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2 Jun 1997

Volume 70, Issue 22, pp. 2931-3055

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A tunneling field-effect transistor with 25 nm metallurgical channel length

Fu-Cheng Wang, W. E. Zhang, C. H. Yang, M. J. Yang, B. R. Bennett, R. A. Wilson, and D. R. Stone

Appl. Phys. Lett. 70, 3005 (1997); http://dx.doi.org/10.1063/1.118731 (3 pages) | Cited 6 times

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A tunneling field-effect transistor with an ultrashort channel-length of 25 nm has been experimentally realized using InAs/AlSb heterostructures. The conduction between the source and the drain is through a sequential process, including tunneling and drift-diffusion mechanisms. According to its operating principle, the transistor is inherently free of the conventional short-channel effects. The results demonstrate a new scheme of building nanometer-scale transistors. © 1997 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Sequential excited-to-excited states resonant tunneling and electric field domains in long period superlattices

Yu. A. Mityagin, V. N. Murzin, Yu. A. Efimov, and G. K. Rasulova

Appl. Phys. Lett. 70, 3008 (1997); http://dx.doi.org/10.1063/1.118732 (3 pages) | Cited 6 times

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The sequential excited-to-excited state resonant tunneling effect was observed in weakly coupled long period superlattices resulting in additional negative differential conductivity resonances in multistable current–voltage characteristics. The results obtained show the evidence of the highly nonequilibrium distribution of carriers over subbands with energies below the optical phonon energy in SL. A new type of electric field domain due to resonant tunneling between excited subbands in adjacent wells is considered, and experimental evidence of such a domain existence is given. © 1997 American Institute of Physics.
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73.40.Gk Tunneling
73.61.Ey III-V semiconductors

Electronic structure at InP organic polymer layer interfaces

N. Kinrot, Yoram Shapira, and M. A. Bica de Moraes

Appl. Phys. Lett. 70, 3011 (1997); http://dx.doi.org/10.1063/1.118733 (3 pages) | Cited 8 times

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Organic polymer layer/p-InP(100) interfaces have been investigated using surface photovoltage spectroscopy (SPS) in conjunction with ultraviolet-visible absorption spectroscopy (AS), infrared transmission spectroscopy (IRTS), time-resolved photoluminescence (PL), and x-ray photoemission spectroscopy (XPS). Prior to deposition, the etched p-InP(100) surfaces exhibited two gap states, attributed to excess surface P and adsorbed O, respectively. Postdeposition measurements show that N-containing layers suppress the former state at the interface, while the latter state is suppressed if S and F are present in the organic polymer film. A mechanism of these interfacial phenomena is suggested. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Rv Polymers and organic compounds
71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures

Direct formation of nanocrystalline silicon by electron cyclotron resonance chemical vapor deposition

Won Chel Choi, Eun Kyu Kim, Suk-Ki Min, Chong-Yun Park, Joon Hyung Kim, and Tae-Yeon Seong

Appl. Phys. Lett. 70, 3014 (1997); http://dx.doi.org/10.1063/1.118734 (3 pages) | Cited 12 times

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We have confirmed the direct formation of nanosized crystalline silicon during the deposition of amorphous silicon layers by electron cyclotron resonance chemical vapor deposition (ECRCVD) on silicon and silicon–dioxide substrates. Two photoluminescence (PL) peaks at 680 and 838 nm were observed at room temperature from the samples. From cross-sectional high-resolution transmission electron microscopy (HRTEM) measurements, it was confirmed that nanosize silicon crystallites of 3–5 nm in diameter were randomly distributed throughout the amorphous silicon layer. Theoretical calculations using quantum size effects gave an average crystalline size of 4 nm which was consistent with the PL peak energy at 680 nm obtained from the sample. Also, the size of the crystallites could be controlled by the change of the substrate temperature during the deposition process. © 1997 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.-b Nanoscale materials and structures: fabrication and characterization

Growth and characterization of (InSb)m(InP)n short period superlattices

T. Utzmeier, G. Armelles, P. A. Postigo, F. Briones, P. Castrillo, A. Sanz-Hervas, M. Aguilar, and E. J. Abril

Appl. Phys. Lett. 70, 3017 (1997); http://dx.doi.org/10.1063/1.118735 (3 pages) | Cited 1 time

