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26 Jun 2000

Volume 76, Issue 26, pp. 3849-4013

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Photoinduced oxide film formation on n-type GaN surfaces using alkaline solutions

T. Rotter, D. Mistele, J. Stemmer, F. Fedler, J. Aderhold, J. Graul, V. Schwegler, C. Kirchner, M. Kamp, and M. Heuken

Appl. Phys. Lett. 76, 3923 (2000); http://dx.doi.org/10.1063/1.126822 (3 pages) | Cited 40 times

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We report on photoassisted wet chemical formation of thin oxide films on n-GaN layers in potassium hydroxide based electrolytes at room temperature. The kinetics of the oxide formation and dissolution were examined via photocurrent transients. The tendency of the photocurrent to level out during photoelectrochemical etching experiments is associated with a quasiequilibrium state at the semiconductor/electrolyte interface. Homogeneous oxide films were grown in weak alkaline solutions (11<pH<13) under potentionstatic control with oxidation rates of up to 250 nm/h and characterized by Auger electron spectroscopy. Consequences on wet photochemical etch strategies are discussed. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
82.45.-h Electrochemistry and electrophoresis
81.65.Cf Surface cleaning, etching, patterning
79.20.Fv Electron impact: Auger emission
72.80.Ey III-V and II-VI semiconductors
64.75.-g Phase equilibria
72.40.+w Photoconduction and photovoltaic effects

Avalanche noise measurement in thin Si p+-i-n+ diodes

C. H. Tan, J. C. Clark, J. P. R. David, G. J. Rees, S. A. Plimmer, R. C. Tozer, D. C. Herbert, D. J. Robbins, W. Y. Leong, and J. Newey

Appl. Phys. Lett. 76, 3926 (2000); http://dx.doi.org/10.1063/1.126823 (3 pages) | Cited 20 times

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The avalanche multiplication and excess noise properties of a range of submicron Si diodes have been investigated. In these thin diodes the excess noise is found to fall below that predicted by conventional local noise theory. Modeling of the multiplication and excess noise using a recurrence method, which includes the dead space for carrier ionization, gives good agreement with experiment. This suggests that the dead space can reduce the excess noise in submicron Si diodes. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
81.05.Cy Elemental semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
85.60.Dw Photodiodes; phototransistors; photoresistors

Growth of zinc blende MgS/ZnSe single quantum wells by molecular-beam epitaxy using ZnS as a sulphur source

C. Bradford, C. B. O’Donnell, B. Urbaszek, A. Balocchi, C. Morhain, K. A. Prior, and B. C. Cavenett

Appl. Phys. Lett. 76, 3929 (2000); http://dx.doi.org/10.1063/1.126824 (3 pages) | Cited 27 times

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Zinc blende MgS has been grown on GaAs by molecular beam epitaxy using a novel method where the sources were Mg and ZnS. A reaction at the surface results in the formation of MgS layers with a Zn content estimated by secondary ion mass spectrometry and Auger spectroscopy to be between 0.5% and 2%. Double crystal x-ray rocking curve measurements of ZnSe/MgS/ZnSe layers show layers with good crystallinity. Using this growth technique layers up to 67 nm thick have been grown. Photoluminescence measurements of MgS/ZnSe/MgS single-quantum-well structures show that the confinement of the heavy hole excitons can be as large as 430 meV for a 1.7 nm well. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.55.-a Thin film structure and morphology
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Stark shift in electroluminescence of individual InAs quantum dots

I. E. Itskevich, S. I. Rybchenko, I. I. Tartakovskii, S. T. Stoddart, A. Levin, P. C. Main, L. Eaves, M. Henini, and S. Parnell

Appl. Phys. Lett. 76, 3932 (2000); http://dx.doi.org/10.1063/1.126825 (3 pages) | Cited 22 times

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We have fabricated light-emitting-diode heterostructure devices, in which a layer of InAs self-assembled quantum dots is embedded, with an active area of submicron size. In the electroluminescence spectra of these devices, we observed isolated narrow peaks due to emission from individual dots. From the shift of the peaks in an electric field (the quantum confined Stark effect), we show that the ground and excited states in the dots have different spatial alignments of the electron and hole. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
78.20.Jq Electro-optical effects
85.60.Jb Light-emitting devices

