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15 Jun 2002

Volume 91, Issue 12, pp. 9461-10231

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Silicon nanostructures fabricated by scanning probe oxidation and tetra-methyl ammonium hydroxide etching

F. S.-S. Chien, W.-F. Hsieh, S. Gwo, A. E. Vladar, and J. A. Dagata

J. Appl. Phys. 91, 10044 (2002); http://dx.doi.org/10.1063/1.1476072 (7 pages) | Cited 28 times

Online Publication Date: 30 May 2002

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Fabrication of silicon nanostructures is a key technique for the development of monolithically integrated optoelectronic circuits. We demonstrated that the process of scanning probe microscope (SPM) oxidation and anisotropic tetra-methyl ammonium hydroxide (TMAH) etching is a low-cost and reliable method to produce smooth and uniform silicon nanostructures on a variety of silicon substrates. Etched structures with a pitch of 100 nm, positive- and negative-contrast structures, and features height greater than 100 nm have been produced on bare silicon, and Si3N4-coated and silicon-on-insulator wafers. Evolution of hexagonal pits on two-dimensional grid structures were shown to depend on the pattern spacing and orientation with respect to Si(110) crystal directions. We successfully combined SPM oxidation with traditional optical lithography in a mixed, multilevel patterning method for realizing micrometer-and nanometer-scale feature sizes, as required for photonic device designs. The combination of SPM oxidation and TMAH etching is a promising approach to rapid prototyping of functional nano-photonic devices. © 2002 American Institute of Physics.
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81.16.Pr Micro- and nano-oxidation
81.16.Rf Micro- and nanoscale pattern formation
81.05.Cy Elemental semiconductors
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
81.16.Nd Micro- and nanolithography
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning
07.79.-v Scanning probe microscopes and components
81.65.Mq Oxidation
85.60.-q Optoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer

Numerical analysis on the dispersion process of carbon clusters synthesized by gas evaporation using dc arc

Shu Usuba, Hiroyuki Yokoi, and Yozo Kakudate

J. Appl. Phys. 91, 10051 (2002); http://dx.doi.org/10.1063/1.1478140 (7 pages) | Cited 3 times

Online Publication Date: 30 May 2002

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The dispersion process of typical carbon cluster synthesized by gas evaporation using (dc) arc was numerically investigated under normal gravity (1 G) and nongravity (0 G) conditions to clarify the effect of natural convection. Calculated pressure dependence of residence time of C60 in the temperature state between 1000 and 2000 K under 1 G took a maximum value of about 260 ms at the pressure around 0.06 atm in helium, while under 0 G, it increased almost linearly with pressure. Such features in the pressure dependence of residence time of C60 under both 1 and 0 G were related to its yield by a simple model based on an annealing of imperfect C60 to perfect C60 structure. According to this model, experimentally observed secondary increase of C60 yield was consistently explained in terms of the effect of natural convection. © 2002 American Institute of Physics.
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81.05.ub Fullerenes and related materials
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
81.10.Mx Growth in microgravity environments
61.72.Cc Kinetics of defect formation and annealing

Growth mechanism of carbon nanocoils

Lujun Pan, Mei Zhang, and Yoshikazu Nakayama

J. Appl. Phys. 91, 10058 (2002); http://dx.doi.org/10.1063/1.1471575 (4 pages) | Cited 41 times

Online Publication Date: 30 May 2002

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Carbon nanocoils were prepared by catalytic pyrolysis of acetylene using iron-coated indium tin oxide as the catalyst. The effects of the constitution of catalyst, the growth temperature and time, the flow rate of acetylene gas on the growth of carbon nanocoils were investigated. It is found that the coils grow mainly from the interface of iron and indium tin oxide films. The coils generally consist of two or more nanotubes. Each coil has its own external diameter and pitch, which is determined by the structure of the catalyst at its tip. The growth of the carbon nanocoil is considered to be due to the nonuniformity of the carbon extrusion speed at different parts of the catalyst particle containing iron, tin, indium and/or oxygen. It is confirmed that iron is crucial in the formation of a nanotubule and indium tin oxide induces the helical growth of the nanotubule. © 2002 American Institute of Physics.
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81.07.De Nanotubes
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.10.Fq Growth from melts; zone melting and refining

Formation of a single interface-near, δ-like Ge nanocluster band in thin SiO2 films using ion-beam synthesis

