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9 Apr 2001

Volume 78, Issue 15, pp. 2095-2255

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Mechanism of radio-frequency current collapse in GaN–AlGaN field-effect transistors

A. Tarakji, G. Simin, N. Ilinskaya, X. Hu, A. Kumar, A. Koudymov, J. Yang, M. Asif Khan, M. S. Shur, and R. Gaska

Appl. Phys. Lett. 78, 2169 (2001); http://dx.doi.org/10.1063/1.1363694 (3 pages) | Cited 57 times

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The mechanism of radio-frequency current collapse in GaN–AlGaN heterojunction field-effect transistors (HFETs) was investigated using a comparative study of HFET and metal–oxide–semiconductor HFET current–voltage (I–V) and transfer characteristics under dc and short-pulsed voltage biasing. Significant current collapse occurs when the gate voltage is pulsed, whereas under drain pulsing the I–V curves are close to those in steady-state conditions. Contrary to previous reports, we conclude that the transverse electric field across the wide-band-gap barrier layer separating the gate and the channel rather than the gate or surface leakage currents or high-field effects in the gate–drain spacing is responsible for the current collapse. We find that the microwave power degradation in GaN–AlGaN HFETs can be explained by the difference between dc and pulsed I–V characteristics. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
84.30.Jc Power electronics; power supply circuits

Low-noise GaN Schottky diodes on Si(111) by molecular beam epitaxy

Peter W. Deelman, Robert N. Bicknell-Tassius, Sergey Nikishin, Vladimir Kuryatkov, and Henryk Temkin

Appl. Phys. Lett. 78, 2172 (2001); http://dx.doi.org/10.1063/1.1357448 (3 pages) | Cited 12 times

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We report on the achievement of mesa-isolated Schottky diodes fabricated from n-GaN epilayers grown by gas-source molecular beam epitaxy on Si(111) that exhibit extremely low noise and dark current. Silicon dioxide grown by plasma-enhanced chemical vapor deposition provided both surface passivation and electrical isolation, and the Schottky contact was a 10 nm Pd thin film. The dark current of an 86×86 μm2 diode was 2.10×10−8 A/cm2 at −2 V bias, and the zero-bias noise power density at 1 Hz is as low a 9×10−29 A2/Hz. © 2001 American Institute of Physics.
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85.30.Kk Junction diodes
81.65.Rv Passivation
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Commensurability effects in lateral surface-doped superlattices

R. A. Deutschmann, C. Stocken, W. Wegscheider, M. Bichler, and G. Abstreiter

Appl. Phys. Lett. 78, 2175 (2001); http://dx.doi.org/10.1063/1.1362283 (3 pages) | Cited 1 time

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We fabricate density-modulated two-dimensional electron systems by shallow compensation doping the donor layer of a modulation-doped heterostructure. Zinc acceptor atoms are diffused from the sample surface which is heated by a focused laser beam. Low-temperature magnetotransport experiments provide evidence that high-quality lateral surface superlattices can be fabricated. In weak periodic one-dimensional potentials, commensurability oscillations are recovered, whereas in strong periodic two-dimensional potentials the semiclassically expected antidot resistance resonances are found to dominate the low-field transport. Additionally, the homogeneity of the laser-induced doping is confirmed by magnetic focusing experiments. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.Cd Superlattices
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.uj III-V and II-VI semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Deep centers in a free-standing GaN layer

Z.-Q. Fang, D. C. Look, P. Visconti, D.-F. Wang, C.-Z. Lu, F. Yun, H. Morkoç, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 78, 2178 (2001); http://dx.doi.org/10.1063/1.1361273 (3 pages) | Cited 41 times

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Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap B′ with activation energy ET = 0.53 eV was found in the Ga-face sample. Also, trap E1 (ET = 0.18 eV), believed to be related to the N vacancy, was found in the N-face sample, and trap C (ET = 0.35 eV) was in the Ga-face sample. Trap C may have arisen from reactive-ion-etching damage. © 2001 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Ns Metal-nonmetal contacts
85.30.Kk Junction diodes
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Effects of oxide seed and cap layers on magnetic properties of a synthetic spin valve

Tsann Lin and Daniele Mauri

Appl. Phys. Lett. 78, 2181 (2001); http://dx.doi.org/10.1063/1.1361103 (3 pages) | Cited 14 times

