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30 Dec 2002

Volume 81, Issue 27, pp. 5099-5257

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The Mn3+/2+ acceptor level in group III nitrides

T. Graf, M. Gjukic, M. S. Brandt, M. Stutzmann, and O. Ambacher

Appl. Phys. Lett. 81, 5159 (2002); http://dx.doi.org/10.1063/1.1530374 (3 pages) | Cited 108 times

Online Publication Date: 19 December 2002

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Molecular-beam-epitaxy grown GaN:Mn and AlN:Mn layers with Mn concentrations around 1020 cm−3 were investigated by optical absorption and photoconductivity measurements. From electron spin resonance Mn is known to be mostly present in the neutral acceptor state in GaN without codoping. This leads to a reassignment of the optical absorption features to a charge transfer from the neutral Mn3+ oxidation state, either by direct photoionization at 1.8 eV or through a photothermal ionization process via an excited state at 1.42 eV above the Mn3+ ground state by spin-allowed Mn3+ 5E→5T internal absorption. The position of the Mn3+/2+ acceptor level at 1.8 eV above the valence-band edge of GaN makes the realization of carrier-mediated ferromagnetism rather unlikely in GaN:Mn. © 2002 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
75.50.Pp Magnetic semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.40.Fy Semiconductors

Electrical detection of spin accumulation and spin precession at room temperature in metallic spin valves

F. J. Jedema, M. V. Costache, H. B. Heersche, J. J. A. Baselmans, and B. J. van Wees

Appl. Phys. Lett. 81, 5162 (2002); http://dx.doi.org/10.1063/1.1532753 (3 pages) | Cited 17 times

Online Publication Date: 19 December 2002

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We have fabricated a multiterminal lateral mesoscopic metallic spin valve demonstrating spin precession at room temperature (RT), using tunnel barriers in combination with metallic ferromagnetic electrodes as a spin injector and detector. The observed modulation of the output signal due to the spin precession is discussed and explained in terms of a time-of-flight experiment of electrons in a diffusive conductor. The obtained spin relaxation length λsf = 500 nm in an aluminum strip will make detailed studies of spin dependent transport phenomena possible and allow one to explore the possibilities of the electron spin for new electronic applications at RT. © 2002 American Institute of Physics.
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72.25.Ba Spin polarized transport in metals
73.23.-b Electronic transport in mesoscopic systems
73.40.Gk Tunneling

Onset of long-range diffusion and exponent of 1/fα noise in metal films with electromigration damage

Swastik Kar and A. K. Raychaudhuri

Appl. Phys. Lett. 81, 5165 (2002); http://dx.doi.org/10.1063/1.1523155 (3 pages) | Cited 5 times

Online Publication Date: 19 December 2002

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Investigations of low-frequency conductance fluctuations have been done on silver films which have been made to undergo electromigration damage. The system shows a clear increase in noise magnitude after electromigration damage. The noise spectral power shows a distinct presence of 1/f3/2 component arising out of long-range diffusion. The temperature dependence of noise (150 K<T<350 K) shows a marked deviation from the Dutta–Horn type behavior with the 1/f3/2 term showing a strong dominance at higher temperatures. We propose that the increase of noise in metal films after electromigration damage arise predominantly from this spectral component. © 2002 American Institute of Physics.
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73.61.At Metal and metallic alloys
66.30.Qa Electromigration
73.50.Td Noise processes and phenomena

Effect of crystal defects on the electrical properties in epitaxial tin dioxide thin films

J. E. Dominguez, L. Fu, and X. Q. Pan

Appl. Phys. Lett. 81, 5168 (2002); http://dx.doi.org/10.1063/1.1530745 (3 pages) | Cited 19 times

Online Publication Date: 19 December 2002

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Epitaxial (101) tin dioxide thin films with thickness ranging from 6 and 100 nm were deposited on the (10math2) α-Al2O3 substrate by femtosecond pulsed laser ablation. Due to the lattice and thermal expansion mismatch with the substrate, the SnO2 film shows interfacial misfit dislocations, antiphase boundaries (APBs), and partial dislocations. The APBs lie along the (math01) planes with a displacement of 1/2[101]. The densities of APBs and partial dislocations vary with film thickness, whereas the average spacing of misfit dislocations remains constant. Hall effect measurements showed that both electron concentration and mobility decrease with a reduction in the film thickness, which is ascribed to the scattering of electrons by crystal defects and interfaces and the effect of a native space charge region at the near-surface region of the films. The response of the films to reducing gases was found to depend on the electron concentration of the film and the relative fraction, with respect to film thickness, of material that is depleted of electrons. © 2002 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
72.80.Ga Transition-metal compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
65.40.De Thermal expansion; thermomechanical effects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis

Interface states at ZnSe/Ge heterojunctions: the role of atomic interdiffusion and disorder

M. Peressi, F. Favot, G. Cangiani, and A. Baldereschi

Appl. Phys. Lett. 81, 5171 (2002); http://dx.doi.org/10.1063/1.1532555 (3 pages) | Cited 4 times

Online Publication Date: 19 December 2002

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The origin of electronic states localized at ZnSe/Ge (110) interface is investigated by means of ab initio pseudopotential calculations. Some selected interface configurations are considered, one corresponding to the abrupt interface and others corresponding to partially disordered interfaces, with Zn-Ge or Se-Ge swaps. Remarkably, the existence of interface electronic states within the heterojunction band gap critically depends on the atomic-scale morphology of the interface: unlike the abrupt case, disordered interfaces exhibit localized states extending over the whole interface Brillouin zone. The presence of interfacial density of states, experimentally detectable, is therefore an indication of disorder and atomic interdiffusion. © 2002 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Bulk and surface contributions to resonant second-harmonic generation from Si(001) surfaces

Yong Qiang An and Steven T. Cundiff

Appl. Phys. Lett. 81, 5174 (2002); http://dx.doi.org/10.1063/1.1533122 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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The spectra of the isotropic and anisotropic contributions to second-harmonic generation from modified Si(001) surfaces are separated using polarization selection and rotational anisotropy. A bulk anisotropic resonance is observed at a two-photon energy of 3.42±0.01 eV. The isotropic surface contributions for native oxide Si and thermal oxide Si show peaks at 3.39±0.01 eV and 3.35±0.01 eV, respectively. Interference between these contributions and the bulk signal can shift the apparent resonance position if they are not separated. The surface produces a noninterfering contribution that is comparable to the interfering contribution for H-terminated Si but negligible for oxidized silicon. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ek Optical activity
81.65.Mq Oxidation

Growth of Au-catalyzed ordered GaAs nanowire arrays by molecular-beam epitaxy

Z. H. Wu, X. Y. Mei, D. Kim, M. Blumin, and H. E. Ruda

Appl. Phys. Lett. 81, 5177 (2002); http://dx.doi.org/10.1063/1.1532772 (3 pages) | Cited 55 times

Online Publication Date: 19 December 2002

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Ordered gallium arsenide (GaAs) nanowires are grown by molecular-beam epitaxy on GaAs (111)B substrates using Au-catalyzed vapor–liquid–solid growth defined by nanochannel alumina (NCA) templates. Field-emission scanning electron microscope images show highly ordered nanowires with a growth direction perpendicular to the substrate. The size (i.e., diameter) distribution of the wires is drastically narrowed by depositing the gold catalyst through an NCA template mask; this narrows the size distribution of the gold dots and arranges them in a well-ordered array, as defined by the NCA template. The nanowire diameter distribution full width at half maximum on the masked substrate is 5.1 nm, compared with 15.7 nm on an unmasked substrate. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires

Kinetics of electric-field-enhanced crystallization of amorphous silicon in contact with Ni catalyst

Hae-Yeol Kim, Binn Kim, Jong-Uk Bae, Kwang-Jo Hwang, Hyun-Sik Seo, and Chang-Dong Kim

Appl. Phys. Lett. 81, 5180 (2002); http://dx.doi.org/10.1063/1.1532533 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2002

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Electric-field-enhanced crystallization of hydrogenated amorphous silicon in contact with nickel catalyst (Ni/a-Si:H) has been investigated. In order to elucidate the crystallization kinetics quantitatively, in situ conductivity measurement was used. With the change of Ni dose (4×1013 ∼ 1.3×1015 cm−2) and annealing temperature (550 ∼ 500 °C), crystallization rate varied drastically at the electric field of 33 V cm−1. The activation energy for the crystallization was found to be strongly dependent on the Ni dose, 85 kJ mol−1 for 1.3×1015 Ni cm−2, 243 kJ mol−1 for 6×1014 Ni cm−2, and 276 kJ mol−1 for 4×1013 Ni cm−2, respectively. The polycrystalline silicon films were composed of needle-like crystallites of ∼ 5 μm (long axis) and their thin-film transistors (TFTs) showed field effect mobility of 43 cm2 V−1 s−1. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.Tv Field effect devices
73.61.Cw Elemental semiconductors