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Short period superlattices of (InSb)m(InP)n were grown on semi-insulating (001) InP substrates by atomic layer molecular beam epitaxy. High resolution x-ray diffractometry was used to study the structural quality of the superlattices. Raman spectroscopy, in conjunction with theoretical calculations, provided information about intermixing at the interfaces. © 1997 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
78.30.Fs III-V and II-VI semiconductors

Method for fabricating submicron silicide structures on silicon using a resistless electron beam lithography process

D. Drouin, J. Beauvais, R. Lemire, E. Lavallée, R. Gauvin, and M. Caron

Appl. Phys. Lett. 70, 3020 (1997); http://dx.doi.org/10.1063/1.118736 (3 pages) | Cited 13 times

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A novel resistless lithography process using a conventional electron beam system is presented. Metallic lines with widths of less than 50 nm were produced on silicon substrates. The process is based on localized heating with a focused electron beam of thin platinum layers deposited on silicon. It is demonstrated that silicide formation occurs at the Pt-Si interface. By using a dilute solution of aqua regia, it is possible to obtain a sufficient difference in etch rates between exposed and unexposed regions of the platinum thin film to selectively remove only the unexposed areas. © 1997 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.05.Cy Elemental semiconductors
61.80.Fe Electron and positron radiation effects

Surface morphology and optical characterization of GaN grown on α-Al2O3 (0001) by radio-frequency-assisted molecular beam epitaxy

M. Yeadon, F. Hamdani, G. Y. Xu, A. Salvador, A. E. Botchkarev, J. M. Gibson, and H. Morkoç

Appl. Phys. Lett. 70, 3023 (1997); http://dx.doi.org/10.1063/1.118737 (3 pages)

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Wurtzitic GaN epilayers have been grown on sapphire (0001) substrates by radio-frequency atomic nitrogen plasma-assisted molecular beam epitaxy. Atomic force microscopy, reflectivity, and photoluminescence measurements have been performed in order to investigate the influence of in situ and ex situ annealing on the surface morphology and optical properties. We demonstrate a significant improvement in both the structural and optical quality of our GaN epilayers using in situ annealed low-temperature-deposited GaN buffer layers. © 1997 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

InGaAs metal-semiconductor-metal photodetectors with a hybrid combination of transparent and opaque electrodes

Walter Wohlmuth, Mohamed Arafa, Patrick Fay, and Ilesanmi Adesida

Appl. Phys. Lett. 70, 3026 (1997); http://dx.doi.org/10.1063/1.118738 (3 pages) | Cited 6 times

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A metal-semiconductor-metal photodetector (MSMPD) with a hybrid combination of transparent cadmium-tin-oxide and opaque Ti:Au electrodes is proposed and demonstrated. A significant decrease in dark current is obtained by independently engineering the Schottky barrier heights at the anode and cathode. In addition, the use of transparent electrodes enables more light to be coupled into the front-side illuminated MSMPDs thereby increasing the responsivity. For an applied bias of 5 V, these devices exhibited an extremely low dark current density of 21.2 fA/μm2 and a high responsivity of 0.56 A/W to perpendicularly incident 1.31 μm wavelength light. © 1997 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.40.Sx Metal-semiconductor-metal structures
73.30.+y Surface double layers, Schottky barriers, and work functions

Doping silver into YBa2Cu3O7−δ films by 800 keV Ag+ implantation at room temperature and elevated temperatures

Yupu Li, J. R. Liu, Xingtian Cui, J. Z. Qu, Q. Y. Chen, and Wei-Kan Chu

Appl. Phys. Lett. 70, 3029 (1997); http://dx.doi.org/10.1063/1.118739 (3 pages) | Cited 4 times

