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19 Sep 2005

Volume 87, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 123111 (2005); http://dx.doi.org/10.1063/1.2053370 (3 pages)

Xianghui Zhang, Ye Zhang, Jun Xu, Zhe Wang, Xihong Chen, Dapeng Yu, Peng Zhang, Hanhong Qi, and Yongjun Tian
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Generalized stacking fault energies, ductilities, and twinnabilities of Ni and selected Ni alloys

Donald J. Siegel

Appl. Phys. Lett. 87, 121901 (2005); http://dx.doi.org/10.1063/1.2051793 (3 pages) | Cited 34 times

Online Publication Date: 12 September 2005

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The generalized stacking fault energies, Rice-criterion ductilities, and twinnabilities of selected Ni-x solid-solution alloys (x = Nb, W, Mn, Fe, Cu) are calculated using density functional theory to elucidate how alloying alters the mechanical properties of pure Ni. Relative to Ni, the alloys have smaller stacking fault energies (γsf), similar ductilities, and a greater tendency to undergo deformation twinning. The results are compared to experimental studies of the mechanical properties of nanocrystalline (nc) Ni alloys from the literature, and it is suggested that the higher strain-hardening rate recently reported for nc-Ni-Cu (relative to nc-Ni-Fe) does not arise from differences in γsf, but from a higher dislocation density caused by more facile dislocation nucleation.
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61.72.Nn Stacking faults and other planar or extended defects
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

Third-order optical nonlinearity in regio-controlled polythiophene films

Hideo Kishida, Keisuke Hirota, Takeru Wakabayashi, Hiroshi Okamoto, Hisashi Kokubo, and Takakazu Yamamoto

Appl. Phys. Lett. 87, 121902 (2005); http://dx.doi.org/10.1063/1.2051795 (3 pages) | Cited 21 times

Online Publication Date: 12 September 2005

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We have investigated the third-order optical nonlinearity of poly(3-hexylthiophenes) with various head-to-tail coupling ratios (r), using the third-harmonic generation method. An increase in r leads to a reduction in optical gap energy (Eg) and an increase in the third-order nonlinear susceptibility (χ(3)). For r = 0 to 0.80, χ(3) is scaled by Eg as χ(3)∝Eg−6.7, while for r ∼ 1, χ(3) is considerably enhanced beyond this scaling law. We discuss how the behavior of χ(3) is based upon the conjugation-length dependence of the transition dipole moments.
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42.70.Jk Polymers and organics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Qn Polymers; organic compounds
43.25.Dc
42.70.Qs Photonic bandgap materials

Thermal annealing effect on the band gap and dielectric functions of silicon nanocrystals embedded in SiO2 matrix

L. Ding, T. P. Chen, Y. Liu, C. Y. Ng, Y. C. Liu, and S. Fung

Appl. Phys. Lett. 87, 121903 (2005); http://dx.doi.org/10.1063/1.2051807 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2005

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The thermal annealing effect on band gap and dielectric functions of silicon nanocrystals (nc-Si) embedded in a SiO2 matrix synthesized by Si ion implantation is investigated by spectroscopic ellipsometry. A large band-gap expansion of nc-Si relative to bulk crystalline silicon has been observed. The band gap of the nc-Si for the nonannealing condition (i.e., as implanted) is 1.78 eV while it is 1.72 eV for the annealing at 1000 °C for 100 min. The slight decrease in the band gap is attributed to the slight increase in the nc-Si size with annealing. The dielectric functions of nc-Si show a significant suppression, as compared to bulk crystalline silicon, due to the quantum size effect. Annealing results in a small change in the static dielectric constant, which can be explained in terms of the size effect also.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.20.Mq Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
77.22.Ch Permittivity (dielectric function)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Chemical fluctuation-induced nanodomains in Cu(In,Ga)Se2 films

Yanfa Yan, R. Noufi, K. M. Jones, K. Ramanathan, M. M. Al-Jassim, and B. J. Stanbery

Appl. Phys. Lett. 87, 121904 (2005); http://dx.doi.org/10.1063/1.2053349 (3 pages) | Cited 21 times

