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PHYSICS OF SEMICONDUCTORS: 28th International Conference on the Physics of Semiconductors - ICPS 2006 Date: 24-28 July 2006 Location: Vienna (Austria) ISBN: 978-0-7354-0397-0 Editor(s): Wolfgang Jantsch, Friedrich Schaffler

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More Accurate Models Of The Interfaces Oxide Charge From The Ultra‐Thin SOI Films

Cristian Ravariu, Florin Babarada, Adrian Rusu, and Florina Ravariu

AIP Conf. Proc. 893, pp. 3-4; doi:http://dx.doi.org/10.1063/1.2729741 (2 pages)

Online Publication Date: 4 May 2007

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An inherent SOI device dedicated for the in situ electrical characterization of wafers is the pseudo‐MOS transistor that easily provides a key parameter: Flat‐Band Voltage, VFB. Usual models for this voltage were established for SOI structures with 0,2μm…2μm film thickness and 0,4…100μm oxide thickness. The classical models of VFB, deduced for micronic sizes, present some deficiencies in the nanodevice area. An interface charge about 1012e/cm2 in micronic sizes means 1e/100nm2 equivalent with one electron per device area in the nano‐domain. This paper analyses the flat‐band voltage modeling, due to the consequences of the down‐scaling of the SOI wafers. © 2007 American Institute of Physics
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Dielectric discontinuity at a twin boundary in Si(111)

Jun Nakamura and Akiko Natori

AIP Conf. Proc. 893, pp. 5-6; doi:http://dx.doi.org/10.1063/1.2729742 (2 pages)

Online Publication Date: 4 May 2007

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Spatial variations in dielectric constant for the Si films having various stackings have been illustrated using the first‐principles calculations based on the density functional theory in external electric fields. The theoretical value of the optical dielectric constant, ε∞, at the innermost region of the 3C‐Si(111) film agrees well with the experimental one above 8 bi‐layers. Furthermore, the local variation of ε∞ at the twin boundary has been demonstrated. ε∞ changes abruptly at the twin boundary. Such a locality in the variation of ε∞ originates from the local atomic arrangement at the boundary. © 2007 American Institute of Physics
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77.55.-g Dielectric thin films
73.61.Cw Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.22.Ch Permittivity (dielectric function)

Core‐Level Photoelectron Spectroscopy Probing Local Strain at Silicon Surfaces and Interfaces

Oleg V. Yazyev and Alfredo Pasquarello

AIP Conf. Proc. 893, pp. 7-8; doi:http://dx.doi.org/10.1063/1.2729743 (2 pages)

Online Publication Date: 4 May 2007

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Using a first‐principles approach, we investigate the origin of the fine structure in Si 2p photoelectron spectra at the Si(100)2×1 surface and at the Si(100)‐SiO2 interface. Calculated and measured shifts show very good agreement for both systems. By using maximally localized Wannier functions, we provide an interpretation in which the effects due to the electronegativity of second nearest neighbor atoms and due to the local strain field are distinguished. Hence, in combination with accurate modeling, photoelectron spectroscopy can provide a direct measure of the strain field at the atomic scale. © 2007 American Institute of Physics
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
68.35.Gy Mechanical properties; surface strains

Atomic Force Microscopy Simulations of Methyl‐terminated Si(100)2×1 Surfaces

Akira Masago, Satoshi Watanabe, Katsunori Tagami, and Masaru Tsukada

AIP Conf. Proc. 893, pp. 9-10; doi:http://dx.doi.org/10.1063/1.2729744 (2 pages)

Online Publication Date: 4 May 2007

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To assist in investigating the behavior of organic molecules adsorbed on a Si surface using non‐contact atomic force microscopy (NC‐AFM), we are developing a simulator using the density‐functional based tight‐binding method. As a simple application, we simulated the tip‐sample distance dependence of the force and frequency shift for the bare Si(111) surface and the methyl‐terminated Si(001) surface by considering the van der Waals force. In the case of the bare Si(111) surface, we obtained good agreement with experimental data. In the case of the methyl‐terminated Si(001), the force behavior is similar to the Si(111) case in the repulsive force region, whereas it is much smaller in the attractive force region. © 2007 American Institute of Physics
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68.37.Ps Atomic force microscopy (AFM)
68.47.Fg Semiconductor surfaces
68.08.De Liquid-solid interface structure: measurements and simulations
68.43.Bc Ab initio calculations of adsorbate structure and reactions

