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3 Jul 2000

Volume 77, Issue 1, pp. 1-153

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Protection of SrBi2Ta2O9 ferroelectric capacitors from hydrogen damage by optimized metallization for memory applications

Suk-Kyoung Hong, Chung Won Suh, Chang Goo Lee, Seok Won Lee, Eung Youl Kang, Nam Soo Kang, Cheol Seong Hwang, and Oh Seong Kwon

Appl. Phys. Lett. 77, 76 (2000); http://dx.doi.org/10.1063/1.126882 (3 pages) | Cited 12 times

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The degradation behavior of integrated Pt/SrBi2Ta2O9/Pt capacitors by hydrogen impregnation during the intermetal dielectric deposition and passivation is investigated. The hydrogen ions generated as a reaction byproduct from the SiH4-based deposition processes of the dielectric films induce reduction in the remanent polarization (Pr) as well as the imprint behavior of the small size capacitors (2×2 μm2). The degree of degradation is quite dependent on the size of the individual capacitors. The smaller capacitors underwent more serious degradation implying that the hydrogen ions impregnate into the SBT layer mainly along the etched side area of the capacitors not through the top Pt electrode. Metallization adopting TiN/Al/TiN/Ti multilayer is very effective in suppressing the hydrogen impregnation. In particular, the Ti layer appears to block the hydrogen penetration. Therefore, the optimized metallization scheme, wider metal lines than the top electrode area by 1 μm, successfully protects the integrated capacitors from the hydrogen damage. 12 μC/cm2 of 2Pr and 1.1 V of 2Vc (coercive voltage) with an imprinting voltage of 0.16 V were obtained from the passivated 2×2 μm2 array capacitors by the optimized metallization. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.40.Ls Metallization, contacts, interconnects; device isolation
84.30.Sk Pulse and digital circuits
77.22.Ej Polarization and depolarization

Dispersion of metal nanoparticles for aligned carbon nanotube arrays

Hiroki Ago, Toshiki Komatsu, Satoshi Ohshima, Yasunori Kuriki, and Motoo Yumura

Appl. Phys. Lett. 77, 79 (2000); http://dx.doi.org/10.1063/1.126883 (3 pages) | Cited 51 times

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We report that Co metal nanoparticles (an average diameter of 4 nm) chemically synthesized by a reverse micelle method catalyzes the growth of multiwall carbon nanotubes (MWNTs) aligned perpendicular to a substrate. The surface of the nanoparticles is covered with surfactants so that the nanoparticles can be dispersed in organic solvent. The dispersion of the nanoparticles was cast directly onto a plane Si substrate for thermal pyrolysis of acetylene. We have found that the pretreatment of the metal nanoparticles with hydrogen sulfide before the pyrolysis straightens the MWNTs, suggesting sulfurization of the nanoparticle catalyst plays an important role in regular growth of the MWNTs. The dispersion of the nanoparticles offers a conventional and processible approach to synthesize large area aligned MWNT arrays. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Origin of hexagonal-shaped etch pits formed in (0001) GaN films

S. K. Hong, T. Yao, B. J. Kim, S. Y. Yoon, and T. I. Kim

Appl. Phys. Lett. 77, 82 (2000); http://dx.doi.org/10.1063/1.126884 (3 pages) | Cited 39 times

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We report the origin of hexagonal-shaped etch pits generally observed by conventional wet etching processes on (0001) GaN-based films based on the investigation with transmission electron microscopy on GaN films after being etched with molten KOH. The origin of hexagonal-shaped etch pits is identified as nanopipes through careful characterization of abnormal contrast of nanopipe (open-core screw dislocation), “lobe contrast” of end-on edge and screw (full-core) dislocations, visible and invisible conditions of edge and screw dislocations. Consideration of energetics of these defects also suggests preferential etch pit formation at nanopipes because of much higher energy. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Polarized luminescence in CdS/ZnSe quantum-well structures

M. Schmidt, M. Grün, S. Petillon, E. Kurtz, and C. Klingshirn

Appl. Phys. Lett. 77, 85 (2000); http://dx.doi.org/10.1063/1.126885 (3 pages) | Cited 15 times

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The photoluminescence from type II CdS/ZnSe quantum-well structures is found to be polarized with respect to the 〈110〉 directions with polarization degrees up to 20%. The absolute polarization direction is related to the interface bond directions in samples with differently prepared interfaces. The observations are explained by the detailed analysis of the epitaxial growth process and polarization sensitive luminescence experiments. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Effective surface Debye temperature for NiMnSb(100) epitaxial films

