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13 Dec 2004

Volume 85, Issue 24, pp. 5819-6053

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5968 (2004); http://dx.doi.org/10.1063/1.1830083 (3 pages)

A. Urbieta, P. Fernández, and J. Piqueras
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Why can CuInSe2 be readily equilibrium-doped n-type but the wider-gap CuGaSe2 cannot?

Yu-Jun Zhao, Clas Persson, Stephan Lany, and Alex Zunger

Appl. Phys. Lett. 85, 5860 (2004); http://dx.doi.org/10.1063/1.1830074 (3 pages) | Cited 20 times

Online Publication Date: 9 December 2004

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The wider-gap members of a semiconductor series such as diamond→Si→Ge or AlN→GaN→InN often cannot be doped n-type at equilibrium. We study theoretically if this is the case in the chalcopyrite family CuGaSe2→CuInSe2, finding that: (i) Bulk CuInSe2 (CIS, Eg=1.04 eV) can be doped at equilibrium n-type either by Cd or Cl, but bulk CuGaSe2 (CGS, Eg=1.68 eV) cannot; (ii) result (i) is primarily because the Cu-vacancy pins the Fermi level in CGS farther below the conduction band minimum than it does in CIS, as explained by the “doping limit rule;” (iii) Cd doping is better than Cl doping, in that CdCu yields in CIS a higher net donor concentration than ClSe; and (iv) in general, the system shows massive compensation of acceptors (CdIII,VCu) and donors (ClSe,CdCu,InCu).
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61.72.up Other materials
61.72.S- Impurities in crystals
61.72.Bb Theories and models of crystal defects
61.72.J- Point defects and defect clusters
73.20.At Surface states, band structure, electron density of states

Grown-in twin boundaries affecting deformation mechanisms in nc-metals

A. G. Frøseth, P. M. Derlet, and H. Van Swygenhoven

Appl. Phys. Lett. 85, 5863 (2004); http://dx.doi.org/10.1063/1.1835531 (3 pages) | Cited 26 times

Online Publication Date: 9 December 2004

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Molecular dynamics simulations have recently shown that the presence of grown-in twin boundaries in nc-Al promotes slip activity in the form of twin boundary migration. In this letter we investigate the effect of grown-in twin boundaries on the plastic deformation mechanism in nc-Ni and Cu, and show that (1) for these particular fcc metals twin boundary migration is not the favored deformation mechanism and (2) that the Schmid factors of the grown-in twin plane play a correspondingly important role. The results are explained in terms of the different ratios of the extrema of the generalized planar fault curves.
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81.05.Bx Metals, semimetals, and alloys
61.72.Mm Grain and twin boundaries
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.46.-w Structure of nanoscale materials

Noncontact surface tension and viscosity measurements of rhenium in the liquid and undercooled states

Takehiko Ishikawa, Paul-François Paradis, and Shinichi Yoda

Appl. Phys. Lett. 85, 5866 (2004); http://dx.doi.org/10.1063/1.1836002 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2004

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Surface tension and viscosity of liquid rhenium, which have hardly been measured due to the extremely high melting temperature of rhenium, were measured using an electrostatic levitation method combined with the oscillation drop technique. Sample position instability problems caused by the photon pressure of the heating lasers and by sample evaporation were solved by modifying the electrodes design. Good sample stability allowed the measurements of the surface tension and the viscosity over wide temperature ranges including the undercooled states. Over the 2800–3600 K interval, the surface tension of rhenium was measured as σ(T)=2.71×103−0.23(T−Tm), where Tm is the melting temperature, 3453 K. At Tm, the datum agrees well with the literature values. Similarly, on the same temperature range, the viscosity was determined as η(T)=0.08 exp[1.33×105∕(RT)] (mPa s).
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68.03.Cd Surface tension and related phenomena
66.20.-d Viscosity of liquids; diffusive momentum transport
68.03.Fg Evaporation and condensation of liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys

Defects and strain relaxation in silicon-germanium-on-insulator formed by high-temperature oxidation

S. W. Bedell, K. Fogel, D. K. Sadana, and H. Chen

Appl. Phys. Lett. 85, 5869 (2004); http://dx.doi.org/10.1063/1.1835532 (3 pages) | Cited 13 times

