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19 Aug 2002

Volume 81, Issue 8, pp. 1369-1534

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Molar volumes of molten indium at high pressures measured in a diamond anvil cell

Guoyin Shen, Nagayoshi Sata, Mathew Newville, Mark L. Rivers, and Stephen R. Sutton

Appl. Phys. Lett. 81, 1411 (2002); http://dx.doi.org/10.1063/1.1499737 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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Molar volumes of molten indium have been measured in an isothermal compression up to 8.5 GPa at 710(3) K in an externally heated diamond anvil cell. The measurement is based on the x-ray diffraction and x-ray absorption of materials using a synchrotron monochromatic x-ray microbeam. The fit to the results with the Birch–Murnaghan equation of state gives parameters of V0 = 16.80 cm3, K0 = 23.9(6) GPa, assuming that K′ = 4. This method should be applicable for measuring molar volumes of liquids and other amorphous materials in the diamond anvil cell. © 2002 American Institute of Physics.
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61.25.Mv Liquid metals and alloys
78.70.Dm X-ray absorption spectra
64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
62.10.+s Mechanical properties of liquids

Silver as a sensitizer for erbium

C. Strohhöfer and A. Polman

Appl. Phys. Lett. 81, 1414 (2002); http://dx.doi.org/10.1063/1.1499509 (3 pages) | Cited 48 times

Online Publication Date: 9 August 2002

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The photoluminescence of Er3+in borosilicate glass is strongly enhanced by the presence of silver. Samples prepared by a combination of erbium ion implantation and Na+↔Ag+ ion exchange show an increase of the Er3+excitation efficiency of up to a factor 70 when excited at 488 nm. Excitation of Er3+ is possible over a broad wavelength range in the near ultraviolet and visible. Our data suggest that absorption of light occurs at a silver ion/atom pair or similar defect, followed by energy transfer to Er3+. We can exclude that silver nanocrystals are part of the dominant excitation mechanism, neither via local field enhancement effects due to their surface plasmon resonance nor via absorption and subsequent energy transfer to Er3+. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators

Thermal stability of polycrystalline silicon electrodes on ZrO2 gate dielectrics

Charles M. Perkins, Baylor B. Triplett, Paul C. McIntyre, Krishna C. Saraswat, and Eric Shero

Appl. Phys. Lett. 81, 1417 (2002); http://dx.doi.org/10.1063/1.1499513 (3 pages) | Cited 34 times

Online Publication Date: 9 August 2002

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Thermal stability of gate stack structures composed of ZrO2 gate dielectrics and silicon electrodes was investigated. The ZrO2 films were deposited by atomic layer deposition, while the polycrystalline silicon electrodes were deposited using different variants of chemical (CVD) and physical vapor deposition (PVD). Zirconium silicide formation was noted in all CVD-electroded samples after subsequent annealing treatments at temperatures above 750 °C, but not in the room temperature PVD-electroded samples, even after gate annealing at 1050 °C. The dependence of zirconium silicide formation on the Si deposition process was explained using thermodynamic arguments which explicitly include the effects of oxygen deficiency of the metal oxide films. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.35.Ct Interface structure and roughness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Cd Deposition by sputtering
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Lp Transmission electron microscopy (TEM)

Spectroscopic ellipsometry study of optical transitions in Zn1−xCoxO alloys

Kwang Joo Kim and Young Ran Park

Appl. Phys. Lett. 81, 1420 (2002); http://dx.doi.org/10.1063/1.1501765 (3 pages) | Cited 111 times

Online Publication Date: 9 August 2002

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Zn1−xCoxO (x ⩽ 0.22) films were prepared on (0001)-oriented Al2O3 substrates by rf magnetron sputtering. The alloys show wurtzite crystal structure with the c-axis lattice constant increasing with increasing x. The optical properties of the samples were measured by spectroscopic ellipsometry at room temperature in the 1.5–5 eV photon energy region. As x increases, the optical band gap absorption edge (E0) of the alloys shows a redshift from that of pure ZnO, reaching 350 meV for x = 0.22. The excitonic character of the E0 edge is gradually reduced as x increases and is replaced by the three-dimensional critical-point shape. Optical absorption structures are also observed below the E0 edge near 2 eV and interpreted as due to the transitions between the crystal-field-split 3d levels of tetrahedral Co2+ ions substituting Zn2+ ions. © 2002 American Institute of Physics.
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78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Lateral indium–indium pair correlations within the wetting layers of buried InAs/GaAs quantum dots

