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17 Jun 1996

Volume 68, Issue 25, pp. 3525-3661

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The nonlinear transport regime of a T‐shaped quantum interference transistor

R. Šordan and K. Nikolić

Appl. Phys. Lett. 68, 3599 (1996); http://dx.doi.org/10.1063/1.116650 (3 pages) | Cited 3 times

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We present the current–voltage characteristics of a T‐shaped semiconductor electron waveguide structure in the nonlinear regime. This system is interesting as a potential quantum interference transistor. Calculated zero‐temperature I–V characteristics are with multiple peaks and exhibit regions of negative‐differential resistance. The peak‐to‐valley ratio has maximum value of 3:1. The calculated values of the transconductance and the differential drain conductance are small, which suggests limited abilities for conventional applications of the transistor. © 1996 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.20.Dp General theory, scattering mechanisms
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Photon assisted field electron emission from SiO2/Si substrates

I. Jiménez and J. L. Sacedón

Appl. Phys. Lett. 68, 3602 (1996); http://dx.doi.org/10.1063/1.116651 (3 pages) | Cited 2 times

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We report the observation of a field‐emission effect in SiO2/Si samples assisted by the presence of photons. Electric fields in the oxide of the order of 10 MV/cm−1 are attained by photocharging during x‐ray illumination and bring the vacuum level to a position below the equilibrium Fermi level. Hot electrons are injected from the Si substrate, traverse the SiO2 layer, and are emitted directly into vacuum. The large photocharging effect is related to the surface topography, consisting of multiple Si tips of about 1 μm high. © 1996 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Recombination velocity at oxide–GaAs interfaces fabricated by in situ molecular beam epitaxy

M. Passlack, M. Hong, J. P. Mannaerts, J. R. Kwo, and L. W. Tu

Appl. Phys. Lett. 68, 3605 (1996); http://dx.doi.org/10.1063/1.116652 (3 pages) | Cited 33 times

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The recombination velocity at oxide–GaAs interfaces fabricated by in situ multiple‐chamber molecular beam epitaxy has been investigated. Ga2O3, Al2O3, SiO2, and MgO films have been deposited on clean, atomically ordered n‐ and p‐type (100) GaAs surfaces using molecular beams of Ga–, Al–, Si–, and Mg oxide, respectively. Based on the internal quantum efficiency measured for incident light power densities 1≤P0≤104 W/cm2, the interface recombination velocity S has been inferred using a self‐consistent numerical heterostructure device model. While Al2O3–, SiO2–, and MgO–GaAs structures are characterized by an interface recombination velocity which is comparable to that of a bare GaAs surface (≂ 107 cm/s), S observed at Ga2O3–GaAs interfaces is as low as 4000–5000 cm/s. The excellent Ga2O3–GaAs interface recombination velocity is consistent with the previously reported low interface state density in the mid 1010 cm−2 eV−1 range. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Growth and strain symmetrization of Si/Ge/C/Sn quaternary alloys by molecular beam epitaxy

F. J. Guarin, S. S. Iyer, A. R. Powell, and B. A. Ek

Appl. Phys. Lett. 68, 3608 (1996); http://dx.doi.org/10.1063/1.115745 (3 pages) | Cited 8 times

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We have synthesized, via molecular beam epitaxy alloys of SixSnyC1−x−y with symmetric strain. In this work we report the growth of systems with varying compositions/band gaps including the first silicon‐based quaternary (Si/Ge/Sn/C) system, which offers an additional degree of freedom for strain and band gap engineering in Si‐based alloys. We report the growth of Si.955Sn.03C.015 alloys up to 4500 Å in thickness and quaternaries of composition in the neighborhood of Si.835Ge.125Sn.03C.01. Infrared absorption spectroscopy and photoluminescence data have provided evidence of the potential for significant band gap modification in these alloys. © 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

Transverse magnetic and transverse electric polarized inter‐subband absorption and photoconductivity in p‐type SiGe quantum wells

T. Fromherz, P. Kruck, M. Helm, G. Bauer, J. F. Nützel, and G. Abstreiter

Appl. Phys. Lett. 68, 3611 (1996); http://dx.doi.org/10.1063/1.115746 (3 pages) | Cited 13 times