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A synthetic spin valve comprising Al2O3/Ni–Cr–Fe/Ni–Fe/Pt–Mn/Co–Fe/Ru/Co–Fe/Cu/Co–Fe/Ni–Fe/Cu/Al2O3/Ta films has been annealed and evaluated as a read sensor for ultrahigh-density ( ≥ 20 Gb/in.2) recording. The Al2O3 film used as its oxide seed layer provides an in situ flat surface for the Pt–Mn, Co–Fe and Ni–Fe films to develop strong {111} crystalline textures, thereby increasing its giant magnetoresistance coefficient to as high as 13.8%. Another Al2O3 film used as its oxide cap layer protects the Co–Fe/Ni–Fe sense layers from interface mixing and oxygen interdiffusion, thus improving the soft magnetic properties and thermal stability of the sense layers. Antiferromagnetic/ferromagnetic coupling between the Pt–Mn pinning and Co–Fe/Ru/Co–Fe synthetic pinned layers is strong and thermally stable enough for proper sensor operation. Ferromagnetic/ferromagnetic coupling across the Cu spacer layer is antiparallel, and hence it is feasible to achieve optimal biasing of magnetoresistance responses. This synthetic spin valve is sandwiched into a read gap 0.1 μm in thickness, and is patterned and lapped into a read sensor 0.42 and 0.23 μm in physical width and height, respectively. With a sense current of 4 mA, this read sensor exhibits an effective read width of 0.31 μm, stable magnetoresistance responses, and signal sensitivity of 6.64 mV/μm. © 2001 American Institute of Physics.
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85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics

Spin filtering in a magnetic–electric barrier structure

G. Papp and F. M. Peeters

Appl. Phys. Lett. 78, 2184 (2001); http://dx.doi.org/10.1063/1.1360224 (3 pages) | Cited 102 times

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The spin-dependent tunnelling of two-dimensional electrons through a magnetic barrier can be substantially enhanced by the addition of an electric barrier. The spin polarization is found to be strongly dependent on the incident wave vector parallel to the barrier, the incident electron energy, and the height of the electric barrier. The conductance for the spin-up and spin-down electrons can be tuned with this electrical barrier. © 2001 American Institute of Physics.
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75.45.+j Macroscopic quantum phenomena in magnetic systems
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
73.40.Gk Tunneling
73.23.Hk Coulomb blockade; single-electron tunneling

Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal ε-Co nanoparticles

Victor F. Puntes, Kannan M. Krishnan, and Paul Alivisatos

Appl. Phys. Lett. 78, 2187 (2001); http://dx.doi.org/10.1063/1.1362333 (3 pages) | Cited 132 times

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A method of producing high-quality magnetic colloidal dispersions by the rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce monodispersed, stabilized, defect-free ε-cobalt nanocrystals, with spherical shapes and sizes ranging from 3 to 17 nm. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant (oleic acid, phosphonic oxides and acids, etc.), its concentration, and the reaction temperature. These particles have been observed to produce two-dimensional self-assemblies when evaporated at low rates in a controlled atmosphere. A collective behavior due to dipolar interactions has been observed in the low susceptibility measurements corresponding to a highly ordered fine particles system. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.16.Be Chemical synthesis methods
81.16.Dn Self-assembly
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Cy Elemental semiconductors
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.07.Wx Nanopowders
81.05.Bx Metals, semimetals, and alloys
75.50.Mm Magnetic liquids
68.65.Cd Superlattices
81.07.Bc Nanocrystalline materials

Magnetic recording medium with improved temporal stability

P. J. Jensen

Appl. Phys. Lett. 78, 2190 (2001); http://dx.doi.org/10.1063/1.1362282 (3 pages) | Cited 10 times

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The current effort to fabricate nonvolatile magnetic recording media with a high areal density is deteriorated by the increasing temporal instability of the stored information. If the stored energy per magnetic particle competes with the thermal energy, spontaneous magnetic reversal processes may occur. Deposition of the magnetic particles on top of an antiferromagnetic substrate will increase its energy barrier due to the exchange coupling between the two subsystems. For this, the magnetic moments of the antiferromagnet in the vicinity of the magnetic particle have to deviate from their undisturbed arrangement. This disturbance vanishes within a few lattice constants. In the framework of a classical spin model, we calculate the spin arrangements and the resulting energy barriers for typical systems. © 2001 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.10.Hk Classical spin models
75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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All-fiber phase modulator based on lead zirconate titanate thin-film coating

