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18 Sep 2000

Volume 77, Issue 12, pp. 1741-1913

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Distinguishing between interface dipoles and band bending at metal/tris-(8-hydroxyquinoline) aluminum interfaces

I. G. Hill, A. J. Mäkinen, and Z. H. Kafafi

Appl. Phys. Lett. 77, 1825 (2000); http://dx.doi.org/10.1063/1.1310637 (3 pages) | Cited 45 times

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Using a combination of photoelectron spectroscopies and ellipsometry to study the thin-film growth of Alq3 (tris-(8-hydroxyquinoline) aluminum) on Ag, we have been able to distinguish between molecular orbital energy shifts due to “band bending” and interface dipole formation. We have observed large binding energy shifts (≈0.5 eV) of the organic molecular levels at low coverages. We conclude that these shifts are consistent with the formation of a polarized molecular layer, or interface dipole, and are inconsistent with an electrostatic band-bending model. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures

Contribution of ions and radicals in etching of Si1−xGex epitaxial films using an electron-cyclotron-resonance chlorine plasma

Hajime Takeuchi, Takashi Matsuura, and Junichi Murota

Appl. Phys. Lett. 77, 1828 (2000); http://dx.doi.org/10.1063/1.1310624 (3 pages) | Cited 5 times

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Etching of undoped Si1−xGex epitaxial films (x = 0−1) has been investigated using an electron-cyclotron-resonance chlorine plasma. It is found that the etch rate of Si1−xGex increases with increasing Ge fraction and decreases with increasing Cl2 pressure. From the comparison of the etch rate with the number of the incident ions toward the wafer and the relative radical density in the plasma, it is also found that the etching of Si1−xGex with low x is induced mainly by chlorine ions, and for high x, the contribution of radicals to the etching becomes larger. From the angular resolved x-ray photoelectron spectroscopy analysis, it is found that the etching by chlorine radicals causes surface segregation of Si with the concentration of about 1–1.5×1014 cm−2 on the etched Si1−xGex surface. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Hd Other semiconductors
79.60.Dp Adsorbed layers and thin films
68.35.Fx Diffusion; interface formation

The role of dc current limitations in Fowler–Nordheim electron emission from carbon films

J. B. Cui, K. B. K. Teo, J. T. H. Tsai, J. Robertson, and W. I. Milne

Appl. Phys. Lett. 77, 1831 (2000); http://dx.doi.org/10.1063/1.1310628 (3 pages) | Cited 24 times

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We investigated the electron field emission characteristics of carbon films deposited by filtered cathodic vacuum arc. A special sandwich structure was created using alternating layers of carbon and aluminum. This structure allows both field emission and dc current–voltage characteristics to be measured on the same film. The emission current was found to follow the Fowler–Nordheim law below a critical field, Ecri. Above Ecri, the current deviates from the Fowler–Nordheim law but follows the dc current–voltage characteristics of the film. It is concluded that the frequently observed deviation of electron emission from the Fowler–Nordheim law at high field is due to the current limitation of the resistive carbon film. The important implication of this finding for device fabrication is discussed. © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.61.Cw Elemental semiconductors

Ab initio energetics of boron-interstitial clusters in crystalline Si

Thomas J. Lenosky, Babak Sadigh, Silva K. Theiss, Maria-Jose Caturla, and Tomas Diaz de la Rubia

Appl. Phys. Lett. 77, 1834 (2000); http://dx.doi.org/10.1063/1.1310627 (3 pages) | Cited 39 times

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We have performed an extensive first-principles study of the energetics of boron clustering in silicon in the presence of excess self-interstitial atoms (SIAs). We consider complexes with up to four B atoms and two SIAs. We have conducted an extensive search for the ground-state configurations and charge states of these clusters. We find the cluster containing three B atoms and one SIA(B3I) to be remarkably stable, while all our clusters with more than 80% boron content are unstable. Hence, we propose B3I to be a stable nucleus that can grow to larger clusters. The energetics presented here can be used as input to large-scale predictive models for B diffusion and activation during ion implantation and thermal annealing. © 2000 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities

Amorphic diamond/silicon semiconductor heterojunctions exhibiting photoconductive characteristics

F. Davanloo, C. B. Collins, K. J. Koivusaari, and S. Leppävuori

Appl. Phys. Lett. 77, 1837 (2000); http://dx.doi.org/10.1063/1.1311312 (3 pages) | Cited 2 times

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Amorphic diamond deposited from an intense laser plasma of C3+ and C4+ exhibits semiconductor properties. Although this material has a measured electrical breakdown strength of 3×109 V/m, it is shown to form a heterojunction with both p- and n-type Si. Regardless of the doping type and its concentration in the Si, current is rectified in the same direction with the diamond layer acting as the cathode. A photoconductive effect is observed for these junction devices and current levels from the heterojunction vary with the amount of reverse bias and the illumination. The spectral response is estimated to mostly lie in the range of 600–900 nm. © 2000 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Jc Amorphous semiconductors; glasses
73.40.Ei Rectification
77.22.Jp Dielectric breakdown and space-charge effects
73.61.Cw Elemental semiconductors

