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24 Apr 2000

Volume 76, Issue 17, pp. 2325-2474

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Strong exciton-erbium coupling in Si nanocrystal-doped SiO2

P. G. Kik, M. L. Brongersma, and A. Polman

Appl. Phys. Lett. 76, 2325 (2000); http://dx.doi.org/10.1063/1.126334 (3 pages) | Cited 137 times

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Silicon nanocrystals were formed in SiO2 using Si ion implantation followed by thermal annealing. The nanocrystal-doped SiO2 layer was implanted with Er to a peak concentration of 1.8 at. %. Upon 458 nm excitation the sample shows a broad nanocrystal-related luminescence spectrum centered around 750 nm and two sharp Er luminescence lines at 982 and 1536 nm. By measuring the excitation spectra of these features as well as the temperature-dependent intensities and luminescence dynamics we conclude that (a) the Er is excited by excitons recombining within Si nanocrystals through a strong coupling mechanism, (b) the Er excitation process at room temperature occurs at a submicrosecond time scale, (c) excitons excite Er with an efficiency >55%, and (d) each nanocrystal can have at most ∼1 excited Er ion in its vicinity. © 2000 American Institute of Physics.
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71.35.Gg Exciton-mediated interactions
78.55.Ap Elemental semiconductors
78.55.Hx Other solid inorganic materials
61.72.up Other materials

Luminescence enhancement of EuS nanoclusters in zeolite

Wei Chen, Xinhui Zhang, and Yining Huang

Appl. Phys. Lett. 76, 2328 (2000); http://dx.doi.org/10.1063/1.126335 (3 pages) | Cited 20 times

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Large luminescence enhancement was observed in EuS clusters formed in ultrastable zeolite-Y by solid-state diffusion in vacuum at 600 °C. The emission of EuS clusters shifts to higher energies relative to that of bulk EuS powder. The blueshift and the emission enhancement are attributed to quantum-size confinement and are discussed based on the magnetic exciton and the magnetic polaron models, respectively. © 2000 American Institute of Physics.
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78.66.Li Other semiconductors
78.66.Vs Fine-particle systems
78.55.Mb Porous materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors

Optical fiber for dispersion addressing

Denis Donlagić and Brian Culshaw

Appl. Phys. Lett. 76, 2331 (2000); http://dx.doi.org/10.1063/1.126336 (3 pages) | Cited 1 time

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This letter presents a fully distributed forward propagating system, suitable for use with microbend sensors. The principle relies on selected mode launch in specially designed multimode fiber where a short pulse is launched into the fundamental mode. In the presence of microbend disturbance located down the sensing fiber, light couples from the fundamental to higher-order modes that propagate at different group velocity than the fundamental mode. The position of the disturbance is determined by the time delay between the pulse carried by the fundamental mode and by the pulse carried by higher-order modes. The group velocity difference is maximized by proper construction of the refractive index profile of the proposed fiber. Experimentally produced fibers exhibited difference of group velocities in ranges over 1%. This allows for easy reconstruction of position and amplitude of microbend deformations located down the sensing fiber. © 2000 American Institute of Physics.
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42.81.Pa Sensors, gyros
42.81.Dp Propagation, scattering, and losses; solitons

Electrically controllable azimuth optical rotator

Zhizhong Zhuang, Young Jin Kim, and J. S. Patel

Appl. Phys. Lett. 76, 2334 (2000); http://dx.doi.org/10.1063/1.126337 (3 pages) | Cited 2 times

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The transformation of the state of polarization (SOP) of light from one state to another can be graphically illustrated by a trajectory on the Poincaré sphere (PS). We use this method to illustrate the control of the azimuth SOP rotation on the PS. Traditionally, azimuth rotation is achieved by the use of a Faraday rotator or by the mechanical movements of birefringent wave plates. In this letter, an electrically controllable azimuth optical rotator is introduced theoretically and verified experimentally. It consists of two quarter-wave plates and one liquid-crystal variable wave plate and allows polarization rotation of an arbitrary polarized light by an angle determined by the magnitude of the applied field. This electrical approach avoids the errors and inconvenience associated with the magnetic field and the mechanical movements of other methods. © 2000 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Kr Display devices, liquid-crystal devices
42.25.Ja Polarization