Online Publication Date: 9 December 2004

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SiGe layers were grown on silicon-on-insulator substrates and oxidized at temperatures from 1200 to 1300 °C to form silicon-germanium-on-insualtor (SGOI) layers. Strain relaxation of the SGOI film is shown to be dislocation mediated and the residual strain scaled with the final SGOI thickness in a manner consistent with equilibrium theory. Stacking faults (SF) are observed in the relaxed SGOI layer and their density increases exponentially with decreasing film thickness. In films below ∼500 math, the SF density becomes comparable with the dislocation density which may be responsible for differences between equilibrium and measured residual strain in thin SGOI layers.
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81.05.Hd Other semiconductors
61.72.Nn Stacking faults and other planar or extended defects
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Does In-bonding delay GaN-segregation in GaInAsN? A Raman study

T. Tite, O. Pagès, and E. Tournié

Appl. Phys. Lett. 85, 5872 (2004); http://dx.doi.org/10.1063/1.1829387 (3 pages) | Cited 5 times

Online Publication Date: 9 December 2004

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The longitudinal (LO) and transverse (TO) optical Ga–N phonons of thick as-grown Ga1−yInyAs1−xNx∕GaAs (001) layers with x∼3%–4%, i.e., just above the N-solubility limit xs∼2% in GaAs, and y up to 30% are studied by Raman scattering. We observe a three-mode behavior which we associate with Ga–N modes from the isolated Ga4N complexes (∼460 cm−1), the Ga3InN ones (∼480 cm−1) and the GaN-segregated region (∼425 cm−1). The corresponding N fractions are derived via combined contour modeling of the three-mode TO and LO Ga–N Raman lineshapes. We find that substantial In-bonding minimizes GaN segregation only in a very narrow x range of ∼1% just above xs.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Nanoparticle iron-phosphate anode material for Li-ion battery

Dongyeon Son, Eunjin Kim, Tae-Gon Kim, Min Gyu Kim, Jaephil Cho, and Byungwoo Park

Appl. Phys. Lett. 85, 5875 (2004); http://dx.doi.org/10.1063/1.1835995 (3 pages) | Cited 34 times

Online Publication Date: 9 December 2004

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Nanoparticle crystalline iron phosphates (FePO4⋅2H2O and FePO4) were synthesized using a (CTAB) surfactant as an anode material for Li rechargeable batteries. The electrochemical properties of the nanoparticle iron phosphates were characterized with a voltage window of 2.4–0 V. A variscite orthorhombic FePO4⋅2H2O showed a large initial charge capacity of 609 mAh∕g. On the other hand, a tridymite triclinic FePO4 exhibited excellent cyclability: the capacity retention up to 30 cycles was ∼80%, from 485 to 375 mAh∕g. The iron phosphate anodes exhibited the highest reported capacity, while the cathode LiFePO4 has an ideal capacity of 170 mAh∕g.
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82.47.Aa Lithium-ion batteries
82.45.Fk Electrodes
82.45.Yz Nanostructured materials in electrochemistry
61.46.-w Structure of nanoscale materials

Ga+ implantation in the organic crystal (TMTSF)2PF6 by focused ion beam

K. Wang, O. Schneegans, A. Moradpour, and F. Jomard

Appl. Phys. Lett. 85, 5878 (2004); http://dx.doi.org/10.1063/1.1834988 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Ga ion implantation in the organic crystal (TMTSF)2PF6 (TMTSF: tetramethyl tetraselena fulvalene) is performed using focused ion beam. It is shown that heavy-ion deep implantation inside the sample is obtained for relatively weak ion energy. The electric conduction of the impact areas, at first strongly reduced by ion irradiation, is observed to be reinforced by further ion implantation. The conduction behaviors of the Ga-rich zones can be described by a small polaron hopping model.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.72.up Other materials
61.80.Jh Ion radiation effects
81.65.Cf Surface cleaning, etching, patterning
61.72.S- Impurities in crystals
61.82.Pv Polymers, organic compounds
72.20.Ee Mobility edges; hopping transport

Effects of periodic delta-doping on the properties of GaN:Si films grown on Si (111) substrates

L. S. Wang, K. Y. Zang, S. Tripathy, and S. J. Chua

Appl. Phys. Lett. 85, 5881 (2004); http://dx.doi.org/10.1063/1.1832758 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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In this study, the effects of periodic Si delta-doping on the morphological and optical properties of GaN films grown on Si (111) substrate have been investigated. It is found that the flow rate of Si dopant during growth significantly affects the surface morphology, structural and optical quality of GaN. Compared to undoped GaN on Si(111), films grown using periodic delta-doping show a significant reduction of the in plane tensile stress, which is confirmed by the blueshift of the E2(TO) phonon and band edge photoluminescence peaks. The crack density in GaN films also reduces due to delta-doping.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.55.Cr III-V semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