Online Publication Date: 12 September 2005

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The microstructure and chemistry of CuInSe2 single-crystals and Cu(In,Ga)Se2 thin films from high-efficiency devices are investigated by transmission electron microscopy and x-ray energy-dispersive spectroscopy. We find strong chemical fluctuations at the nanoscale, which result in a lattice comprising a mixture of relatively Cu-poor and Cu-rich nanodomains in both cases. These nanodomains are crystallographically coherent, and no structural lattice defects are found at the interfaces between them. These nanodomains may interconnect, forming three-dimensional, interpenetrating Cu-poor and Cu-rich percolation networks. Such interconnected structures may play a role in the high device performance of Cu(In,Ga)Se2 thin-film photovoltaics.
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82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.05.Hd Other semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)

Thermally-induced formation of Si wire array on an ultrathin (111) silicon-on-insulator substrate

Zainal A. Burhanudin, Ratno Nuryadi, Yasuhiko Ishikawa, Michiharu Tabe, and Yukinori Ono

Appl. Phys. Lett. 87, 121905 (2005); http://dx.doi.org/10.1063/1.2053354 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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We have found that a Si wire array is formed by thermal agglomeration of an ultrathin (111) Si layer in a bonded silicon-on-insulator (SOI) structure, although previous studies for crystalline and amorphous Si layers on SiO2 only showed island formation. As starting material, (111) bonded SOI wafers with the top Si layers thinned to 5–9 nm were used. The samples were then subjected to a thermal treatment at 950 °C in an ultrahigh vacuum. Atomic force microscopy revealed that the (111) top Si layer is deformed into three sets of wire arrays in the three equivalent 〈11math〉 directions. It is also shown that the patterning of a Si layer leads to the wire array selectively formed in one of these three directions.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)

The change of electric field and of some other insulating properties during isochronal annealing in thermally poled Ge-doped silica films

Qiming Liu, Bertrand Poumellec, Delfin Braga, Guy Blaise, Yitao Ren, and Martin Kristensen

Appl. Phys. Lett. 87, 121906 (2005); http://dx.doi.org/10.1063/1.2053361 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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The secondary electron emission contrast between poled and unpoled regions in thermally poled Ge-doped silica films were measured according to different annealing temperatures and electron doses with electron acceleration energy of 5 keV. It is used for measuring the change on annealing of poling induced electric field and other insulating properties like electron traps population and conductivity in high field. Concerning the change of the contrast at low dose arising from the poling electric field, we show that this field begins to disappear at around 450 °C and is erased completely at 650 °C. Using a larger dose allows measuring the change in conductivity contrast. We find a stability similar to the electric field with a disappearance around 450 ∼ 650 °C. On the contrary, for intermediate dose, the contrast remains for larger annealing temperature. It allows measuring properties of the electron traps. Their number appears to be modified in the poling process.
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73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
77.22.Ej Polarization and depolarization
79.20.Hx Electron impact: secondary emission
81.40.Gh Other heat and thermomechanical treatments

Theoretical expression for elastic relaxation in strained-layer superlattice specimens thinned for transmission electron microscopy

Hiroshi Shimotahira and Kenichi Nakamura

Appl. Phys. Lett. 87, 121907 (2005); http://dx.doi.org/10.1063/1.2042541 (3 pages)

Online Publication Date: 12 September 2005

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We derived a theoretical expression for elastic relaxation in a strained-layer superlattice (SLS) grown coherently on substrates. The derived formula takes into account two types of elastic relaxation: one between adjacent layers in the SLS, and another between the whole SLS and the substrates. Numerical calculations for a strained multi-quantum-well laser diode as an example of a SLS showed that elastic relaxation due to the average strain of the whole SLS occurs even for a relatively thick specimen, while periodic elastic relaxation due to the strain between layers in the SLS occurs near the specimen surface. These theoretical results are in good agreement with those obtained by computer simulations based on finite-element method.
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68.65.Cd Superlattices
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Lp Transmission electron microscopy (TEM)

Microscopic failure behavior of nanoporous gold

Juergen Biener, Andrea M. Hodge, and Alex V. Hamza

Appl. Phys. Lett. 87, 121908 (2005); http://dx.doi.org/10.1063/1.2051791 (3 pages) | Cited 35 times

Online Publication Date: 13 September 2005

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We report on the fracture behavior of nanoporous (np)-Au with an open sponge-like morphology of interconnecting ligaments on the nanometer length scale. Despite its macroscopic brittleness, np-Au is microscopically a very ductile material as ligaments strained by as much as 200% can be observed in the vicinity of crack tips. Cell-size effects on the microscopic failure mechanism were studied by annealing treatments that increased the typical pore size/ligament diameter from ∼ 100 nm to  ∼ 1 μm. Ligaments with diameter of ∼ 100 nm fail by plastic flow and necking, whereas failure by slip was observed for larger ligaments with a diameter of ∼ 1 μm. The absence of slip marks in 100-nm-sized ligaments suggests a strongly suppressed dislocation activity, consistent with the high yield strength of np-Au.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.46.-w Structure of nanoscale materials
62.20.M- Structural failure of materials
81.40.Gh Other heat and thermomechanical treatments