1.54 μm emission dynamics of erbium-doped zinc-oxide thin films

Shuji Komuro, Tooru Katsumata, Takitaro Morikawa, Xinwei Zhao, Hideo Isshiki, and Yoshinobu Aoyagi

Appl. Phys. Lett. 76, 3935 (2000); http://dx.doi.org/10.1063/1.126826 (3 pages) | Cited 44 times

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Erbium-related 1.54 μm emission dynamics of Er-doped ZnO thin films has been investigated for the different excitation conditions. The excitation was achieved either by exciting indirectly Er3+ ions due to an electron–hole-mediated process or exciting directly discrete energy levels of Er3+ ions. There is no change in the 1.54 μm emission spectrum feature in spite of the different excitation conditions, whereas dramatic change can be seen in the rise time of 1.54 μm emission. The shorter rise time of 1.54 μm emission observed for indirect excitation implies an excitation efficiency superior to direct excitation of Er3+ ions. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Ultraviolet photon counting with GaN avalanche photodiodes

K. A. McIntosh, R. J. Molnar, L. J. Mahoney, K. M. Molvar, N. Efremow, and S. Verghese

Appl. Phys. Lett. 76, 3938 (2000); http://dx.doi.org/10.1063/1.126827 (3 pages) | Cited 18 times

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Photon counting, utilizing Geiger-mode avalanche response, has been demonstrated at 300 K in avalanche photodiodes fabricated in GaN grown by hydride vapor-phase epitaxy. Measurements have been made using both passive-quench and time-gated modes of operation. The two important figures of merit for photon-counting applications, photon detection efficiency (PDE) and dark count rate, were measured. A maximum PDE of 13% was measured at 325 nm with a dark count rate of 400 kHz. Typical mesa-etched devices exhibit a parasitic shunt leakage current of less than 20 nA at 90% of breakdown voltage. © 2000 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
07.60.Dq Photometers, radiometers, and colorimeters
42.50.Ar Photon statistics and coherence theory

Channeling as a mechanism for dry etch damage in GaN

Elaine D. Haberer, Ching-Hui Chen, Amber Abare, Monica Hansen, Steve Denbaars, Larry Coldren, Umesh Mishra, and Evelyn L. Hu

Appl. Phys. Lett. 76, 3941 (2000); http://dx.doi.org/10.1063/1.126828 (3 pages) | Cited 13 times

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Etch damage of GaN was investigated using a quantum-well probe structure. A clear decrease in photoluminescence (PL) intensity was observed and was aggravated with increasing ion-beam voltage. The magnitude of decrease in PL intensity was much larger than expected, even greater than for GaAs subjected to similar etch conditions. Angle-dependent bombardment studies were carried out to investigate channeling as a damage mechanism in GaN. The large decrease in PL intensity observed near normal incidence or along the [0001] direction suggests that channeling is a damage mechanism for low-energy bombardment in GaN. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Transport properties of Bi nanowire arrays

Yu-Ming Lin, Stephen B. Cronin, Jackie Y. Ying, M. S. Dresselhaus, and Joseph P. Heremans

Appl. Phys. Lett. 76, 3944 (2000); http://dx.doi.org/10.1063/1.126829 (3 pages) | Cited 83 times

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To explain various temperature-dependent resistivity measurements [R(T)] on bismuth (Bi) nanowires as a function of wire diameter down to 7 nm, a semiclassical transport model is developed, which explicitly considers anisotropic and nonparabolic carriers in cylindrical wires, and the relative importance of various scattering processes. R(T) of 40 nm Bi nanowires with various Te dopant concentrations is measured and interpreted within this theoretical framework. © 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.At Metal and metallic alloys
81.05.Bx Metals, semimetals, and alloys

Formation of single and double self-organized InAs quantum dot by selective area metal-organic vapor phase epitaxy

Cheol-Koo Hahn, Junichi Motohisa, and Takashi Fukui

Appl. Phys. Lett. 76, 3947 (2000); http://dx.doi.org/10.1063/1.126830 (3 pages) | Cited 20 times

