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19 Jan 1998

Volume 72, Issue 3, pp. 269-391

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The formation of GaN dots on AlxGa1−xN surfaces using Si in gas-source molecular beam epitaxy

Xu-Qiang Shen, Satoru Tanaka, Sohachi Iwai, and Yoshinobu Aoyagi

Appl. Phys. Lett. 72, 344 (1998); http://dx.doi.org/10.1063/1.120731 (3 pages) | Cited 27 times

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Nanoscale GaN dots were successfully formed on AlxGa1−xN/6H-SiC(0001) surfaces by gas-source molecular beam epitaxy. It was found that the growth mode can be changed by introducing Si before GaN growth, where the Si is believed to play an important role in the change of the AlxGa1−xN surface free energy. Without introducing Si, the GaN growth mode was two dimensional and (1×3) reconstruction was observed. The growth mode of GaN was changed from two-dimensional to three-dimensional by introducing Si on the AlxGa1−xN surface. In situ reflection high-energy electron diffraction and atomic force microscopy observations were used to monitor and characterize the growth processes and surface morphology. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.Md Surface thermodynamics, surface energies

Bistable electroluminescence in p-i-n light-emitting tunnel-diodes enhanced by aperiodic-superlattice injectors

S. M. Cao, M. Willander, A. A. Toropov, T. V. Shubina, B. Ya. Mel’tser, P. S. Kop’ev, T. Lundström, P. O. Holtz, J. P. Bergman, and B. Monemar

Appl. Phys. Lett. 72, 347 (1998); http://dx.doi.org/10.1063/1.120732 (3 pages) | Cited 1 time

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A p-i-n resonant tunnel diode is designed and investigated using photoluminescence (PL) spectroscopy. The device is based on an Al0.4Ga0.6As/GaAs graded-index waveguide heterostructure enhanced by aperiodic-superlattice injectors for simultaneous resonant injection of electrons and heavy holes. The bias-dependent study of photocurrent, electroluminescence (EL) and PL show strong resonance behavior in the optical intensity confirming the field-dependent resonant injection of the excited states in the emission layers. Pronounced voltage-current bistability due to injection efficiency leads to multiple-wavelength EL and lasing action. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Dw Photodiodes; phototransistors; photoresistors
42.55.Px Semiconductor lasers; laser diodes
85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
42.79.Ry Gradient-index (GRIN) devices
42.79.Gn Optical waveguides and couplers

Efficiency of NH3 as nitrogen source for GaN molecular beam epitaxy

M. Mesrine, N. Grandjean, and J. Massies

Appl. Phys. Lett. 72, 350 (1998); http://dx.doi.org/10.1063/1.120733 (3 pages) | Cited 42 times

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We show that optical reflectivity measurements can be used to evaluate the part of a NH3 flux which reacts with a Ga-terminated GaN surface or with a Ga-flux simultaneously impinging on the surface, as in standard molecular beam epitaxy situation. At least for temperatures not exceeding 700 °C, the ratio of the reacted part of the NH3 flux to the incident flux can be assimilated to the NH3 cracking efficiency. Being nearly zero below a threshold temperature of 450 °C, it increases with temperature but remains low ( ∼ 4%) explaining why an exceptionally high V/III flux ratio is necessary to grow GaN using NH3. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Hf Product distribution
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High carrier mobility in polycrystalline thin film diamond

Hui Jin Looi, Richard B. Jackman, and John S. Foord

Appl. Phys. Lett. 72, 353 (1998); http://dx.doi.org/10.1063/1.120734 (3 pages) | Cited 62 times

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Polycrystalline diamond films have been found to display p-type surface conductivity. No bulk impurity is added to the films; the p-type characteristics of the undoped diamond are thought to be due to a surface or near surface hydrogenated layer. Carrier concentrations within the range 1017–1019 cm−3 have been measured; control over the carrier concentration can be achieved by annealing the “as-grown” films in air. For a given annealing temperature a stable carrier concentration arises. The Hall carrier mobility has been explored and a value of >70 cm2/Vs has been measured for a film with a carrier concentration of ∼ 5×1017 cm−3, the highest reported for polycrystalline thin film diamond and equivalent to boron doped single crystal diamond. © 1998 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.25.+i Surface conductivity and carrier phenomena

Strong ultraviolet photoluminescence from silicon oxide films prepared by magnetron sputtering

H. Z. Song, X. M. Bao, N. S. Li, and X. L. Wu

Appl. Phys. Lett. 72, 356 (1998); http://dx.doi.org/10.1063/1.120735 (3 pages) | Cited 55 times

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Intense ultraviolet photoluminescence centered at 370 nm was observed from magnetron-sputtered silicon oxide films after they were annealed at about 1000 °C in N2 atmosphere. This photoluminescence is found to be associated with the formation of nanocrystal silicon particles in the specially structured SiO2, which highly resembles the oxide layer of porous silicon. The luminescence centers at the interface between the nanocrystal silicon particles and the SiO2 matrix are responsible for the strong ultraviolet luminescence. © 1998 American Institute of Physics.
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81.15.Cd Deposition by sputtering
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Self-organized growth of ZnTe nanoscale islands on (001)GaAs

