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17 Feb 2003

Volume 82, Issue 7, pp. 1003-1136

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 1069 (2003); http://dx.doi.org/10.1063/1.1544428 (3 pages)

M. L. Povinelli, Steven G. Johnson, J. D. Joannopoulos, and J. B. Pendry
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Ga vacancies and grain boundaries in GaN

J. Oila, K. Saarinen, A. E. Wickenden, D. D. Koleske, R. L. Henry, and M. E. Twigg

Appl. Phys. Lett. 82, 1021 (2003); http://dx.doi.org/10.1063/1.1542946 (3 pages) | Cited 12 times

Online Publication Date: 10 February 2003

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We have applied a low-energy positron beam to study epitaxial Si-doped GaN layers, where the grain size varies from 0.2 to 2–5 μm. Negatively charged Ga vacancies are found in n-type samples. Their concentration is independent of the grain size, suggesting that Ga vacancies exist in the grain interior. Positrons are observed to get trapped also at other negatively charged centers. The positron trapping rate at these defects correlates with the grain-boundary density. We attribute the observed shallow positron traps, which do not contain open volume, to negatively charged edge-type dislocations which define the grain boundaries. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.70.Bj Positron annihilation

Localized epitaxial growth of α-Al2O3 thin films on Cr2O3 template by sputter deposition at low substrate temperature

P. Jin, S. Nakao, S. X. Wang, and L. M. Wang

Appl. Phys. Lett. 82, 1024 (2003); http://dx.doi.org/10.1063/1.1544442 (3 pages) | Cited 23 times

Online Publication Date: 10 February 2003

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Low-temperature growth of α-Al2O3 films by sputtering was studied with x-ray diffraction and high-resolution transmission electron microscopy (HRTEM). Pure α-Al2O3 film was formed at 400 °C using Cr2O3 as template, whereas amorphous or θ-Al2O3 was formed without Cr2O3. HRTEM revealed localized epitaxial growth of α-Al2O3 on Cr2O3 with the relationship [011]Al2O3/[011]Cr2O3, suggesting the importance of Cr2O3 as a structural template for the growth of α-Al2O3, in addition to other contributions such as good stoichiometry, low sputter pressure, and low deposition rate under optimized deposition conditions. Successful growth of α-Al2O3 by sputtering at 400 °C or below makes the film widely applicable to even glass substrates. © 2003 American Institute of Physics.
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81.15.Cd Deposition by sputtering
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)

Behavior of monocrystalline silicon under cyclic microindentations with a spherical indenter

I. Zarudi, L. C. Zhang, and M. V. Swain

Appl. Phys. Lett. 82, 1027 (2003); http://dx.doi.org/10.1063/1.1541110 (3 pages) | Cited 28 times

Online Publication Date: 10 February 2003

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This study discusses the behavior of high-pressure phases of monocrystalline silicon when subjected to cyclic indentations with a spherical indenter. It was found that specific phases form in the second and subsequent indentation cycles under low maximum loads. An increase of the maximum indentation load causes changes of subsequent indentation cycles of the phase transformation events to occur earlier on both loading and unloading. The repeated indentations result in the formation of a multiphase structure in the deformed zone, featuring a nonhysteresis behavior. After a critical stage, the properties of the transformed material are stabilized and further indentations can no longer alter the load–displacement curve. It was also found that the greater the maximum load, the faster the occurence of property stabilization. © 2003 American Institute of Physics.
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62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
64.70.K- Solid-solid transitions
64.75.-g Phase equilibria

Ni-based bulk metallic glass formation in the Ni–Nb–Sn and Ni–Nb–Sn–X (X = B,Fe,Cu) alloy systems

Haein Choi-Yim, Donghua Xu, and William L. Johnson

Appl. Phys. Lett. 82, 1030 (2003); http://dx.doi.org/10.1063/1.1544434 (3 pages) | Cited 109 times

Online Publication Date: 10 February 2003

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Refractory Ni-based bulk metallic glasses are formed in the three-component Ni–Nb–Sn system near a ternary eutectic composition located within the three-phase field bounded by the three intermetallics Ni3Nb, Ni6Nb7 (μ-phase), and Ni2NbSn (BiF3-type). Bulk amorphous alloys of composition Ni60Nb40−xSnx with 3<x<9 were prepared by injection-casting the molten alloys into copper models. X-ray diffraction and differential scanning calorimetry studies show the cast strips to be fully amorphous up to thicknesses from 0.5 to 3 mm as x is varied. Maximum glass-forming ability (GFA) observed when x is between 6 and 7. These refractory bulk amorphous alloys exhibit high glass transition temperatures 881<Tg<895 K, a large, stable, undercooled liquid region with ΔT = Tx−Tg, at ∼40–60 K, very high Vickers hardness (VH ∼ 1000–1280 Kg/mm2), and estimated yield strengths in the range of 3 to 3.8 GPa. The effects of small quaternary additions of B and Fe on the GFA of the ternary alloys are also reported. © 2003 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.05.Kf Glasses (including metallic glasses)
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
81.40.Lm Deformation, plasticity, and creep
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Evidence for a Type-II band alignment between cubic and hexagonal phases of GaN