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Position- and number-controlled InAs self-organized quantum dots (SOQDs) were formed by selective-area-metal-organic chemical vapor phase epitaxy on the partially SiNx patterned GaAs (001) substrate. The mask layer was patterned along the [110] direction, and somewhat wider rectangular openings were also attached to the line. As a result of GaAs SA growth, a pyramidal shaped structure was formed on the rectangular region of the pattern. The top area of the pyramidal structure is a very narrow hexagonal-shaped (001) facet which is surrounded by two-{111}B and four-{124} facets. The SOQD was preferentially formed on the top (001) facet because the growth rate on the (001) facet is far much higher than on the surrounding sidewalls. It is found that the number of SOQDs formed is strongly dependent on the width of the top (001)-facet so that control of single, double, and multiple SOQD(s) is possible. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Doping screening of polarization fields in nitride heterostructures

Aldo Di Carlo, Fabio Della Sala, Paolo Lugli, Vincenzo Fiorentini, and Fabio Bernardini

Appl. Phys. Lett. 76, 3950 (2000); http://dx.doi.org/10.1063/1.126831 (3 pages) | Cited 29 times

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Using self-consistent tight-binding calculations, we show that modulation doping can be used to screen macroscopic polarization fields in nitride quantum wells. The blue-shift of photoluminescence peak as well as the reduction of radiative recombination lifetime at increasing doping density is explained and correlated to polarization-field screening. The field-induced ionization of the dopants and its relation with alloy composition in the heterostructure barriers is also analyzed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

High-energy recoil implantation of boron into silicon

Lin Shao, Xinming Lu, Jianyue Jin, Qinmian Li, Jiarui Liu, P. A. W. van der Heide, and Wei-Kan Chu

Appl. Phys. Lett. 76, 3953 (2000); http://dx.doi.org/10.1063/1.126832 (3 pages) | Cited 18 times

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One approach to fabricate shallow junctions made of B-doped Si is to deposit B on Si, followed by knocking the B into the Si substrate with Si ions. Conventional belief is that the higher the implantation energy, the deeper the recoil profile. While this is true for low-energy incident ions, we show here that the situation is reversed for incident Si ions of higher energy due to the fact that recoil probability at a given angle is a strong function of the energy of the primary projectile. Our experiments show that 500 keV high-energy recoil implantation produces a shallower B profile than lower-energy implantation such as 10 and 50 keV. The secondary ion mass spectrometry analysis shows that the distribution of recoiled B atoms scattered by the energetic Si ions agrees with that calculated on the basis of interatomic potential suggested by W. D. Wilson, L. G. Haagmark, and J. P. Biersack [Phys. Rev. B 15, 2458 (1977)]. Sub-100 nm p+/n junctions have been realized with a 500 keV Si ion beam. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.S- Impurities in crystals

Piezoresistive effect in metal–semiconductor–metal structures on p-type GaN

R. Gaska, M. S. Shur, A. D. Bykhovski, J. W. Yang, M. A. Khan, V. V. Kaminski, and S. M. Soloviov

Appl. Phys. Lett. 76, 3956 (2000); http://dx.doi.org/10.1063/1.126833 (3 pages) | Cited 11 times

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We report on a strong piezoresistive effect in metal–semiconductor–metal structures fabricated on p-type GaN. The maximum measured gauge factor was 260, which is nearly two times larger than for piezoresistive silicon transducers. We attribute this large sensitivity to applied strain to the combination of two mechanisms: (i) a high piezoresistance of bulk p-GaN and (ii) a strong piezoresistive effect in a Schottky contact on p-GaN. The obtained results demonstrate that GaN-based structures can be suitable for stress/pressure sensor applications. © 2000 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
73.50.Dn Low-field transport and mobility; piezoresistance
73.30.+y Surface double layers, Schottky barriers, and work functions
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Lw Balance systems, tensile machines, etc.

Nanocrystalline p-type transparent Cu–Al–O semiconductor prepared by chemical-vapor deposition with Cu(acac)2 and Al(acac)3 precursors

Hao Gong, Yue Wang, and Yi Luo

Appl. Phys. Lett. 76, 3959 (2000); http://dx.doi.org/10.1063/1.126834 (3 pages) | Cited 54 times