Reconstruction Induced Surface Strain in GaAs (001) Surfaces Characterized by Reflectance Modulated Spectroscopies

L. F. Lastras‐Martínez, J. M. Flores‐Camacho, R. E. Balderas‐Navarro, A. Lastras‐Martínez, and M. Cardona

AIP Conf. Proc. 893, pp. 11-12; doi:http://dx.doi.org/10.1063/1.2729745 (2 pages)

Online Publication Date: 4 May 2007

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Reflectance modulated (RM) spectroscopies constitute powerful tools for the study and characterization of the piezo‐optical properties of semiconductors. RM techniques are very sensitivity to the orientation of the surface dimers in reconstructed surfaces, as well as to the surface electric field and to the surface stoichiometry. In this communication we report on RM experiments carried out in ultra high vacuum on GaAs (001) surfaces with different reconstructions. We show experimentally that between c(4×4) and (2×4) surfaces there is an inversion of the surface electric field which is induced by a direct piezoelectric effect related to the surface strain. © 2007 American Institute of Physics
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78.68.+m Optical properties of surfaces
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

New Insight In The Metal‐Semiconductor Interface Formation: Generation And Removal Of Donor‐Like Surface States On Cs/p‐GaAs(001)

V. L. Alperovich, A. G. Zhuravlev, O. E. Tereshchenko, H. E. Scheibler, and A. S. Terekhov

AIP Conf. Proc. 893, pp. 13-14; doi:http://dx.doi.org/10.1063/1.2729746 (2 pages)

Online Publication Date: 4 May 2007

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Photoreflectance spectroscopy is applied for detailed measurements of the evolution of surface band bending φs under cesium adsorption and desorption on the As‐rich and Ga‐rich p‐GaAs(001) surfaces. Two new observations are reported. Firstly, under Cs adsorption on the Ga‐rich p‐GaAs(100) surface with the (4×2)/c(8×2) reconstruction, the dependence of φs on the Cs coverage θ contains several maxima and minima, which were not observed earlier for adsorbate‐semiconductor interfaces. Secondly, the dependence φs(θ) has a shape of a reproducible hysteresis loop under the adsorption of cesium and its subsequent thermodesorption. The results are discussed in connection with the experimental data on the atomic structure of the Cs/GaAs(001) interface and possible mechanisms of generation and removal of Cs‐induced donor‐like surface states. © 2007 American Institute of Physics
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73.40.Sx Metal-semiconductor-metal structures
73.20.At Surface states, band structure, electron density of states
78.68.+m Optical properties of surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

A unified model for α2‐β2(2×4) reconstructed semiconductor surfaces based on first principles calculations

Frank Grosse and Hannes Guhl

AIP Conf. Proc. 893, pp. 15-16; doi:http://dx.doi.org/10.1063/1.2729747 (2 pages)

Online Publication Date: 4 May 2007

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It is shown that the α2‐β2‐(2×4) reconstruction, which is stable for a larger number of (001) III‐V semiconductor surfaces, can be described as a generalized 9‐state Potts model. The interaction parameters vary between the different materials and under applied strain. The model allows the calculation of equilibrium properties by the transfer matrix method and the non‐equilibrium dynamics by a kinetic Monte Carlo simulation. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
63.10.+a General theory
68.35.B- Structure of clean surfaces (and surface reconstruction)

In‐segregation measurements by RHEED during growth: comparison between vicinal and nominal substrates

S. Martini, A. A. Quivy, E. C. F. da Silva, and A. E. B. Marques

AIP Conf. Proc. 893, pp. 17-18; doi:http://dx.doi.org/10.1063/1.2729748 (2 pages)

Online Publication Date: 4 May 2007

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The surface segregation of indium atoms was investigated in situ and in real time by reflection high‐energy electron diffraction (RHEED) during molecular‐beam epitaxy of InGaAs layers on misoriented GaAs(001) substrates. The strong damping of the RHEED oscillations was quantitatively related to the strength of the segregation process that was found to decrease with increasing miscut angle. © 2007 American Institute of Physics
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Theoretical Comparison of the Effects of Nitrogen‐Doping and Oxygen‐Doping on Silicon Crystal Growth