Realization of a complex-coupled InGaN/GaN-based optically pumped multiple-quantum-well distributed-feedback laser

Daniel Hofstetter, Linda T. Romano, Thomas L. Paoli, David P. Bour, and Michael Kneissl

Appl. Phys. Lett. 76, 2337 (2000); http://dx.doi.org/10.1063/1.126338 (3 pages) | Cited 1 time

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We demonstrate an optically pumped complex-coupled InGaN/GaN-based multiple-quantum-well distributed-feedback laser in the violet/blue spectral region. The third-order grating providing feedback was defined holographically and dry etched through a portion of the active region by chemically assisted ion-beam etching. Epitaxial overgrowth of the GaN waveguide completed the device structure without introducing dislocations, as shown by transmission electron microscopy. The laser emitted light at 392.7 nm with high side-mode suppression and a narrow linewidth of 1.5 Å. In contrast to Fabry–Pérot lasers fabricated from the same piece of material, only a very minor change in emission wavelength was observed when operating the device at higher pump intensities. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.40.Eq Holographic optical elements; holographic gratings
81.65.Cf Surface cleaning, etching, patterning
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Fd III-V semiconductors
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Features of hydrogenated amorphous silicon films developed under an unexplored region of parameter space of radio-frequency plasma-enhanced chemical vapor deposition

Sukti Hazra, A. R. Middya, C. Longeaud, and Swati Ray

Appl. Phys. Lett. 76, 2340 (2000); http://dx.doi.org/10.1063/1.126339 (3 pages) | Cited 4 times

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Searching to improve stability of electronic properties under intense light illumination, hydrogenated amorphous silicon (a-Si:H) films have been fabricated by radio-frequency plasma-enhanced chemical vapor deposition with helium dilution of silane. The deposition conditions which correspond to the transition between the α regime and the powder regime have not been explored properly yet. The resulting materials show many new features: hydrogen bonding mostly monohydride, lower bonded hydrogen content, compact structure, higher efficiency-mobility-lifetime product (ημτ) and density of states (DOS) above Fermi level lower than the reported values of the state-of-the-art a-Si:H films. The saturation time under light-soaking (AM 1) is fast (within 20 h) and the saturated value of ημτ and the DOS above the Fermi level is comparable to that of annealed state standard a-Si:H films. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Repeated crystallization in undercooled Zr41Ti14Cu12Ni10Be23 liquids

Jan Schroers, William L. Johnson, and Ralf Busch

Appl. Phys. Lett. 76, 2343 (2000); http://dx.doi.org/10.1063/1.126340 (3 pages) | Cited 27 times

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Isothermal crystallization studies are performed on Zr41Ti14Cu12Ni10Be23 melts. Undercooling experiments are carried out repeatedly at 907, 860, and 750 K. The scattering of the time to reach the onset of crystallization is investigated. Results from experiments performed at 907 K show a large scatter of the onset time of crystallization. For the experiments carried out at 860 and 750 K, scattering of the onset time is two orders of magnitude smaller. These results indicate that, at high temperatures, the crystallization is governed by the time scale of the statistical nucleation events. At low temperatures, the crystallization is controlled by diffusion, resulting in a well-defined onset time for crystallization. © 2000 American Institute of Physics.
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64.70.D- Solid-liquid transitions
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Fq Growth from melts; zone melting and refining
64.60.Q- Nucleation

Direct synthesis of silicon nanowires, silica nanospheres, and wire-like nanosphere agglomerates

