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29 Apr 1996

Volume 68, Issue 18, pp. 2467-2591

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In‐plane‐gate transistors on nonepitaxial silicon directly written by focused‐ion‐beam implantation

C. Crell, K. Wieczorek, H.‐U. Schreiber, and A. D. Wieck

Appl. Phys. Lett. 68, 2538 (1996); http://dx.doi.org/10.1063/1.116176 (3 pages) | Cited 5 times

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It is demonstrated that focused‐ion‐beam written in‐plane‐gate transistors, working at room temperature can be realized on (100) silicon‐on‐insulator wafers, separated by implanted oxygen, without the need for epitaxial growth processes. Typical channel widths are in the sub‐μm range. Their electrical features at room temperature are characterized by transport and Hall measurements. The channel current is measured as a function of the geometrical channel width and the implanted dose. Activation of the implanted gallium by rapid thermal annealing changes the character of the insulating lines from Ohmic barriers to npn‐junctions. Consequently the leakage current across the barriers decreases significantly, the direct current output characteristics of the transistors are improved with higher implantation doses and smaller geometrical channel widths are achievable. © 1996 American Institute of Physics.
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85.40.Sz Deposition technology
85.30.Tv Field effect devices

Valence‐band discontinuities of wurtzite GaN, AlN, and InN heterojunctions measured by x‐ray photoemission spectroscopy

G. Martin, A. Botchkarev, A. Rockett, and H. Morkoç

Appl. Phys. Lett. 68, 2541 (1996); http://dx.doi.org/10.1063/1.116177 (3 pages) | Cited 314 times

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The valence‐band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x‐ray photoemission spectroscopy. A significant forward–backward asymmetry was observed in the InN/GaN–GaN/InN and InN/AlN–AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
79.60.Jv Interfaces; heterostructures; nanostructures

Ultrafast dynamics of nonlinear absorption in low‐temperature‐grown GaAs

S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith

Appl. Phys. Lett. 68, 2544 (1996); http://dx.doi.org/10.1063/1.116178 (3 pages) | Cited 44 times

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We present the results of a study of the subpicosecond dynamic behavior of optically induced absorption changes in low‐temperature‐grown GaAs. We show that the observed behavior is dominated by mid‐gap trap states, and can be accurately modeled by the rate equations previously developed to describe quasi‐cw results. Our data give the first approximate values for trap emptying times in this material. © 1996 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
71.55.Eq III-V semiconductors

Infrared reflection of GaN and AlGaN thin film heterostructures with AlN buffer layers

C. Wetzel, E. E. Haller, H. Amano, and I. Akasaki

Appl. Phys. Lett. 68, 2547 (1996); http://dx.doi.org/10.1063/1.116179 (3 pages) | Cited 24 times

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Infrared reflection spectroscopy is applied to state‐of‐the‐art thin film heterostructures of group‐III nitrides on sapphire and Si substrates. The individual layers of GaN and AlGaN and the AlN buffer layer are identified by their phonon frequencies. Under non‐perpendicular incidence of the light, A1(LO) phonon modes are observed in the wurtzite system. The presence of the very thin AlN buffer layer manifests itself in clear features of the AlN phonons. The A1(LO) phonon mode energy is determined in AlxGa1−xN for x≊0.15. Raman spectra confirm our findings. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.20.-e Phonons in crystal lattices

Influence of the semi‐insulating GaAs Schottky pad on the Schottky barrier in the active layer

J. Wu, Z. G. Wang, L. Y. Lin, C. B. Han, M. Zhang, and S. W. Bai

Appl. Phys. Lett. 68, 2550 (1996); http://dx.doi.org/10.1063/1.116180 (3 pages)

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The influence of the sidegate voltage on the Schottky barrier in the ion‐implanted active layer via the Schottky pad on the semi‐insulating GaAs substrate was observed, and the mechanism for such an influence was proposed. © 1996 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices

Infrared light emission from semiconductor double wells

W. Pötz

Appl. Phys. Lett. 68, 2553 (1996); http://dx.doi.org/10.1063/1.116181 (3 pages) | Cited 10 times