Scanning transmission electron microscopy of gate stacks with HfO2 dielectrics and TiN electrodes

Melody P. Agustin, Leonardo R. C. Fonseca, Jacob C. Hooker, and Susanne Stemmer

Appl. Phys. Lett. 87, 121909 (2005); http://dx.doi.org/10.1063/1.2053362 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2005

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High-angle annular dark-field (HAADF) imaging and electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopy were used to investigate HfO2 gate dielectrics grown by atomic layer deposition on Si substrates, and their interfaces with TiN electrodes and silicon, as a function of annealing temperature. Annealing at high temperatures (900 °C) caused significant roughening of both bottom (substrate) and top (electrode) interface. At the bottom interface, HAADF images showed clusters of Hf atoms that protruded into the interfacial SiO2 layer. Low-loss EELS established that even crystalline HfO2 films exposed to relative high temperatures (700 °C) exhibited significant differences in their electronic structure relative to bulk HfO2. Further annealing caused the electronic structure to more closely resemble that of bulk HfO2, with the most significant change due to annealing with the TiN electrode.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
79.20.Uv Electron energy loss spectroscopy
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)

High performance reflection gratings in nematiclike photorefractive polymers

O-Pil Kwon, Seong-Ji Kwon, Mojca Jazbinsek, Peter Günter, and Suck-Hyun Lee

Appl. Phys. Lett. 87, 121910 (2005); http://dx.doi.org/10.1063/1.2053363 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2005

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Photorefractive materials based on the nematiclike photoconductive polymers PPT-TPA consisting of the rigid backbone poly(p-phenyleneterephthalate), PPT, and pendent photoconducting triphenylamine (TPA) groups were studied in reflection grating geometry and compared to the layered photorefractive composites PPT-CZs with photoconducting carbazole (CZ) groups. The order level of the mesophase structure has a crucial influence on the trapping characteristics of the composites. The nematiclike composites although of lower photoconductivity exhibit one order of magnitude faster response than in the layered composites in the reflection grating regime. This is attributed to the increased trapping rate as a result of the specific mesophase structure.
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42.70.Jk Polymers and organics
42.70.Gi Light-sensitive materials
42.79.Dj Gratings
72.40.+w Photoconduction and photovoltaic effects

Strengthening TiN diffusion barriers for Cu metallization by lightly doping Al

L. C. Yang, C. S. Hsu, G. S. Chen, C. C. Fu, J. M. Zuo, and B. Q. Lee

Appl. Phys. Lett. 87, 121911 (2005); http://dx.doi.org/10.1063/1.2056583 (3 pages) | Cited 9 times

Online Publication Date: 14 September 2005

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Thin films of Ti1−xAlxN were deposited on (100) Si by ultrahigh-vacuum dual-target reactive sputtering, and the impact of lightly doping Al of x as small as 0.09 on altering the films’s microstructure upon thermal annealing, and hence the performance of the films (40 nm thick) as diffusion barriers for Cu metallization was evaluated. The results of transmission electron microscopy, Rutherford backscattering spectroscopy, and grazing-incidence x-ray diffraction show that the TiN barrier layer gives the commonly observed voided, columnar grains composed of 5 nm sized subgrains. Upon annealing, the subgrains tend to coalesce into 20 nm sized equiaxed grains full of crystalline defects, initiating an inward penetration of Cu and a partial dissociation of TiN, transforming themselves, respectively, into pyramidal (or columnar) Cu3Si precipitates and a dendritic Ti5Si3 layer just after 550 °C, 10 min annealing. However, the lightly doped Al not only overrides the tendency to form intercolumnar voids inherent in sputter deposition by self-shadowing and statistical roughening, but also substantially enhances the microstructural and thermochemical stability, hence significantly improving barrier property, as evidenced from an annealing test at an elevated temperature (600 °C) for a prolonged period of 30 min.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
66.30.-h Diffusion in solids
61.72.up Other materials
81.15.Cd Deposition by sputtering
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
81.40.Gh Other heat and thermomechanical treatments
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Intermixing and phase separation at the atomic scale in Co-rich (Co,Fe) and Cu multilayered nanostructures