J. L. Gole, J. D. Stout, W. L. Rauch, and Z. L. Wang

Appl. Phys. Lett. 76, 2346 (2000); http://dx.doi.org/10.1063/1.126341 (3 pages) | Cited 79 times

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Elevated temperature synthesis has been used to generate virtually defect free SiO2 sheathed crystalline silicon nanowires and silica (SiO2) nanospheres which can be agglomerated to wire-like configurations impregnated with crystalline silicon. The SiO2 passivated (sheathed) crystalline silicon nanowires, generated with a modified approach using a heated Si–SiO2 mix, with their axes parallel to 〈111〉 are found to be virtually defect free. Modifications to the system allow the simultaneous formation of SiO2 nanospheres (d ∼ 10–30 nm) as virtually monodisperse gram quantity powders which form large surface area catalysts for the selective conversion of ethanol to acetaldehyde. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Cy Elemental semiconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Manganese surface segregation in NiMnSb

Delia Ristoiu, J. P. Nozières, C. N. Borca, B. Borca, and P. A. Dowben

Appl. Phys. Lett. 76, 2349 (2000); http://dx.doi.org/10.1063/1.126342 (3 pages) | Cited 43 times

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A quantitative analysis of the surface composition of the Heusler alloy NiMnSb has been undertaken using angle-resolved x-ray photoemission spectroscopy and the surface composition characterized. With sufficient annealing cycles, the stoichiometric surface evolves to a surface that is manganese rich. This indicates that the surface enthalpy is different from the bulk for the Heusler alloy NiMnSb. © 2000 American Institute of Physics.
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64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
81.05.Bx Metals, semimetals, and alloys
65.20.-w Thermal properties of liquids
65.40.gd Entropy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Unusual disparity in electroluminescence and photoluminescence spectra of vacuum-evaporated films of 1,1-bis ((di-4-tolylamino) phenyl) cyclohexane

J. Kalinowski, G. Giro, M. Cocchi, V. Fattori, and P. Di Marco

Appl. Phys. Lett. 76, 2352 (2000); http://dx.doi.org/10.1063/1.126343 (3 pages) | Cited 64 times

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The electroluminescence (EL) and photoluminescence (PL) spectra of thin films of 1,1-bis((di-4-tolyloamino)phenyl) cyclohexane (TAPC) appear to be completely different. Whereas the broad PL spectra reveal major maxima at ≅370 and 450 nm, a strong regular band at 580 nm is characteristic of the EL spectra. It is shown that in contrast to PL, which is composed of molecular exciton (monomer) and excimer emission, EL can be explained by the direct cross recombination transition between electrons and holes trapped on tritolylamine (TTA) subunits of different TAPC molecules. Such a pair of trapped carriers, formed selectively under recombination of statistically independent (here injected at opposite electrodes) electrons and holes, is considered as a particular excited state (“electromer”) responsible also for the EL emission of some other compounds containing TTA or triphenylamine moieties, as for example an amino-substituted triphenylbenzene. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Exciton-related photoluminescence in homoepitaxial GaN of Ga and N polarities

V. Kirilyuk, A. R. A. Zauner, P. C. M. Christianen, J. L. Weyher, P. R. Hageman, and P. K. Larsen

Appl. Phys. Lett. 76, 2355 (2000); http://dx.doi.org/10.1063/1.126344 (3 pages) | Cited 25 times

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A photoluminescence (PL) study of GaN homoepitaxial layers grown by metal–organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (000math) GaN substrates. In contrast to broad PL emission in exact (000math) layers, narrow-bound (0.9 meV) and free- (A and B) excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga- and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.Gg Exciton-mediated interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Effect of plasma-induced damage on interfacial reactions of titanium thin films on silicon surfaces

T. Yamaguchi, H. Nikoh, A. Hama, N. Fujimura, and T. Ito

Appl. Phys. Lett. 76, 2358 (2000); http://dx.doi.org/10.1063/1.126345 (3 pages) | Cited 1 time