D. M. Costantini, H. G. Limberger, R. P. Salathé, C. A. P. Muller, P. Muralt, and N. Setter

Appl. Phys. Lett. 78, 2193 (2001); http://dx.doi.org/10.1063/1.1364508 (3 pages) | Cited 1 time

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An all-fiber phase modulator based on lead titanate zirconate coating deposited by dc reactive magnetron sputtering was fabricated and optically characterized. The frequency response showed a flat broadband structure up to 600 kHz, with an efficiency of 0.73 rad/(V m). This is an order of magnitude higher than that for sputtered zinc oxide based phase modulators. Radial mode resonance peaks were observed between 10 and 700 MHz, with a maximum phase modulation amplitude of 0.3 rad at the fundamental radial resonance frequency of 25.6 MHz. © 2001 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.81.Wg Other fiber-optical devices
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering
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Thermal annealing effect on the intersublevel transitions in InAs quantum dots

Y. Berhane, M. O. Manasreh, H. Yang, and G. J. Salamo

Appl. Phys. Lett. 78, 2196 (2001); http://dx.doi.org/10.1063/1.1363693 (3 pages) | Cited 8 times

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Isochronal thermal annealing effect on the photoluminescence (PL) spectra of intersublevel transitions in InAs self-assembled quantum dots was investigated. Several peaks due to intersublevel transitions in the quantum dots were observed in the PL spectra of two samples consisting of 10 stacks of InAs quantum dots and InP barriers. Isochronal furnace annealing in the temperature range of 500–800 °C was conducted on the two samples. The results show that the intensity of the PL peaks was dramatically reduced, and a new peak attributed to the wetting layer was observed after the samples were thermally annealed above 550 °C. A small blue shift of the PL peaks due to intermixing was observed. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Unambiguous observation of subband transitions from longitudinal valley and oblique valleys in IV–VI multiple quantum wells

H. Z. Wu, N. Dai, M. B. Johnson, P. J. McCann, and Z. S. Shi

Appl. Phys. Lett. 78, 2199 (2001); http://dx.doi.org/10.1063/1.1361104 (3 pages) | Cited 14 times

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PbSe/PbSrSe multiple-quantum-well (MQW) structures were grown on BaF2(111) substrates by molecular-beam epitaxy and characterized by Fourier transform infrared transmission spectroscopy. To reduce unwanted Fabry–Pérot interference fringes, the top surface of the MQW samples was coated with an anti-interference film, enabling clear observation of subband transitions without superposed interference fringes. Transition energies involving longitudinal and oblique valleys were unambiguously resolved and are in good agreement with calculations made using the envelope wave function approximation. © 2001 American Institute of Physics.
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78.67.De Quantum wells
81.07.St Quantum wells
78.30.Hv Other nonmetallic inorganics

Scattering (stochastic) recoupling of a coupled ten-stripe AlGaAs–GaAs–InGaAs quantum-well heterostructure laser

D. A. Kellogg and N. Holonyak

Appl. Phys. Lett. 78, 2202 (2001); http://dx.doi.org/10.1063/1.1363691 (3 pages) | Cited 1 time

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Data are presented on coupled ten-stripe AlGaAs–GaAs–InGaAs quantum well heterostructure (QWH) lasers recoupled stochastically at the cleaved end mirrors. Recoupling of neighboring elements of a ten-stripe laser is accomplished by the scattering (random feedback) afforded by applying ∼10-μm-diam Al powder or 0.3 μm α-Al2O3 polishing compound in microscopy immersion oil or in epoxy at the cleaved ends (mirrors). Data on QWH samples with the end mirrors coated with the scatterer (Al or Al2O3 powder in “liquid”) exhibit spectral and far-field broadening, as well as increased laser threshold because of the reduced cavity Q. Single mode operation is possible with the conventional evanescent wave coupling of the ten-stripe QWH and is destroyed, even the laser operation itself, with the scattering recoupling (dephasing) at the end mirrors, which is reversible (removable). The narrow ten-stripe QWH laser with strong end-mirror scattering, a long amplifier with random feedback, indicates that a photopumped III–V or II–VI powder (a random “wall” cavity) has little or no merit. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Pk Continuous operation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors

Fabrication of nanoperiodic surface structures by controlled etching of dislocations in bicrystals

Rikard A. Wind, Martin J. Murtagh, Fang Mei, Yu Wang, Melissa A. Hines, and Stephen L. Sass