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P-type transparent copper–aluminum–oxide semiconductor films are prepared by the use of the chemical-vapor deposition (CVD) technique with Cu(acac)2 and Al(acac)3 precursors. Transmission electron microscopy and electron diffraction suggest that the films contain nanocrystalline phases of CuAlO2 and Cu2O, in which CuAlO2 is dominant. Both Hall technique and Seebeck measurement reveal that the film is p type, and a very high room-temperature conductivity of 2 S cm−1 is achieved. This success of high-conductive p-type transparent semiconductor using CVD further paves the way for transparent semiconductor p–n junctions as well as industrial mass production of the relevant devices. The Hall measurement of the film shows a sheet mobility of 0.16 cm2 V−1 S−1 and a carrier concentration of 1.8×1019 cm−3. A wide optical gap of 3.75 eV due to quantum confinement is found, and the activation energy for the positive holes is 0.12 eV. © 2000 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors

An electron microscopy study of the growth of Ge nanoparticles in SiO2

C. Bonafos, B. Garrido, M. Lopez, A. Perez-Rodriguez, J. R. Morante, Y. Kihn, G. Ben Assayag, and A. Claverie

Appl. Phys. Lett. 76, 3962 (2000); http://dx.doi.org/10.1063/1.126835 (3 pages) | Cited 27 times

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Ion implantation followed by high temperature annealing can be used to synthesize group IV semiconducting nanoparticles in SiO2. The density and the size distribution of these nanocrystals obviously depend on the implantation and annealing conditions. While their size can be measured by “classical” transmission electron microscopy techniques, their density cannot because no diffraction occurs in the amorphous matrix. In this letter, we use electron energy loss spectroscopy to overcome this problem. We have measured the evolution of the size distribution, the density, and the atomic fraction occupied by the Ge precipitates during annealing. We show that the nanocrystals grow in size and reduce their density, while the overall number of atoms they contain remains constant. This observation proves that the nanoparticles undergo a conservative ripening during annealing. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
61.72.up Other materials
79.20.Kz Other electron-impact emission phenomena
61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.Cc Kinetics of defect formation and annealing
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Magnetic tunnel junction performance versus barrier thickness: NiFe/AlOx/NiFe junctions fabricated from a wedged Al layer

M. Covington, J. Nowak, and D. Song

Appl. Phys. Lett. 76, 3965 (2000); http://dx.doi.org/10.1063/1.126836 (3 pages) | Cited 24 times

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The resistance–area product (R∗A) and the magnetoresistance (MR) of NiFe/AlOx/NiFe spin-dependent tunnel junctions exhibit a strong dependence on the thickness of Al before oxidation. We obtain these data from wafers where we uniformly oxidize an Al layer with a wedged thickness profile, enabling us to reliably characterize the effect of Al thickness variations with subangstrom precision. The R∗A drops from 104 to 102 Ω μm2 as the Al thickness decreases from 9 to 4 Å, respectively. The MR is highest (21%) for an Al thickness of 7 Å, where the Al layer is fully oxidized and the oxidation of the bottom NiFe electrode is minimal. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Direct measurement of the dependence of granular giant magnetoresistance on the relative orientation of magnetic granules

Jianbiao Dai and Jinke Tang

Appl. Phys. Lett. 76, 3968 (2000); http://dx.doi.org/10.1063/1.126837 (3 pages) | Cited 2 times

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Experiments have been designed to vary the relative angle between the magnetic moments of different Co granules in Cu80Co20 granular system. The moments of granules are mostly aligned in the same direction by field cooling to low temperature in a high magnetic field. A small field applied at an angle relative to the cooling field rotates the moments of a portion of the granules that have small particle size and coercivity. It is found that the giant magnetoresistance (GMR) varies linearly with cos ϕ, where ϕ is the relative angle between the magnetic axes of granules. This behavior disappears if the sample is cooled in zero fields, or if the rotating field is too large or small, or if the measuring temperature is higher than the blocking temperature. Our results show that the GMR in granular structures has the same angular dependence as the layered films and confirm the existing theories and recent microscopic models of granular GMR suggesting a crucial role of the relative orientations of the magnetic granules in determining the spin dependent scattering. © 2000 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructure and magnetic properties of FePt–Al–O granular thin films

M. Watanabe, T. Masumoto, D. H. Ping, and K. Hono

Appl. Phys. Lett. 76, 3971 (2000); http://dx.doi.org/10.1063/1.126838 (3 pages) | Cited 81 times

