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21 Mar 2005

Volume 86, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 123102 (2005); http://dx.doi.org/10.1063/1.1885187 (3 pages)

Jong H. Na, Robert A. Taylor, James H. Rice, James W. Robinson, Kwan H. Lee, Young S. Park, Chang M. Park, and Tae W. Kang
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On the band structure lineup at interfaces of SiO2, Si3N4, and high-κ dielectrics

Winfried Mönch

Appl. Phys. Lett. 86, 122101 (2005); http://dx.doi.org/10.1063/1.1866641 (3 pages) | Cited 12 times

Online Publication Date: 14 March 2005

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The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures and the barrier heights of Schottky contacts are given by the branch-point energies of the IFIGS of the semiconductors and respective electric-dipole terms. The branch-point energies of SiO2, Si3N4, and of the high-κ dielectrics Al2O3, HfO2, and ZrO2 are determined as 3.99±0.10, 1.93±0.14, 3.23±0.42, 2.62±0.18, and ≈ 3.2 eV, respectively, from experimental valence-band offsets of heterostructures of these insulators.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.20.At Surface states, band structure, electron density of states
71.20.Ps Other inorganic compounds

Current transport property of n-GaN/n-6H–SiC heterojunction: Influence of interface states

Y. Huang, X. D. Chen, S. Fung, C. D. Beling, C. C. Ling, X. Q. Dai, and M. H. Xie

Appl. Phys. Lett. 86, 122102 (2005); http://dx.doi.org/10.1063/1.1886906 (3 pages) | Cited 1 time

Online Publication Date: 14 March 2005

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Heterostructures of n-GaN/n-6H–SiC grown by hydride vapor phase epitaxy (HVPE) and molecular-beam epitaxy (MBE) are characterized with the current–voltage (I–V), capacitance–voltage (C–V), and deep level transient spectroscopy (DLTS) techniques. Using different contact configurations, the I–V results reveal a rectifying barrier in the n-GaN/n-6H–SiC heterostructures. When GaN is negatively biased, the current is exponentially proportional to the applied voltage with the built-in barrier being 0.4–1.1 eV for the HVPE samples and 0.5 eV for the MBE sample. DLTS measurements reveal intense band-like deep level states in the interfacial region of the heterostructure, and the Fermi-level pinning by these deep level defects is invoked to account for the interfacial rectifying barrier of the heterostructures.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
71.55.Eq III-V semiconductors
73.40.Ei Rectification
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.30.+y Surface double layers, Schottky barriers, and work functions

Spin current injection by intersubband transitions in quantum wells

E. Ya. Sherman, Ali Najmaie, and J. E. Sipe

Appl. Phys. Lett. 86, 122103 (2005); http://dx.doi.org/10.1063/1.1882747 (3 pages) | Cited 5 times

Online Publication Date: 15 March 2005

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We show that a pure spin current can be injected in quantum wells by the absorption of linearly polarized infrared radiation, leading to transitions between subbands. The magnitude and the direction of the spin current depend on the Dresselhaus and Rashba spin–orbit coupling constants and light frequency and, therefore, can be manipulated by changing the light frequency and/or applying an external bias across the quantum well. The injected spin current should be observable either as a voltage generated via the anomalous spin-Hall effect, or by spatially resolved pump–probe optical spectroscopy.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
72.25.Hg Electrical injection of spin polarized carriers
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.Dc Spin polarized transport in semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Midgap levels in both n- and p-type 4H–SiC epilayers investigated by deep level transient spectroscopy

K. Danno, T. Kimoto, and H. Matsunami

Appl. Phys. Lett. 86, 122104 (2005); http://dx.doi.org/10.1063/1.1886904 (3 pages) | Cited 22 times

Online Publication Date: 15 March 2005

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Midgap levels in n- and p-type 4H–SiC epilayers have been investigated by deep level transient spectroscopy (DLTS). The EH6/7 center (Ec−1.55 eV) is the dominant midgap level as observed in DLTS spectra for n-type epilayers. The activation energy of EH6/7 center is unchanged regardless of applied electric field, indicating that the charge state of the EH6/7 center may be neutral after electron emission [acceptor-like (0/−) trap]. In p-type epilayers, a deep level located at 1.49 eV above the valence band edge has been detected. The lack of Poole–Frenkel effect in emission time constant from this deep level suggests that this level is donor-like (+/0). From the energy level and charge state, this defect center may originate from a single carbon vacancy (VC), which has been extensively studied by electron paramagnetic resonance.
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73.20.At Surface states, band structure, electron density of states
73.61.Le Other inorganic semiconductors
71.55.-i Impurity and defect levels
73.50.Fq High-field and nonlinear effects
76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters

Comparison of the electronic properties of sublimation- and vapor-Bridgman-grown crystals of tetracene

J. Niemax, A. K. Tripathi, and J. Pflaum

Appl. Phys. Lett. 86, 122105 (2005); http://dx.doi.org/10.1063/1.1884751 (3 pages) | Cited 6 times

Online Publication Date: 16 March 2005

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The hole mobilities in a vapor-Bridgman-grown crystal and in sublimation-grown crystals of tetracene were measured along the c*-direction in a temperature range from 300 to 450 K by the time-of-flight method. The mobility was found to increase as a function of temperature in the vapor-Bridgman-grown crystal, indicating that the transport was thermally activated. After reaching its maximum of about 1 cm2/V s at 320 K, the mobility in the sublimation-grown crystals decreased with temperature in accordance with band transport models. Gas chromatography measurements indicated that the difference in the electronic transport properties could be related to a higher concentration of chemical impurities in the vapor-Bridgman crystal.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.S- Impurities in crystals
82.80.Bg Chromatography

Electronic mean free path in as-produced and purified single-wall carbon nanotubes

H. Kajiura, A. Nandyala, U. C. Coskun, A. Bezryadin, M. Shiraishi, and M. Ata

Appl. Phys. Lett. 86, 122106 (2005); http://dx.doi.org/10.1063/1.1885189 (3 pages) | Cited 1 time

Online Publication Date: 17 March 2005

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The effect of purification on room temperature electronic transport properties of single-wall nanotubes (SWNT) was studied by submerging the nanotubes into liquid mercury. The conductance plots of purified SWNTs showed plateaus, indicating weak dependence of the electrical resistance on the length of the tube connecting the electrodes, providing evidence of quasiballistic conduction in SWNTs. The electronic mean free path of the purified SWNTs reached a few microns, which is longer than that of the as-produced SWNTs, and which is consistent with the calculation based on the scattering by acoustic phonons.
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73.63.Fg Nanotubes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport
61.46.-w Structure of nanoscale materials

Hydrogen passivation effect in nitrogen-doped ZnO thin films

Xiaonan Li, Brian Keyes, Sally Asher, S. B. Zhang, Su-Huai Wei, Timothy J. Coutts, Sukit Limpijumnong, and Chris G. Van de Walle

Appl. Phys. Lett. 86, 122107 (2005); http://dx.doi.org/10.1063/1.1886256 (3 pages) | Cited 34 times

Online Publication Date: 17 March 2005

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The role of hydrogen in nitrogen-doped ZnO thin films was studied by Fourier transform infrared (FTIR) absorption and modeled by first-principles calculations to understand the difficulty of doping ZnO p-type with nitrogen. Nitrogen-doped ZnO films were fabricated by low-pressure metal-organic chemical vapor deposition (MOCVD). High levels of nitrogen incorporation were observed, but the acceptor concentrations remained low. Theoretical analysis suggests there is a high probability that NO− and H+ charged defects combine to form the neutral defect complexes, thereby compensating the nitrogen-related acceptors. Calculated values of the vibrational frequencies of the related infrared modes agree well with the measured spectra. Thus, we believe the difficulty of achieving p-type doping in MOCVD-grown ZnO films is due, at least partially, to inadvertent passivation by hydrogen.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.S- Impurities in crystals
73.61.Ga II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.20.My Galvanomagnetic and other magnetotransport effects

Effect of magnesium on the structure and growth of GaN(0001)

John E. Northrup

Appl. Phys. Lett. 86, 122108 (2005); http://dx.doi.org/10.1063/1.1886257 (3 pages) | Cited 9 times

Online Publication Date: 17 March 2005

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First-principles total energy calculations were performed to determine the effect of Mg on the structure and growth of the GaN(0001) surface. The relative stabilities of possible Mg-rich reconstructions were determined with respect to those of the clean surface. In very Mg-rich conditions it is proposed that the surface structure comprises ½ to ¾ ML of Mg substituting for Ga in the top layer. The stability of these structures reduces the range of Ga chemical potentials for which the Ga-bilayer is stable and therefore provides an explanation for why the window for smooth growth of GaN is narrowed when Mg is present. A structural model for the 2×2 reconstruction of the GaN(0001):Mg surface is proposed.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Wm Other nonelectronic physical properties
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors

Application of the thermionic field emission model in the study of a Schottky barrier of Ni on p-GaN from current–voltage measurements

Yow-Jon Lin

Appl. Phys. Lett. 86, 122109 (2005); http://dx.doi.org/10.1063/1.1890476 (3 pages) | Cited 21 times