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Solid-state reactions of titanium thin films on Si surfaces damaged and amorphized by CHF3/O2 plasma treatment were investigated. The formation temperature of the C49–TiSi2 phase increased due to plasma-induced damage and contamination from decomposed gas elements. The presence of a plasma-induced damage layer suppressed the interdiffusion of Ti and Si. The Ti5Si3 phase was formed initially at an annealing temperature of 400 °C when a plasma-induced damage layer was present at the interface. The increase of the C49–TiSi2 formation temperature may be caused by the transformation of the Ti5Si3 phase into C49–TiSi2 rather than by the direct nucleation of the C49–TiSi2 phase with a clean interface. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.65.Cf Surface cleaning, etching, patterning
73.40.Ns Metal-nonmetal contacts
61.80.Jh Ion radiation effects

Narrow photoluminescence peaks from localized states in InGaN quantum dot structures

Osamu Moriwaki, Takao Someya, Koichi Tachibana, Satomi Ishida, and Yasuhiko Arakawa

Appl. Phys. Lett. 76, 2361 (2000); http://dx.doi.org/10.1063/1.126346 (3 pages) | Cited 69 times

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Microscopic photoluminescence spectra were measured for self-assembled InGaN quantum dots (QDs) grown by metalorganic chemical vapor deposition. A thin aluminum layer with 400 nm square apertures was formed on the sample surface to reduce the number of QDs measured. We observed very sharp peaks whose spectral linewidths were typically 170 μeV at 3.5 K, the linewidth being limited by spectral resolution. Such sharp lines were not observed in similar experiments on a reference sample having single InGaN quantum well structure. These experimental results suggest that excitons are strongly confined in our InGaN QD structure. © 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
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Long-term thermal stability of Ti/Al/Pt/Au Ohmic contacts to n-type GaN

Ching-Ting Lee and Hsiao-Wei Kao

Appl. Phys. Lett. 76, 2364 (2000); http://dx.doi.org/10.1063/1.126347 (3 pages) | Cited 78 times

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We present a study of the long-term thermal stability and low specific contact resistance of Ti/Al/Pt/Au multilayer contacts to n-type GaN. The Ohmic performance can be maintained up to 60 and 540 min for thermal annealing at 950 and 850 °C, respectively, and even longer than 600 min for thermal annealing at 750 °C. By comparing the specific contact resistances for Ti/Al/Pt/Au and Ti/Al/Au Ohmic contacts to n-type GaN, the long-term thermal stability may be deduced as due to the contribution of the Pt barrier for preventing Au penetration. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.61.Ey III-V semiconductors
68.60.Dv Thermal stability; thermal effects

Controlling the diameter, growth rate, and density of vertically aligned carbon nanotubes synthesized by microwave plasma-enhanced chemical vapor deposition

Young Chul Choi, Young Min Shin, Young Hee Lee, Byung Soo Lee, Gyeong-Su Park, Won Bong Choi, Nae Sung Lee, and Jong Min Kim

Appl. Phys. Lett. 76, 2367 (2000); http://dx.doi.org/10.1063/1.126348 (3 pages) | Cited 97 times

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Vertically aligned carbon nanotubes were synthesized on Ni-deposited Si substrates using microwave plasma-enhanced chemical vapor deposition. The grain size of Ni thin films varied with the rf power density during the rf magnetron sputtering process. We found that the diameter, growth rate, and density of carbon nanotubes could be controlled systematically by the grain size of Ni thin films. With decreasing the grain size of Ni thin films, the diameter of the nanotubes decreased, whereas the growth rate and density increased. High-resolution transmission electron microscope images clearly demonstrated synthesized nanotubes to be multiwalled. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
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.)