In situ low-angle x-ray scattering study of phase separation in initially mixed HfO2–SiO2 thin film interfaces

Jeong-Hee Ha, David Chi, and Paul C. McIntyre

Appl. Phys. Lett. 85, 5884 (2004); http://dx.doi.org/10.1063/1.1831554 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2004

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In this letter, we report on phase separation kinetics at initially mixed interfaces of HfO2–SiO2 multilayers measured by low-angle x-ray scattering. Multilayers were fabricated by sputtering and ultraviolet ozone oxidation of ultrathin Hf and Si precursor films. The multilayers were subjected to isothermal anneals in the temperature range 680–762 °C during in situ x-ray scattering measurements. The evolution of the intensity of the multilayer x-ray satellite peaks, the Fourier components of the composition modulation, were consistent with diffusional phase separation of HfO2 and SiO2 during the anneals. The effective interdiffusivity mathL of the HfO2–SiO2 alloy present at the interfaces in the as-deposited multilayers was estimated from the measured intensity change of the first-order satellite reflection as a function of annealing time. The extracted activation energy for the phase separation process was 2.06±0.15 eV for the multilayer samples studied.
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64.75.-g Phase equilibria
78.70.Ck X-ray scattering
68.65.Ac Multilayers
81.15.Cd Deposition by sputtering
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers

Impact of polydispersity on light propagation in colloidal photonic crystals

Mathieu Allard and Edward H. Sargent

Appl. Phys. Lett. 85, 5887 (2004); http://dx.doi.org/10.1063/1.1835533 (3 pages) | Cited 13 times

Online Publication Date: 9 December 2004

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The influence of polydispersity, or variations in the size of particles, on the transmittance of slabs of colloidal photonic crystals is analyzed. A model based on simulated annealing simulates the assembly of particles with a given size distribution into a dense array. The model reveals the existence of a transition between ordered and random packing at a polydispersity between 3% and 4%; this transition is associated with large changes in optical properties, in the form of greatly increased scattering and reduced contrast associated with the transmittance in and out of the stop band. The predictions of the model correspond closely to experimental measurements.
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42.70.Qs Photonic bandgap materials
82.70.Dd Colloids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Structure and intermixing of GaSb∕GaAs quantum dots

R. Timm, H. Eisele, A. Lenz, S. K. Becker, J. Grabowski, T.-Y. Kim, L. Müller-Kirsch, K. Pötschke, U. W. Pohl, D. Bimberg, and M. Dähne

Appl. Phys. Lett. 85, 5890 (2004); http://dx.doi.org/10.1063/1.1833560 (3 pages) | Cited 20 times

Online Publication Date: 9 December 2004

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We present cross-sectional scanning tunneling microscopy results of GaSb quantum dots in GaAs, grown by metalorganic chemical vapor deposition. The size of the optically active quantum dots with base lengths of 4–8 nm and heights of about 2 nm is considerably smaller than previously published data obtained by other characterization methods. The local stoichiometry, obtained from atomically resolved images, shows a strong intermixing in the partly discontinuous wetting layer with an average GaSb content below 50%, while the GaSb content of the partly intermixed quantum dots is between 60% and 100%.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.66.Bi Elemental solids
61.66.Dk Alloys

Near room temperature droplet epitaxy for fabrication of InAs quantum dots

Jong Su Kim and Nobuyuki Koguchi

Appl. Phys. Lett. 85, 5893 (2004); http://dx.doi.org/10.1063/1.1839642 (3 pages) | Cited 37 times

Online Publication Date: 9 December 2004

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By using the droplet epitaxy method, we succeed in fabricating the InAs quantum dots (QDs) with the spatial density of 4×1010∕cm2 and an average lateral size of 20 nm on GaAs (001) at the droplets deposition temperature of 50 °C and subsequent annealing process under As4 flux. These QDs shows the intense photoluminescence even at room temperature indicating that high-quality InAs QDs can be fabricated by near room temperature droplets deposition and crystallization process by 400 °C in situ annealing.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
64.70.K- Solid-solid transitions
68.35.B- Structure of clean surfaces (and surface reconstruction)

Wave-shaped Si crystal wafers obtained by plastic deformation and preparation of their solar cells

Kazuo Nakajima, Kozo Fujiwara, and Wugen Pan

Appl. Phys. Lett. 85, 5896 (2004); http://dx.doi.org/10.1063/1.1834719 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2004