X. H. Lu, P. Y. Yu, L. X. Zheng, S. J. Xu, M. H. Xie, and S. Y. Tong

Appl. Phys. Lett. 82, 1033 (2003); http://dx.doi.org/10.1063/1.1541113 (3 pages) | Cited 12 times

Online Publication Date: 10 February 2003

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The photoluminescence spectra of a series of thin, undoped, hexagonal GaN films containing cubic GaN inclusions grown by molecular-beam epitaxy on 6H-SiC have been studied as a function of temperature and excitation power. The dependence of the line shape and peak position of a peak at ∼3.17 eV on laser power suggests that it is associated with a spatially indirect Type-II transition between hexagonal and cubic GaN. The values of the band offsets extracted from our data are in good agreement with theoretical predictions. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology

Experimental demonstration of photonic crystal waveplates

D. R. Solli, C. F. McCormick, R. Y. Chiao, and J. M. Hickmann

Appl. Phys. Lett. 82, 1036 (2003); http://dx.doi.org/10.1063/1.1541938 (3 pages) | Cited 23 times

Online Publication Date: 10 February 2003

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We have constructed and experimentally tested a microwave half-waveplate using the dispersive birefringent properties of a bulk, two-dimensional, photonic crystal away from its band gap. Our waveplate device exhibited a 200:1 polarization contrast, limited by our experimental resolution. We anticipate that photonic crystal waveplates will have important practical applications in several areas, including integrated photonic circuits. © 2003 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
42.82.Gw Other integrated-optical elements and systems
42.25.Lc Birefringence
84.40.-x Radiowave and microwave (including millimeter wave) technology

High-temperature elastic properties of in situ-reinforced Si3N4

Geoffrey A. Swift, Ersan Üstündag, Bjørn Clausen, Mark A. M. Bourke, and Hua-Tay Lin

Appl. Phys. Lett. 82, 1039 (2003); http://dx.doi.org/10.1063/1.1554478 (3 pages) | Cited 5 times

Online Publication Date: 10 February 2003

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A high-temperature tensile stress study of a monolithic silicon nitride (Si3N4) was performed with time-of-flight neutron diffraction. A dedicated engineering diffractometer was employed at temperatures reaching 1375 °C. Rietveld refinements of diffraction spectra allowed the determination of (1) the coefficient of thermal expansion tensor during heating and (2) lattice strains during loading. The stress–strain response of individual lattice reflections was used to calculate the single-crystal elastic stiffness tensor of Si3N4 at 1375 °C via a self-consistent model. © 2003 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
65.40.De Thermal expansion; thermomechanical effects
62.20.D- Elasticity
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
62.20.F- Deformation and plasticity

Electronic structure and energetics of RCo5H4 and RCo5 (R = La,Pr)

L. G. Hector and J. F. Herbst

Appl. Phys. Lett. 82, 1042 (2003); http://dx.doi.org/10.1063/1.1553999 (3 pages) | Cited 4 times

Online Publication Date: 10 February 2003

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Calculations of the spin-dependent electronic structure and enthalpies of formation, ΔH, of the ternary hydrides LaCo5H4, PrCo5H4, and their parent intermetallics are reported. All four compounds are found to be metallic and ferromagnetic. We obtain ΔH(LaCo5H4) = −45.6 kJ/mole H2, ΔH(PrCo5H4) = −39.8 kJ/mole H2, and ΔH(LaCo5) = −12.6 kJ/LaCo5, values which compare very favorably with experiment. With the assumption of the free-ion 4f moment for Pr, the calculated magnetic moments agree well with available measurements. © 2003 American Institute of Physics.
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71.20.Eh Rare earth metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
65.40.G- Other thermodynamical quantities
75.30.Cr Saturation moments and magnetic susceptibilities
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Thermomigration in Pb–Sn solder joints under joule heating during electric current stressing

Hua Ye, Cemal Basaran, and Douglas Hopkins

Appl. Phys. Lett. 82, 1045 (2003); http://dx.doi.org/10.1063/1.1554775 (3 pages) | Cited 75 times

Online Publication Date: 10 February 2003

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Electromigration of solder joint under high dc current density is known as a reliability concern for the future high-density flip chip packaging and power packaging. Biased mass diffusion within solder joint from cathode to anode under high dc current density is observed in these experiments. In this letter, the experiments on flip chip solder joints under dc current stressing are conducted and thermomigration due to the thermal gradient in the solder joint caused by joule heating is reported. A three-dimensional coupled electric thermal finite-element (FE) simulation of a realistic flip chip module shows the existence of thermal gradient in the solder joint which is high enough to trigger thermomigration. © 2003 American Institute of Physics.
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81.20.Vj Joining; welding
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
02.70.Dh Finite-element and Galerkin methods
66.30.Qa Electromigration
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