C. N. Borca, Takashi Komesu, Hae-kyung Jeong, P. A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, and J. P. Nozières

Appl. Phys. Lett. 77, 88 (2000); http://dx.doi.org/10.1063/1.126886 (3 pages) | Cited 30 times

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The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145±13 K. This is far smaller than the bulk Debye temperature of 312±5 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
68.35.Ja Surface and interface dynamics and vibrations
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Single titanium crystals encapsulated in carbon nanocages obtained by laser vaporization of sponge titanium in benzene vapor

Hong Chen, Rong-bin Huang, Zi-chao Tang, Lan-sun Zheng, Guang-wen Zhou, and Ze Zhang

Appl. Phys. Lett. 77, 91 (2000); http://dx.doi.org/10.1063/1.126887 (3 pages) | Cited 3 times

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A technique, laser vaporization by ablating at a solid target in the vapor phase, is developed to produce encapsulated titanium nanocrystals. By vaporizing sponge titanium in benzene vapor, the single titanium crystals encapsulated in carbon nanocages have been synthesized in good yields. The sizes of the encapsulated crystals are around 5–15 nm and the numbers of the wrapped graphitic layers are on the order of 3–10 layers. Characteristic lattice spacings and angles observed by high-resolution transmission electron microscopy identify two phases of the nanocrystals inside the carbon onion cavities as α-Ti and β-Ti. The latter has never been stable below 850 °C until the experiment. The encapsulated titanium crystals adsorbed a large amount of hydrogen released in the synthesis. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
64.70.Hz Solid-vapor transitions
79.20.Ds Laser-beam impact phenomena
81.05.Bx Metals, semimetals, and alloys
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On the band gap anomaly in I–III–VI2, I–III3–VI5, and I–III5–VI8 families of Cu ternaries

S. M. Wasim, C. Rincón, G. Marín, and J. M. Delgado

Appl. Phys. Lett. 77, 94 (2000); http://dx.doi.org/10.1063/1.126888 (3 pages) | Cited 18 times

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The experimentally observed energy band gap difference (ΔE1) between the I–III3–VI5 and I–III–VI2 and the energy band gap difference (ΔE2) between the I–III5–VI8 and I–III–VI2 phases of Cu–In–Se, Cu–Ga–Se, Cu–In–Te, and Cu–Ga–Te systems is explained in terms of the relative shift of the conduction band minimum (CBM) and the valence band maximum (VBM) caused due to the presence of the ordered VCu and [In(Ga)Cu+2+2 VCu−1] defect pair and to the effect of the p–d hybridization. The nearly linear variation of ΔE1 and ΔE2 with p–d hybridization of the corresponding I–III–VI2 phase suggests that in selenides the lowering of the VBM predominates over that of the CBM. In the case of the Cu–In–Te system, they are very near the same magnitude, whereas in Cu–Ga–Te the lowering of the CBM predominates over that of the VBM. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds

Exploring the effects of tensile and compressive strain on two-dimensional electron gas properties within InGaN quantum wells

S. F. LeBoeuf, M. E. Aumer, and S. M. Bedair

Appl. Phys. Lett. 77, 97 (2000); http://dx.doi.org/10.1063/1.126889 (3 pages) | Cited 9 times

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With the advent of high-quality AllnGaN quaternary cladding, InGaN quantum wells (QWs) have now been studied under both compressive and tensile strain, as well as no strain at all! This has allowed the experimental investigation of the two-dimensional electron gas (2DEG) properties within InGaN QWs that have been subjected to a full range of strain, opening the doors to a new realm of strain engineering. We present the capacitance–voltage-derived 2DEG properties of several In0.08Ga0.92N QWs subject to various degrees of strain. Strained In0.08Ga0.92N QWs clad with GaN exhibit better 2DEG confinement than their unstrained Al0.24In0.09Ga0.67N-clad counterparts. For the case of compressive-strained QWs, it was found that the peak 2DEG concentration increases linearly with well width. In contrast, such dependence was not observed for the case of unstrained QWs with lattice-matched cladding. Of further interest, the 2DEGs for compressive and tensile In0.08Ga0.92N QWs are localized at opposite interfaces, which is attributed to strain-induced piezoelectric fields pointing in opposite directions. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
77.65.Ly Strain-induced piezoelectric fields
68.35.Gy Mechanical properties; surface strains

Near-field scanning optical microscopy cross-sectional measurements of crystalline GaAs solar cells