H. Kageshima, A. Taguchi, and K. Wada

AIP Conf. Proc. 893, pp. 19-20; doi:http://dx.doi.org/10.1063/1.2729749 (2 pages)

Online Publication Date: 4 May 2007

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The equilibrium densities of the defects formed in the crystal under the vacancy‐rich condition are simulated based on the thermodynamics with the detail balance condition. The formation enthalpies used in the simulations are evaluated using the first‐principles calculations. It is found that, when nitrogen and oxygen are simultaneously doped into the crystal, the void suppression effect by the nitrogen doping is diminished because the oxygen doping enhances the total vacancy density. This is consistent with the experimentally reported high nitrogen‐doping density for Czochralski Si relative to Float‐Zone Si. © 2007 American Institute of Physics
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.Bb Theories and models of crystal defects
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

The effect of Mn ions on the growth of cubic GaN

Eunae Choi, Joongoo Kang, and K. J. Chang

AIP Conf. Proc. 893, pp. 21-22; doi:http://dx.doi.org/10.1063/1.2729750 (2 pages)

Online Publication Date: 4 May 2007

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We perform first‐principles pseudopotential calculations to investigate the effect of Mn delta‐doping on the stability of the zinc‐blende and wurtzite structures in GaN. In bulk GaN, it is possible for the zinc‐blende structure to become a stable phase againt the wurtzite one with increasing the concentration of the delta‐doped Mn ions. On GaN surfaces, it costs very high energies to form inversion domains with a Mn exposure because the MnN bond is not strong enough to stabilize the inverted structures. In the initial growth of GaN, we also examine the formation of stacking faults by the Mn delta‐doping, which generate cubic bonds, and find that the stacking faults easily occur on the Ga‐polar surface rather than on the N‐polar one. On the Ga‐polar surface, the Mn ions tend to remain on the surface than in the bulk region, suggesting that these ions act as a surfactant. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Annealing effect on the buffer layer of high‐quality crystalline GaN

Tzong‐Bin Wang, Wei‐Chou Hsu, Rong‐Tay Hsu, Yu‐Huei Wu, and Yu‐Shyan Lin

AIP Conf. Proc. 893, pp. 23-24; doi:http://dx.doi.org/10.1063/1.2729751 (2 pages)

Online Publication Date: 4 May 2007

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High‐quality GaN films are prepared by low‐pressure metal‐organic chemical vapor deposition (LP‐MOCVD). In situ optical reflectance traces reveal that the ramping time from low temperature to high temperature in the growth of the nucleation layer significantly affects the surface roughness. Atomic force microscopy (AFM) images demonstrate that the increased ramping time improves the surface roughness and the quality of GaN films. Moreover, the surface roughness also influences the lateral growth and coalescence step. Furthermore, the dependence of the Hall measurement on temperature is investigated. The mobility of the lightly doped GaN is as high as 622 cm2/V‐s at a corresponding carrier concentration of 1.1 ×1017 cm−3. The results of this study demonstrate that the proposed GaN films are of high quality and have the excellent electronic property. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.10.Bk Growth from vapor
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness

Surface‐strain Induced Hexagonal/Cubic Polymorphism In InGaN Epitaxial Growth

Yuki Takei and Takashi Nakayama

AIP Conf. Proc. 893, pp. 25-26; doi:http://dx.doi.org/10.1063/1.2729752 (2 pages)

Online Publication Date: 4 May 2007

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The energetics and growth dynamics of InGaN layers on strained InN substrates are studied using the first‐principles calculations. It is shown that the diffusion of adsorbed atoms is suppressed when the grown layers receive the tensile stress from the substrate and the bonding between adsorbed and surface atoms is weakened. The present results indicate that the surface strain is one of relevant factors to promote InGaN hexagonal/cubic polymorphism in epitaxy. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
81.15.Aa Theory and models of film growth
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
68.55.A- Nucleation and growth

Morphology and Optical Properties of Porous GaAs Layers

Nicolas L. Dmitruk, Sergij Yu. Kutovyi, Igor M. Dmitruk, Natalia I. Berezovska, Irene Simkiene, and Julija Sabataityte

AIP Conf. Proc. 893, pp. 27-28; doi:http://dx.doi.org/10.1063/1.2729753 (2 pages)