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We have investigated the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration of ps=2.8×1012 cm−2 both transverse magnetic and transverse electric polarized absorptions have been observed, and transitions to several excited states are clearly identified by comparison with self‐consistent Luttinger–Kohn type calculations. The photoconductivity is surprisingly little sensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsivity. © 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
73.50.Pz Photoconduction and photovoltaic effects
78.66.Li Other semiconductors

Photoluminescence studies of self‐assembled InSb, GaSb, and AlSb quantum dot heterostructures

E. R. Glaser, B. R. Bennett, B. V. Shanabrook, and R. Magno

Appl. Phys. Lett. 68, 3614 (1996); http://dx.doi.org/10.1063/1.115747 (3 pages) | Cited 70 times

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Photoluminescence (PL) spectroscopy has been performed on a set of self‐assembled InSb, GaSb, and AlSb quantum dot (QD) heterostructures grown on GaAs. Strong emission bands with peak energies near 1.15 eV and linewidths of ∼80 meV are observed at 1.6 K from 3 monolayer (ML) InSb and GaSb QDs capped with GaAs. The PL from a capped 4 ML AlSb QD sample is weaker with peak energy at 1.26 eV. The PL bands from these Sb‐based QD samples shift to lower energy by 20–50 meV with decreasing excitation power density. This behavior suggests a type II band lineup. Support for this assignment, with electrons in the GaAs and holes in the (In,Ga,Al)Sb QDs, is found from the observed shift of GaSb QD emission to higher energies when the GaAs barrier layers are replaced by Al0.1Ga0.9As.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Preparation of GaN films on sapphire by metalorganic chemical vapor deposition using dimethylhydrazine as nitrogen source

Hitoshi Sato, Hirokazu Takahashi, Atsushi Watanabe, and Hiroyuki Ota

Appl. Phys. Lett. 68, 3617 (1996); http://dx.doi.org/10.1063/1.115748 (3 pages) | Cited 13 times

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We report the preparation of high quality GaN films using dimethylhydrazine as a nitrogen source. GaN films were deposited on (0001) sapphire substrates by low‐pressure metalorganic chemical vapor deposition. The film has excellent morphology in flat surface free from cracks. The full width at half maximum of the x‐ray diffraction rocking curve measured from (0002) plane of GaN has exhibited as narrow as 147 arcsec. The optical quality of the film is concluded to be excellent from the photoluminescence property measured at room temperature, where the intensity of the band edge emission is much stronger than that of deep level emission. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

A design of reflection scanning near‐field optical microscope and its application to AlGaAs/GaAs heterostructures

G. Guttroff, J. M. Keto, C. K. Shih, A. Anselm, and B. G. Streetman

Appl. Phys. Lett. 68, 3620 (1996); http://dx.doi.org/10.1063/1.115749 (3 pages) | Cited 7 times

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A scanning near‐field microscope design using the reflected light intensity as the feedback mechanism is described. Multiple fibers with high numerical apertures provide a high collection efficiency in a reflection geometry. The performance with regard to its response to large spatial variations has been tested by using a Si‐grating sample and with regard to variations of local indices of refraction by using GaAs/AlGaAs heterostructure samples. In addition, spatially resolved spectroscopy on GaAs/AlGaAs heterostructures has been obtained. © 1996 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.66.Fd III-V semiconductors
07.79.Fc Near-field scanning optical microscopes

Magnetic field behavior of small sputtered step‐edge junctions

M. Vaupel, G. Ockenfuss, and R. Wördenweber

Appl. Phys. Lett. 68, 3623 (1996); http://dx.doi.org/10.1063/1.115750 (3 pages) | Cited 8 times

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YBa2Cu3O7 step‐edge junctions with widths down to 0.5 μm are fabricated on SrTiO3 substrates by Ar ion‐beam milling of the steps, high‐pressure on‐axis magnetron sputtering, electron beam patterning and ion‐beam etching of the microbridge. For ratios of film thickness to step height of ∼1/2 the current‐voltage characteristics show Shapiro steps under microwave irradiation and resistively shunted junction like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer pattern. The period of the current variation ΔB0 depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: ΔB0=1.84ϕ0/w2. Junctions with widths of 0.7 μm possess a large magnetic field stability with ΔB0≊100 G. Small junctions (w<1 μm) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the electrodes. © 1996 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects

Spatially resolved analyses of epitaxial and electrical properties of YBa2Cu3O7 devices

N. Dieckmann, A. Bock, and U. Merkt

Appl. Phys. Lett. 68, 3626 (1996); http://dx.doi.org/10.1063/1.115751 (3 pages) | Cited 12 times

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We use scanning micro‐Raman spectroscopy (SMRS) to characterize the epitaxial film quality as well as low‐temperature scanning laser microscopy (LTSLM) to image electrical properties of YBa2Cu3O7 devices locally in both lateral dimensions. Investigations have been performed on crossovers as used in flux transformers of magnetometers, patterned in a multilayer process on SrTiO3 (100) substrates. We find a correlation between an inhomogeneous superconducting performance and a disturbance of epitaxy on locations where the crossovers pass edges of the underlying bridge. The distribution of the oxygen is not affected at these points. © 1996 American Institute of Physics.
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78.30.-j Infrared and Raman spectra
74.78.-w Superconducting films and low-dimensional structures
85.25.Cp Josephson devices

Overcoming weak links at grain boundaries in Bi2Sr2CaCu2Ox thick films by incorporation of superconducting whiskers

Ryoji Funahashi, Ichiro Matsubara, Lucangelo Dimesso, Toru Ogura, Kazuo Ueno, Hiroshi Ishikawa, Masayoshi Konishi, and Nobuhito Ohno

Appl. Phys. Lett. 68, 3629 (1996); http://dx.doi.org/10.1063/1.115752 (3 pages) | Cited 5 times

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Bi2Sr2CaCu2Ox (Bi‐2212) superconducting thick films incorporating Bi‐2212 superconducting whiskers have been prepared using a partial melting method. Hysteresis behavior of critical current density (Jc) for magnetic field is observed in a film without whiskers (monolithic film), but not noticeably in composite film (whisker content: 20 wt %). It is found from ac susceptibility measurement that a peak in χ″, resulting from weak links, appears at a higher temperature for the composite film than for the monolithic film. Jc decreases with increasing magnetic field more rapidly for the monolithic film than for the composite film less than 1 T. These results indicate that the incorporation of the whiskers is effective for overcoming weak links. In consequence Jc for the composite film is about three times higher than for the monolithic film. It is clear from SEM observation that a microstructural improvement leads to an increase in Jc. © 1996 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures

Nanometer‐scale surface modifications of YBa2Cu3O7−δ thin films using a scanning tunneling microscope

G. Bertsche, W. Clauss, and D. P. Kern

Appl. Phys. Lett. 68, 3632 (1996); http://dx.doi.org/10.1063/1.115753 (3 pages) | Cited 17 times

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Systematic modifications on the nanometer scale of YBa2Cu3O7−δ (YBCO) epitaxial, thin films have been achieved by using a scanning tunneling microscope in air at room temperature. Working with tunneling parameters slightly above those used for imaging results in irreversible, nanometer‐sized surface modifications. The surface topography of our YBCO films showed characteristic growth spirals, of which one revealed a remarkable ‘‘S’’‐shaped top end. This unusual growth behavior indicates possibly a distortion caused by a line defect in the second to last turn of the spiral. We succeeded in cutting through this structure by producing a 2.5 nm wide groove across it. This corresponds to the controlled removal of only a few unit cells of YBCO. As an alternative modification technique, bias voltage pulses were applied, leading to the formation of 3 nm wide craters. © 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
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Structure of cross‐tie wall in thin Co films resolved by magnetic force microscopy

M. Löhndorf, A. Wadas, H. A. M. van den Berg, and R. Wiesendanger

Appl. Phys. Lett. 68, 3635 (1996); http://dx.doi.org/10.1063/1.115754 (3 pages) | Cited 19 times

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We have studied the magnetic domain structure of a thin polycrystalline Co film by magnetic force microscopy (MFM). Domain walls of the cross‐tie type have been observed for a Co film of 50 nm thickness. Due to the high lateral resolution of MFM we have been able to study the magnetic structure of a single cross tie. We have determined locations of Bloch lines within a domain wall comparing the experimental data with a theoretical model of a cross‐tie wall. In order to explain our experimental results we have proposed a model for the interaction between a MFM tip and a cross‐tie wall. © 1996 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Giant magnetoresistance of a two‐dimensional ferromagnet La2−2xCa1+2xMn2O7

