity of the substrate. © 1998 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

A Fullerene derivative as an electron beam resist for nanolithography

A. P. G. Robinson, R. E. Palmer, T. Tada, T. Kanayama, and J. A. Preece

Appl. Phys. Lett. 72, 1302 (1998); http://dx.doi.org/10.1063/1.120978 (3 pages) | Cited 36 times

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We have explored the application of chemical derivatives of C60 as high-resolution electron beam resists. Facile spin coating was used to produce ∼ 100-nm-thick films of a C60 tris adduct (three functional groups) on Si surfaces. We find that these films function as high-resolution negative resists for electron beam lithography using monochlorobenzene as a developer. The film has a sensitivity of ∼ 1 mC/cm2 for 20 keV electrons, an order of magnitude higher than that of C60 itself, and the dry-etch durability is much better than that of conventional novolac based electron beam resists. Features with widths of 20 nm were produced. © 1998 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Thermal characteristics of silicon nitride membranes at sub-Kelvin temperatures

M. M. Leivo and J. P. Pekola

Appl. Phys. Lett. 72, 1305 (1998); http://dx.doi.org/10.1063/1.120979 (3 pages) | Cited 40 times

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We have performed calorimetric measurements on 200 nm thin silicon nitride membranes at temperatures from 0.07 to 1 K. Besides full windows, membranes cut into a thermally isolating suspended bridge geometry were investigated. Based on dc and ac measurements employing normal-metal/insulator/superconductor (NIS) tunnel junctions both as a thermometer and a heater, we report on heat transport and thermal relaxation in silicon nitride films. The bridge structure improves thermal isolation and, consequently, energy sensitivity by two orders of magnitude over those of the full membrane with the same size, and makes such a structure very attractive for bolometric and microrefrigeration applications. © 1998 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.20.Fw Calorimeters

Nitrogen plasma annealing for low temperature Ta2O5 films

G. B. Alers, R. M. Fleming, Y. H. Wong, B. Dennis, A. Pinczuk, G. Redinbo, R. Urdahl, E. Ong, and Z. Hasan

Appl. Phys. Lett. 72, 1308 (1998); http://dx.doi.org/10.1063/1.120569 (3 pages) | Cited 66 times

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A low temperature oxygen/nitrogen plasma process is reported that substantially reduces leakage currents in chemical vapor deposited (CVD) and physical vapor deposited (PVD) films of tantalum oxide. We show that a combination of nitrogen and oxygen in a remote downstream microwave plasma source reduces leakage currents in CVD films of tantalum oxide and also reduces trap densities as measured by charge pumping. The as deposited CVD films show a high level of photoluminescence that is substantially lowered by the plasma anneal due to a reduction in the density of midgap states. For films deposited by PVD in the thickness range of 100 nm we find low leakage currents with a substantial improvement from the introduction of nitrogen into the plasma. However, PVD films in the thickness range of 20 nm show larger relative leakage currents and less of an improvement from the addition of nitrogen. The role of nitrogen in lowering leakage currents and charge trapping is thought to occur from a reduction in the density of bulk trap states in the oxide due to partial incorporation of nitrogen in the oxide. Both of these low temperature deposition and annealing processes are compatible with integration into the upper levels of metallization for high density circuits.© 1998 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.-b Surface treatments
73.61.Ng Insulators
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Polyquinoline/bismaleimide composites as high-temperature-resistant materials

Hari Singh Nalwa, Masahiro Suzuki, Akio Takahashi, and Akira Kageyama

Appl. Phys. Lett. 72, 1311 (1998); http://dx.doi.org/10.1063/1.121683 (3 pages) | Cited 7 times

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Polyquinoline/bismaleimide composites containing bismaleimide contents between 5 and 50 wt % have been investigated as high-temperature-resistant materials. The effect of bismaleimide loading on thermal, mechanical, and dielectric properties of polyquinoline has been reported. The dielectric constant of composite thin films was found to vary between 2.90 and 3.10 with the loss tangent ranging between 0.004 and 0.007, depending upon the incorporated bismaleimide content. The thermal, mechanical, and dielectric properties of polyquinoline/bismaleimide composite thin films are discussed. © 1998 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
77.84.Jd Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects

Deposition of tetrahedral hydrogenated amorphous carbon using a novel electron cyclotron wave resonance reactor

M. Weiler, K. Lang, E. Li, and J. Robertson

Appl. Phys. Lett. 72, 1314 (1998); http://dx.doi.org/10.1063/1.121069 (3 pages) | Cited 34 times

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Highly tetrahedral hydrogenated amorphous carbon (ta-C:H) is deposited with a novel, 13.6 MHz excited electron cyclotron wave resonance (ECWR) plasma source. The ion flux of an acetylene and a nitrogen plasma was investigated by mass spectrometry and retarding field measurements. The ECWR gives a dissociation degree between 15% and 80% depending on gas flow rate. Ion current densities up to 2 mA/cm2 can be achieved, corresponding to ta-C:H deposition rates of 2 nm/s. The fraction of sp3 bonded carbon atoms and mass density are strongly related to the amount of hydrogen in the ion flux. For low hydrogen ion fluxes (10%), a sp3 fraction of 70% and a mass density of 2.85 g/cm3 can be achieved. At higher hydrogen ion fluxes (40%), the sp3 fraction and the mass density fall to 55% and 2.55 gm/cm3, respectively. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
52.70.Nc Particle measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.25.-b Plasma properties
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Quality improvements of ZnxCdyMg1−x−ySe layers grown on InP substrates by a thin ZnCdSe interfacial layer

L. Zeng, B. X. Yang, M. C. Tamargo, E. Snoeks, and L. Zhao

Appl. Phys. Lett. 72, 1317 (1998); http://dx.doi.org/10.1063/1.120980 (3 pages) | Cited 14 times

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The quality of lattice-matched ZnxCdyMg1−x−ySe epitaxial layers grown on (001) InP substrates with a III-V buffer layer has been improved by initially growing a ZnCdSe interfacial layer (50 Å) at low temperature. The widths of double crystal x-ray rocking curves for ZnxCdyMg1−x−ySe epilayers with band gaps as high as 3.05 eV were reduced to about 70 arcsec. The defect density evaluated from etch pit density and plan-view transmission electron microscopy measurements was reduced by two orders of magnitude, to 106–107 cm−2. The photoluminescence band edge emission became more symmetric and slightly narrower. It is proposed that an initial two-dimensional growth mode has been achieved by incorporating such a lattice-matched ZnCdSe layer. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
78.55.Et II-VI semiconductors

Band alignment in Si1−yCy/Si(001) heterostructures

R. L. Williams, G. C. Aers, N. L. Rowell, K. Brunner, W. Winter, and K. Eberl

Appl. Phys. Lett. 72, 1320 (1998); http://dx.doi.org/10.1063/1.120981 (3 pages) | Cited 10 times

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Photoluminescence peak energy shifts under applied [110] and [100] uniaxial stress are interpreted within the framework of a multi-band Kohn–Luttinger model which takes into account the mixing of heavy, light, and spin-orbit split-off holes within the valence band. Experimental data are presented for 0.5%, 1%, and 1.7% Si1−yCy/Si samples which are best fitted with a conduction band offset of approximately 70%. At this value of the conduction band offset, we show that small amounts of space charge induced band bending are required to explain the experimentally observed results. © 1998 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.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Li Other semiconductors
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Hole transport over heterobarriers in InP based multiple quantum well structures

C. Knorr, T. Riedl, M. Geiger, F. Scholz, and A. Hangleiter

Appl. Phys. Lett. 72, 1323 (1998); http://dx.doi.org/10.1063/1.120982 (3 pages)