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We can prepare wave-shaped crystal wafers by the plastic deformation of Si crystal wafers, and we report on the characteristics of solar cells fabricated using the wave-shaped Si wafers, in order to demonstrate whether the shaped wafers are of high quality to be used in the preparation of devices or not. To obtain wave-shaped Si wafers, graphite dies were used. The diameter of the convex and concave waves formed in the dies is 4 mm. The Si wafers were pressed by an overload of 200 N. A thickness versus temperature region for obtaining well wave-shaped Si wafers by plastic deformation was determined. Solar cells were prepared using wave-shaped wafers pressed at 1100 and 1200 °C. The wafers were annealed at 1109 and 1209 °C, respectively, for 1 h in a hydrogen atmosphere. The conversion efficiency of the wave-shaped solar cells is 6.0%–10.1%. Thus, it is clarified that the wave-shaped wafers are of high quality to be used in the preparation of devices. The quality of the wafers can be significantly improved by suitable thermal treatments.
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84.60.Jt Photoelectric conversion
81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
61.72.Cc Kinetics of defect formation and annealing
62.20.F- Deformation and plasticity

Patterned nanoclusters in the indium-doped SrTiO3 films

M. Zhang, X. L. Ma, D. X. Li, H. B. Lu, Z. H. Chen, and G. Z. Yang

Appl. Phys. Lett. 85, 5899 (2004); http://dx.doi.org/10.1063/1.1836879 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Highly dense, dimensionally uniform, and self-organized nanoclusters have been formed in the indium-doped SrTiO3 film, which was grown by computer-controlled laser molecular-beam epitaxy on SrTiO3 substrate. On the basis of transmission electron microscopy and three-dimensional strain mapping from a high-resolution lattice image, it is found that the nanoclusters exhibit a dome-shaped structure with a flat bottom, whose diameter distribution ranges from 1.6 nm to 6.4 nm. Nanobeam composition analysis shows that the nanoclusters are rich of doping element compared with their surrounding medium.
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61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Chemical ordering in ilmenite-hematite bulk ceramics through proton irradiation

D. M. Allen, L. Navarrete, J. Dou, R. Schad, P. Padmini, P. Kale, R. K. Pandey, S. Shojah-Ardalan, and R. Wilkins

Appl. Phys. Lett. 85, 5902 (2004); http://dx.doi.org/10.1063/1.1834989 (3 pages) | Cited 7 times

Online Publication Date: 9 December 2004

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We demonstrated the capability of MeV proton irradiation to promote chemical ordering processes in a solid at low temperature. We used the ilmenite–hematite solid solution system which allows estimation of the degree of ordering through measurement of its magnetization. Normally, ordering through diffusion would require high temperature annealing. At high temperatures, however, the equilibrium state would be less ordered and thus the achievable ordering incomplete. High energetic protons continuously transfer energy to the sample through electronic interaction which locally deposits large quantities of energy without a general increase of the sample temperature. This promotes diffusion processes which allow the system to relax towards the ordered equilibrium state.
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81.05.Mh Cermets, ceramic and refractory composites
61.80.Jh Ion radiation effects
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
61.82.Ms Insulators
66.30.Ny Chemical interdiffusion; diffusion barriers
64.70.K- Solid-solid transitions

X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment

B. Abendroth, R. Gago, F. Eichhorn, and W. Möller

Appl. Phys. Lett. 85, 5905 (2004); http://dx.doi.org/10.1063/1.1836868 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2–10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress–release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.82.Ms Insulators
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.A- Nucleation and growth
61.80.Jh Ion radiation effects
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
81.40.Gh Other heat and thermomechanical treatments

Columnar [001]-oriented nitrogen order in Ga(NAs) and (GaIn)(NAs) alloys

O. Rubel, K. Volz, T. Torunski, S. D. Baranovskii, F. Grosse, and W. Stolz

Appl. Phys. Lett. 85, 5908 (2004); http://dx.doi.org/10.1063/1.1829801 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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Show Abstract
By calculations in the framework of the valence force field method, we show that nitrogen atoms in diluted GaAs1−xNx tend to align along the [001] direction. In quaternary alloys Ga1−yInyAs1−xNx this tendency is observed only in “as-grown” samples, while in the annealed samples nitrogen atoms build more energetically favorable bonds with indium. Experimentally observed inhomogeneous strain profiles in these material systems, as well as their dissolution upon annealing, agree qualitatively with results of the calculations.
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61.50.-f Structure of bulk crystals
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
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