Mechanically induced Si layer transfer in hydrogen-implanted Si wafers

K. Henttinen, I. Suni, and S. S. Lau

Appl. Phys. Lett. 76, 2370 (2000); http://dx.doi.org/10.1063/1.126349 (3 pages) | Cited 23 times

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Mechanically induced layer transfer of single-crystal silicon by hydrogen ion implantation, low-temperature wafer bonding, and subsequent mechanical splitting of the implanted wafer has been investigated. The bond strength measurements using the crack opening method in room environment yield a surface energy of ≥ 2000 mJ/m2 after exposure to oxygen plasma and subsequent hydrophilic silicon/silicon dioxide bonding at 200 °C. Mechanically induced layer transfer was carried out for silicon wafers implanted to a dose of 5×1016 H2/cm2 at 100 keV and annealed for 2 h at 200 °C. No feature was observed by atomic force microscopy (AFM) measurements on the unbonded free surface after this heat treatment. For lower doses of implantation, annealing at higher temperatures is required to enable the mechanical transfer. AFM measurements on the split silicon surface indicate that low-temperature wafer bonding and mechanical transfer yield a root mean square surface roughness of 4 nm which is less than in the standard Smart-Cut® process. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.-b Surface treatments
68.35.Md Surface thermodynamics, surface energies
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)

Low temperature deposition of nanocrystalline silicon carbide thin films

S. Kerdiles, A. Berthelot, F. Gourbilleau, and R. Rizk

Appl. Phys. Lett. 76, 2373 (2000); http://dx.doi.org/10.1063/1.126350 (3 pages) | Cited 36 times

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Silicon carbide thin films have been deposited by reactive magnetron sputtering in a pure hydrogen plasma at substrate temperatures, Ts, ranging between 100 and 600 °C. The infrared (IR) absorption spectra and the transmission electron microscopy observations reveal an onset of crystallization at Ts as low as 300 °C. The crystalline fraction increases with Ts and reaches a value of about 60% for Ts = 600 °C. Both refractive index n and room temperature dark conductivity σd(RT) show quite consistent behaviors with the structural evolution of the layers. Thus n increases from 1.9 to 2.4 and σd(RT) improves by six orders of magnitude when Ts is raised from 100 to 600 °C. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
73.50.Pz Photoconduction and photovoltaic effects
73.61.Le Other inorganic semiconductors

Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels

Rustem F. Ismagilov, Abraham D. Stroock, Paul J. A. Kenis, George Whitesides, and Howard A. Stone

Appl. Phys. Lett. 76, 2376 (2000); http://dx.doi.org/10.1063/1.126351 (3 pages) | Cited 165 times

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This letter quantifies both experimentally and theoretically the diffusion of low-molecular-weight species across the interface between two aqueous solutions in pressure-driven laminar flow in microchannels at high Péclet numbers. Confocal fluorescent microscopy was used to visualize a fluorescent product formed by reaction between chemical species carried separately by the two solutions. At steady state, the width of the reaction–diffusion zone at the interface adjacent to the wall of the channel and transverse to the direction of flow scales as the one-third power of both the axial distance down the channel (from the point where the two streams join) and the average velocity of the flow, instead of the more familiar one-half power scaling which was measured in the middle of the channel. A quantitative description of reaction–diffusion processes near the walls of the channel, such as described in this letter, is required for the rational use of laminar flows for performing spatially resolved surface chemistry and biology inside microchannels and for understanding three-dimensional features of mass transport in shearing flows near surfaces. © 2000 American Institute of Physics.
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47.55.Kf Particle-laden flows
47.70.Fw Chemically reactive flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.15.-x Laminar flows
47.80.-v Instrumentation and measurement methods in fluid dynamics
07.60.Pb Conventional optical microscopes
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.45.-a Nonlinear dynamics and chaos
05.60.-k Transport processes
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Effect of GaAsyP1−y(0 ⩽ y<1) interlayers on the structural, optical, and electrical characteristics of GaAs/InGaP heterojunction