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Thin films ( ∼ 0.43 and ∼ 0.95 μm thick) of YBa2Cu3O7−δ on (100) LaAlO3 substrates have been implanted with 800 keV Ag+ to a dose of 5×1014/cm2, at room temperature (i.e., the total range ≈ 0.4 μm and the damage level ≈ 3.1 displacements per atom) and at elevated temperatures (450, 650, and 780 °C), followed by an in situ annealing schedule in flowing oxygen ambient. We have found that the implantation at room temperature amorphizes the implanted layer. In such a case, the implanted layer cannot regrow to the superconducting phase if there is no crystal seed remaining in the bottom of the film, whereas implantation at elevated temperatures plus an in situ annealing schedule, including a step at 870 °C in flowing oxygen ambient, can maintain the crystal structure and superconductivity of the films. For the thicker film, we have found that after the implantation at 450 or 650 °C and the in situ annealing, the total volume of the film has recovered to the superconducting 123 phase with a Tc = 89 K. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.62.Dh Effects of crystal defects, doping and substitution
61.72.up Other materials

Compact lumped-element microwave resonators using epitaxial YBa2Cu3O7−x/NdAlO3/YBa2Cu3O7−x trilayers

Muralidhar R. Rao

Appl. Phys. Lett. 70, 3032 (1997); http://dx.doi.org/10.1063/1.118740 (3 pages)

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Thick, high-quality epitaxial trilayers of YBa2Cu3O7−x/NdAlO3/YBa2Cu3O7 were grown on (100) MgO substrates by pulsed laser deposition. Compact resonators based on such trilayers were designed, fabricated, and tested. The resonant frequencies of the resonators were varied from 1.6 to 9.4 GHz by varying the device geometry within a die size of 2×2 mm. The values of the capacitive and inductive elements of the resonator and series resistance were estimated, and the frequency response of the circuit model was simulated. The measured and simulated resonant frequencies, insertion losses, and quality factors were in agreement. The contact resistivity of the Ag-YBa2Cu3O7−x contacts at the capacitor pads was found to dominate the loss in the resonator. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures
84.40.Dc Microwave circuits
85.25.Am Superconducting device characterization, design, and modeling

Strain stabilized metal–insulator transition in epitaxial thin films of metallic oxide CaRuO3

R. A. Rao, Q. Gan, C. B. Eom, R. J. Cava, Y. Suzuki, J. J. Krajewski, S. C. Gausepohl, and M. Lee

Appl. Phys. Lett. 70, 3035 (1997); http://dx.doi.org/10.1063/1.118741 (3 pages) | Cited 36 times

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We report the observation of both metallic and semiconducting behavior in epitaxial thin films of the metallic oxide CaRuO3 deposited under identical conditions. X-ray diffraction studies showed that while semiconducting films with enlarged unit cells were obtained on single-crystal (100) SrTiO3 substrates, metallic films with lattice parameters close to the bulk material grew on (100) LaAlO3 substrates and poor crystalline quality SrTiO3 substrates. It is believed that a strain induced substitution of the small Ru4+ cations by the larger Ca2+ cations occurs, breaking the conduction pathway within the three-dimensional network of the RuO6 octahedra and leading to a metal–insulator transition. This unique phenomenon, which is not observed in bulk material, can be significant in technologically important epitaxial perovskite oxide heterostructures. © 1997 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Le Other inorganic semiconductors
68.60.Bs Mechanical and acoustical properties

Field-angle dependence of alternating current loss in multifilamentary high-Tc superconducting tapes

M. P. Oomen, J. Rieger, M. Leghissa, and H. H. J. ten Kate

Appl. Phys. Lett. 70, 3038 (1997); http://dx.doi.org/10.1063/1.118742 (3 pages) | Cited 23 times

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The energy loss in multifilamentary superconducting tapes has been measured for various orientations of the external ac magnetic field. When the ac loss in parallel and perpendicular fields is known, the loss at intermediate field angles can be predicted over a wide range of field amplitudes. The prediction is based upon the following assumptions: For low-field amplitudes, the current patterns that would be induced in the tape by the parallel and perpendicular field components can be summed. For high-field amplitudes, the tape only carries the current pattern induced by the perpendicular field component. These assumptions are supported by theory. © 1997 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors

Estimating the effective magnetostriction of a composite: A simple model

J. F. Herbst, T. W. Capehart, and F. E. Pinkerton

Appl. Phys. Lett. 70, 3041 (1997); http://dx.doi.org/10.1063/1.118743 (3 pages) | Cited 19 times

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For a composite consisting of magnetostrictive particles dispersed in a nonmagnetostrictive matrix, a simple, approximate model for the effective magnetostriction, defined as the ratio of the magnetostriction of the composite to that of the magnetostrictive component, is described. The predictions of the model compare well with measurements on SmFe2-based composites having Al and Fe matrices. © 1997 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Tt Fine-particle systems; nanocrystalline materials