B. Shin, B. Lita, R. S. Goldman, J. D. Phillips, and P. K. Bhattacharya

Appl. Phys. Lett. 81, 1423 (2002); http://dx.doi.org/10.1063/1.1501760 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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We have investigated lateral In–In pair correlations within the wetting layers of buried InAs/GaAs quantum dots imaged with cross-sectional scanning tunneling microscopy. We quantified the number of In–In pairs along the [110] direction as a function of the spacing between them. Since the number of In–In pairs exceeds that of a randomly generated distribution of In atoms, significant lateral In clustering within the wetting layers is apparent. A comparison of the experimentally determined and randomly generated In–In pair distributions reveals nearest-neighbor In–In pair interaction energies similar to those calculated for InGaAs alloy surfaces [J. -H. Cho, S. B. Zhang, and A. Zunger, Phys. Rev. Lett. 84, 3654 (2000)]. The In–In pair correlations increase with high temperature annealing, indicating that vertical In–Ga interdiffusion occurs simultaneously with lateral In segregation. Together, these results suggest that initial In clustering in the wetting layer may be frozen at the surface during growth, and that annealing increases the effective sizes of these clusters, driving the system toward its segregated equilibrium state. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Deformation potentials of the E2(high) phonon mode of AlN

A. Sarua, M. Kuball, and J. E. Van Nostrand

Appl. Phys. Lett. 81, 1426 (2002); http://dx.doi.org/10.1063/1.1501762 (3 pages) | Cited 29 times

Online Publication Date: 9 August 2002

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AlN layers grown on (111)-oriented silicon substrates were studied by Raman spectroscopy. The deformation potentials of the nonpolar E2(high) phonon mode of hexagonal AlN were derived from phonon frequency shifts under biaxial stress applied to the layer. Stress was applied by mechanical bending of the wafer with resulting in-plane biaxial stress in AlN. The technique allows one to avoid the uncertainty of x-ray diffraction strain determination inherent to experimental methods commonly used for deformation potentials determination in III–V nitrides. The obtained values for the phonon deformation potentials are in reasonably good agreement with previous theoretical calculations. For pure biaxial stress, we determine a phonon frequency shift of 3 cm−1/GPa. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity

Healing kinetics of interfacial voids in GaAs wafer bonding

YewChung Sermon Wu and Guo-Zen Hu

Appl. Phys. Lett. 81, 1429 (2002); http://dx.doi.org/10.1063/1.1502194 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2002

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A periodic structure of bonded GaAs wafers has been proposed for quasi-phase-matched second-harmonic generation. After bonding, voids were formed at the interface due to the natural topographical irregularities and contamination on the wafer surface. Within the voids, crystallites with diamond-shaped and dendritic geometries were found, which corresponded to the bonded regions. In this study, artificial voids were introduced at the bonded interface to study the growth kinetics of these crystallites, that is the healing kinetics of these voids. It was found that the crystallite geometries and the growth rates are controlled by the nucleation of new surface layers on the bonded planes, which was the slowest stage during the healing process. © 2002 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.Ct Interface structure and roughness
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.35.Md Surface thermodynamics, surface energies
81.65.-b Surface treatments
81.05.Ea III-V semiconductors

Anisotropic liquid crystal gels for switchable polarizers and displays

Hongwen Ren and Shin-Tson Wu

Appl. Phys. Lett. 81, 1432 (2002); http://dx.doi.org/10.1063/1.1502021 (3 pages) | Cited 14 times

Online Publication Date: 9 August 2002

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An anisotropic liquid crystal gel with low operating voltage, high contrast ratio, broad bandwidth, wide viewing angle, and fast response time was demonstrated. In the voltage-off state, the gel is highly transparent. When the gel is activated by an electric field, light scattering occurs for the polarization along the molecular axis. By incorporating a λ/4 film between the gel and a reflector, this reflective device is useful for modulating unpolarized light. Potential applications of such anisotropic gel as a broadband switchable polarizer, reflective display, and transflective display are emphasized. © 2002 American Institute of Physics.
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42.70.Df Liquid crystals
82.70.Gg Gels and sols
42.79.Kr Display devices, liquid-crystal devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Carbon site switching in carbon-doped GaAs