Yong-Hwan Kwon, Weon G. Jeong, Yong-Hoon Cho, and Byung-Doo Choe

Appl. Phys. Lett. 76, 2379 (2000); http://dx.doi.org/10.1063/1.126352 (3 pages) | Cited 11 times

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The effect of GaAsyP1−y(0 ⩽ y<1) interlayers on the characteristics of GaAs/InGaP heterojunction has been investigated. For samples having GaAsyP1−y interlayers in the range of 0<y ⩽ 0.75 inserted in the GaAs-on-InGaP interface, sharp GaAs band-edge emissions are recovered. These results are attributed to smoothly grown InGaAs(P) interfacial layers with the band-gap energy higher than that of GaAs through transmission electron microscopy measurements. In addition, the amount of carrier depletion at the GaAs-on-InGaP interface is smaller with the use of GaAsyP1−y interlayers than that for no interlayer in capacitance–voltage measurements. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.35.Ct Interface structure and roughness
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Cooperative nucleation leading to ripple formation in InGaAs/GaAs films

Nehal S. Chokshi and Joanna Mirecki Millunchick

Appl. Phys. Lett. 76, 2382 (2000); http://dx.doi.org/10.1063/1.126353 (3 pages) | Cited 18 times

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In0.25Ga0.75As epilayers were grown on GaAs (001) substrates (1.8% misfit strain) by molecular beam epitaxy to investigate the two-dimensional to three-dimensional transition as a function of thickness (t ⩽ 30 MLs). Tapping-mode atomic force micrographs show the evolution of the morphology as a function of thickness. As the film is deposited, the nucleation of 3D islands followed by cooperative nucleation of pits is observed. As the thickness increases, both islands and pits continue to nucleate and grow until they coalesce, resulting in a fully formed ripple morphology running along the [1math0]. The ripples also exhibit a secondary alignment roughly along the 〈310〉 which is attributed to the nucleation of islands with {136} faces. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
64.60.Q- Nucleation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Thermoelectric properties of Bi2Sr2Co2Ox polycrystalline materials

Ryoji Funahashi, Ichiro Matsubara, and Satoshi Sodeoka

Appl. Phys. Lett. 76, 2385 (2000); http://dx.doi.org/10.1063/1.126354 (3 pages) | Cited 88 times

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Bi2Sr2Co2O9 (BC-2202) polycrystalline materials with a layered structure have been prepared by partial melting. The chemical compositions of the samples are Bi2Sr2Co2Ox (2202), Bi1.8Sr2Co2Ox (Bi-1.8), and Bi2Sr1.8Co2Ox (Sr-1.8). All three samples are p-type conductors. The electric properties, namely, the Seebeck coefficient (S) and electric resistivity (ρ), of the samples are dependent on chemical composition. The S values increase with temperature at T>673 K and, at 973 K, reach 100, 110, and 150 μV K−1 for the 2202, the Bi-1.8, and the Sr-1.8 samples, respectively. Thermal conductivity (κ) for all samples is lower than for ordinary conducting oxides. The figure of merit (Z) increases with temperature for all samples. Z values at 973 K are 0.77×10−4, 0.61×10−4, and 2.0×10−4 K−1 for the 2202, Bi-1.8, and Sr-1.8 samples, respectively. The thermoelectric properties depend on the chemical composition of the BC-2202 phase. The BC-2202 material thus appears to be a promising thermoelectric material due to its high performance at high temperature (∼1000 K). © 2000 American Institute of Physics.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Dynamic behavior of hot-electron–hole plasma in highly excited GaN epilayers

S. Juršėnas, G. Kurilčik, G. Tamulaitis, A. Žukauskas, R. Gaska, M. S. Shur, M. A. Khan, and J. W. Yang

Appl. Phys. Lett. 76, 2388 (2000); http://dx.doi.org/10.1063/1.126355 (3 pages) | Cited 11 times