Appl. Phys. Lett. 78, 2205 (2001); http://dx.doi.org/10.1063/1.1362330 (3 pages) | Cited 24 times

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A method for the fabrication of periodic arrays of surface features with controlled spacings of 2–100 nm has been developed. This process relies on the selective etching of dislocations formed at a twist–bonded interface in a bicrystal. The production of nanoscale periodic silicon surface features with a mean spacing of 38 nm is reported. The etch rate of edge and screw dislocations is compared, and the rate of dislocation etching is found to be poorly correlated to strain. This observation calls long-held theories of dislocation etching into question. © 2001 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
81.05.Cy Elemental semiconductors

High-efficiency nickel phase zone plates with 20 nm minimum outermost zone width

M. Peuker

Appl. Phys. Lett. 78, 2208 (2001); http://dx.doi.org/10.1063/1.1361285 (3 pages) | Cited 30 times

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Fresnel zone plates for high-resolution imaging in the soft x-ray regime were fabricated in nickel by a trilevel process, which makes use of electron-beam lithography, reactive-ion etching, and electrodeposition. In order to improve the zone plate’s resolution, which is determined by its outermost zone width, ZEP-7000 electron-beam resist was employed. Residues, which arose during pattern transfer by reactive-ion etching, and which hindered etching in small structures, were suppressed by a cleaning procedure. For improved electrodeposition process control, a nickel electroplating bath was optimized. Zone plates with minimum outermost zone widths of 20, 25 and 30 nm were fabricated, yielding 9.2%, 16.2% and 18.0% first-order diffraction efficiency, respectively, at λ = 2.4 nm. © 2001 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ci Filters, zone plates, and polarizers
81.15.Pq Electrodeposition, electroplating
81.65.Cf Surface cleaning, etching, patterning
42.86.+b Optical workshop techniques

Bright blue electroluminescence from an InGaN/GaN multiquantum-well diode on Si(111): Impact of an AlGaN/GaN multilayer

A. Dadgar, J. Christen, T. Riemann, S. Richter, J. Bläsing, A. Diez, A. Krost, A. Alam, and M. Heuken

Appl. Phys. Lett. 78, 2211 (2001); http://dx.doi.org/10.1063/1.1362327 (3 pages) | Cited 42 times

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We present an electroluminescence test structure which consists of an InGaN/GaN multiquantum well as active region on the top of an AlGaN/GaN multilayer grown by metalorganic vapor phase epitaxy on Si(111) substrate. The integral room-temperature electroluminescence spectrum reveals a peak emission wavelength of 467 nm and a significantly higher brightness than an identical reference structure on sapphire substrate. In microelectroluminescence imaging, two emission peaks at 465 and 476 nm can be separated originating from locally different areas of the diode. Cathodoluminescence measurements in cross section and high-resolution x-ray diffraction measurements show that the structure is less strained than a sample without the AlGaN/GaN multilayer. The AlGaN/GaN multiple layer sequence which has a total thickness of 1.5 μm causes lattice relaxation during growth after a thickness of around 0.9 μm as directly visualized by cathodoluminescence line scans across the diode. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.67.De Quantum wells
68.65.Fg Quantum wells
81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence

Diameter-controlled synthesis of single-crystal silicon nanowires

Yi Cui, Lincoln J. Lauhon, Mark S. Gudiksen, Jianfang Wang, and Charles M. Lieber

Appl. Phys. Lett. 78, 2214 (2001); http://dx.doi.org/10.1063/1.1363692 (3 pages) | Cited 369 times

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Monodisperse silicon nanowires were synthesized by exploiting well-defined gold nanoclusters as catalysts for one-dimensional growth via a vapor–liquid–solid mechanism. Transmission electron microscopy studies of the materials grown from 5, 10, 20, and 30 nm nanocluster catalysts showed that the nanowires had mean diameters of 6, 12, 20, and 31 nm, respectively, and were thus well defined by the nanocluster sizes. High-resolution transmission electron microscopy demonstrated that the nanowires have single-crystal silicon cores sheathed with 1–3 nm of amorphous oxide and that the cores remain highly crystalline for diameters as small as 2 nm. © 2001 American Institute of Physics.  
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81.16.Hc Catalytic methods
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

Z. Pan, L. H. Li, Y. W. Lin, B. Q. Sun, D. S. Jiang, and W. K. Ge

Appl. Phys. Lett. 78, 2217 (2001); http://dx.doi.org/10.1063/1.1362335 (3 pages) | Cited 66 times