M. Longo, N. Lovergine, A. M. Mancini, A. Passaseo, G. Leo, M. Mazzer, M. Berti, and A. V. Drigo

Appl. Phys. Lett. 72, 359 (1998); http://dx.doi.org/10.1063/1.120736 (3 pages) | Cited 6 times

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The Stransky–Krastanow metalorganic vapor phase epitaxy growth of self-organized ZnTe islands on homoepitaxial (001)GaAs is demonstrated. The −7.4% lattice mismatch of the ZnTe/GaAs heterostructure leads to a strain-driven distribution of nanoscale ZnTe islands on top of a two-dimensionally (2D) grown wetting layer. Atomic force microscopy and Rutherford backscattering spectrometry are used to determine the island dimensions and the thickness of the wetting layer. The density of the islands, their average diameter, and aspect ratio turn out to be about 520 μm−2, 13.6 nm, and 0.20, respectively, for a 1.2 ML thick 2D layer. Furthermore, the average aspect ratio of the islands decreases by increasing the thickness of the wetting layer, as expected by the progressive extinction of the strain-driven island nucleation. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
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

Effect of matrix on InAs self-organized quantum dots on InP substrate

V. M. Ustinov, E. R. Weber, S. Ruvimov, Z. Liliental-Weber, A. E. Zhukov, A. Yu. Egorov, A. R. Kovsh, A. F. Tsatsul’nikov, and P. S. Kop’ev

Appl. Phys. Lett. 72, 362 (1998); http://dx.doi.org/10.1063/1.120737 (3 pages) | Cited 48 times

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InAs self-organized quantum dots in In0.53Ga0.47As and In0.52Al0.48As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Defect-induced Raman scattering in resonance with yellow luminescence transitions in hexagonal GaN on a sapphire substrate

De-Sheng Jiang, M. Ramsteiner, K. H. Ploog, H. Tews, A. Graber, R. Averbeck, and H. Riechert

Appl. Phys. Lett. 72, 365 (1998); http://dx.doi.org/10.1063/1.120738 (3 pages) | Cited 9 times

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Strong defect-specific low-frequency peaks are detected in low-temperature Raman spectra of hexagonal GaN grown by molecular beam epitaxy on sapphire substrate. The intensity of these peaks is found to be enhanced by excitation in resonance with yellow luminescence transitions. The validity of the assignment to electronic Raman scattering (ERS), as proposed before for their counterparts in cubic GaN on GaAs [M. Ramsteiner, J. Menniger, O. Brandt, H. Yang, and K. H. Ploog, Appl. Phys. Lett. 69, 1276 (1996)], is confirmed. Our results imply that the observed ERS peaks are related to shallow donors which are not necessarily hydrogenic. One Raman peak at very low frequency (11.7 meV) is alternatively explained by a pseudo-localized vibrational mode. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
63.20.Pw Localized modes
78.55.Cr III-V semiconductors

Nearly noise-free transistor operated in the 2–18 GHz range

J. A. Fendrich and M. Feng

Appl. Phys. Lett. 72, 368 (1998); http://dx.doi.org/10.1063/1.120739 (3 pages) | Cited 3 times

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Temperature dependent measurements of the noise parameters of a pseudomorphic high electron mobility transistor show the minimum noise figure vanishes at low temperatures for frequencies from 2 GHz up to 18 GHz and for most currents. We propose that the exponential decrease seen in the noise figure with temperature is due to a reduction of thermally activated noise sources with an activation energy of ∼95 meV. Other noise-parameter data suggest a flattening of the noise figure paraboloid as temperature is decreased. These results demonstrate the feasibility of designing a near 0.1 dB noise figure amplifier for high-frequency operation over a wide range of currents. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
73.61.Ey III-V semiconductors

Microscopic nature of Staebler-Wronski defect formation in amorphous silicon

R. Biswas and B. C. Pan

Appl. Phys. Lett. 72, 371 (1998); http://dx.doi.org/10.1063/1.120740 (3 pages) | Cited 29 times

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Light-induced metastable defects in a-Si:H are proposed to be silicon dangling bonds accompanied by pairs of hydrogen atoms breaking a silicon bond, forming a complex with two Si-H bonds. This supports the model of Branz. These defects are the analog of the H2∗ defect in c-Si and their energy correlates with the bond-angle strain. Several features of the annealing are well described by this defect complex. © 1998 American Institute of Physics.
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71.55.Cn Elemental semiconductors
71.55.Jv Disordered structures; amorphous and glassy solids
72.80.Ng Disordered solids
72.40.+w Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect

Measurement of the zero-bias electron transmittance as a function of energy for half- and quarter-electron-wavelength semiconductor quantum-interference filters

D. K. Guthrie, P. N. First, T. K. Gaylord, E. N. Glytsis, and R. E. Leibenguth

Appl. Phys. Lett. 72, 374 (1998); http://dx.doi.org/10.1063/1.120741 (3 pages) | Cited 3 times

