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18 Oct 1993

Volume 63, Issue 16, pp. 2165-2297

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True oxide electron beam induced current for low‐voltage imaging of local defects in very thin silicon dioxide films

W. S. Lau, D. S. H. Chan, J. C. H. Phang, K. W. Chow, K. S. Pey, Y. P. Lim, and B. Cronquist

Appl. Phys. Lett. 63, 2240 (1993); http://dx.doi.org/10.1063/1.110539 (3 pages) | Cited 5 times

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A new low‐voltage contrast mechanism due to electron hole pairs generated in the oxide by an electron beam was observed at an electric field lower than 3.5 MV/cm in addition to the tunneling current microscopy (TCM) contrast mechanism at electric fields higher than 3.5 MV/cm. The new contrast mechanism is opposite in sign to the TCM contrast mechanism. Good contrast can be obtained at an electric field as low as 2.4 MV/cm, which is two to three times smaller than that needed for TCM contrast. Potential applications include large area imaging and quantitative imaging of oxide defects.
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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
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Strain and charge distribution in GaN‐AlN‐GaN semiconductor‐insulator‐semiconductor structure for arbitrary growth orientation

Alexei Bykhovski, Boris Gelmont, and Michael Shur

Appl. Phys. Lett. 63, 2243 (1993); http://dx.doi.org/10.1063/1.110540 (3 pages) | Cited 33 times

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We demonstrate that, in a GaN‐AlN‐GaN semiconductor‐insulator‐semiconductor structure, the strain‐induced electric fields across the interface depend on the angle, θ, between the c axis and the growth direction. The magnitude of the strain induced polarization has a maximum in (0001) crystallographic direction (θ=0°) and a subsidiary maximum near θ=70°. This angular dependence is a unique feature of wurtzite‐type structures. Considering θ as an independent parameter for device design, one can obtain structures with flat band voltage shift from 0 to 1.5 V for 30 Å AlN film, with different positions of accumulation‐depletion regions, and with electron (hole) charge varying from 0 to more than 1012 cm−2.  
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77.65.-j Piezoelectricity and electromechanical effects
73.20.At Surface states, band structure, electron density of states
73.40.Ty Semiconductor-insulator-semiconductor structures
68.55.-a Thin film structure and morphology

Control of porous silicon luminescent pattern formation by ion implantation

Xi‐Mao Bao and Hai‐Qiang Yang

Appl. Phys. Lett. 63, 2246 (1993); http://dx.doi.org/10.1063/1.110541 (2 pages) | Cited 24 times

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We present a method to generate luminescent patterns of porous silicon. The crystal Si samples were selectively amorphized by self‐implantation through a deposited Al mask. After anodization, the porous Si formed on the crystal regions exhibits visible luminescence, while that on the preamorphized regions does not. The limit of resolution of the light‐emitting patterns is about 2 μm.
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78.55.Hx Other solid inorganic materials
61.80.Jh Ion radiation effects
81.65.-b Surface treatments

Carrier lifetime versus anneal in low temperature growth GaAs

E. S. Harmon, M. R. Melloch, J. M. Woodall, D. D. Nolte, N. Otsuka, and C. L. Chang

Appl. Phys. Lett. 63, 2248 (1993); http://dx.doi.org/10.1063/1.110542 (3 pages) | Cited 81 times

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The photoexcited carrier lifetimes in ex situ‐annealed low temperature growth GaAs are measured with a femtosecond transient absorption experiment. The study encompassed two low temperature growth GaAs films with approximately 0.3% and 0.9% excess arsenic incorporated during growth. The observed lifetimes are found to be a function of the spacing of arsenic precipitates formed during the 30 s anneals to temperatures between 650 and 1000 °C. The carrier lifetime for unannealed films was found to be less than ∼200 fs. The carrier lifetimes increased from ∼2 to ∼10 ps as the average precipitate spacing was increased from ∼400 to ∼900 Å. These results are in sharp contrast to recent reports of subpicosecond lifetimes in similar GaAs annealed at 600 °C.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Pz Photoconduction and photovoltaic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing