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We have investigated the optical transitions in Ga1−yInyNxAs1−x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Qc, electron effective mass me∗, and band gap energy Eg were estimated. It was found that the Qc is dependent on the indium concentration, but independent on the nitrogen concentration over the range x = (0–1)%. The me∗ of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the me∗ and Eg of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
81.05.Ea III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
78.67.De Quantum wells
72.40.+w Photoconduction and photovoltaic effects
73.63.Hs Quantum wells

Effect of phosphorus on Ge/Si(001) island formation

T. I. Kamins, D. A. A. Ohlberg, and R. Stanley Williams

Appl. Phys. Lett. 78, 2220 (2001); http://dx.doi.org/10.1063/1.1361096 (3 pages) | Cited 5 times

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Adding PH3 during chemical vapor deposition of Ge on Si(001) partially suppresses island formation and changes the shape of the islands that do form. A shape not previously seen in undoped layers grown by chemical vapor deposition is a large pyramid, with base edges aligned along the 〈110〉 directions and sides bounded by {111} planes near the base and {113} planes near the top. This suggests that phosphorus changes the thermodynamics of island formation. During annealing in H2, the shape of the large pyramids changes toward a multifaceted structure. The presence of PH3 during annealing of undoped islands retards coarsening, probably by decreasing surface diffusion. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Evolution of nanoscale texture in ultrathin TiN films

M. J. Williamson, D. N. Dunn, R. Hull, S. Kodambaka, I. Petrov, and J. E. Greene

Appl. Phys. Lett. 78, 2223 (2001); http://dx.doi.org/10.1063/1.1360235 (3 pages) | Cited 10 times

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We investigate the evolution of texture and grain morphology in fine-grained TiN thin films using cross correlation of dark-field images obtained using annular objective apertures with radii that correspond to different low index TiN reflections. This technique enables parallel analyses of the orientations of thousands of grains, with a spatial resolution of order 10 nm. Preferred grain orientations were determined for 40 and 100 nm thick TiN layers grown on SiO2 by magnetically unbalanced reactive magnetron sputter deposition. We find that no single orientation is dominant in the 40 nm films but that a 〈100〉 texture has developed by the time these films reach 100 nm in thickness. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
85.40.Ls Metallization, contacts, interconnects; device isolation
68.37.Lp Transmission electron microscopy (TEM)
61.46.-w Structure of nanoscale materials

Electron field emission from carbon nanoparticles prepared by microwave-plasma chemical-vapor deposition

J. Yu, E. G. Wang, and X. D. Bai

Appl. Phys. Lett. 78, 2226 (2001); http://dx.doi.org/10.1063/1.1361286 (3 pages) | Cited 22 times

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Carbon nanoparticles were prepared from H2 and CH4 at various temperatures. The carbon nanoparticles were well graphitized, and the degree of graphitization increased with increasing growth temperature. Field-emission measurements showed that the carbon nanoparticles were excellent electron field emitters, comparable to carbon nanotubes. The field-emission properties became better with increasing growth temperature, and the threshold fields of the carbon nanoparticles deposited at 400, 500, 670 °C were 3.2, 3, and 1 V/μm, respectively. The low-threshold field of the carbon nanoparticles is attributed to the field-enhancement effect and the higher degree of graphitization. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
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Electronic sensing of vapors with organic transistors

B. Crone, A. Dodabalapur, A. Gelperin, L. Torsi, H. E. Katz, A. J. Lovinger, and Z. Bao

Appl. Phys. Lett. 78, 2229 (2001); http://dx.doi.org/10.1063/1.1360785 (3 pages) | Cited 195 times

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We show that organic thin-film transistors have suitable properties for use in gas sensors. Such sensors possess sensitivity and reproducibility in recognizing a range of gaseous analytes. A wealth of opportunities for chemical recognition arise from the variety of mechanisms associated with different semiconductor–analyte interactions, the ability to vary the chemical constitution of the semiconductor end/side groups, and also the nature of the thin-film morphology. © 2001 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.30.Tv Field effect devices
85.65.+h Molecular electronic devices

Fabrication of InAs/AlSb/GaSb heterojunction bipolar transistors on Al2O3 substrates by wafer bonding

P. D. Moran, D. Chow, A. Hunter, and T. F. Kuech

Appl. Phys. Lett. 78, 2232 (2001); http://dx.doi.org/10.1063/1.1359140 (3 pages) | Cited 12 times