J. Mimila-Arroyo, S. W. Bland, and A. Lusson

Appl. Phys. Lett. 81, 1435 (2002); http://dx.doi.org/10.1063/1.1502005 (3 pages)

Online Publication Date: 9 August 2002

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Carbon thermal stability in carbon-doped GaAs layers is studied. Epitaxial layers were grown by low-pressure metalorganic chemical vapor deposition extrinsically doped with an atomic carbon concentration around 1×1020 cm−3. The hole concentration is found to be a complex function of the annealing time, increasing from an initial value ∼ 7.2×1019 cm−3, to some intermediate value whereupon the hole concentration decreases before resuming its increase to a value consistent with the atomic concentration. The observed carrier loss and its subsequent recovery is explained by a double-site switch of one carbon from the CAs–Ga–CAs dimer. First, the carbon moves to an interstitial site Ci, where it behaves like a double donor, followed by a move to a more distant As substitutional site where it behaves as a normal shallow acceptor. This process allows to recover an additional hole concentration equal to the initial carbon dimer concentration. Both processes follow a first-order kinetics with different kinetic coefficients. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
68.60.Dv Thermal stability; thermal effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Measurement of the thermo-optic coefficients in sol-gel derived inorganic–organic hybrid material films

Eun-Seok Kang, Tae-Ho Lee, and Byeong-Soo Bae

Appl. Phys. Lett. 81, 1438 (2002); http://dx.doi.org/10.1063/1.1501448 (3 pages) | Cited 26 times

Online Publication Date: 9 August 2002

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Thermo-optic coefficients (dn/dT) of inorganic–organic hybrid material films prepared by sol-gel process of organoalkylsilanes are measured using the prism coupler equipped with autocontrolled hot stage. In order to validate the reliability of this method, dn/dT of polymethylmethacrylate film is measured. dn/dT of inorganic–organic hybrid material films are negative and as high as the order of 10−4, which are comparable to those of optical polymers. Their dn/dT increase with increasing organic content in the film and mainly depend on their thermal expansion. © 2002 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
68.60.Dv Thermal stability; thermal effects
42.70.Jk Polymers and organics
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Theoretical and experimental investigation of boron diffusion in polycrystalline HfO2 films

Chun-Li Liu, Z. X. Jiang, R. I. Hegde, D. D. Sieloff, R. S. Rai, D. C. Gilmer, C. C. Hobbs, P. J. Tobin, and Shifeng Lu

Appl. Phys. Lett. 81, 1441 (2002); http://dx.doi.org/10.1063/1.1501766 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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We present ab initio modeling results including formation, migration, and activation energies for B diffusion through bulk and grain boundaries in polycrystalline HfO2 films. Modeling results clearly indicate that B can penetrate through a 40 Å HfO2 film via grain boundary diffusion, but not by bulk diffusion. Secondary ion mass spectroscopy analysis of B concentration profiles for polysilicon/HfO2/Si gate stacks after different anneals showed double B peaks at the interfaces and thus confirmed the modeling prediction. © 2002 American Institute of Physics.
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68.60.Wm Other nonelectronic physical properties
66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals
61.72.Mm Grain and twin boundaries
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Structural and optical properties of wurtzite MgxZn1−xS (0 ⩽ x ⩽ 0.25) films grown on (0001) Al2O3 by pulsed-laser deposition

H. C. Ong and J. Y. Dai

Appl. Phys. Lett. 81, 1444 (2002); http://dx.doi.org/10.1063/1.1502191 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2002

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Wurtzite MgxZn1−xS (0 ⩽ x ⩽ 0.25) thin films have been epitaxially grown on (0001) Al2O3 using pulsed-laser deposition. High-quality films can be prepared at a growth temperature of 450–550 °C with (0001) ω-rocking curve full width at half maximum as narrow as 0.09°. High-resolution cross-sectional transmission electron microscopy of the films deposited at 500 °C shows the presence of the mixture of zinc-blende and wurtzite phases at the interface, and therefore the interfacial region is highly defective. However, above the critical thickness of ∼5 nm, the film bulk consists of pure wurtzite material with a very high level of crystallinity. The band edge of MgxZn1−xS films examined by transmission spectroscopy at room temperature increases from 3.75 eV at x = 0 to 3.95 at x = 0.25. © 2002 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors
68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds
81.15.Fg Pulsed laser ablation deposition