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A microscopic theoretical analysis of coherent charge oscillations in optically excited GaAs‐ AlxGa1−xAs double wells and resulting infrared light emission is presented. Our non‐phenomenological study is based on generalized Boltzmann–Bloch equations which account for the laser field within the rotating‐wave approximation, the dynamics of interacting electron‐hole pairs in the heterostructure, excitonic effects, and the destruction of phase coherence by the inter‐carrier Coulomb interaction. Emitted THz electromagnetic pulses are analyzed. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Strongly localized excitons in gallium nitride

C. Wetzel, S. Fischer, J. Krüger, E. E. Haller, R. J. Molnar, T. D. Moustakas, E. N. Mokhov, and P. G. Baranov

Appl. Phys. Lett. 68, 2556 (1996); http://dx.doi.org/10.1063/1.116182 (3 pages) | Cited 46 times

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We report on strong excitonic luminescence in wurtzite GaN at 3.309 and 3.365 eV (T=6 K). These lines lie well below the band gap and are found commonly in layers grown by different techniques and on different substrates. From detailed photoluminescence investigations we find small thermal activation energies and a very weak electron–phonon coupling. The photoluminescence behavior under hydrostatic pressure is indicative of strongly localized defects. These findings are similar to observations of excitons localized at extended defects such as dislocations in II–VI compounds. © 1995 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Magnetically tunable YBaCuO microstrip resonators and bandpass filters

A. Trotel, M. Pyée, B. Lavigne, D. Chambonnet, and P. Lederer

Appl. Phys. Lett. 68, 2559 (1996); http://dx.doi.org/10.1063/1.116183 (3 pages) | Cited 13 times

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We report experimental results on frequency tuning in superconductive resonators and bandpass filters with controlling magnetic fields. The frequency shifts are attributed to the presence of vortices modifying the microwave penetration depth and therefore the kinetic inductance of the circuit. 7‐pole microstrip filters with a center frequency of 14 GHz and a bandwidth of 4% were fabricated using YBaCuO films deposited on MgO substrate with Au ground plane. A negative frequency shift of −12 MHz for fields lower than 0.1 mT was observed at 40 K. © 1996 American Institute of Physics.
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85.25.-j Superconducting devices

Tunneling through grain boundaries of YBa2Cu3O7 step‐edge junctions

H. R. Yi, D. Winkler, and T. Claeson

Appl. Phys. Lett. 68, 2562 (1996); http://dx.doi.org/10.1063/1.116184 (3 pages) | Cited 4 times

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Tunneling experiments were done on YBa2Cu3O7 step‐edge junctions. The temperature dependence of the superconducting gap parameter, Δ(T), was measured. From the peak‐to‐peak distance in the conductance curve, Δ was estimated to vary from 24 to 32 meV at 4.2 K. The conductance at high‐voltage bias does not increase with increasing voltage. The tunneling results, together with the well‐behaved magnetic field dependence of the critical Josephson current, hysteresis, and Fiske‐type resonances in current‐voltage curves, indicate a dielectric behavior of the grain boundary junction, i.e., a tunnel junction. © 1996 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Growth of HgBa2Ca2Cu3O8+δ thin films on LaAlO3 substrates using fast temperature ramping Hg‐vapor annealing

S. H. Yun, J. Z. Wu, S. C. Tidrow, and D. W. Eckart

Appl. Phys. Lett. 68, 2565 (1996); http://dx.doi.org/10.1063/1.116185 (3 pages) | Cited 23 times

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The fast temperature ramping Hg‐vapor annealing (FTRA) process has been used for growth of superconducting Hg‐based cuprate thin films on (100) LaAlO3 substrates. The film/substrate interface chemical reactions and the formation of a CaHgO2 impurity phase have been effectively reduced with adoption of the FTRA process. A zero‐resistance superconducting transition temperature of 128 K and critical current densities of up to 1.4×106 A/cm2 at 77 K and 2.5×105 A/cm2 at 110 K and zero field have been obtained. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.78.-w Superconducting films and low-dimensional structures

High‐precision laser cutting of high‐temperature superconductors

Th. Schuster, H. Kuhn, A. Raiber, T. Abeln, F. Dausinger, H. Hügel, M. Kläser, and G. Müller‐Vogt

Appl. Phys. Lett. 68, 2568 (1996); http://dx.doi.org/10.1063/1.116186 (3 pages) | Cited 1 time