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High-frequency integrated circuit applications of GaSb-based materials are hampered by the lack of a suitable lattice-matched insulating substrate. Wafer bonding was used to fabricate InAs/AlSb/GaSb-based heterojunction bipolar transistors (HBTs) on an insulating sapphire substrate through a low temperature bonding process that results in a high bond strength and permitted the mechanical and chemomechanical removal of the initial GaSb substrate. The use of selective etches allows for the retention of the epitaxial device layers over virtually the entire wafer area. Minimal degradation of the transferred layers occurred in the bonding and substrate removal process. The resulting transferred structures were fabricated into functional HBTs exhibiting a dc current gain of ∼5. © 2001 American Institute of Physics.
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85.30.Pq Bipolar transistors
81.65.Cf Surface cleaning, etching, patterning
81.65.Ps Polishing, grinding, surface finishing

Effect of threading dislocations on AlGaN/GaN heterojunction bipolar transistors

L. McCarthy, I. Smorchkova, H. Xing, P. Fini, S. Keller, J. Speck, S. P. DenBaars, M. J. W. Rodwell, and U. K. Mishra

Appl. Phys. Lett. 78, 2235 (2001); http://dx.doi.org/10.1063/1.1358358 (3 pages) | Cited 21 times

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We demonstrate an AlGaN/GaN heterojunction bipolar transistor on a substrate grown using the lateral epitaxial overgrowth (LEO) technique. Common emitter characteristics show a current gain of 3. Active layers were grown by plasma-assisted molecular-beam epitaxy on metal–organic chemical-vapor-deposition-grown templates on sapphire. The collector–emitter leakage mechanism in these devices is found to be local punch-through associated with base layer compensation near the dislocations. LEO wing regions (nondislocated) were found to reduce the emitter–collector leakage by four orders of magnitude over adjacent window regions which had a dislocation density of 108 cm−2. Varying the doping profile through the base confirms that the mechanism for leakage is local punch-through due to compensation. This compensation mechanism is consistent with simulations which assume a donor-state line density of 107 cm−1. The implications of the emitter–collector leakage for dc device characterization are also discussed. © 2001 American Institute of Physics.
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85.30.Pq Bipolar transistors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Observation of double peak in the substrate current versus gate voltage characteristics of n-channel metal–oxide–semiconductor field effect transistors

K. G. Anil, I. Eisele, and S. Mahapatra

Appl. Phys. Lett. 78, 2238 (2001); http://dx.doi.org/10.1063/1.1361279 (3 pages) | Cited 1 time

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By employing sensitive current measurements at low drain voltages for n-channel metal–oxide–semiconductor field effect transistors with different channel dopings, substrate current versus gate voltage characteristics with two peaks were obtained for devices with low channel doping at 77 K. This differs from the single peak bell shaped curves reported in the literature. The data are analyzed and suggest that the second peak is due to the contribution of electron–electron interactions to the high energy tail of the electron energy distribution. Indirect contributions by the thermal tail of the electron energy distribution and ionized impurity scattering that make the second peak visible are also discussed. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Fq High-field and nonlinear effects

Heterojunction wavelength-tailorable far-infrared photodetectors with response out to 70 μm

A. G. U. Perera, S. G. Matsik, B. Yaldiz, H. C. Liu, A. Shen, M. Gao, Z. R. Wasilewski, and M. Buchanan

Appl. Phys. Lett. 78, 2241 (2001); http://dx.doi.org/10.1063/1.1361283 (3 pages) | Cited 17 times

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Results are presented on the performance of a heterojunction interfacial workfunction internal photoemission (HEIWIP) wavelength-tailorable detector. The detection mechanism is based on free-carrier absorption in the heavily doped emitter regions and internal emission across a workfunction barrier caused by the band gap offset at the heterojunction. The HEIWIP detectors have the high responsivity of free-carrier absorption detectors and the low dark current of quantum well infrared photodector type detectors. For a 70±2 cutoff wavelength detector, a responsivity of 11 A/W and a D∗ = 1×1013 cmmath/W with a photocurrent efficiency of 24% was observed at 20 μm. From the 300 K background photocurrent, the background limited performance (BLIP) temperature for this HEIWIP detector was estimated to be 15 K. This HEIWIP detector provides an exciting approach to far-infrared detection. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.50.Pz Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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