Depth-profiling plasma-induced densification of porous low-k thin films using positronium annihilation lifetime spectroscopy

Jia-Ning Sun, David W. Gidley, Yifan Hu, William E. Frieze, and E. Todd Ryan

Appl. Phys. Lett. 81, 1447 (2002); http://dx.doi.org/10.1063/1.1501767 (3 pages) | Cited 22 times

Online Publication Date: 9 August 2002

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Positronium annihilation lifetime spectroscopy (PALS) has been used to depth profile the densification induced in a porous low-dielectric constant (k) thin film by typical device integration processing, including exposure to plasmas and oxygen ashing. Such “integration damage” has previously been observed as an undesirable increase in k accompanied by shrinkage in the porous film thickness. PALS confirms that the structural damage is confined to a surface layer of collapsed pores with the underlying pores being undamaged. The dense layer thickness determined by PALS increases with plasma exposure time. © 2002 American Institute of Physics.
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52.77.-j Plasma applications
78.70.Bj Positron annihilation
81.05.Rm Porous materials; granular materials

Lattice-matched HfN buffer layers for epitaxy of GaN on Si

R. Armitage, Qing Yang, H. Feick, J. Gebauer, E. R. Weber, Satoko Shinkai, and Katsutaka Sasaki

Appl. Phys. Lett. 81, 1450 (2002); http://dx.doi.org/10.1063/1.1501447 (3 pages) | Cited 24 times

Online Publication Date: 9 August 2002

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Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 μm. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained. © 2002 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology

Copper diffusion characteristics in single-crystal and polycrystalline TaN

H. Wang, Ashutosh Tiwari, X. Zhang, A. Kvit, and J. Narayan

Appl. Phys. Lett. 81, 1453 (2002); http://dx.doi.org/10.1063/1.1502193 (3 pages) | Cited 20 times

Online Publication Date: 9 August 2002

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We have investigated the diffusivity of copper in single-crystal (NaCl-structured) and polycrystalline TaN thin films grown by pulsed-laser deposition. Polycrystalline TaN films were grown directly on Si(100), while single-crystal films were grown with TiN buffer layers. Both poly- and single-crystal films with Cu overlayers were annealed at 500, 600, 650, and 700 °C in vacuum to study the copper diffusion characteristics. The diffusion of copper into TaN was studied using scanning transmission electron microscopy (STEM) Z contrast, where the contrast is proportional to Z2 (atomic number), and TEM. The diffusion distances (2math) are found to be about 5 nm at 650 °C for 30 min annealing. The diffusivity of Cu into single-crystal TaN follows the relation D = (160±9.5)exp[−(3.27±0.1)eV/kB T] cm2 s−1 in the temperature range of 600–700 °C. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.60.Wm Other nonelectronic physical properties
85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)

Dislocation and morphology control during molecular-beam epitaxy of AlGaN/GaN heterostructures directly on sapphire substrates

M. J. Manfra, N. G. Weimann, J. W. P. Hsu, L. N. Pfeiffer, K. W. West, and S. N. G. Chu

Appl. Phys. Lett. 81, 1456 (2002); http://dx.doi.org/10.1063/1.1498867 (3 pages) | Cited 19 times

Online Publication Date: 9 August 2002

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We report on the growth and transport characteristics of high-density ( ∼ 1013 cm−2) two-dimensional electron gases confined at the AlGaN/GaN interface grown by plasma-assisted molecular-beam epitaxy on sapphire substrates. For structures consisting of a 25 nm Al0.30Ga0.70N barrier deposited on a 2 μm insulating GaN buffer, room-temperature mobilities averaging 1400 cm2/V s at a sheet charge density of 1.0×1013 cm−2 are consistently achieved. Central to our approach is a sequence of two Ga/N ratios during the growth of the insulating GaN buffer layer. The two-step buffer layer allows us to simultaneously optimize the reduction of threading dislocations and surface morphology. Our measured sheet resistivities as low as 350Ω/□ compare favorably with those achieved on sapphire or SiC by any growth method. Representative current–voltage characteristics of high-electron-mobility transistors fabricated from this material are presented. © 2002 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.Tv Field effect devices
52.77.Dq Plasma-based ion implantation and deposition
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