Magnetotransport in lateral periodic potentials formed by surface‐layer‐induced modulation in InAs‐AlSb quantum wells

Chanh Nguyen, Berinder Brar, Vijay Jayaraman, Axel Lorke, and Herbert Kroemer

Appl. Phys. Lett. 63, 2251 (1993); http://dx.doi.org/10.1063/1.110543 (3 pages) | Cited 2 times

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We report the realization of strong lateral superlattice potentials in not‐intentionally doped InAs‐AlSb quantum wells. By spatially alternating the surface layer between thin layers of InAs and GaSb, which shift the pinning position of the Fermi level at the surface, we induce a lateral density modulation of 4×1011 cm−2, equivalent to a potential modulation of 30 meV inside quantum wells 20 nm away from the surface. Both one‐ and two‐dimensional lateral potentials were fabricated and studied by magnetotransport measurements. Strong commensurability oscillations are observed.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Photoluminescence in ZnSe‐based quantum well wire structures

J. Ding, A. V. Nurmikko, D. C. Grillo, Li He, J. Han, and R. L. Gunshor

Appl. Phys. Lett. 63, 2254 (1993); http://dx.doi.org/10.1063/1.110544 (3 pages) | Cited 13 times

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We have fabricated quantum well wire structures by using electron beam lithography and reactive ion etching techniques on (Zn,Cd)Se/Zn(S,Se) multiple quantum well structures. Photoluminescence efficiencies have been studied as a function of the wire width (down to about 400 Å), and temperature. The results indicate that the sidewall surfaces exposed during the dry etching play an important role in providing nonradiative centers for the optically injected carriers, strongly diminishing the radiative efficiencies in the smallest structures.
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78.55.Et II-VI semiconductors
81.65.-b Surface treatments
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Planar field‐induced quantum dot transistor

Y. Wang and S. Y. Chou

Appl. Phys. Lett. 63, 2257 (1993); http://dx.doi.org/10.1063/1.110545 (3 pages) | Cited 18 times

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We propose and demonstrate a new field‐induced quantum dot transistor that has a nanoscale dot‐gate inside the gap of a split gate. Because of the novel structure and small dot size, strong oscillations in the drain current as a function of the gate bias were observed at a temperature up to 4.2 K or with a drain bias up to 5 mV. Temperature dependent study showed that the energy gaps in the dot are as large as 4.5 meV. Simulation indicates that, in the device, quantum size effect and Coulomb effect are comparable; both contribute significantly to the energy gaps in the quantum dot.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Pressure‐induced phase transition in porous silicon

J. M. Ryan, P. R. Wamsley, and K. L. Bray

Appl. Phys. Lett. 63, 2260 (1993); http://dx.doi.org/10.1063/1.110546 (3 pages) | Cited 16 times

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High pressure studies of porous silicon reveal that a phase transition occurs at ∼170 kbar. The phase transition is detected by an abrupt change in color of porous silicon from orange‐yellow to black. Photoluminescence measurements show an initial blue shift of the luminescence peak. At ∼25 kbar the blue shift ceases and a reversal of shift is observed. The red shift continues up to ∼90 kbar at which point the luminescence is quenched. The shift reversal is interpreted as a pressure‐induced direct–indirect transition in porous silicon. The results are best explained in the context of the quantum confinement model.
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78.55.Hx Other solid inorganic materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Very high mobility two‐dimensional hole gas in Si/GexSi1−x/Ge structures grown by molecular beam epitaxy

Y. H. Xie, Don Monroe, E. A. Fitzgerald, P. J. Silverman, F. A. Thiel, and G. P. Watson

Appl. Phys. Lett. 63, 2263 (1993); http://dx.doi.org/10.1063/1.110547 (2 pages) | Cited 106 times