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The room-temperature spontaneous luminescence of electron–hole plasma was investigated in GaN epilayers under extremely high quasi-steady-state photoexcitation. The photoluminescence spectra were measured for excitation power densities up to 200 MW/cm2 both under quasiresonant and off-resonant excitation conditions. High carrier temperatures up to 1000 K were observed under off-resonant excitation. A nonmonotonous dependence of the luminescence band peak position Ep on the excitation power density was observed. We attribute this nonmonotonous behavior of Ep to two competing mechanisms: (i) band-gap shrinkage due to carrier screening effects (redshift); and (ii) nonequilibrium carrier heating (blueshift). The obtained results are in a good agreement with finite-temperature theory of the band-gap renormalization. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Mx High-frequency effects; plasma effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Individual and collective effects of oxygen and ethanol on the conductance of SnO2 thin films

Vladimir V. Kissine, Victor V. Sysoev, and Sergey A. Voroshilov

Appl. Phys. Lett. 76, 2391 (2000); http://dx.doi.org/10.1063/1.126381 (3 pages) | Cited 4 times

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We study the changes in the conductance of the fully depleted SnO2 films exposed both to oxygen or ethanol vapors in vacuum and to their mixture in the air. The dependence of free carrier concentration on the acceptor-like and/or donor-like gas pressure is discussed assuming the flat-band condition. We show that the gas sensitivity of the depleted semiconductor layer can be explained taking into account the compensation of the sample conductivity by the surface adsorbed species. The results of calculations are in good agreement with our experimental data. © 2000 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Evidence of interdot electronic tunneling in vertically coupled In0.4Ga0.6As self-organized quantum dots

J. Urayama, T. B. Norris, B. Kochman, J. Singh, and P. Bhattacharya

Appl. Phys. Lett. 76, 2394 (2000); http://dx.doi.org/10.1063/1.126356 (3 pages) | Cited 12 times

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Ultrafast differential transmission spectroscopy with a resonant pump reveals evidence of electronic tunneling among the excited levels of vertically aligned In0.4Ga0.6As self-organized quantum dots. This evidence of tunneling is observed as a rapid spectral redistribution of electrons within a few hundred femtoseconds of optical excitation. Measurements show that this spectral spread is independent of carrier density and, therefore, indicate that carrier–carrier scattering is not the main mechanism for carrier redistribution. Instead, electronic tunneling is responsible for the interdot coupling; tunneling rate calculations agree reasonably with the experiment, supporting this conclusion. © 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.Gk Tunneling
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Evidence of an oxygen recombination center in p+–n GaInNAs solar cells

A. Balcioglu, R. K. Ahrenkiel, and D. J. Friedman

Appl. Phys. Lett. 76, 2397 (2000); http://dx.doi.org/10.1063/1.126383 (3 pages) | Cited 22 times

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We have studied deep-level impurities in p+–n GaInNAs solar cells using deep-level transient spectroscopy (DLTS). These films were grown by atmospheric- and low-pressure metalorganic vapor-phase epitaxy. The base layer is doped with silicon, and the emitter layer is zinc doped. Two types of samples have been studied: samples were grown with and without the addition of oxygen impurity. Two electron traps were found in all samples. These are designated as: E1, at EC−0.23–EC−0.27eV, E2 at EC−0.45eV, and E2∗ at 0.77 eV. With the addition of oxygen impurity, DLTS showed additional traps designated as E3 (electron) at EC−0.59eV and H3 (hole) at EV+0.59 eV. Using secondary ion mass spectroscopy, the oxygen concentration was found to be about 2–3×1019 and 1×1017 cm−3 in two sets of samples. However, only samples containing oxygen contained the two near-midgap levels (E3 and H3). We present evidence that these levels are associated with the oxygen defect. As we change the dc bias voltage, the E3 trap disappears in unison with the appearance of the H3 trap. Furthermore, E3 and H3 trap levels have comparable capture cross sections. This oxygen-related trap is an effective recombination center. The measured Shockley–Hall–Read lifetime for this center is about 0.6 μs. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
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