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A laser‐cutting technique was used to pattern high‐temperature superconducting single crystals with high precision into various shapes. The low mean power of 135 mW of the laser enables one to produce cuts of arbitrary shape without affecting the superconducting parameters. This was proven by local observations of the magnetic flux distribution using the magnetooptical Faraday effect. © 1996 American Institute of Physics.
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74.72.-h Cuprate superconductors
85.25.-j Superconducting devices
81.65.-b Surface treatments

Ultra‐smooth, highly ordered, thin films of La0.67Ca0.33MnO3±d

V. A. Vas’ko, C. A. Nordman, P. A. Kraus, V. S. Achutharaman, A. R. Ruosi, and A. M. Goldman

Appl. Phys. Lett. 68, 2571 (1996); http://dx.doi.org/10.1063/1.116187 (3 pages) | Cited 29 times

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We report the growth and characterization of ultra‐smooth, highly ordered, strained La2/3Ca1/3MnO3±d thin films (approximately 600 Å in thickness). The thin films were deposited by ozone‐assisted, block‐by‐block, molecular beam epitaxy on SrTiO3 (001) substrates without any post‐deposition annealing. Scanning tunneling microscopy images showed oriented, unit‐cell‐high terraces characteristic of a step‐flow growth mechanism. The root‐mean‐square roughness of the surface of an imaged film was determined to be 2 Å. This same film showed negative magnetoresistance values, [R(H=0)−R(Happlied)]/R(H=0), at 150 K of 93% and 5% in applied magnetic fields of 5.12 and 4×10−2 T, respectively. © 1996 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
75.47.De Giant magnetoresistance

An approach to electrical studies of single nanocrystals

David L. Klein, Paul L. McEuen, Janet E. Bowen Katari, Richard Roth, and A. Paul Alivisatos

Appl. Phys. Lett. 68, 2574 (1996); http://dx.doi.org/10.1063/1.116188 (3 pages) | Cited 134 times

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We present electrical measurements of single Au and CdSe nanocrystals. The devices are fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind nanocrystals in tunneling contact between two closely spaced metallic leads. The current–voltage characteristics of these devices exhibit a Coulomb staircase with a charging energy of ∼50 meV. This technique is readily adapted to the study of a host of nanocrystals made by solution chemistry. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.23.Hk Coulomb blockade; single-electron tunneling

Fatigue of piezoelectric properties in Pb(Zr,Ti)O3 films

A. L. Kholkin, E. L. Colla, A. K. Tagantsev, D. V. Taylor, and N. Setter

Appl. Phys. Lett. 68, 2577 (1996); http://dx.doi.org/10.1063/1.116189 (3 pages) | Cited 75 times

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Piezoelectric properties of Pb(Zr,Ti)O3 thin films are investigated as a function of the number of bipolar (switching) and unipolar (nonswitching) voltage pulses. The longitudinal piezoelectric coefficient d33 decreases with bipolar fatigue reflecting the decrease of switchable polarization. Simultaneously, a strong vertical shift of piezoelectric hysteresis loops is observed, which is considered as the buildup of fixed internal polarization due to the pinning of ferroelectric domains in a preferred orientation. Piezoelectric fatigue induced by unipolar (nonswitching) pulses is considerably smaller than the fatigue under bipolar conditions and can be described by the internal bias field which shifts piezoelectric hysteresis loops along the field axis. © 1996 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

Enhancement of titanium nitride barrier metal properties by nitrogen radical assisted metalorganic chemical vapor deposition

Y. H. Chang, J. S. Chun, J. E. Oh, S. J. Won, S. H. Paek, H. D. Lee, S. I. Lee, J. S. Choi, and J. G. Lee

Appl. Phys. Lett. 68, 2580 (1996); http://dx.doi.org/10.1063/1.116190 (3 pages) | Cited 12 times

