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16 Jun 1997

Volume 70, Issue 24, pp. 3185-3313

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Reverse current transient behavior in amorphous silicon Schottky diodes at low biases

R. I. Hornsey, K. Aflatooni, and A. Nathan

Appl. Phys. Lett. 70, 3260 (1997); http://dx.doi.org/10.1063/1.119141 (3 pages) | Cited 5 times

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The application of hydrogenated amorphous silicon Schottky diodes to large-area imaging requires knowledge of the variation in reverse-bias current over long timescales. When the diode is subject to electrical stress, a power-law dependence of reverse current with time is observed. This is followed by a stretched-exponential behavior during the subsequent zero-bias recovery period. Both of these results are attributed to dispersive electron transport in the Schottky diode. © 1997 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Jc Amorphous semiconductors; glasses
85.30.Hi Surface barrier, boundary, and point contact devices

Ballistic electron luminescence studies of superlattice minibands

M. V. Petrov and S. A. Lyon

Appl. Phys. Lett. 70, 3263 (1997); http://dx.doi.org/10.1063/1.119142 (3 pages) | Cited 4 times

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Short-period superlattice minibands have been studied by ballistic electron luminescence spectroscopy. Using a combination of optical and electrical measurements in a single device, electron transport through an AlGaAs/GaAs superlattice was observed. The optical measurement provided a precise energy scale for calibration of voltages obtained in the electrical experiment. A three terminal n-p-p device was used, where the electrons were injected through an emitter-base tunnel barrier into a p-type base, which was separated from the p-doped collector by a superlattice. Luminescence emitted by ballistic electrons recombining in the base was used to measure their kinetic energy. Oscillations in the transistor gain were detected and are due to transport through the superlattice miniband. © 1997 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.23.Ad Ballistic transport
78.66.Fd III-V semiconductors

Growth and characterization of InSbBi for long wavelength infrared photodetectors

J. J. Lee, J. D. Kim, and M. Razeghi

Appl. Phys. Lett. 70, 3266 (1997); http://dx.doi.org/10.1063/1.119158 (3 pages) | Cited 13 times

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The epitaxial growth of InSbBi ternary alloys by low-pressure metalorganic chemical vapor deposition is reported on. X-ray diffraction spectra showed well resolved peaks of InSbBi and InSb films. Bi incorporation was confirmed by energy dispersive x-ray analysis. Photoresponse spectrum up to 9.3 μm which corresponds to 0.13 eV energy band gap has been measured in a sample with Bi composition of 5.8 at.% at 77 K. Electron mobility at room temperature ranges from 44 100 to 4910 cm2/Vs as Bi composition increases. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Detection of combinative infrared absorption bands in thin silicon dioxide films

Sang M. Han and Eray S. Aydil

Appl. Phys. Lett. 70, 3269 (1997); http://dx.doi.org/10.1063/1.118424 (3 pages) | Cited 10 times

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Multiple total internal reflection Fourier transform infrared spectroscopy is used to detect combinational phonon bands of SiO2 at 1645, 1852, and 2000 cm−1 in thin films produced by plasma enhanced chemical vapor deposition. The isotopic shifts of these bands in films deposited from SiH4/18O2 mixtures proved that combinations of SiO2 phonons give rise to the additional absorption peaks. Detection of these combinative phonon bands enables one to use Si multiple total internal reflection crystals for studying Si–O phonon absorptions in SiO2 films on Si. In principle, films as thin as a few angstroms can be detected using the infrared absorption by the combinational bands. © 1997 American Institute of Physics.
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78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Nanooxidation using a scanning probe microscope: An analytical model based on field induced oxidation

D. Stiévenard, P. A. Fontaine, and E. Dubois

Appl. Phys. Lett. 70, 3272 (1997); http://dx.doi.org/10.1063/1.118425 (3 pages) | Cited 96 times

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The formation of a nanometer-size oxide pattern on silicon using a scanning probe microscope (SPM) has been widely reported in the literature. No analytical model has been proposed, however, to explain the variation of the oxide height with both polarization and speed of the SPM tip. In this letter, we explain quantitatively the variation of the oxide height with the polarization and the speed of the tip with a model based on field induced oxidation. Data analysis also allows us to estimate the thermal activation energy of the oxidation process, ( ∼ 0.15 eV). This low value is compared with activation energies measured for thermal and plasma oxidation of silicon. © 1997 American Institute of Physics.
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81.65.Mq Oxidation
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
07.79.Cz Scanning tunneling microscopes