Effects of nitric-oxide-plasma treatment on the electrical properties of tetraethylorthosilicate-deposited silicon dioxides on strained-Si1−xGex layers

B. Senapati, S. K. Samanta, S. Maikap, L. K. Bera, and C. K. Maiti

Appl. Phys. Lett. 77, 1840 (2000); http://dx.doi.org/10.1063/1.1311311 (3 pages) | Cited 5 times

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Gate-quality ultrathin silicon dioxide films on strained-Si0.74Ge0.26 layers have been deposited by microwave plasma-enhanced chemical vapor deposition technique using tetraethylorthosilicate. Effect of nitric-oxide (NO)-plasma treatment on the electrical properties of the deposited oxides have been studied using a metal–insulator–semiconductor structure. A significant improvement in the interface trap level density (Dit) and charge trapping behavior under Fowler–Nordheim constant current stressing is observed for NO-plasma treated deposited oxide films. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Mq Oxidation
77.55.-g Dielectric thin films
85.30.Tv Field effect devices
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Direct determination of electron effective mass in GaNAs/GaAs quantum wells

P. N. Hai, W. M. Chen, I. A. Buyanova, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 77, 1843 (2000); http://dx.doi.org/10.1063/1.1311324 (3 pages) | Cited 105 times

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Electron effective mass (me∗) in GaNxAs1−x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The me∗ values of 0.12m0 and 0.19m0 are directly determined for the 70-Å-thick QWs with N composition of 1.2% and 2.0%, respectively. This sizable increase in the electron effective mass is consistent with the earlier theoretical predictions based on the strong interaction of the lowest conduction band states with the upper lying band states or impurity band induced by the incorporation of N. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
76.40.+b Diamagnetic and cyclotron resonances

Growth of hexagonal GaN on Si(111) coated with a thin flat SiC buffer layer

D. Wang, Y. Hiroyama, M. Tamura, M. Ichikawa, and S. Yoshida

Appl. Phys. Lett. 77, 1846 (2000); http://dx.doi.org/10.1063/1.1311607 (3 pages) | Cited 20 times

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Hexagonal GaN films were grown on Si(111) covered with a thin flat SiC buffer layer under both N- and Ga-rich growth conditions. A flat 2.5-nm-thick SiC layer was an effective buffer layer for GaN growth. The growth mode and microstructure of GaN depended strongly on the Ga/N flux ratios. Under N-rich growth conditions, the growth mode was three dimensional; GaN showed statistical roughening of the surface and a characteristic columnar structure. Under Ga-rich conditions, the GaN growth mode was two dimensional; GaN films with a flat surface and an almost stacking-fault-free microstructure were obtained. The two-dimensional growth mode was facilitated by strong wetting between Ga and SiC(111) at the first Ga-layer deposition on SiC. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
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)

Electric-field dependence of mobile proton-induced switching in protonated gate oxide field-effect transistors

R. A. B. Devine

Appl. Phys. Lett. 77, 1849 (2000); http://dx.doi.org/10.1063/1.1311608 (3 pages) | Cited 3 times

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The switching characteristics of protonated gate oxide field-effect transistors for use as integrated memory element devices have been studied. The rate of switching of the source drain current in devices having 20 and 40 nm gate oxide thicknesses which contain mobile protons is found to vary exponentially with the electric field applied across the oxide. The time t1/2 at which the current attains half the maximum value is found to vary as the oxide thickness to the power √3→2. Extrapolation to the case of devices with 4 nm thick gate oxide for fields ∼4 MV cm−1 indicates 3.2 ⩽ t1/2 ⩽ 6.5 ms time scales should be attainable. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
66.30.H- Self-diffusion and ionic conduction in nonmetals

Simultaneous measurement of electron and hole mobilities in polymer light-emitting diodes

H. C. F. Martens, J. N. Huiberts, and P. W. M. Blom

Appl. Phys. Lett. 77, 1852 (2000); http://dx.doi.org/10.1063/1.1311599 (3 pages) | Cited 80 times

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The transport properties of electrons and holes in a poly(p-phenylene vinylene)-based polymer light-emitting diode (PLED) have been investigated. Using admittance spectroscopy, we are able to simultaneously obtain the electron and hole mobility, μ = μ0 exp(γmath), in a single PLED. The dynamics of the electron and hole transport are separated in the frequency domain as a result of the different transit times. At room temperature, we find μ0 = 5.6×10−11 m2/V s and γ = 5.0×10−4 (m/V)1/2 for holes. For electrons μ0 = 1.0×10−12 m2/V s and γ = 8.0×10−4 (m/V)1/2 are obtained. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

High figure of merit in partially filled ytterbium skutterudite materials

G. S. Nolas, M. Kaeser, R. T. Littleton, and T. M. Tritt

Appl. Phys. Lett. 77, 1855 (2000); http://dx.doi.org/10.1063/1.1311597 (3 pages) | Cited 190 times