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We have investigated the microstructures and magnetic properties of L10 ordered FePt granular thin films prepared by ion beam sputtering and subsequent annealing. As-deposited FePt–Al–O films are composed of fine spherical FePt particles of ∼2 nm diameter with disordered face-centered-cubic structure. These particles are embedded in the amorphous aluminum oxide matrix with average spacing of ∼1.3 nm, and the film exhibits superparamagnetism. By annealing above 650 °C, the nanoparticles transform to the L10 ordered phase and the grains are coarsened to ∼20 nm, which results in a high coercivity up to 10 kOe. In the films with a high Al content, most of the particles are isolated by the amorphous aluminum oxide matrix, while the grains are interconnected in the films with a low Al content. The changes in magnetic properties are discussed based on the microstructural observation results. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing

Structural origin of coercivity enhancement and exchange-bias field in double antiferromagnet/ferromagnet bilayers

C. Hou, H. Fujiwara, and K. Zhang

Appl. Phys. Lett. 76, 3974 (2000); http://dx.doi.org/10.1063/1.126839 (3 pages) | Cited 5 times

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An experimental method to identify the structural origins of the coercivity enhancement and the exchange-bias field of polycrystalline ferro-antiferromagnetic (F/AF) coupled systems is proposed. The exchange-bias field and the coercivity of the FI layer of the samples of the structure FI/AFI are compared with those of the FII layer of the samples of the structure FII/AFII/FIII/AFIII. It is concluded that, for a given temperature, it is those AF grains which stop their growth at a critical thickness that contribute to the coercivity enhancement, and those which grow over the critical thickness that contribute to the exchange-bias field. Meanwhile the effective magnetic surface anisotropy introduced to the top surface of the AFII layer by the FIII layer can increase the exchange-bias field of the FII layer when the AFII layer is thin. © 2000 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.70.Rf Surface magnetism
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Electron emission from Pb-based ferroelectrics, antiferroelectrics, and paraelectrics by pulse electric field

Yong Tae Kim, Ki Hyun Yoon, Tae Heui Kim, and Kyung Bong Park

Appl. Phys. Lett. 76, 3977 (2000); http://dx.doi.org/10.1063/1.126840 (3 pages) | Cited 3 times

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Pulse electric-field-induced electron emissions from Pb-based ferroelectrics, antiferroelectrics, and paraelectrics were investigated. The electron emission charge increased exponentially with applied pulse field regardless of the dielectric phases. Electrons were emitted at the falling point as well as at the rising point of an applied pulse field when the antiferroelectrics and paraelectrics were used. The variation of emission charge from antiferroelectrics and paraelectrics was similar to that from ferroelectrics, as the emission charge increased exponentially with the polarization change [Ps-(−Pr)]. © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis

Optical properties of PbZrxTi1−xO3 on platinized silicon by infrared spectroscopic ellipsometry

Zhiming Huang, Xiangjiang Meng, Pingxiong Yang, Zhanhong Zhang, and Junhao Chu

Appl. Phys. Lett. 76, 3980 (2000); http://dx.doi.org/10.1063/1.126841 (3 pages) | Cited 28 times

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A method of analyzing infrared spectroscopic ellipsometry (IRSE) measurement data is proposed for lead zirconate titanate PbZrxTi1−xO3 (PZT) thin films grown on Pt/Ti/SiO2/Si substrates with x = 0.3 and 0.5. The IRSE data measured at an angle of incidence 75° for x = 0.3 and 70° for x = 0.5 are fitted by a dielectric function formula. The refractive index and extinction coefficient of PZT with x = 0.3 and 0.5 are determined in the spectral range of 2.5–12.5 μm. As the wavelength increases, the refractive index decreases, on the contrary, the extinction coefficient increases. The absorption coefficient for x = 0.5 is greater than that for x = 0.3 by a factor of 1.5. The effective static ionic charges have also been derived, which are smaller than they would be in a purely ionic material for PZT thin films. © 2000 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
77.55.-g Dielectric thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)

Self-field ac losses of a twisted multifilamentary (Bi, Pb)2Sr2Ca2Cu3O10/AgAu tape

C. M. Friend and Y. B. Huang

Appl. Phys. Lett. 76, 3983 (2000); http://dx.doi.org/10.1063/1.126842 (3 pages) | Cited 1 time