H. Asano, J. Hayakawa, and M. Matsui

Appl. Phys. Lett. 68, 3638 (1996); http://dx.doi.org/10.1063/1.115755 (3 pages) | Cited 76 times

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Bulk samples of La2−2xCa1+2xMn2O7 with the layered Sr3Ti2O7‐type perovskite structure have been successfully synthesized and investigated with respect to their magnetic and electrical properties. It is found that La2−2xCa1+2xMn2O7 (x=0.25) is a metallic ferromagnet with a magnetic transition temperature Tc of 215 K. The large magnetoresistance (MR) effect with Δρ/ρ0 of ∼60% at 1.8 T was observed in a wide temperature range below a cusp temperature in resistivity of 96 K, which is well below the magnetic Tc. This behavior is quite different from that of the well‐known double‐exchange ferromagnets such as La1−xCaxMnO3, where large MR effects are restricted to a narrow temperature range around the ferromagnetic transition. The present result could be interpreted by using the double‐exchange theory incorporating the anisotropy resulting from the two‐dimensional Mn‐O‐Mn networks in La2−2xCa1+2xMn2O7. © 1996 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
72.15.Gd Galvanomagnetic and other magnetotransport effects

Spin reversal in ultra‐thin magnetic films with fourfold anisotropy

S. T. Chui

Appl. Phys. Lett. 68, 3641 (1996); http://dx.doi.org/10.1063/1.115756 (3 pages) | Cited 13 times

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We discuss the coercive behaviour of systems with fourfold symmetry. In agreement with recent experiments, in simulation studies we found a two step process with two coercive fields for the x and the y magnetizations. A new physical picture for the spin reversal is obtained. Dipolar effects are found to be very important. © 1996 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces

1/f resistance noise in the large magnetoresistance manganites

G. B. Alers, A. P. Ramirez, and S. Jin

Appl. Phys. Lett. 68, 3644 (1996); http://dx.doi.org/10.1063/1.115757 (3 pages) | Cited 39 times

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Resistance noise has been measured in thin films of La0.6Y0.07Ca0.33MnO3 at the ferromagnetic metal to paramagnetic‐insulator transition where a large magnetoresistance is observed. Fluctuations in resistance were found to have a 1/f power law form throughout the transition where f is frequency. This intrinsic 1/f noise is much larger than what is typical for metallic films and is consistent with the fluctuation‐dissipation theorem and magnetization fluctuations in the ferromagnetic phase. The implications of this large low frequency noise for practical magnetoresistive devices will be addressed. © 1996 American Institute of Physics.
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73.50.Td Noise processes and phenomena
75.47.De Giant magnetoresistance

Positive giant magnetoresistance in antiferromagnetic RE2Ni3Si5 (RE=Tb, Sm, Nd)

Chandan Mazumdar, A. K. Nigam, R. Nagarajan, C. Godart, L. C. Gupta, B. D. Padalia, G. Chandra, and R. Vijayaraghavan

Appl. Phys. Lett. 68, 3647 (1996); http://dx.doi.org/10.1063/1.115758 (3 pages) | Cited 20 times

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Positive giant magnetoresistance (GMR), Δρ/ρ, is reported here in polycrystalline antiferromagnetic materials RE2Ni3Si5 (RE=Tb, Sm, Nd); Δρ/ρ, at 4.4 K and in a field of 45 kOe, is 85%, 75%, and 58%, respectively. Positive GMR of such large magnitude has not been reported earlier in magnetically ordered polycrystalline compounds. The observed GMR is not correlated to the RE‐moments. It is, however, associated with the magnetic ordering of the lattice as its magnitude is significantly reduced in the paramagnetic state. Surprisingly, MR in Y2Ni3Si5, a non‐magnetic rare earth analogue, is also relatively large (16% at 4.4 K; 45 kOe) and is even slightly higher than that of antiferromagnetically ordered Gd2Ni3Si5 (12% at 4.4 K; 45 kOe). The layered structure of the materials is suggested to be responsible for the observed GMR. © 1996 American Institute of Physics.
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75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects

A ferroelectric transparent thin‐film transistor

M. W. J. Prins, K.‐O. Grosse‐Holz, G. Müller, J. F. M. Cillessen, J. B. Giesbers, R. P. Weening, and R. M. Wolf

Appl. Phys. Lett. 68, 3650 (1996); http://dx.doi.org/10.1063/1.115759 (3 pages) | Cited 76 times

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Operation is demonstrated of a field‐effect transistor made of transparant oxidic thin films, showing an intrinsic memory function due to the usage of a ferroelectric insulator. The device consists of a high mobility Sb‐doped n‐type SnO2 semiconductor layer, PbZr0.2Ti0.8O3 as a ferroelectric insulator, and SrRuO3 as a gate electrode, each layer prepared by pulsed laser deposition. The hysteresis behavior of the channel conductance is studied. Using gate voltage pulses of 100 μs duration and a pulse height of ±3 V, a change of a factor of two in the remnant conductance is achieved. The dependence of the conductance on the polarity of the gate pulse proves that the memory effect is driven by the ferroelectric polarization. The influence of charge trapping is also observed and discussed. © 1996 American Institute of Physics.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Simulation of scanning tunneling microscope interaction with resists

E. A. Dobisz, H. W. P. Koops, and F. K. Perkins

Appl. Phys. Lett. 68, 3653 (1996); http://dx.doi.org/10.1063/1.115760 (3 pages) | Cited 3 times

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Three‐dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were performed for resist thicknesses of 1–50 nm and tip‐resist separations of 1–20 nm. For a fixed 10 nm tip‐resist separation, the axial electric field at the tip decreases by a factor of 2.3 over the resist thickness range. The results show that the tip‐resist separation must decrease with increasing resist thickness, to achieve the operating conditions and the energy of electrons entering the resist can be significantly less than the applied tip‐substrate bias. © 1996 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Nitrogen doped fluorinated amorphous carbon thin films grown by plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics

Kazuhiko Endo and Toru Tatsumi

Appl. Phys. Lett. 68, 3656 (1996); http://dx.doi.org/10.1063/1.115761 (3 pages) | Cited 11 times

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Nitrogen doped fluorinated amorphous carbon thin films for low dielectric constant interlayer dielectrics have been investigated. The films were deposited with a parallel‐plate plasma enhanced chemical vapor deposition. Source gases were CH4, CF4, and N2. The thermal stability of the films can be improved by the addition of N2. X‐ray photoelectron spectroscopy (XPS) measurement revealed that the C‐N bonds were formed in the films with the addition of N2. The dielectric constant of the films was increased from 2.1 to 2.4 at the nitrogen concentration of 10%. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Experimental investigation of dipole‐dipole interaction in a water‐free glass particle/oil electrorheological fluid

Weijia Wen and Kunquan Lu

Appl. Phys. Lett. 68, 3659 (1996); http://dx.doi.org/10.1063/1.115762 (3 pages) | Cited 17 times

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An experimental investigation of the dipole interaction in a water‐free glass/oil electrorheological fluid under an alternating electric field is presented in this letter. The values of the dielectric constant ϵ and conductivity σ of glass and oil with respect to the frequency of the external electric field are measured, respectively. Corresponding to the changes in ϵ and σ, the square of the absolute dielectric mismatch parameter ∣β∣ {β=(ϵp(ω)−ϵf(ω)]/[ϵp(ω)+2ϵf(ω)], where ϵ=ϵ+σ/iϵ0ω, and subscripts p and f indicate the glass and oil} decreases as the frequency is increased. After comparing the variation tendency of the ∣β∣2 with the yield stress of the electrorheological (ER) fluid in a measured frequency range we found that they coincide very well. This result confirms that the polarization theory can explain the mechanism of the ER effect not only in a dc electric field but also in that with a wide frequency range. However, the interaction within the multipoles should be considered in an exact calculation. © 1996 American Institute of Physics.
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83.80.Gv Electro- and magnetorheological fluids
83.60.Np Effects of electric and magnetic fields
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
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