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Ballistic electron emission spectroscopy has been used to measure the electron transmittance function of both half- and quarter-electron-wavelength (using optics terminology) quantum-interference filters under zero applied voltage bias. At the design energy, these devices exhibit constructive and destructive interference, respectively. Second-derivative spectra from current versus voltage measurements clearly show both tunneling and above-barrier quasibound energy states. The spectra accurately reproduce the transmittance functions of the designed structures, attaining nearly the temperature-limited resolution at 77 K and 300 K. The presence of the above-barrier resonances has been confirmed conclusively by measurements on these complementary half- and quarter-wavelength device structures. © 1998 American Institute of Physics.
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85.35.Ds Quantum interference devices
42.79.Ci Filters, zone plates, and polarizers
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Observation of voltage-locked states in strongly coupled stacked Josephson junctions

G. Carapella and G. Costabile

Appl. Phys. Lett. 72, 377 (1998); http://dx.doi.org/10.1063/1.120742 (3 pages) | Cited 5 times

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We have fabricated and tested two stacks of strongly coupled long Josephson junctions with access to the intermediate electrode so that they can be independently biased. In these samples, we find four families of voltage-locked states in zero external magnetic field. One of these families is identified with the zero field steps already observed and interpreted in the case of weaker coupling; the others appear to be new phenomena. The voltage spacing of one of them suggests the necessity of a refinement of the current model to obtain a full description of the dynamical states in stacked junctions. © 1998 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
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Structure and magnetic properties of exchange-spring Sm–Co/Co superlattices

Eric E. Fullerton, J. Samuel Jiang, C. H. Sowers, J. E. Pearson, and S. D. Bader

Appl. Phys. Lett. 72, 380 (1998); http://dx.doi.org/10.1063/1.120743 (3 pages) | Cited 49 times

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We present structural and magnetic properties of epitaxial Sm–Co/Co superlattice films prepared via magnetron sputtering. X-ray diffraction and cross-sectional transmission electron microscopy show that the films are structurally coherent. The oriented nature of the interleaved ferromagnetically “hard” and “soft” layers comprising the superlattice provides a realization of the ideal nanostructure of exchange-spring magnets as well as a model system to study layer thickness dependences of the magnetic properties. The superlattice films have an effective fourfold, in-plane magnetic anisotropy. Room-temperature hysteresis loops are relatively square and the demagnetization of the Co is reversible, as expected of exchange-spring magnets with aligned hard magnet layers.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Sequential position readout from arrays of micromechanical cantilever sensors

H. P. Lang, R. Berger, C. Andreoli, J. Brugger, M. Despont, P. Vettiger, Ch. Gerber, J. K. Gimzewski, J. P. Ramseyer, E. Meyer, and H.-J. Güntherodt

Appl. Phys. Lett. 72, 383 (1998); http://dx.doi.org/10.1063/1.120749 (3 pages) | Cited 62 times

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Sequential position readout from a microfabricated array of eight cantilever-type sensors (silicon technology) is demonstrated. In comparison with single sensors we find that mechanical disturbances from noise, such as from vibrations, turbulent gas flow, or abrupt pressure changes, can be effectively removed in array sensors by recording difference signals with respect to reference cantilevers. We demonstrate that chemically specific responses can be extracted in a noisy environment using a sensor to detect specific chemical interactions and an uncoated cantilever as reference. © 1998 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Point-contact electrodes to probe charging effects in individual ultrasmall cobalt clusters

R. Desmicht, G. Faini, V. Cros, A. Fert, F. Petroff, and A. Vaurès

Appl. Phys. Lett. 72, 386 (1998); http://dx.doi.org/10.1063/1.120744 (3 pages) | Cited 21 times

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A new technique to probe a single nanometer-scale magnetic particle by measuring the tunneling current through point-contact electrodes is described. The tunnel junctions are formed by a bulk cobalt bottom electrode, a monolayer of ultrasmall Co clusters sandwiched between two Al2O3 barriers and a point-contact top electrode, defined by e-beam lithography and permitting to study the quantum transport through an isolated cluster. We report on single electron charging effects such as Coulomb blockade and Coulomb staircase which are undoubtedly consistent with the tunneling through a single Co cluster. One of our devices exhibits a Coulomb gap of 380 mV which is, to our knowledge, one of the largest values ever reported in metallic granular systems. © 1998 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
75.50.Tt Fine-particle systems; nanocrystalline materials
73.61.At Metal and metallic alloys

Stable field-induced electron emission from a solidified liquid metal ion source

L. W. Chen and Y. L. Wang

Appl. Phys. Lett. 72, 389 (1998); http://dx.doi.org/10.1063/1.120745 (3 pages) | Cited 7 times

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Stable field-induced electron emission is derived from a tungsten tip covered by indium which has been solidified from its liquid state during an ion emission process. By choosing different ion emission currents at the beginning of the solidification process, the final geometry of the solidified emitter can be reshaped and the characteristics of the electron emission changed. The Fowler–Nordheim equation is used to infer the geometry of the electron emitter prepared by various solidification processes. The dual ion/electron point source is expected to have high potential applications in focused ion and electron beam technologies. © 1998 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
64.70.D- Solid-liquid transitions
29.25.Bx Electron sources
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