Synthesis and characterization of hard magnetic materials: PrFe10.5V1.5Nx

Weihua Mao, Benpei Cheng, Jinbo Yang, Xiedi Pei, and Yingchang Yang

Appl. Phys. Lett. 70, 3044 (1997); http://dx.doi.org/10.1063/1.118744 (3 pages) | Cited 5 times

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The PrFe10.5V1.5 intermetallics and their nitrides were successfully synthesized. In terms of magnetocrystalline anisotropy, PrFe10.5V1.5Nx are characteristics of an easy axis from 0 K to Curie temperature, with an anisotropy field up to 152.9 kOe at 1.5 K and 108.4 kOe at room temperature. In combination with a high Curie temperature of 820 K and a large saturation magnetization of 157.46 emu/g at 1.5 K and 142.77 emu/g at room temperature, these nitrides are favorable for permanent magnet applications. As a preliminary attempt, magnetic powders based on PrFe10.5V1.5Nx were obtained with a maximum energy product of 16.0 and 28.8 MGOe at room temperature and 1.5 K, respectively. © 1997 American Institute of Physics.
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75.50.Ww Permanent magnets
75.30.Gw Magnetic anisotropy
81.05.Bx Metals, semimetals, and alloys

Magnetic properties of nanostructured Mn oxide particles

J. Li, Y. J. Wang, B. S. Zou, X. C. Wu, J. G. Lin, L. Guo, and Q. S. Li

Appl. Phys. Lett. 70, 3047 (1997); http://dx.doi.org/10.1063/1.118745 (3 pages) | Cited 17 times

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Nanostructured Mn oxide particles with an average size of about 7 nm have been prepared by a microemulsion method. X-ray diffraction analysis indicates that the particles possess orthorhombic structure of MnO(OH). The particles are ferromagnetic at low temperature. The Curie temperature is about 35 K and each MnO(OH) molecule generates a magnetic moment of about 0.7 μB. The appearance of the ferromagnetism at low temperature may result from size effect. © 1997 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials

Optimum tunnel barrier in ferromagnetic–insulator–ferromagnetic tunneling structures

Jagadeesh S. Moodera, Elizabeth F. Gallagher, Keziah Robinson, and Janusz Nowak

Appl. Phys. Lett. 70, 3050 (1997); http://dx.doi.org/10.1063/1.118168 (1 page) | Cited 117 times

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Al2O3 tunnel barriers I, formed by the oxidization of Al metal of various thicknesses between two ferromagnetic (FM) films were investigated to understand the influence of overlayer metal Al on the junction magnetoresistance (JMR). The optimum thickness of Al was observed to lie in the range of 1–1.6 nm to achieve good JMR in FM–I–FM junctions. Additionally, such junctions can be used to study the magnetic proximity effect in ferromagnet/normal metal bilayer systems. © 1997 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
73.40.Gk Tunneling
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Improvement of leakage currents of Pt/(Ba, Sr)TiO3/Pt capacitors

Jae-Hyun Joo, Jeong-Min Seon, Yoo-Chan Jeon, Ki-Young Oh, Jae-Sung Roh, and Jae-Jeong Kim

Appl. Phys. Lett. 70, 3053 (1997); http://dx.doi.org/10.1063/1.118746 (3 pages) | Cited 50 times

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Pt/(Ba, Sr)TiO3/Pt capacitors fabricated by sputtering technique showed abnormally higher leakage current when negative bias was applied to the top electrode. In this letter, two kinds of processes were attempted to reduce high leakage current of Pt/BST/Pt capacitors for dynamic random access memory devices: (1) postannealing under O2 atmosphere and (2) adding oxygen into sputtering gas of platinum top electrode. These processes were very effective to reduce the oxygen vacancy in the BST films which are mostly responsible for such a high leakage current. The higher reverse currents were significantly lowered by these processes, so that we could obtain symmetric current versus voltage curves of Pt/BST/Pt capacitors. © 1997 American Institute of Physics.  
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.05.Mh Cermets, ceramic and refractory composites
77.55.-g Dielectric thin films
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