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We present evidence of a relatively high dimensionless figure of merit (ZT) in a polycrystalline skutterudite partially filled with ytterbium ions. The small-diameter yet heavy-mass Yb atoms partially filling the voids of the host CoSb3 system exhibit low values of thermal conductivity while the quite favorable electronic properties are not substantially perturbed by the addition of Yb. This combination is ideal for thermoelectric applications exemplifying the “phonon-glass electron-crystal” concept of a thermoelectric material, resulting in ZT = 0.3 at room temperature and ZT ∼ 1 at 600 K for Yb0.19Co4Sb12. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
72.80.Ga Transition-metal compounds
61.72.Qq Microscopic defects (voids, inclusions, etc.)

GaN homoepitaxy by metalorganic chemical-vapor deposition on free-standing GaN substrates

C. R. Miskys, M. K. Kelly, O. Ambacher, G. Martínez-Criado, and M. Stutzmann

Appl. Phys. Lett. 77, 1858 (2000); http://dx.doi.org/10.1063/1.1311596 (3 pages) | Cited 29 times

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Lattice-matched GaN layers are grown by metalorganic chemical-vapor deposition on free-standing GaN substrates, which were fabricated by laser-induced liftoff of 300-μm-thick films grown by hydride vapor-phase epitaxy. Pretreatment of the free-standing films before the homoepitaxial growth of GaN involved mechanical polishing of the Ga-face surface and a final Cl-based plasma etch. By a combination of high-resolution x-ray diffraction, atomic-force microscopy, as well as Raman and photoluminescence spectroscopy, the structural and optical properties of the lattice-matched GaN layers are characterized. X-ray diffraction patterns of (0002), (0004), and (0006) reflexes with a full width at half maximum (FWHM) of as low as 20 arcsec are obtained. The dislocation density is determined to be 2×107 cm−2 and the surface morphology is dominated by bilayer steps with terraces of about 200 nm. The lattice mismatch between the GaN substrate and the homoepitaxial layer is below 3×10−5, resulting in a very narrow FWHM of the excitonic luminescence of 0.5 meV. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Nanocrystalline gallium nitride thin films

Nisha Preschilla A., S. Major, Nigvendra Kumar, I. Samajdar, and R. S. Srinivasa

Appl. Phys. Lett. 77, 1861 (2000); http://dx.doi.org/10.1063/1.1311595 (3 pages) | Cited 25 times

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Nanocrystalline gallium nitride (GaN) thin films were deposited on quartz substrates by reactive rf sputtering of GaAs target with nitrogen as the reactive cum sputtering gas. X-ray diffraction and transmission electron microscopy confirmed the presence of GaN crystallites with particle size increasing from 3 to 16 nm, as the substrate temperature was increased from 400 to 550 °C. The particle size in films grown at temperatures below 550 °C were less than the exciton Bohr radius of GaN. The band gap of these films obtained from absorption and photoluminescence measurements showed a blueshift with respect to bulk GaN. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
61.72.Mm Grain and twin boundaries
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Cd Deposition by sputtering
71.20.Nr Semiconductor compounds

Coherent population transfer in coupled semiconductor quantum dots

Ulrich Hohenester, Filippo Troiani, Elisa Molinari, Giovanna Panzarini, and Chiara Macchiavello

Appl. Phys. Lett. 77, 1864 (2000); http://dx.doi.org/10.1063/1.1311820 (3 pages) | Cited 34 times

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We propose a solid-state implementation of stimulated Raman adiabatic passage in two coupled semiconductor quantum dots. Proper combination of two pulsed laser fields allows the coherent carrier transfer between the two nanostructures without suffering significant losses due to environment coupling. By use of a general solution scheme for the carrier states in the double-dot structure, we identify the pertinent dot and laser parameters. © 2000 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.65.-k Nonlinear optics
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Examination of tunnel junctions in the AlGaN/GaN system: Consequences of polarization charge

Madhusudan Singh, Yifei Zhang, Jasprit Singh, and Umesh Mishra

Appl. Phys. Lett. 77, 1867 (2000); http://dx.doi.org/10.1063/1.1311818 (3 pages) | Cited 15 times

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A strong piezoelectric effect and a large spontaneous polarization allow one to incorporate a large electric field (>106 V/cm) and high sheet charge (>1013 cm−2) without doping in the AlGaN/GaN heterostructure. Theoretical studies are done to examine how polarization effects can be exploited to design metal–AlGaN/GaN tunnel junctions. We find that with a proper choice of AlGaN thickness undoped junctions can be made with very high metal to two-dimensional electron gas tunneling. Thus, a Schottky junction can be converted to a tunnel junction without doping. The tunneling probabilities approach those produced in a system doped at ∼ 4×1019 cm−3. This work suggests that very interesting tunnel junctions can be made from undoped AlGaN/GaN heterostructures. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
77.22.Ej Polarization and depolarization
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