M. Klimenkov, J. von Borany, W. Matz, R. Grötzschel, and F. Herrmann

J. Appl. Phys. 91, 10062 (2002); http://dx.doi.org/10.1063/1.1478795 (6 pages) | Cited 8 times

Online Publication Date: 30 May 2002

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The possibility to create a δ-like, interface-near Ge nanocluster band in a 20 nm thin SiO2 layer by ion-beam synthesis is demonstrated. The role of the post-implantation annealing conditions for the formation of Ge nanoclusters in the center of the layer, near the interface, or in both regions is discussed. The presence of hydrogen in the annealing atmosphere accelerates the redistribution of Ge in SiO2. By applying a two-step annealing process, preannealing in hydrogen containing atmosphere at low temperature followed by a rapid thermal annealing at high temperature, the controlled fabrication of a single δ-like, interface-near Ge nanocluster band was achieved. In some clusters 〈100〉 lattice planes of Ge were observed. From this and the similar contrast situation for amorphous clusters it is concluded that the interface-near clusters consist of elementary germanium. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing

Growth of nanocrystalline diamond protective coatings on quartz glass

W. B. Yang, F. X. Lü, and Z. X. Cao

J. Appl. Phys. 91, 10068 (2002); http://dx.doi.org/10.1063/1.1479476 (6 pages) | Cited 25 times

Online Publication Date: 30 May 2002

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Transparent diamond films with a crystallite size well controlled below 70 nm were grown by hydrogen and methane microwave plasma-enhanced chemical vapor deposition on quartz glass substrates, which had been scratched with 0.5 μm diamond powder. A complementary set of analyzing tools was employed to study the microstructure, the optical and mechanical properties of the deposits. Transmission electron microscopy revealed a nucleation density generally larger than 1011/cm2, which is of the same order of magnitude as the spotlike defects on the pretreated surface of the substrates. The Vicker’s hardness of the deposits scatters between 61 and 95 GPa. An optimal transmittance of 65% in the visible light range is achieved in coatings of 1.0 μm in thickness when the surface roughness measures about 10 nm or less. The nanocrystalline diamond films thus prepared can meet the requirements on transparent protective coatings for optical components. © 2002 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
78.40.Ha Other nonmetallic inorganics

Mechanism of thermokinetical selection between carbon nanotube and fullerene-like nanoparticle formation

Oleg A. Louchev, Yoichiro Sato, and Hisao Kanda

J. Appl. Phys. 91, 10074 (2002); http://dx.doi.org/10.1063/1.1479469 (7 pages) | Cited 5 times

Online Publication Date: 30 May 2002

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Open edge stability of carbon nanotube growth is suggested to depend on kinetically defined competition between pentagon and hexagon formation. Nanotube growth is possible when the time of hexagon formation, determined by the surface diffusion flux to the growth edge (proportional to carbon vapor pressure), is much lower than that of pentagon formation, which depends on the temperature. The competition of pentagon/hexagon formation at the growth edge together with thermal effects of condensation heat release and heat dissipation by radiation and collisions with inert gas (He), is shown to define selection between nanotube nucleus evolution into (i) continuous nanotube growth or (ii) fullerene- or cage-like nanoparticle formation. The involvement of catalyst nanoparticles enhances the formation of nanotubes by enhancing growth edge stability against pentagon formation under pressure-temperature conditions at which the open edge would otherwise become unstable closing nucleus into the fullerene-like nanoparticle. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
81.07.De Nanotubes
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.07.Bc Nanocrystalline materials

In search of nanoperfection: Experiment and Monte Carlo simulation of nucleation-controlled step doubling

Yi Wang, T. P. Pearl, S. B. Darling, J. L. Gimmell, and S. J. Sibener

J. Appl. Phys. 91, 10081 (2002); http://dx.doi.org/10.1063/1.1473697 (7 pages) | Cited 1 time

Online Publication Date: 30 May 2002

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In order to make effective use of the extreme density of nanoscale elements that form spontaneously in self-assembling architectures, one must address the associated issue of minimizing defect creation during the formation of such structures. In this article we examine the competing roles that nucleation kinetics and two-dimensional growth processes play in nanostructure formation and defect minimization. We employ oxygen-induced step doubling of vicinal Ni(977) surfaces as our physical system, using elevated temperature scanning tunneling microscopy and Monte Carlo simulations to extract the desired details of interface evolution. Two interesting topological defect features are observed on the surface after doubling reaches its asymptotic limit: (i) “frustrated ends,” which form when two counter-propagating step-doubling events having a single step in common intersect, leaving a stable topological defect, and (ii) residual “isolated single steps,” which form when a single step is unable to partner with an adjacent step. This latter defect occurs when a single step is surrounded on both sides by previously doubled structures. In an attempt to understand and control these results, Monte Carlo simulations indicate that experimental control of the delicate and competing interplay of nucleation kinetics and two-dimensional growth kinetics is the key to the formation of more perfect interfaces. In this instance this corresponds to using a small initial oxygen exposure and reduced substrate temperature to achieve a doubled surface of higher perfection. Such optimized interfaces can act as templates for guiding the hierarchical assembly of nanowires and other nanoscale molecular assemblies. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
02.70.Uu Applications of Monte Carlo methods
61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics
81.16.Dn Self-assembly
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Investigations of the electron field emission properties and microstructure correlation in sulfur-incorporated nanocrystalline carbon thin films