Peter F. Ladwig, Jesse D. Olson, Joseph H. Bunton, David J. Larson, Robert M. Ulfig, Richard L. Martens, Tye T. Gribb, Thomas F. Kelly, Martin C. Bonsager, Allan E. Schultz, Bharat B. Pant, and Y. Austin Chang

Appl. Phys. Lett. 87, 121912 (2005); http://dx.doi.org/10.1063/1.2032593 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2005

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Despite the fact that Co-rich (Co,Fe) alloys and Cu are immiscible materials in bulk form, evidence of thermally induced mixing at the atomic scale has been observed in thin-film multilayers of (Co,Fe) and Cu. However, long term anneals at lower temperatures produced a breakup of the multilayers into a two-phase mixture of (Co,Fe) and Cu particles. The observations were made with the use of the three-dimensional atom probe technique, with supporting evidence from differential scanning calorimetry and x-ray diffraction. Besides their scientific importance, these results are of interest where these (Co,Fe) and Cu thin films are used to produce the giant magnetoresistive effect.
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68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Gh Other heat and thermomechanical treatments
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.De Giant magnetoresistance

“Bridge Model” of nanoparticles deposited on pores area of the substrate during a membrane fabrication

Zhongliang Shi, Shanqiang Wu, and Jerzy A. Szpunar

Appl. Phys. Lett. 87, 121913 (2005); http://dx.doi.org/10.1063/1.2056587 (3 pages)

Online Publication Date: 15 September 2005

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The initial observations of a palladium membrane deposited by an electroless process and an aluminium membrane deposited by a sputtering process on the porous stainless steel substrates illustrate that the membranes are made of their nanoparticles and the pore areas at the surface of the substrate are covered by palladium or aluminium nanoparticles, which are like building bridges there. A “Bridge Model” is presented to illustrate the deposition progress of the fabrication of a membrane on the porous substrate. Scanning electron microscope micrographs from the cross section of the the palladium membrane deposited on the substrate confirm the presence of this bridge. The result will be beneficial for the design and fabrication of various nanomembranes and micromembranes on the porous substrates as well the effective control of them by the deposition processes.
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81.07.Bc Nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Lateral phase separation in AlGaN grown on GaN with a high-temperature AlN interlayer

Q. Sun, Y. Huang, H. Wang, J. Chen, R. Q. Jin, S. M. Zhang, H. Yang, D. S. Jiang, U. Jahn, and K. H. Ploog

Appl. Phys. Lett. 87, 121914 (2005); http://dx.doi.org/10.1063/1.2056588 (3 pages) | Cited 10 times

Online Publication Date: 15 September 2005

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The influences of a high-temperature (HT) AlN interlayer (IL) on the phase separation in crack-free AlGaN grown on GaN have been studied. The depth-dependent cathodoluminescence (CL) spectra indicate a relatively uniform Al distribution in the growth direction, but the monochromatic CL images and the CL spectra obtained by line scan measurements reveal a lateral phase separation in AlGaN grown on relatively thick HT-AlN ILs. Moreover, when increasing the thickness of HT-AlN IL, the domain-like distribution of the AlN mole fraction in AlGaN layers is significantly enhanced through a great reduction of the domain size. The morphology of mesa-like small islands separated by V trenches in the HT-AlN IL, and the grain template formed by the coalescence of these islands during the subsequent AlGaN lateral overgrowth, are attributed to be responsible for the formation of domain-like structures in the AlGaN layer.
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81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Integration of carbon nanotubes into diluted magnetic semiconductor

Yun-Hi Lee, J. M. Yoo, J. Ah Lee, S. Y. Ahn, J. Joo, S. Lee, D. H. Kim, B. K. Ju, and K. J. Song

Appl. Phys. Lett. 87, 121915 (2005); http://dx.doi.org/10.1063/1.2045557 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2005