Online Publication Date: 4 May 2007

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Morphology and optical properties of the porous GaAs layers formed on a single crystal GaAs were investigated by using SEM, AFM, monochromatic multi‐angle‐of‐incidence (MAI) ellipsometry, and photoluminescence and Raman scattering spectroscopies. The pore layer was composed of the two‐layer structure: GaAs pores and its oxide above it. The formation of the two‐layer structure caused the alternation of optical constants and the enhancement of Raman scattering and above‐band‐edge photoluminescence, which could be related to quantum confinement of excitons. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)

TEM and HRXRD Analysis of LP MOVPE Grown InGaP/GaAs epilayers

Claudio Pelosi, Matteo Bosi, Giovanni Attolini, Fabrizio Germini, Cesare Frigeri, and Tatiana Prutskij

AIP Conf. Proc. 893, pp. 29-30; doi:http://dx.doi.org/10.1063/1.2729754 (2 pages)

Online Publication Date: 4 May 2007

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The diffusion phenomena at interfaces between GaAs/InGaP layers grown by low pressure MOVPE have been studied by dark field (DF) transmission Electron Microscopy (TEM) and High resolution X‐ray Diffractometry (HRXRD). By comparing the results of the two techniques a mismatched layer containing P or P and In has been evidenced. The causes of this behavior are briefly discussed. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
61.05.cp X-ray diffraction

In‐Plane Band Gap Engineering by Hydrogenation of Dilute Nitride Semiconductors

M. Felici, A. Polimeni, F. Masia, R. Trotta, G. Pettinari, M. Capizzi, G. Salviati, L. Lazzarini, N. Armani, M. Piccin, G. Bais, F. Martelli, S. Rubini, A. Franciosi, and L. Mariucci

AIP Conf. Proc. 893, pp. 31-32; doi:http://dx.doi.org/10.1063/1.2729755 (2 pages)

Online Publication Date: 4 May 2007

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We present two different methods to pattern the band gap of dilute nitrides in their growth plane by exploiting the unique capability of H to passivate N in these materials. By deposition of metallic masks on and subsequent H irradiation of GaAs1−xNx, we artificially create zones of the crystal having the band gap of untreated GaAs1−xNx well surrounded by GaAs‐like barriers. Alternatively, by focusing an energetic e−‐beam on the surface of hydrogenated GaAs1−xNx we displace H atoms from their N passivation sites, thus leading to a controlled decrease in the crystal band gap in the spatial region where the e−‐beam is steered. © 2007 American Institute of Physics
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81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
81.65.Rv Passivation

Frequency‐ and temperature‐dependent conductivity at the metal‐insulator transition in phosphorus doped silicon studied by far‐infrared ellipsometry

J. Humlíček, A. Dubroka, P. Maršík, D. Munzar, A. V. Boris, and C. Bernhard

AIP Conf. Proc. 893, pp. 33-34; doi:http://dx.doi.org/10.1063/1.2729756 (2 pages)

Online Publication Date: 4 May 2007

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We report on far‐infrared ellipsometric measurements of Si:P with the phosphorus concentration at the metal‐insulator (MI) transition, for temperatures from 15 to 300 K in the 50–600 cm−1 spectral range. Temperature coefficients of the complex conductivity have been measured with high resolution; they reveal a nontrivial evolution of the optical response. © 2007 American Institute of Physics
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71.30.+h Metal-insulator transitions and other electronic transitions
78.30.Am Elemental semiconductors and insulators

Sensitive Ultrafast THz Mobility Measurement

J. N. Heyman, D. Bell, T. Khumalo, S. Nabanja, and N. Coetes

AIP Conf. Proc. 893, pp. 35-36; doi:http://dx.doi.org/10.1063/1.2729757 (2 pages)

Online Publication Date: 4 May 2007

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We have developed a sensitive ultrafast technique for measuring the mobility of photocarriers in semiconductors from THz emission measurements in a magnetic field. In GaAs, this zero‐background technique requires ∼10pJ/pulse photoexcitation, and can be easily implemented with an unamplified Ti:S laser.
We have also investigated cyclotron emission from semi‐insulating GaAs and InP at low temperatures (T<100K), and measured electron, light‐hole and heavy‐hole cyclotron emission as a function of pump photon energy. We see a resonant enhancement of the light‐hole effective mass when the light‐hole kinetic energy equals the optical phonon energy, similar to the well‐known electron magneto‐polaron resonance. © 2007 American Institute of Physics
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78.47.-p Spectroscopy of solid state dynamics
72.80.Ey III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects

Programming the Shape of Highly Ordered Ge Islands on Si: from Dots to Rods

O. D. Dubon, J. T. Robinson, Y. Cao, and J. A. Liddle

AIP Conf. Proc. 893, pp. 37-38; doi:http://dx.doi.org/10.1063/1.2729758 (2 pages)

Online Publication Date: 4 May 2007

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In the Ge on Si model heteroepitaxial system, we show that metal patterns on the Si surface induce the assembly of deposited Ge atoms into highly ordered islands whose shapes are programmed by a combination of metal species and substrate orientation. The island shapes including truncated pyramids and nanorods are radically different from those grown on metal‐free surfaces and arise by a process whereby intermixing between deposited Ge and substrate Si atoms from the onset of island formation facilitate the island shape evolution. © 2007 American Institute of Physics
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Dn Self-assembly

Ordering of Strained Ge Islands on Prepatterned Si(001) Substrates: Morphological Evolution and Nucleation Mechanisms

Gang Chen, H. Lichtenberger, G. Bauer, W. Jantsch, and F. Schäffler

AIP Conf. Proc. 893, pp. 39-40; doi:http://dx.doi.org/10.1063/1.2729759 (2 pages)

Online Publication Date: 4 May 2007

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We investigate the initial stage of the two‐dimensional to three‐dimensional transition of strained Ge layers deposited on pit‐patterned Si(001) templates. Within the pits, which assume the shape of inverted, truncated pyramids after optimized growth of a Si buffer layer, the Ge wetting layer develops a complex morphology consisting exclusively of {105} and (001) facets. These results are attributed to a strain‐driven step‐meandering instability on the faceted sidewalls of the pits, and a step‐bunching instability at the sharp concave intersections of these facets. Although both instabilities are strain driven, their coexistence becomes mainly possible by the geometrical restrictions in the pits. It is shown that the morphological transformation of the pit surface into low‐energy facets has strong influence on the preferential nucleation of Ge islands at the flat bottom of the pits. © 2007 American Institute of Physics
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81.05.Cy Elemental semiconductors
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Kinetic Lattice Monte Carlo Simulations of Germanium Island Growth on Prepatterned Silicon (100) Substrates

R. Akis and D. K. Ferry

AIP Conf. Proc. 893, pp. 41-42; doi:http://dx.doi.org/10.1063/1.2729760 (2 pages)

Online Publication Date: 4 May 2007

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We have performed Kinetic Lattice Monte Carlo (KLMC) simulations of Ge island growth on Si (100) substrates that have been prepatterned to contain pits as well as trenches and plateaus. We obtain dome shaped islands that compare well with experimental observations. © 2007 American Institute of Physics
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63.10.+a General theory
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.05.Cy Elemental semiconductors
61.66.Bi Elemental solids
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Fractal Growth Of Silicon Nanocrystallites During Pulsed Laser Ablation

Ikurou Umezu, Mitsuru Inada, Toshiharu Makino, and Akira Sugimura

AIP Conf. Proc. 893, pp. 43-44; doi:http://dx.doi.org/10.1063/1.2729761 (2 pages)

Online Publication Date: 4 May 2007

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Surface hydrogenated silicon nanocrystallites were prepared by PLA in hydrogen gas. The deposits are aggregated and they are composed of primary particles which mean diameter is about 4–5 nm. The fractal dimension of deposits was analyzed by box counting method. The fractal dimension decreased from 3 to 1.7 with increasing background gas pressure. This means the aggregation mechanism change from ballistic aggregation on the substrate to cluster‐cluster aggregation in the plume. © 2007 American Institute of Physics
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81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
81.07.Bc Nanocrystalline materials
61.46.Hk Nanocrystals
61.43.Hv Fractals; macroscopic aggregates (including diffusion-limited aggregates)

Synthesis and Properties of ZnSe Precursor and ZnSe Nanoribbon Arrays on Zn Substrates