S. Gupta, B. R. Weiner, and G. Morell

J. Appl. Phys. 91, 10088 (2002); http://dx.doi.org/10.1063/1.1477255 (10 pages) | Cited 14 times

Online Publication Date: 30 May 2002

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Results are reported on the electron field emission properties of sulfur (S)-incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum (Mo) substrates by hot-filament chemical vapor deposition (HFCVD) technique. In addition to the conventionally used methane (CH4) as carbon precursor with high hydrogen (H2) dilution, hydrogen sulfide–hydrogen (H2S)/H2 premix gas was used for sulfur incorporation. The field emission properties for the S-incorporated films were investigated systematically as a function of substrate temperature (TS) and sulfur concentration. Lowest turn-on field achieved was observed at around 4.0 V/μm for the n-C:S sample grown at TS of 900 °C with 500 ppm of H2S. These results are compared with those films grown without sulfur (n-C) at a particular TS. The turn-on field was found to be almost half for the S-assisted film thus demonstrating the effect of sulfur addition to the chemical vapor deposition process. An inverse relation between turn-on field (EC), growth temperature and sulfur concentration was found. The S incorporation also causes significant microstructural changes, as characterized with non-destructive complementary ex situ techniques: scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy (RS). S-assisted films show relatively smoother and finer-grained surfaces than those grown without it. These findings are discussed in terms of the dual role of sulfur in enhancing the field emission properties by controlling the sp2 C cluster size and introducing substantial structural defects through its incorporation. The in-plane correlation length (La) of sp2 C cluster was determined from the intensity ratio of the D- and G-bands [I(D)/I(G)] in the visible RS as a function of deposition temperature and sulfur concentration using a phenomenological model. The turn-on field was found to decrease with increasing sp2 C cluster size in general ranging from 0.8 to 1.4 nm. The films having sp2 C clusters of around 1.4 nm had the lowest turn-on field and steep rising emission currents, providing an estimate of optimum size for La for the material grown hereby. These findings are assessed in terms of a reduced field emission barrier brought about by the sulfur addition and the need for relatively longer conductive paths capable of withstanding the relatively large emission currents. It is because the sp2 C cluster size predominate the chemical environment, chemical order, sp3 content or local conductivity. Besides, although most of the S is expected to be electrically inactive, under the high doping conditions (larger S/C) hereby employed, there may be some amount of S in donor states, an indication of the availability of conduction electrons. These results also suggest that the behaviors of sulfur-incorporated nanocrystalline carbon thin films are closer to that grown with phosphorus (P) and Nitrogen (N) elements. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
78.30.Hv Other nonmetallic inorganics

Blueshifts in the ultraviolet absorption spectra of amphoteric SnO2−x nanocrystalline particles

Shin Tsunekawa, Junyong Kang, Katsuhiko Asami, and Atsuo Kasuya

J. Appl. Phys. 91, 10098 (2002); http://dx.doi.org/10.1063/1.1481206 (5 pages) | Cited 4 times

Online Publication Date: 30 May 2002

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Blueshifts in the ultraviolet absorption spectra of amphoteric SnO2−x nanocrystalline particles differ greatly in acidic and alkaline sols. X-ray diffraction measurements show that the average lattice strain of the nanocrystalline particles in aqueous ammonia sols is about twice as large as that in oxalic acid sols. The size dependence of the blueshift without lattice strain is proposed to be about three times as large as that in an alkaline sol with large strain. X-ray photoelectron spectroscopic measurements reveal that the valence of Sn in acidic and alkaline sols is not 4 but less than 3. It is strongly suggested that the blueshift depends not only on the crystalline size but also most importantly on the lattice strain and second on the valence state of the Sn ions. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.40.Ha Other nonmetallic inorganics
79.60.Jv Interfaces; heterostructures; nanostructures
61.46.-w Structure of nanoscale materials
82.70.Gg Gels and sols

Photovoltage spectroscopy of InAs/GaAs quantum dot structures

J. Toušková, E. Samochin, J. Toušek, J. Oswald, E. Hulicius, J. Pangrác, K. Melichar, and T. Šimeček

J. Appl. Phys. 91, 10103 (2002); http://dx.doi.org/10.1063/1.1480118 (4 pages) | Cited 13 times

Online Publication Date: 30 May 2002

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In addition to widely used photoluminescence spectroscopy photovoltaic measurement of quantum dot structures can give complementary information about electron and hole transitions. Structures with self-organized InAs quantum dots in GaAs matrix were grown by the Stranski–Krastanov mechanism using the low pressure metalorganic vapor phase epitaxy technique. Two types of samples were studied, with single and multiple quantum dot layers. We have shown that surface photovoltage spectroscopy can be used for the study of single, as well as multiple quantum dot layer structures. © 2002 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.63.Kv Quantum dots
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
73.21.La Quantum dots
81.16.Dn Self-assembly
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Field emission properties of carbon nanohorn films