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Carbon nanotubes (CNTs) were grown using catalytic pyrolysis of acetylene on a thin-film-diluted magnetic semiconductor (Co-8 at. % doped TiO2) without consuming the host layer of semiconductor TiO2. Effects of the thickness of the diluted magnetic semiconductor layer and the stacking structure on the growth of the carbon nanotubes were examined. The external diameter and crystalline structure of the nanotubes showed correlation with the structure of the magnetic catalyst Co within the nanotubes or at the end of the tube. After the growth of CNTs, the TiO2 layer still maintained its semiconducting properties in view of the temperature dependent resistance behavior. Moreover, we studied the influence of the electrical resistivity, i.e, the thickness as a process parameter, of the diluted magnetic semiconductor underlayer, which determines the growth height and the crystalline quality of the carbon nanotubes, on the nanotubes’ growth behavior. Finally, we measured the magnetic behavior of the heterosystem and interpreted the results due to the action of the properties of the catalytic diluted magnetic semiconductor underlayer. Our result shows a promising recipe for the fabrication of one-dimensional CNT—two-dimensional magnetic-metal-doped magnetic semiconductor and/or wide-band-gap insulator.
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81.07.De Nanotubes
75.50.Pp Magnetic semiconductors
61.46.-w Structure of nanoscale materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
75.70.Ak Magnetic properties of monolayers and thin films
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Surface stability and evolution of biaxially strained epitaxial thin films

Y. W. Zhang

Appl. Phys. Lett. 87, 121916 (2005); http://dx.doi.org/10.1063/1.2053367 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2005

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First-order perturbation analysis has been performed to investigate the stability and the fastest growth mode of a biaxially strained epitaxial thin film surface by stress-induced surface diffusion. It is found that the normalized critical wavelength along one principal direction depends on the Poisson’s ratio of the film, and also the perturbed wavelength and stress level along the other principal direction. The fastest growth analysis shows that when the absolute value of the ratio of the two principal stresses deviates from unity, a gradual transition from nanoisland formation to nanowire formation occurs. The larger the deviation, the stronger the tendency for the formation of a nanowire; finite element simulations confirm the tendency.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.35.Fx Diffusion; interface formation
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Atomic-scale manipulation of potential barriers at SrTiO3 grain boundaries

Pradyumna Prabhumirashi, Vinayak P. Dravid, Andrew R. Lupini, Matthew F. Chisholm, and Stephen J. Pennycook

Appl. Phys. Lett. 87, 121917 (2005); http://dx.doi.org/10.1063/1.2046734 (3 pages) | Cited 8 times

Online Publication Date: 16 September 2005

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In oxide grain boundaries (GBs), oxygen ions and their vacancies serve as a common denominator in controlling properties such as GB barrier height and capacitance. Therefore, it is critical to analyze, control and manipulate oxygen and vacancies at oxide interfaces as most of the practical devices are almost always influenced by the presence of electrostatic potential barriers at interfaces. Here, we report adjustment of a single GB potential barrier via manipulation of oxygen vacancy concentration using simple oxidation and reduction treatments. We validate our analysis with aberration-corrected HAADF imaging and column-by-column EELS coupled with macroscopic transport measurements of isolated GBs to gain important insight into the physical attributes of GB potential barriers.
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61.72.Mm Grain and twin boundaries
79.20.Uv Electron energy loss spectroscopy
81.65.Mq Oxidation
68.37.Lp Transmission electron microscopy (TEM)
61.72.J- Point defects and defect clusters

Impact of metal silicide precipitate dissolution during rapid thermal processing of multicrystalline silicon solar cells

T. Buonassisi, A. A. Istratov, S. Peters, C. Ballif, J. Isenberg, S. Riepe, W. Warta, R. Schindler, G. Willeke, Z. Cai, B. Lai, and E. R. Weber

Appl. Phys. Lett. 87, 121918 (2005); http://dx.doi.org/10.1063/1.2048819 (3 pages) | Cited 20 times

Online Publication Date: 16 September 2005

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Synchrotron-based analytical x-ray microprobe techniques were employed to study the dissolution of iron, copper, and nickel silicide precipitates at structural defects in cast multicrystalline silicon in response to rapid thermal processing (RTP). A direct correlation was observed between iron silicide precipitate dissolution, increased minority carrier recombination, and decreased device performance after high-temperature (1000 °C) RTP. In contrast, iron precipitates comparable in size to as-grown material remained after lower-temperature RTP (860 °C); in this case the material exhibited higher minority carrier diffusion length and better solar cell performance. RTP at both temperatures effectively dissolved nickel and copper silicide precipitates. It is concluded that iron dissolved from structural defect reservoirs detrimentally affects the cell performance, likely by forming distributed point defects and smaller precipitates. For cast multicrystalline silicon, higher performance can be expected by inhibiting the dissolution of these precipitates, i.e., by reducing the time and/or temperature of processing steps.
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84.60.Jt Photoelectric conversion
64.75.-g Phase equilibria
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
66.30.-h Diffusion in solids
61.72.J- Point defects and defect clusters
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