M. K. Herndon, W. C. Bradford, R. T. Collins, B. E. Hawkins, T. F. Kuech, D. J. Friedman, and S. R. Kurtz

Appl. Phys. Lett. 77, 100 (2000); http://dx.doi.org/10.1063/1.126890 (3 pages) | Cited 3 times

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Near-field scanning optical microscopy (NSOM) was used to study cleaved edges of GaAs solar cell devices. Using visible light for excitation, the NSOM acquired spatially resolved traces of the photocurrent response across the various layers in the device. For excitation energies well above the band gap, carrier recombination at the cleaved surface had a strong influence on the photocurrent signal. Decreasing the excitation energy, which increased the optical penetration depth, allowed the effects of surface recombination to be separated from collection by the pn junction. Using this approach, the NSOM measurements directly observed the effects of a buried minority carrier reflector/passivation layer. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
07.79.Fc Near-field scanning optical microscopes
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
81.65.Rv Passivation

n-Si/SiO2/Si heterostructure barrier varactor diode design

Y. Fu, M. Mamor, M. Willander, S. Bengtsson, and L. Dillner

Appl. Phys. Lett. 77, 103 (2000); http://dx.doi.org/10.1063/1.126891 (3 pages) | Cited 1 time

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Symmetric C–V and antisymmetric I–V characteristics are essential for a heterostructure barrier varactor (HBV) to generate odd harmonics in a frequency multiplier. Practically high multiplier efficiency is obtained when the shape of the C–V characteristic is sharp near zero bias and the conduction current is low. Here we present the design of an n-type Si/SiO2/Si-based HBV and its state-of-the-art device performance. Self-consistent solutions of the Schrödinger and Poisson equations show a drastic decrease of the conduction current due to the large electron effective mass and the SiO2 barrier height. The shape of the C–V curve can be easily tuned by modifying the thickness of the SiO2 layer. By the techniques compatible with the conventional Si technology, a Si/SiO2/Si varactor junction (having a SiO2 layer of 20 nm) has been processed and the device characteristics are very promising. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
84.32.Tt Capacitors
73.40.Ty Semiconductor-insulator-semiconductor structures
73.61.Cw Elemental semiconductors
84.30.-r Electronic circuits

Imaging of a silicon pn junction under applied bias with scanning capacitance microscopy and Kelvin probe force microscopy

G. H. Buh, H. J. Chung, C. K. Kim, J. H. Yi, I. T. Yoon, and Y. Kuk

Appl. Phys. Lett. 77, 106 (2000); http://dx.doi.org/10.1063/1.126892 (3 pages) | Cited 25 times

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Scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) are used to image the electrical structure of a silicon pn junction under applied bias. With SCM, the carrier density inside a diode is imaged directly. With KPFM, the surface potential distribution of an operating diode is measured, revealing different behavior from that in bulk. The surface potential drop is extended deep into the lightly p-doped region at reverse bias, reflecting the existence of the surface space-charge region as confirmed by the numerical simulation. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
77.22.Jp Dielectric breakdown and space-charge effects

Ultrafast optical characterization of carrier capture times in InxGa1−xN multiple quantum wells

Ü. Özgür, M. J. Bergmann, H. C. Casey, H. O. Everitt, A. C. Abare, S. Keller, and S. P. DenBaars

Appl. Phys. Lett. 77, 109 (2000); http://dx.doi.org/10.1063/1.126893 (3 pages) | Cited 12 times

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Subpicosecond wavelength-degenerate differential transmission optical spectroscopy was used to characterize the electron capture time in a 10-period InxGa1−xN multiple-quantum-well (MQW) structure. Photoluminescence and photoluminescence excitation spectroscopies demonstrated enhanced MQW emission for injection within ±50 meV of the barrier energy. Time-resolved differential transmission measurements for excitation in this region reveal efficient electron capture in the quantum wells with a time constant between 310 and 540 fs. A slower exponential relaxation, with strongly wavelength-dependent subnanosecond decay constants, is also observed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.47.-p Spectroscopy of solid state dynamics

Energy dependence of transient enhanced diffusion and defect kinetics

Hugo Saleh, Mark E. Law, Sushil Bharatan, Kevin S. Jones, Viswanath Krishnamoorthy, and Temel Buyuklimanli

Appl. Phys. Lett. 77, 112 (2000); http://dx.doi.org/10.1063/1.126894 (3 pages) | Cited 9 times