L. J. Zhao, Q. Pang, Y. Cai, X. D. Luo, N. Wang, W. K. Ge, J. N. Wang, Y. P. Fang, X. G. Wen, and S. H. Yang

AIP Conf. Proc. 893, pp. 45-46; doi:http://dx.doi.org/10.1063/1.2729762 (2 pages)

Online Publication Date: 4 May 2007

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Well‐aligned ZnSe precursor nanoribbon arrays on zinc surface were fabricated via a solvothermal method using Zn foil as Zn source, Se powder as Se source and ethylenediamine (en) as solvent. The ZnSe nanoribbon arrays can be easily obtained by heating the ZnSe precursors in N2 at 300°C for 5 hours. The as‐prepared precursors as well as the annealed products are characterized by scanning electron microscopy and powder X‐ray diffraction. Field emission (FE) experiments on annealed sample are also carried out. © 2007 American Institute of Physics
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81.16.Be Chemical synthesis methods
81.07.Bc Nanocrystalline materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.05.cp X-ray diffraction
79.70.+q Field emission, ionization, evaporation, and desorption

Morphology of Si Nanowire Grown via Solid‐Liquid‐Solid Mechanism

Eun Kyung Lee, Byoung Lyong Choi, Kwang Soo Seol, Byung Ki Kim, Jong Min Kim, and Hyeong Joon Kim

AIP Conf. Proc. 893, pp. 47-48; doi:http://dx.doi.org/10.1063/1.2729763 (2 pages)

Online Publication Date: 4 May 2007

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The silicon nanowires are synthesized from both gold nano‐particle coated silicon substrates and gold thin film deposited ones by simple heating under argon atmosphere without any additional silicon sources. The surfaces of the silicon substrates after process are densely covered with a few to tens of micrometer long nanowires in both cases. When gold nano‐particles were used as catalyst, the total diameter of nanowires is ranged from 50nm to 60nm, which is consist of silicon crystal core 10∼15nm and SiOx sheath of 20∼25nm. Especially, we observed the wedge like surface of silicon substrates after the growth of nanowires. The wedge shape and direction are determined by uneven gold film thickness, movement of gold atoms, and the crystal orientation of silicon substrate. © 2007 American Institute of Physics
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Hc Catalytic methods
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
68.55.-a Thin film structure and morphology

Surface Concentration Mapping of InAs/GaAs Quantum Dots

G. Biasiol, S. Heun, G. B. Golinelli, A. Locatelli, T. O. Mentes, F. Z. Guo, and L. Sorba

AIP Conf. Proc. 893, pp. 49-50; doi:http://dx.doi.org/10.1063/1.2729764 (2 pages)

Online Publication Date: 4 May 2007

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By using X‐Ray Photoemission Electron Microscopy we have obtained two‐dimensional maps of the in‐plane surface composition of InAs/GaAs self‐assembled quantum dots. The chemical analysis reveals a higher In composition on the dot surface, with respect to the surrounding wetting layer, with a concentration increasing from the sides to the center of the dots. Comparison with concentrations found in the core of similar dots suggests strong In segregation on their surface, similarly to the surrounding wetting layer. © 2007 American Institute of Physics
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Yz X-ray microscopy
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Dv Composition, segregation; defects and impurities

Optimization of MBE Growth Parameters for GaAs‐based THz Quantum Cascade Lasers

Aaron Maxwell Andrews, Tomas Roch, Alexander Benz, Gernot Fasching, Werner Schrenk, Karl Unterrainer, and Gottfried Strasser

AIP Conf. Proc. 893, pp. 51-52; doi:http://dx.doi.org/10.1063/1.2729765 (2 pages)

Online Publication Date: 4 May 2007

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A 15 μm thick active region terahertz (2.86 THz) quantum cascade laser was optimized for maximum continuous wave temperature operation. Through the use of high‐resolution x‐ray diffraction, improved growth rate and doping calibrations, minimization of flux transients, a double‐metal waveguide, and optimization of doping the threshold current was reduced from 1.88 to 0.20 kA/cm2 and a maximum continuous wave operating temperature of 72K was achieved. The tolerable thickness variation in one cascade was <1.1%. Details of the optimizations are discussed in detail. © 2007 American Institute of Physics
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81.07.St Quantum wells
42.55.Px Semiconductor lasers; laser diodes
81.10.Bk Growth from vapor
81.16.-c Methods of micro- and nanofabrication and processing
68.65.Fg Quantum wells
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