Large photoluminescence enhancements from epitaxial GaAs passivated by postgrowth phosphidization

D. A. Harrison, R. Arès, S. P. Watkins, M. L. W. Thewalt, C. R. Bolognesi, D. J. S. Beckett, and A. J. SpringThorpe

Appl. Phys. Lett. 70, 3275 (1997); http://dx.doi.org/10.1063/1.118426 (3 pages) | Cited 11 times

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Dramatic enhancements of over 300× in the room temperature photoluminescence signal obtained from high purity GaAs epitaxial layers were recorded after a brief heat treatment in tertiarybutylphosphine vapor. Low temperature photoluminescence spectra indicate that, unlike other passivation techniques, the surface layer formed during this simple treatment does not induce any appreciable strain on the underlying epilayer. The increases in photoluminescence intensity are indicative of a reduction in surface recombination brought about by the formation of a very thin GaP layer that protects against surface oxidation. © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.65.Rv Passivation
78.66.Fd III-V semiconductors

Self-organized CdSe quantum dots onto cleaved GaAs (110) originating from Stranski–Krastanow growth mode

Hyun-Chul Ko, Doo-Cheol Park, Yoichi Kawakami, Shizuo Fujita, and Shigeo Fujita

Appl. Phys. Lett. 70, 3278 (1997); http://dx.doi.org/10.1063/1.118427 (3 pages) | Cited 33 times

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Self-organized CdSe/ZnSe quantum dots (QDs) have been fabricated on GaAs (110) crystal surfaces, which were obtained by cleaving GaAs (100) wafers in ultrahigh vacuum. CdSe showed a conventional Stranski–Krastanow growth mode on the ZnSe (110) lower cladding layer, whose surfaces are atomically flat. The wetting layers, which are compose of quantum wells with well widths of 1, 2, and 3 monomolecular layers, showed sharp photoluminescence (PL). The fabricated CdSe QDs showed intense green PL spectra, whose peak is located at 2.192 eV, with a linewidth of 0.24 eV. The state filling effect in CdSe QDs was also observed by employing excitation power dependence of the PL intensity. © 1997 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology

Transient enhanced diffusion of Sb and B due to MeV silicon implants

D. J. Eaglesham, T. E. Haynes, H.-J. Gossmann, D. C. Jacobson, P. A. Stolk, and J. M. Poate

Appl. Phys. Lett. 70, 3281 (1997); http://dx.doi.org/10.1063/1.119150 (3 pages) | Cited 26 times

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We measure the transient enhanced diffusion of shallow molecular-beam-epitaxy grown marker layers of Sb and B due to deep MeV Si+ ion implants at very high doses ( ≈ 1016 cm−2). We expect the near-surface region of these implants to be vacancy rich, and we observe transient enhanced diffusion of Sb (the classic vacancy diffuser). The large enhancements imply a significant vacancy supersaturation ( ≈ 700 at 740 °C). Double implantation of the high-dose MeV Si followed by a shallow (40 keV) Si implant and annealing produces a greatly reduced number of {311} defects compared to a 40 keV implant into virgin Si, again consistent with a vacancy-rich region in the near-surface region of an MeV implant. However, the shallow B marker layers also show transient enhanced diffusion for the same MeV implant under similar annealing conditions, implying that an interstitial supersaturation is present at the same time. We discuss possible mechanisms for a simultaneous supersaturation of both types of point defects. © 1997 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology

Electrical characterization of partially relaxed InxGa1−xAs/GaAs multiple quantum well structures

C. R. Moon, In Kim, Jeong Seok Lee, Byung-Doo Choe, S. D. Kwon, and H. Lim

Appl. Phys. Lett. 70, 3284 (1997); http://dx.doi.org/10.1063/1.118428 (3 pages) | Cited 6 times