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Modulation‐doped Si/GexSi1−x/Ge/GexSi1−x structures were fabricated in which a thin Ge layer was employed as the conduction channel for the two‐dimensional hole gas. The strained heterostructure was fabricated on top of a low threading dislocation density, totally relaxed, GexSi1−x buffer layer with a linearly graded Ge concentration profile. The best mobility of the two‐dimensional hole gas is 55 000 cm2/V s at 4.2 K with a concentration‐dependent hole effective mass of ≤0.10m0. The effect of the Ge/GeSi interface roughness on the 2DHG mobility was studied.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance

Native‐oxide‐defined low‐loss AlGaAs‐GaAs planar waveguide bends

S. J. Caracci, M. R. Krames, N. Holonyak, C. M. Herzinger, A. C. Crook, T. A. DeTemple, and P.‐A. Besse

Appl. Phys. Lett. 63, 2265 (1993); http://dx.doi.org/10.1063/1.110548 (3 pages) | Cited 9 times

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Data are presented on planar waveguide S‐bends fabricated from AlxGa1−xAs‐GaAs p‐n quantum well heterostructure (QWH) laser material by a wet native oxidation process. The oxide’s low refractive index (n∼1.55) is used to define ∼3.5‐μm‐wide single mode guides exhibiting low excess losses for raised‐cosine S‐bends with 100 μm offsets. The waveguide’s routing properties are determined by the lateral effective index profile which is controlled by the native oxide thickness. Guides with two different oxidation depths are investigated. For the deepest oxidation, excess bend losses of 3 dB are measured for transition distances of ∼180 μm and ≲120 μm for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. Theoretical loss calculations for the guides show good agreement with measured data. Guides with a shallow oxidation exhibit 3 dB transition lengths of ∼260 μm and ∼220 μm for the TE and TM polarizations.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
81.65.-b Surface treatments

Coherent‐electron intrinsic multistability in a double‐barrier tunneling diode

Mathias Wagner and Hiroshi Mizuta

Appl. Phys. Lett. 63, 2268 (1993); http://dx.doi.org/10.1063/1.110525 (3 pages) | Cited 1 time

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Recently, a new mechanism leading to electrical multistability in coherent‐electron tunneling devices was proposed. The reflection of coherent electrons at a barrier leads to the formation of resonant states in a quantum well in front of the barrier, and the resulting strongly modulated local density of states allows for multiple stable solutions of the Poisson equation to exist at fixed bias. These solutions are characterized by different resonant states being pinned close to the conduction‐band edge, with each solution having its own unique tunneling characteristics. Here we show how these multiple‐branch I(V) characteristics can be engineered. This approach may open up new possibilities for high‐speed functional devices.
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73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

dc SQUID magnetometers from single layers of YBa2Cu3O7−x

D. Koelle, A. H. Miklich, F. Ludwig, E. Dantsker, D. T. Nemeth, and John Clarke

Appl. Phys. Lett. 63, 2271 (1993); http://dx.doi.org/10.1063/1.110526 (3 pages) | Cited 63 times

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We have fabricated magnetometers patterned in a single layer of YBa2Cu3O7−x involving dc superconducting quantum interference devices (SQUIDs) with bicrystalline grain boundary junctions. The magnetometers consist of either a SQUID with a large area square washer or a single turn pickup loop coupled directly to the body of a small area SQUID. We found that the transfer function falls off with increasing SQUID inductance much more rapidly than predicted; implications for magnetometer performance are discussed. When operated at 77 K with a bias reversal technique a directly coupled magnetometer had a noise of (105±10) fT Hz−1/2 at 1 kHz, increasing to (145±10) fT Hz−1/2 at 1 Hz.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Microwave surface impedance at 10 GHz and quasiparticle scattering in YBa2Cu3O7 films

F. Gao, J. W. Kruse, C. E. Platt, M. Feng, and M. V. Klein

Appl. Phys. Lett. 63, 2274 (1993); http://dx.doi.org/10.1063/1.110527 (3 pages) | Cited 34 times