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Using metalorganic chemical vapor deposition assisted by a nitrogen radical irradiation generated by rf plasma, we have enhanced the quality and the step coverage of titanium nitride barrier metals for the contact holes with a high aspect ratio and a submicron radius. Electrical resistivity measurements show that the film resistivity improves by a factor of five as the proper nitrogen irradiation has been applied. The step coverage in a contact hole with 0.4 μm diam and 3:1 aspect ratio has been improved from 50% to 80% by applying nitrogen plasma, clearly demonstrating the effectiveness of this technique in the conformal deposition of barrier metals for the ultra‐large scale integration. The incident nitrogen radical is believed to play several roles, such as the enhancement of surface migration rate of molecules and the reduction of the amount of hydrocarbon incorporating into the film during the deposition. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation

Two‐bandpass fiber‐optic radiometry for monitoring the temperature of photoresist during dry processing

Yair Dankner, O. Eyal, and A. Katzir

Appl. Phys. Lett. 68, 2583 (1996); http://dx.doi.org/10.1063/1.116191 (3 pages) | Cited 4 times

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The temperature of a thin photoresist layer on a silicon wafer was measured in situ during dry etching by using a silver halide optical fiber noncontact thermometer. A two‐bandpass radiometer was constructed to reduce errors arising from geometrical factors and emissivity changes. Such a system may be used to monitor surface temperatures during dry processing of semiconductors and to prevent overheating that may cause damage, such as cross linking of photoresists. © 1996 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
07.20.Dt Thermometers

Nanolithographic templates from diblock copolymer thin films

P. Mansky, C. K. Harrison, P. M. Chaikin, R. A. Register, and N. Yao

Appl. Phys. Lett. 68, 2586 (1996); http://dx.doi.org/10.1063/1.116192 (3 pages) | Cited 73 times

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We describe a technique for creating a thin polystyrene film containing a periodic array of cylindrical holes, with a hole size of approximately 13 nm and a lattice constant of 27 nm. The starting material is a polystyrene‐polybutadiene diblock copolymer, which self‐assembles into a hexagonally packed array of polybutadiene cylinders embedded in a polystyrene matrix. A technique described previously is used to orient the cylinders normal to the plane of the film. The polybutadiene domains are then removed by reaction with ozone, which attacks the double bonds in the polybutadiene backbone. Films of this type could potentially be used as templates for nanolithography on a scale not readily accessed by other techniques. © 1996 American Institute of Physics.
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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
85.40.Hp Lithography, masks and pattern transfer
FREE

Comment on ‘‘Temporal response of a high‐c superconducting field‐effect transistor’’ [Appl. Phys. Lett. 67, 2076 (1995)]

N. Chandrasekhar, Oriol T. Valls, and A. M. Goldman

Appl. Phys. Lett. 68, 2589 (1996); http://dx.doi.org/10.1063/1.116193 (1 page)

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Abstract Unavailable
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85.25.-j Superconducting devices
85.30.Tv Field effect devices
FREE

Response to ‘‘Comment on ‘Temporal response of a high‐c superconducting field effect transistor’ ’’ [Appl. Phys. Lett. 68, 2589 (1996)]

R. Schneider and R. Auer

Appl. Phys. Lett. 68, 2590 (1996); http://dx.doi.org/10.1063/1.116194 (1 page)

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Abstract Unavailable
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85.25.-j Superconducting devices
85.30.Tv Field effect devices
FREE

Erratum: ‘‘Nitrogen diffusion mechanism in the R2Fe17 lattice’’ [Appl. Phys. Lett. 67, 208 (1995)]

Y. D. Zhang, J. I. Budnick, W. A. Hines, and D. P. Yang

Appl. Phys. Lett. 68, 2591 (1996); http://dx.doi.org/10.1063/1.116791 (1 page)

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Abstract Unavailable
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66.30.J- Diffusion of impurities
61.72.up Other materials
75.50.Bb Fe and its alloys
99.10.Cd Errata
FREE

 Erratum: ‘‘Optical investigation of quaternary GalnAsSb/AlGaAsSb strained multiple quantum wells’’ [Appl. Phys. Lett. 67, 3432 (1995)]

W. Z. Shen, S. C. Shen, W. G. Tang, Y. Zhao, A. Z. Li, W. Z. Shen, S. C. Shen, W. G. Tang, Y. Zhao, and A. Z. Li

Appl. Phys. Lett. 68, 2591 (1996); http://dx.doi.org/10.1063/1.116792 (1 page)

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Abstract Unavailable
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
99.10.Cd Errata
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