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Boron, a p-type dopant, experiences transient enhanced diffusion (TED) via interstitials. The boron TED and {311} dissolution rates are explored as a function of implant energy dependence. Silicon implants of 1014/cm2 at various energies were used to damage the surface of a wafer with an epitaxially grown boron marker layer. Samples were annealed at 750 °C for 15–135 min to observe the diffusion exhibited by the marker layer and to correlate this with the dissolution of {311} type defects. The diffusion enhancement depends strongly on implant energy but the {311} dissolution rate is weakly dependent. © 2000 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Electronic structure of the Fe–Cu–Nb–Si–B alloys by x-ray absorption spectroscopy

Y. H. Cheng, J. C. Jan, J. W. Chiou, W. F. Pong, M.-H. Tsai, H. H. Hseih, Y. K. Chang, T. E. Dann, F. Z. Chien, P. K. Tseng, M. S. Leu, and T. S. Chin

Appl. Phys. Lett. 77, 115 (2000); http://dx.doi.org/10.1063/1.126895 (3 pages) | Cited 1 time

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We measured x-ray absorption near-edge-structure (XANES) spectra of nanocrystalline- (nc-) and amorphous- (a-) Fe73.5Cu1Nb3Si13.5B9 (nc-FCNSB and a-FCNSB) and Fe78Si13B9 (a-FeSiB) alloys at the Fe L3,2 edge using the sample drain current mode and at the Cu L3,2, and Nb L3 edge and Si K edge using the fluorescence mode. The features in the Fe L3-edge XANES spectrum of nc-FCNSB changed shape significantly with the addition of Cu and Nb to the Fe–Si–B alloy under the optimum annealing conditions, indicating that Cu and Nb strongly influence the Fe 3d local electronic structure. Closely examining the Cu L3,2-edge XANES spectrum of nc-FCNSB reveals that the Cu clusters essentially have a body-centered-cubic structure. The white-line features at the Nb L3 edge suggest a slight increase in delocalization of Nb 4d orbits when a-FCNSB is crystallized into nc-FCNSB. The Si K-edge XANES spectrum demonstrates the dominance of Fe–Si bonds around the Si atom in nc-FCNSB. © 2000 American Institute of Physics.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.22.-f Electronic structure of nanoscale materials and related systems
78.70.Dm X-ray absorption spectra
71.20.Gj Other metals and alloys
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Grain-boundary effects on the electrical resistivity and the ferromagnetic transition temperature of La0.8Ca0.2MnO3

Yonglai Fu

Appl. Phys. Lett. 77, 118 (2000); http://dx.doi.org/10.1063/1.126908 (3 pages) | Cited 33 times

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In this letter, grain-boundary effects on the electrical transport and the ferromagnetic transition temperature were investigated in La0.8Ca0.2MnO3. The different ferromagnetic transition temperature (45 K) and the different metal–semiconductor transition temperature (62 K) were observed in the samples with different grain boundaries. Wide grain boundaries can induce large grain-boundary effects on grain, and small grain size also induces large grain-boundary effects on grain due to the increase of grain boundaries. The possible mechanism of grain-boundary effect is explained as the strain effect of grain induced by the distortion at grain boundaries. The strain of grains should enhance the ferromagnetic double exchange interaction. © 2000 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
61.72.Mm Grain and twin boundaries
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
75.30.Et Exchange and superexchange interactions

Asymmetrical magnetoimpedance in as-cast CoFeSiB amorphous wires due to ac bias

D. P. Makhnovskiy, L. V. Panina, and D. J. Mapps

Appl. Phys. Lett. 77, 121 (2000); http://dx.doi.org/10.1063/1.126896 (3 pages) | Cited 15 times

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Asymmetrical giant magnetoimpedance (AGMI), which utilizes a high frequency bias field hb, is realized in a Co-based amorphous wire having a circumferential anisotropy in the outer region. No asymmetry in the dc magnetic configuration is needed in this case. AGMI is discussed in terms of the surface impedance tensor, demonstrating that the effect of hb is related to the role of the off-diagonal component of the impedance in the voltage response measured across the wire. This effect is important for developing autobiased linear magnetic sensors. Using two oppositely biased wires, a near-linear voltage output (±4 mV) is obtained in the range of ±5 Oe for the sensed dc field at a frequency of 8 MHz. © 2000 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.-w Magnetic instruments and components
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Influences of interfacial intrinsic low-dielectric layers on the dielectric properties of sputtered (Ba,Sr)TiO3 thin films

Byoung Taek Lee and Cheol Seong Hwang

Appl. Phys. Lett. 77, 124 (2000); http://dx.doi.org/10.1063/1.126897 (3 pages) | Cited 56 times