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Electronic properties of partially relaxed InxGa1−xAs/GaAs multiple quantum well (MQW) structures are investigated using capacitance–voltage (C–V) profiling and deep level transient spectroscopy (DLTS). As the In composition becomes large, the depletion of carriers confined in QWs and the concentration of dislocation-related deep traps are increased. The carrier depletion is observed to occur predominantly in the QWs adjacent to the bottom layer. This depletion is believed to be due to electron capture at the acceptor-like misfit dislocation-related traps. Our results thus show that the C–V and DLTS measurements, combined with the numerical simulation of C–V profiles, can be used to study the influence of nonuniformly distributed misfit dislocations on the carrier distribution in MQW structures. © 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
73.61.Ey III-V semiconductors

Hydrogen desorption in SiGe films: A diffusion limited process

J. Vizoso, F. Martín, J. Suñé, and M. Nafría

Appl. Phys. Lett. 70, 3287 (1997); http://dx.doi.org/10.1063/1.118429 (3 pages) | Cited 2 times

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A model to explain the hydrogen desorption kinetics in SiGe alloys is presented. This is an extension of a previous desorption model of hydrogen from Si, that considers the presence of three dimer types in the surface in which hydrogen atoms tend to pair before the desorption reaction. Surface diffusion is included in the model. The comparison with experimental results shows that desorption is a diffusion limited process. © 1997 American Institute of Physics.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Microwave coupling of frequency-locked Josephson junction arrays

Insang Song, Yongheum Eom, Gwangseo Park, E.-H. Lee, and S.-J. Park

Appl. Phys. Lett. 70, 3290 (1997); http://dx.doi.org/10.1063/1.118430 (3 pages) | Cited 3 times

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A high temperature superconducting YBa2Cu3Oy array of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency. © 1997 American Institute of Physics.
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85.25.Cp Josephson devices
74.72.-h Cuprate superconductors

Power-dependent microwave properties of superconducting YBa2Cu3O7−x films on buffered polycrystalline substrates

A. T. Findikoglu, P. N. Arendt, S. R. Foltyn, J. R. Groves, Q. X. Jia, E. J. Peterson, L. Bulaevskii, M. P. Maley, and D. W. Reagor

Appl. Phys. Lett. 70, 3293 (1997); http://dx.doi.org/10.1063/1.118431 (3 pages) | Cited 10 times

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We have studied the microwave properties of 0.4 μm thick YBa2Cu3O7−x (YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistance Rs values of about 0.5 mΩ at 76 K and 0.15 mΩ at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures
74.25.N- Response to electromagnetic fields

Gain and noise bandwidth of NbN hot-electron bolometric mixers

H. Ekström, E. Kollberg, P. Yagoubov, G. Gol’tsman, E. Gershenzon, and S. Yngvesson

Appl. Phys. Lett. 70, 3296 (1997); http://dx.doi.org/10.1063/1.119143 (3 pages) | Cited 23 times

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We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K. © 1997 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
73.50.Td Noise processes and phenomena

Tunable magnetic regenerator alloys with a giant magnetocaloric effect for magnetic refrigeration from ∼ 20 to ∼ 290 K

V. K. Pecharsky and K. A. Gschneidner

Appl. Phys. Lett. 70, 3299 (1997); http://dx.doi.org/10.1063/1.119206 (3 pages) | Cited 273 times

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A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x ⩽ 0.5. For the temperature range between ∼ 50 and ∼ 280 K it exceeds the reversible (with respect to alternating magnetic field) ΔSmag for any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large ΔSmag in Gd5(SixGe1−x)4, is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from ∼ 30 to ∼ 276 K by adjusting the Si:Ge ratio without losing the giant magnetic entropy change. © 1997 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Spatial and temperature dependence of magnetic moment perturbations near the (1-10) Fe/Co interface

B. Swinnen, J. Dekoster, J. Meersschaut, S. Cottenier, S. Demuynck, G. Langouche, and M. Rots

Appl. Phys. Lett. 70, 3302 (1997); http://dx.doi.org/10.1063/1.119144 (3 pages) | Cited 2 times