J.-M. Bonard, R. Gaál, S. Garaj, L. Thien-Nga, L. Forró, K. Takahashi, F. Kokai, M. Yudasaka, and S. Iijima

J. Appl. Phys. 91, 10107 (2002); http://dx.doi.org/10.1063/1.1481200 (3 pages) | Cited 20 times

Online Publication Date: 30 May 2002

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Self-supporting carbon films were prepared from a carbonaceous material, nanohorns. Nanohorns are spherical particles built of sharp cones of a single graphene sheet. The films show good field emission characteristics due to the sharp horn-like structures, in particular a low turn-on field and good long-term stability. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials

Formation and disappearance of a nanoscale silver cluster realized by solid electrochemical reaction

K. Terabe, T. Nakayama, T. Hasegawa, and M. Aono

J. Appl. Phys. 91, 10110 (2002); http://dx.doi.org/10.1063/1.1481775 (5 pages) | Cited 42 times

Online Publication Date: 30 May 2002

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We have developed a nanostructuring method using the solid electrochemical reaction induced by a scanning tunneling microscope (STM). This method has some distinctive features that have not previously been obtained by conventional nanostructuring STM methods. The formation and disappearance of the nanostructure are reversible, and the rates can be controlled using STM. These features are realized via a local oxidation/reduction reaction of mobile metal ions in an ionic/electronic mixed conductor. In this study, a crystal of silver sulfide (Ag2S), a mixed conductor, was used as the material for the STM tip. A nanoscale Ag cluster was formed at the apex of the Ag2S tip when a negative bias voltage was applied to the sample. The Ag ions in the Ag2S tip are reduced to Ag atoms by the tunneling electrons from the sample, and the Ag cluster is formed by the precipitation of the Ag atoms at the apex of the tip. The Ag cluster shrank gradually and disappeared when the polarity of the sample bias voltage was switched to positive. Ag atoms in the Ag cluster are oxidized to Ag ions, and the Ag ions redissolve into the Ag2S tip. The formation and disappearance rates of the cluster were controlled by regulating the tunneling current. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
82.45.Qr Electrodeposition and electrodissolution
81.16.Ta Atom manipulation
72.60.+g Mixed conductivity and conductivity transitions
61.46.-w Structure of nanoscale materials

Photoluminescence quenching of a low-pressure metal-organic vapor-phase-epitaxy grown quantum dots array with bimodal inhomogeneous broadening

G. Saint-Girons and I. Sagnes

J. Appl. Phys. 91, 10115 (2002); http://dx.doi.org/10.1063/1.1481968 (4 pages) | Cited 19 times

Online Publication Date: 30 May 2002

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The photoluminescence (PL) behavior of a bimodal In(Ga)As/GaAs quantum dots (QDs) array grown by low-pressure metal-organic-vapor-phase-epitaxy is studied as a function of the temperature. The PL quenching is attributed to the thermal escape of charge carriers out of the QDs for the high-energy emitting QDs population, and to the presence of nonradiative defects in the immediate vicinity of the lower-energy emitting QDs population. The PL intensity behavior of both QDs population is investigated, and the experimental results are fitted with the help of a rate equations model. The nonradiative mechanisms activation energies are found to be about 180 and 40 meV for the high- and low-energy emitting QDs population, respectively. A charge carriers transfer mechanism between the two QDs populations is also evidenced, and the results are discussed in terms of laser applications. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Luminescence of laterally ordered Ge islands along 〈100〉 directions

L. Vescan and T. Stoica

J. Appl. Phys. 91, 10119 (2002); http://dx.doi.org/10.1063/1.1481205 (8 pages) | Cited 16 times

Online Publication Date: 30 May 2002

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The optical properties of coherently strained, self-ordered Ge islands are analyzed in connection with their size distribution. The ordering was achieved by depositing Ge on Si mesas oriented parallel to 〈100〉 directions and grown by selective epitaxy on Si(001) using low pressure chemical vapor deposition. The spontaneous ordered nucleation of Ge islands along mesa edges is driven by the presence of tensile strain at the periphery of the mesas. All photoluminescence peaks of the islands as well as of the wetting layer are well resolved. The emission peaks of ordered islands could be separated from the emission of randomly distributed islands on the (001) plane by varying the width of the straight mesa lines. The peaks of ordered islands are narrower than from random islands in agreement with the atomic force microscopy analysis. This effect is due to the strong island–island interaction in the one-dimensional row. The emission is governed at low temperature by hole transfer from the wetting layer to the islands, and at higher temperature by hole transfer from the islands to the wetting layer. © 2002 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
68.55.A- Nucleation and growth
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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