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The influences of low-dielectric interfacial layers on the dielectric properties of Pt/(Ba,Sr)TiO3/Pt capacitors were investigated before and after postannealing. The interfacial layer is believed to be the intrinsic dead layer (low-dielectric layer) due to the termination of chemical bonds of the (Ba,Sr)TiO3 (BST) material at the interfaces. The dielectric constant of the capacitor decreases with decreasing BST film thickness owing to the low dielectric constant of the dead layer. The dead-layer capacitance varies with processes such as film deposition temperature, and postannealing. Higher deposition temperatures result in a larger dead-layer capacitance and a higher bulk dielectric constant. Although annealing under a N2 atmosphere is less effective in reducing the dead-layer effect than under an O2 atmosphere, it is more effective in increasing the bulk dielectric constant. Therefore, a N2, rather than an O2 atmosphere, results in a larger increase in the overall dielectric constant. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
73.40.Rw Metal-insulator-metal structures
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
61.72.Cc Kinetics of defect formation and annealing

Vacancy formation in (Pb,La)(Zr,Ti)O3 capacitors with oxygen deficiency and the effect on voltage offset

T. Friessnegg, S. Aggarwal, R. Ramesh, B. Nielsen, E. H. Poindexter, and D. J. Keeble

Appl. Phys. Lett. 77, 127 (2000); http://dx.doi.org/10.1063/1.126898 (3 pages) | Cited 65 times

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Vacancy-related defect profiles have been measured for La0.5Sr0.5CoO3/(Pb0.9La0.1)(Zr0.2Ti0.8)O3/La0.5Sr0.5CoO3 ferroelectric capacitors using a variable-energy positron beam. By varying the layer thickness and the postgrowth processing in a reducing ambient, a capacitor showing oxygen deficiency dominantly in the top electrode and one with deficiency in both electrodes were produced. The capacitor with an asymmetric defect profile showed a voltage offset polarization–voltage hysteresis loop, that with a symmetric distribution of vacancy-related defects showed no offset. These results are discussed in the context of current models for imprint. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation
77.80.Dj Domain structure; hysteresis

High ε gate dielectrics Gd2O3 and Y2O3 for silicon

J. Kwo, M. Hong, A. R. Kortan, K. T. Queeney, Y. J. Chabal, J. P. Mannaerts, T. Boone, J. J. Krajewski, A. M. Sergent, and J. M. Rosamilia

Appl. Phys. Lett. 77, 130 (2000); http://dx.doi.org/10.1063/1.126899 (3 pages) | Cited 118 times

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We report on growth and characterization of both epitaxial and amorphous films Gd2O3 of (ε = 14) and Y2O3(ε = 18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single-domain films in the Mn2O3 structure. Typical electrical leakage results are 10−3 A/cm2 at 1 V for single domain epitaxial Gd2O3 and Y2O3 films with an equivalent SiO2 thickness, teq of 15 Å, and 10−6 A/cm2 at 1 V for smooth amorphous Y2O3 films (ε = 18) with a teq of only 10 Å. For all the Gd2O3 films, the absence of SiO2 segregation at the interface is established from infrared absorption measurements. © 2000 American Institute of Physics.
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77.55.-g Dielectric thin films
61.43.-j Disordered solids
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)

Relaxational polarization dynamics in soft ferroelectrics

Yun-Han Chen and Dwight Viehland

Appl. Phys. Lett. 77, 133 (2000); http://dx.doi.org/10.1063/1.126900 (3 pages) | Cited 18 times

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Investigations of the frequency dependence of the P–E (polarization versus field) and ε–E (strain versus field) behavior have been performed on soft 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 polycrystalline ferroelectrics at various maximum field strengths below and above that of the coercive field (Ec). For E<Ec, a strong relaxational polarization was observed. At low frequencies, in this field range, P–E curves indicative of polarization switching were observed with an apparent remanence, however at higher frequencies near-linear P–E behavior was found. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
77.80.Fm Switching phenomena

Imaging of acoustic fields in bulk acoustic-wave thin-film resonators

H. Safar, R. N. Kleiman, B. P. Barber, P. L. Gammel, J. Pastalan, H. Huggins, L. Fetter, and R. Miller

Appl. Phys. Lett. 77, 136 (2000); http://dx.doi.org/10.1063/1.126901 (3 pages) | Cited 7 times