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The spatial dependence of the magnetic moment perturbation near the (1-10)-Fe/Co interface was derived from hyperfine fields determined by perturbed angular correlation. The amplitude of the moment perturbation decays exponentially with the distance to the interface. The moment perturbation itself is modulated by a sine function of the distance d to the interface Δμ = A*exp(−p*∣d∣)*sin(−k*d). Between 90 K and 570 K, we observe that the amplitude and the penetration depth of the perturbation as well as the wave vector of the modulation are essentially constant within the accuracy of the values. In this temperature region the average values for the parameters determining the exact moment perturbation are A = 1.03μB, p = 2.25×109 m and k = 1.45×1010 m−1 when d is defined positive at the Co side of the interface.© 1997 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
76.80.+y Mössbauer effect; other γ-ray spectroscopy

High-sensitive superconducting magnetometry on a two-dimensional electron gas up to 10 Tesla

Ines Meinel, Dirk Grundler, Silke Bargstädt-Franke, Christian Heyn, Detlef Heitmann, and Bernd David

Appl. Phys. Lett. 70, 3305 (1997); http://dx.doi.org/10.1063/1.119145 (3 pages) | Cited 31 times

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We report on new magnetization studies on a two-dimensional electron system (2DES) revealing spin splitting of the Landau levels. For this, we have built a high-sensitive susceptometer consisting of a low-noise thin-film dc superconducting quantum interference device (SQUID) with a multiturn input coil and a wire-wound first-order gradiometer. The system noise level is only 40×10−6 Φ0/√(Hz) down to a frequency of a few Hz in unshielded environment. In background fields up to 10 T, the system exhibits significant low-frequency noise. At frequencies above 1 kHz, however, the SQUID sensitivity is barely affected and we have reached a value of about 10−14 J/T at 1 T and better than 10−13 J/T at 10 T. With this, we have studied the de Haas–van Alphen effect for a tunable 2DES starting from zero carrier density. © 1997 American Institute of Physics.
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73.43.-f Quantum Hall effects
07.55.-w Magnetic instruments and components
85.25.Dq Superconducting quantum interference devices (SQUIDs)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Field emission from nanotube bundle emitters at low fields

Q. H. Wang, T. D. Corrigan, J. Y. Dai, R. P. H. Chang, and A. R. Krauss

Appl. Phys. Lett. 70, 3308 (1997); http://dx.doi.org/10.1063/1.119146 (3 pages) | Cited 243 times

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The fabrication of nanotube field emitters with an onset field as low as 0.8 V/μm is described and the low-field electron emission mechanism is discussed. These emitters are made using nanotube cathode deposit with the addition of epoxy resin. The preferred orientation of nanotubes in nanotube bundles of the deposit is preserved. The nanotube tips are sharpened by exposing the nanotube bundle surface to a microwave oxygen plasma. The local-field enhancement factor is estimated to be 8000 by using the Fowler–Nordheim equation. The low onset field is attributed to the well-distributed, highly orientated sharp tips at the sample surface. © 1997 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.ub Fullerenes and related materials
07.77.Ka Charged-particle beam sources and detectors

Two-dimensional micromechanical bimorph arrays for detection of thermal radiation

S. R. Manalis, S. C. Minne, C. F. Quate, G. G. Yaralioglu, and A. Atalar

Appl. Phys. Lett. 70, 3311 (1997); http://dx.doi.org/10.1063/1.119147 (3 pages) | Cited 30 times

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We demonstrate that two-dimensional arrays of micromechanical bimorphs can be used as thermal sensors to image infrared (IR) radiation. A density of 100 pixels per mm2 is achieved by coiling a bimorph beam into the shape of a flat spiral. Temperature variations of a given spiral are converted to modulations of visible light by illuminating the spiral array with a visible source. The optical properties of the spiral resemble a Fresnel zone plate when light reflected off neighboring rings of the spiral is focused. When a spiral is heated through the absorption of IR radiation, thermally induced bending of the bimorph degrades the focusing efficiency by distorting the spiral. This reduces the optical intensity at the focal point. Arrays of spirals can be monitored with a commercial CCD camera. At 40 Hz, the temperature resolution and noise equivalent power of a 75 μm diam spiral are 50 μK/√Hz and 20 nW/√Hz, respectively, and the thermal response time is 270 μs. © 1997 American Institute of Physics.
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42.79.Ls Scanners, image intensifiers, and image converters
07.10.Cm Micromechanical devices and systems
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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