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Self-field loss measurements at 77 K on a superconducting (Bi, Pb)2Sr2Ca2Cu3O10/AgAu tape with twisted filaments are presented. Using the first- and third-harmonic components of the electric field, the hysteretic losses are separated from the total loss. At peak transport currents less than half the critical current, the hysteretic losses are considerably reduced. However, sizable nonhysteretic losses are also observed. At higher currents, the hysteretic loss increases, dominating the total loss, and is similar to that for an untwisted tape. © 2000 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes

Atomic-level simulation of ferroelectricity in perovskite solid solutions

M. Sepliarsky, S. R. Phillpot, D. Wolf, M. G. Stachiotti, and R. L. Migoni

Appl. Phys. Lett. 76, 3986 (2000); http://dx.doi.org/10.1063/1.126843 (3 pages) | Cited 22 times

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Building on the insights gained from electronic-structure calculations and from experience obtained with an earlier atomic-level method, we developed an atomic-level simulation approach based on the traditional Buckingham potential with shell model which correctly reproduces the ferroelectric phase behavior and dielectric and piezoelectric properties of KNbO3. This approach now enables the simulation of solid solutions and defected systems; we illustrate this capability by elucidating the ferroelectric properties of a KTa0.5Nb0.5O3 random solid solution. © 2000 American Institute of Physics.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
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Theory of ballistic electron emission microscopy with constant current feedback

D. A. Pearson and L. J. Sham

Appl. Phys. Lett. 76, 3989 (2000); http://dx.doi.org/10.1063/1.126844 (3 pages) | Cited 1 time

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A theory of ballistic electron emission microscopy is presented that incorporates constant tunnel current feedback and models the band structure and space charge effects on the electron transmission. The computation is beyond the effective mass approximation but short of being from first principles. We compare theory and experimental Au/GaAs(001) dI/dV data and find that the L point does not contribute to an observable threshold and that the corresponding experimental feature is due to band structure effects. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
68.37.Vj Field emission and field-ion microscopy
73.20.At Surface states, band structure, electron density of states

Enhancement of hot-electron generation rate in Schottky source metal–oxide–semiconductor field-effect transistors

Ken Uchida, Kazuya Matsuzawa, Junji Koga, Shin-ichi Takagi, and Akira Toriumi

Appl. Phys. Lett. 76, 3992 (2000); http://dx.doi.org/10.1063/1.126845 (3 pages) | Cited 16 times

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Source-side hot-electron generation is experimentally demonstrated in Schottky source metal–oxide–semiconductor field-effect transistors (MOSFETs). An asymmetric n-type MOSFET having a CoSi2 layer in place of one of the n+ source/drain regions has been fabricated and intensively investigated. When the CoSi2 layer is used as the source, large gate current and negative-differential conductance (NDC) are simultaneously observed, whereas, when the n+ region is used as the source, both gate current and NDC are not observed. By comparing the device characteristics before and after the NDC observation, it is concluded that the gate current is due to hot electrons generated at the Schottky source side and the NDC is caused by trapped electrons in the oxide. These source-side hot electrons will open up the way to the realization of deca-nanoscaled high-speed devices. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors

Achromatic linear polarization rotator using twisted nematic liquid crystals

Zhizhong Zhuang, Young Jin Kim, and J. S. Patel

Appl. Phys. Lett. 76, 3995 (2000); http://dx.doi.org/10.1063/1.126846 (3 pages) | Cited 18 times

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In this letter, we propose a simple configuration that is capable of rotating a linear polarization state of light by a certain angle for a wide range of wavelengths. The device consists of three liquid-crystal cells: two homogeneous cells and one twisted nematic (TN) cell. It is well known that a thick TN cell can rotate the linear polarization state of light by following the twisted structure. However, for a thin TN cell, achromatic polarization rotation is not possible. By the use of the Poincaré sphere model of the TN structure, we demonstrate that if one thin homogeneous cell is placed before and another one is placed after a thin TN structure, then a linear polarization state can be transformed close to the eigenmodes of TN. Therefore, this structure can be used to achieve the achromatic polarization rotation. This letter provides a detailed discussion of the theoretical analysis and a demonstration of the achromatic linear polarization rotator by the use of a 1.9 μm TN cell for the wavelength range 450–700 nm. © 2000 American Institute of Physics.
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61.30.-v Liquid crystals
78.20.Ek Optical activity
78.20.Fm Birefringence
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