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By using an atomic-force-microscope-based technique, we image the vibration of high-frequency, bulk-mode, thin-film resonators. Our experimental technique is capable of monitoring the vibration of these devices over a broad frequency range, from 1 MHz to beyond 10 GHz, allowing us to obtain quantitative measurements of the piezoelectric properties of thin-film materials in that frequency range. This technique allows us to map the complex vibration modes of a new generation of high-frequency bulk piezoelectric resonators, revealing the presence of vibration patterns of very different characteristic lengths. © 2000 American Institute of Physics.
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43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
07.79.Lh Atomic force microscopes
84.40.-x Radiowave and microwave (including millimeter wave) technology
43.35.Yb Ultrasonic instrumentation and measurement techniques
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Reproducible switching effect in thin oxide films for memory applications

A. Beck, J. G. Bednorz, Ch. Gerber, C. Rossel, and D. Widmer

Appl. Phys. Lett. 77, 139 (2000); http://dx.doi.org/10.1063/1.126902 (3 pages) | Cited 404 times

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Thin oxide films with perovskite or related structures and with transition metal doping show a reproducible switching in the leakage current with a memory effect. Positive or negative voltage pulses can switch the resistance of the oxide films between a low- and a high-impedance state in times shorter than 100 ns. The ratio between these two states is typically about 20 but can exceed six orders of magnitude. Once a low-impedance state has been achieved it persists without a power connection for months, demonstrating the feasibility of nonvolatile memory elements. Even multiple levels can be addressed to store two bits in such a simple capacitor-like structure. © 2000 American Institute of Physics.
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73.61.Ng Insulators
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Photon scanning tunneling microscopy of tailor-made photonic structures

C. Peeters, E. Flück, A. M. Otter, M. L. M. Balistreri, J. P. Korterik, L. Kuipers, and N. F. van Hulst

Appl. Phys. Lett. 77, 142 (2000); http://dx.doi.org/10.1063/1.126903 (3 pages) | Cited 17 times

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Optical field distributions around individually fabricated subwavelength scatterers mapped with a photon scanning tunneling microscope are presented. The photonic structures are produced from ridge waveguides using focused-ion-beam milling. This flexible technique allows us to make single holes and slits of sizes down to 30 nm. A quantitative analysis of the observed optical pattern due to interference between incoming and reflected light yields insight about subwavelength scatterers in waveguides. We conclude that light scattering into high-loss modes of the waveguide occurs. © 2000 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques

Thermal conductivity study of porous low-k dielectric materials

Chuan Hu, Michael Morgen, Paul S. Ho, Anurag Jain, William N. Gill, Joel L. Plawsky, and Peter C. Wayner

Appl. Phys. Lett. 77, 145 (2000); http://dx.doi.org/10.1063/1.126904 (3 pages) | Cited 35 times

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An experimental method based on the 3ω technique has been developed to measure thermal conductivity of porous Xerogel films as a function of porosity. The results show that the thermal conductivity of these porous dielectric films can be an order of magnitude smaller than that of SiO2. To account for the porosity dependence of thermal conductivity, two porosity weighted semiempirical models are introduced. These models suggest the scaling rule expressing the thermal conductivity as a function of porosity. The decrease observed in thermal conductivity of porous films suggests that the tradeoff between thermal and electrical performance is an important consideration when implementing porous dielectric materials as interlevel dielectrics for on-chip interconnects. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.Rm Porous materials; granular materials
82.70.Gg Gels and sols

Visualization of photoexcited free carriers by scanning near-field millimeter-wave microscopy

Tatsuo Nozokido, Jongsuck Bae, and Koji Mizuno

Appl. Phys. Lett. 77, 148 (2000); http://dx.doi.org/10.1063/1.126905 (3 pages) | Cited 4 times

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Visualization of transition phenomena of photoexcited free carriers by scanning near-field millimeter-wave microscopy has been demonstrated. A scanning millimeter-wave microscope using a metal slit-type probe and an image reconstruction algorithm based on computerized tomographic imaging has been used in the experiment to achieve two-dimensional time-resolved imaging. Experiments performed at 60 GHz (λ = 5 mm) under room temperature conditions show that generation, extinction, and diffusion processes of photoexcited free carriers generated in the silicon layer of a silicon on quartz substrate can be imaged with a time division of one nanosecond and a spatial resolution of 110 μm ( ∼ λ/45). © 2000 American Institute of Physics.  
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.50.Pz Photoconduction and photovoltaic effects
78.70.Gq Microwave and radio-frequency interactions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.47.-p Spectroscopy of solid state dynamics
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