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We present a systematic analysis of the hole transport over heterobarriers in the InGaAs(P)/InP material system. The experiments have been performed on our recently developed all-optical switching structures [C. Knorr et al., Appl. Phys. Lett. 69, 4212 (1996)], which offer an elegant access to hole transport rates. We have varied barrier thickness, barrier height, bias voltage, and temperature. The time constants vary from 30 μs to 30 ns. Our model calculations, including all heavy and light hole subbands, show that only thermally assisted tunneling can explain both the temperature and electric field dependence of the transport rates. We have extracted the activation energies. The hole capture time is determined as 250±50 fs. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Nature of the 2.8 eV photoluminescence band in Mg doped GaN

U. Kaufmann, M. Kunzer, M. Maier, H. Obloh, A. Ramakrishnan, B. Santic, and P. Schlotter

Appl. Phys. Lett. 72, 1326 (1998); http://dx.doi.org/10.1063/1.120983 (3 pages) | Cited 128 times

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The blue Mg induced 2.8 eV photoluminescence (PL) band in metalorganic chemical vapor deposition grown GaN has been studied in a large number of samples with varying Mg content. It emerges near a Mg concentration of 1×1019 cm−3 and at higher concentrations dominates the room temperature PL spectrum. The excitation power dependence of the 2.8 eV band provides convincing evidence for its donor–acceptor (D–A) pair recombination character. It is suggested that the acceptor A is isolated MgGa while the spatially separated, deep donor (430 meV) D is attributed to a nearest-neighbor associate of a MgGa acceptor with a nitrogen vacancy, formed by self-compensation. © 1998 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Transmission electron microscopy investigation of structural properties of self-assembled CdSe/ZnSe quantum dots

H. Kirmse, R. Schneider, M. Rabe, W. Neumann, and F. Henneberger

Appl. Phys. Lett. 72, 1329 (1998); http://dx.doi.org/10.1063/1.120984 (3 pages) | Cited 55 times

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CdSe quantum dots on ZnSe, grown by molecular beam epitaxy and formed during reorganization of an initially uniform film by thermal activation, are microstructurally elucidated in cross section and plan view, using transmission electron microscopy. In diffraction contrast, an almost uniform wetting layer is clearly visible. Dark contrast features with a distinctly larger extension into growth direction mark the location of quantum dots. Individual quantum dots can be identified in high-resolution imaging both by lattice expansion and contrasts arising from their strain fields. Plan-view images show the coexistence of two classes of quantum dots with an average lateral size of ⩽ 10 nm (area density 100 μm−2) and 10–50 nm (20 μm−2), respectively. The shape of the larger entities is pyramidlike. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Dv Thermal stability; thermal effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Optical absorption, disorder, and the disorderless limit in amorphous semiconductors

Stephen Karrer O’Leary

Appl. Phys. Lett. 72, 1332 (1998); http://dx.doi.org/10.1063/1.120985 (3 pages) | Cited 16 times

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We study the role that disorder plays in shaping the functional form of the optical absorption spectra of amorphous semiconductors. We find, for hydrogenated amorphous silicon, amorphous germanium, amorphous gallium arsenide, and amorphous indium phosphide, that, while the breadth of the absorption tail is a strong function of disorder, the mean energy gap is insensitive to the amount of disorder. As the disorder is decreased, the optical absorption spectra associated with these amorphous semiconductors approach well defined disorderless limits, the energy gaps associated with these limits being greater than the corresponding crystalline gaps. The physical implications of these results are discussed. © 1998 American Institute of Physics.
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78.40.Fy Semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
78.40.Pg Disordered solids

Sizable photocurrent and emission from solid state devices based on CdS nanoparticles

J. Nanda, K. S. Narayan, Beena Annie Kuruvilla, G. L. Murthy, and D. D. Sarma

Appl. Phys. Lett. 72, 1335 (1998); http://dx.doi.org/10.1063/1.120986 (3 pages) | Cited 31 times

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CdS nanoparticles exhibit size dependent optical and electrical properties. We report here the photocurrent and I–V characteristic studies of CdS nanoparticle devices. A sizable short circuit photocurrent was observed in the detection range governed by the size of the clusters. We speculate on the mechanisms leading to the photocurrent and emission in these nanometer scale systems. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
61.46.-w Structure of nanoscale materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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