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The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth λ(T), complex microwave conductivity σ(T), and quasiparticle scattering rate 1/τ(T) were also determined. After a rapid fall as T is lowered below Tc, the surface resistance Rs exhibits a linear dependence from 65 K down to 6 K. As T drops below Tc, the real part of the conductivity σ1 has a rapid rise, which is attributed to the observed dramatic increase in τ. The normal‐fluid density shows a linear behavior at low temperatures, which is inconsistent with s‐wave BCS superconductivity.
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74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Detecting trapped vortices using variable‐range hopping in a two‐dimensional system

T. Wang, K. P. Clark, G. F. Spencer, F. Li, and W. P. Kirk

Appl. Phys. Lett. 63, 2277 (1993); http://dx.doi.org/10.1063/1.110528 (2 pages) | Cited 1 time

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Giant magnetoresistance was observed in a disordered two‐dimensional electron system in a variable‐range hopping regime. The possibility of utilizing the phenomenon as a magnetic field sensor was demonstrated by the detection of trapped vortices in a superconducting Pb film. The minimum size of such a device is discussed.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
85.30.-z Semiconductor devices

Low temperature optical response of a single grain boundary in superconducting YBa2Cu3O7−δ thin film

S. Bhattacharya, M. Rajeswari, I. Takeuchi, X. X. Xi, S. N. Mao, C. Kwon, Qi Li, and T. Venkatesan

Appl. Phys. Lett. 63, 2279 (1993); http://dx.doi.org/10.1063/1.110503 (3 pages) | Cited 7 times

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We have investigated the optical response from a single grain boundary in a thin film (∼300 nm) of superconducting YBa2Cu3O7−δ fabricated on bicrystals SrTiO3 substrate. We have studied the temperature, bias current, and magnetic field dependence of the optical response in the temperature range of 15 K≤T≤35 K. We find that the optical response from the single grain boundary in this temperature range can be satisfactorily explained in terms of the optical response of a Josephson weak link. The optical response of the grain boundary is qualitatively similar to that of granular films seen in the earlier studies, indicating that the latter may be dominated by the optical response of grain‐boundary weak links.
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74.50.+r Tunneling phenomena; Josephson effects
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Gz Optical properties
74.78.-w Superconducting films and low-dimensional structures

On the determination of the fully critical field and critical current density from the Bean model

L. M. Paulius, C. C. Almasan, and M. B. Maple

Appl. Phys. Lett. 63, 2282 (1993); http://dx.doi.org/10.1063/1.110504 (3 pages) | Cited 1 time

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A direct method for determining the magnetic field Hfcs at which a superconductor enters the fully critical state (i.e., the field at which flux first penetrates throughout the entire sample) is described, and a formula for calculating the critical current density JcH from the value of Hfcs is presented. The behavior of JcH(x) is compared to the variation of the fluxoid pinning energy U, inferred from magnetic relaxation measurements in the Y1−xPrxBa2Cu3O7−δ system.
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74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Sv Critical currents
74.72.-h Cuprate superconductors

Cross‐sectional transmission electron microscopy study for Nb/AlOx‐Al/Nb, Nb/ZrOx‐Zr/Nb, and Nb/HfOx‐Hf/Nb Josephson junctions

Shin’ichi Morohashi and Shinya Hasuo

Appl. Phys. Lett. 63, 2285 (1993); http://dx.doi.org/10.1063/1.110505 (3 pages) | Cited 1 time

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We studied the interfaces of Nb Josephson junctions with an overlayer structure using cross‐sectional transmission electron microscopy. We compared Nb/AlOx‐Al/Nb, Nb/ZrOx‐Zr/Nb, and Nb/HfOx‐Hf/Nb junctions. The interface between the Zr layer and Nb base electrode, and that between the Hf layer and Nb were smoother than that between the Al layer and Nb. The roughness of the interface between Al and Nb is caused not by the roughness of the original Nb base electrode but grain boundary diffusion following Al deposition. Annealing increased the roughness of the interface between Al and Nb, but had very little effects on the interfaces between Zr and Nb, or Hf and Nb. We attribute these effects to the differences in the melting points of the various overlayers.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology

Structure and magnetic properties of Sm2Fe14Ga3Cx (x=0–2.5) compounds prepared by arc melting

Bao‐Gen Shen, Lin‐Shu Kong, Fang‐Wei Wang, and Lei Cao

Appl. Phys. Lett. 63, 2288 (1993); http://dx.doi.org/10.1063/1.110506 (3 pages) | Cited 89 times

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A novel hard magnetic compound series with composition Sm2Fe14Ga3Cx (x=0, 0.5, 1.0, 1.5, 2.0, and 2.5) was prepared by arc melting. The carbides crystallize in the rhombohedral Th2Zn17‐type structure and are single phase except for Sm2Fe14Ga3 and Sm2Fe14Ga3C0.5 which contain some amounts of α‐Fe. The substitution of Ga is found to play an important role in the stability of high carbon rare‐earth iron compounds with 2:17‐type structure. The Curie temperatures of Sm2Fe14Ga3Cx are 200–240 K higher than that of Sm2Fe17. All compounds with x=0–2.5 exhibit an easy c‐axis anisotropy at room temperature. The anisotropy fields increase with increasing carbon concentration from 70 kOe for x=0 to at least 90 kOe for x≥1.5. A room‐temperature coercivity of 15 kOe is obtained in Sm2Fe14Ga3C1.5 prepared by melt spinning at a speed of 30 m/s.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
75.30.Gw Magnetic anisotropy
81.10.Fq Growth from melts; zone melting and refining

Finite element analysis of stress relaxation in thin foil plan‐view transmission electron microscopy specimens

R. Hull

Appl. Phys. Lett. 63, 2291 (1993); http://dx.doi.org/10.1063/1.110507 (3 pages) | Cited 10 times

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Finite element analysis has been used to model stress relaxation in thin foil plan‐view transmission electron microscope specimens of strained epitaxial layers. Relaxation of the orders of 2%–20%, relative to the unthinned specimen, are determined for lattice strains of the order 1%, epitaxial layer thicknesses in the hundreds of angstrom regime and sample thicknesses of the order 1 μm. These calculations show that under carefully controlled experimental conditions, the stresses in thinned samples used for in situ electron microscope observations of dislocation dynamics in strained epitaxial layers are not substantially different from those in unthinned structures.  
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Backscattered deposition in Ar sputter etch of silicon dioxide

C. Y. Chang, J. P. McVittie, K. C. Saraswat, and K. K. Lin

Appl. Phys. Lett. 63, 2294 (1993); http://dx.doi.org/10.1063/1.110508 (3 pages) | Cited 3 times

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Detailed mechanisms of sputter etch of silicon dioxide in argon plasma are studied using a novel test structure. We have found that a significant amount of the sputtered material (up to 50% of the sputter flux) returns, as an isotropic backscattered flux to the wafer. This backscattered flux results in significant deposition that cannot be accounted for by redeposition, i.e., line‐of‐sight deposition of the sputtered material, alone. A profile simulator is used to demonstrate a new physical model for the Ar sputter‐etch process, based on the interaction of three simultaneous processes: (1) sputtering, (2) direct (i.e., line‐of‐sight) redeposition of sputtered material, and (3) isotropic deposition of sputtered material backscattered from the gas phase. Simulated profiles show good agreement with experimental results on the test structure and a common device structure.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
FREE

Erratum: ‘‘Epitaxial bcc FexCo1−x alloy films on ZnSe(001)’’ [Appl. Phys. Lett. 61, 2476 (1992)]

C. J. Gutierrez, J. J. Krebs, and G. A. Prinz

Appl. Phys. Lett. 63, 2297 (1993); http://dx.doi.org/10.1063/1.110813 (1 page)

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In Fig. 2, the units given are incorrect. The proper units for K1 are ‘‘105 erg/cm3’’; not ‘‘erg/cm2’’ as given. The same error in units is found in the discussion of ‖Ku‖ at the end of the second paragraph before the summary. These errors do not affect the conclusions.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
99.10.Cd Errata
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