Surface band bending, nitrogen-vacancy-related defects, and 2.8-eV photoluminescence band of (NH4)2Sx-treated p-GaN

Yow-Jon Lin, Zhi-Long Wang, and Hsing-Cheng Chang

Appl. Phys. Lett. 81, 5183 (2002); http://dx.doi.org/10.1063/1.1533857 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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We have employed the photoluminescence and x-ray photoelectron spectroscopy measurements to study the effects of (NH4)2Sx treatment on the p-type GaN (p-GaN). After (NH4)2Sx treatment, we found that the reduction of the surface state, related to nitrogen-vacancy defects on the p-GaN surface, led to a reduction in surface band bending by 0.25 eV. The surface band bending reduction and surface state reduction caused by the (NH4)2Sx surface treatment could be useful for the formation of ohmic and Schottky contacts between the metal and p-GaN layers. In addition, the intensity of the 2.8-eV photoluminescence band depended on the amount of nitrogen vacancy of p-GaN, which was also investigated in this study. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Characteristics of silicon nanocrystal floating gate memory using amorphous carbon/SiO2 tunnel barrier

Seung Jae Baik and Koeng Su Lim

Appl. Phys. Lett. 81, 5186 (2002); http://dx.doi.org/10.1063/1.1533119 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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Nanocrystal floating gate memory employing an amorphous carbon (a-C)/SiO2 double-layered tunnel barrier was fabricated. The band gap of a-C and conduction band discontinuity between a-C and Si was estimated to be 1.95 and 0.4 eV, respectively. In addition, interface states density of the a-C/SiO2/channel Si was estimated from the capacitance–voltage measurement. The nanocrystal memory using this tunnel barrier exhibited enhanced charge retention than that employing a single SiO2 tunnel barrier whereas the injection efficiency is comparable between them, which is due to the asymmetrical band profile of the tunnel barrier. © 2002 American Institute of Physics.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices

Experimental observation of electron velocity overshoot in AlN

R. Collazo, R. Schlesser, and Z. Sitar

Appl. Phys. Lett. 81, 5189 (2002); http://dx.doi.org/10.1063/1.1534407 (3 pages) | Cited 5 times

Online Publication Date: 19 December 2002

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The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on 6H-SiC was directly measured as a function of the applied electric field. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through 80-nm-thick layers indicated the onset of quasiballistic transport for fields greater than 510 kV/cm. This was evidenced by a symmetric energy distribution centered at energies above the conduction band minimum. Drifted Fermi–Dirac energy distribution was fitted to the measured energy distribution, with the energy scale referenced to the bottom of the AlN conduction band. The drift energy and the carrier temperature were obtained as fitting parameters. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced. In addition, the velocity-field characteristic was derived from these observations. © 2002 American Institute of Physics.
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73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects

Si doping of high-Al-mole fraction AlxGa1−xN alloys with rf plasma-induced molecular-beam-epitaxy

Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, and Alexander N. Cartwright

Appl. Phys. Lett. 81, 5192 (2002); http://dx.doi.org/10.1063/1.1534395 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Kinetic roughening study of perylene on glass and Au substrates

Serkan Zorba, Li Yan, Neil J. Watkins, and Yongli Gao

Appl. Phys. Lett. 81, 5195 (2002); http://dx.doi.org/10.1063/1.1534416 (3 pages) | Cited 3 times

Online Publication Date: 19 December 2002

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We have investigated the growth kinetics of perylene, an organic semiconductor with high carrier mobility, on glass and Au substrates grown side-by-side by vapor deposition using atomic force microscopy. Our results show that kinetic roughening theory can reveal a wealth of information about polycrystalline growth. Higher order height–height correlation functions have been calculated for the perylene thin films on glass and Au. These results show that the height–height correlation function and the Hurst exponent saturate once the nominal perylene film thickness reaches the critical value of 40 Å on glass, and 100 Å on Au. After these thicknesses, overhang structures develop and dynamic scaling analysis becomes inappropriate. In addition, we have observed a complex, multiaffine behavior on both substrates evidenced by order dependence of the Hurst exponent. Grain size distribution and shape analysis were also performed on our films. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ps Atomic force microscopy (AFM)
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