Online Publication Date: 18 March 2005

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Barrier height values of Ni contacts to Mg-doped p-type GaN (p-GaN) were obtained from current–voltage measurements in this study. The induced deep level defect band through high Mg doping led to a reduction of the depletion layer width in the p-GaN near the interface and an increase in the probability of thermionic field emission. It also resulted in an increase in current flow under forward bias condition, which was not analyzed using the thermionic emission model. Further, the calculated barrier height value of Ni contacts to p-GaN using the thermionic field emission model is in good agreement with the value of 1.9 eV obtained from x-ray photoelectron spectroscopy measurements.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Hi Surface barrier, boundary, and point contact devices
79.70.+q Field emission, ionization, evaporation, and desorption
79.40.+z Thermionic emission
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states

Molecular-weight-dependent mobilities in regioregular poly(3-hexyl-thiophene) diodes

Chiatzun Goh, R. Joseph Kline, Michael D. McGehee, Ekaterina N. Kadnikova, and Jean M. J. Fréchet

Appl. Phys. Lett. 86, 122110 (2005); http://dx.doi.org/10.1063/1.1891301 (3 pages) | Cited 85 times

Online Publication Date: 18 March 2005

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We have investigated the transport properties in the direction perpendicular to the substrate of regioregular poly(3-hexyl-thiophene) of different molecular weights (MW) in a diode geometry. In these devices, which exhibit space-charge-limited behavior, we find that the mobility values at room temperature increase from 1.33×10−5 cm2/V s to 3.30×10−4 cm2/V s as the MW is increased from 2.9 to 31.1 kg/mol. The mobility is found to be field independent for high MW films, but field dependent for the low MW films. The current–voltage characteristics of the diodes are also studied as a function of temperature from 160 K to 300 K. The activation energy for carrier transport, extracted from the Arrhenius plot, is found to decrease gradually from 143 meV to 126 meV as the MW is increased.
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85.30.Kk Junction diodes
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
73.50.Fq High-field and nonlinear effects

Electrical characterization of strained Si/SiGe wafers using transient capacitance measurements

Dong Wang, Masaharu Ninomiya, Masahiko Nakamae, and Hiroshi Nakashima

Appl. Phys. Lett. 86, 122111 (2005); http://dx.doi.org/10.1063/1.1891303 (3 pages) | Cited 5 times

Online Publication Date: 18 March 2005

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Interface states density (Nss) and minority carrier generation lifetime (τg) were evaluated for strained Si(St-Si)/SiGe wafers using deep level transient spectroscopy and metal-oxide-semiconductor transient capacitance methods. Nss shows an independence on St-Si thickness (dSi) and an obvious dependence on Ge fraction (Ge%). τg shows a strong dependence on both dSi and Ge%. The reasons of these dependencies are discussed in detail.
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Potential mapping of pentacene thin-film transistors using purely electric atomic-force-microscope potentiometry

Masakazu Nakamura, Naoyuki Goto, Noboru Ohashi, Masatoshi Sakai, and Kazuhiro Kudo

Appl. Phys. Lett. 86, 122112 (2005); http://dx.doi.org/10.1063/1.1891306 (3 pages) | Cited 27 times

Online Publication Date: 18 March 2005

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Potential mapping of organic thin-film transistors (TFTs) has been carried out using originally developed atomic-force-microscope potentiometry (AFMP). The technique is suitable for the accurate measurement at metal–semiconductor boundaries of working TFTs. Potential drops near metal–organic boundaries are observed for both source and drain Au top contacts of a pentacene TFT. The approximate width of the steeper potential slope is 400 nm, which is larger than the spatial resolution of AFMP. The potential drop is considered to be due to a damaged area with low carrier mobility caused by the Au evaporation, which is also reproduced by device simulation.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
68.37.Ps Atomic force microscopy (AFM)

Spectral responsivity measurements of photoconductive diamond detectors in the vacuum ultraviolet region distinguishing between internal photocurrent and photoemission current

T. Saito and K. Hayashi

Appl. Phys. Lett. 86, 122113 (2005); http://dx.doi.org/10.1063/1.1891284 (3 pages) | Cited 9 times

Online Publication Date: 18 March 2005

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Spectral responsivities of photoconductive diamond detectors were measured based on a standard detector calibrated by a rare-gas ionization chamber in the wavelength range from 10 to 60 nm using synchrotron radiation. The photoemission current component was measured separately from the internally generated photocurrent component by using two electrical measurement configurations and by changing the polarity of the applied voltage to the detector. The photoemission current contribution to the total output current was not negligible but dominant in wavelengths longer than 40 nm. On the other hand, the internal photocurrent played a major role in wavelengths shorter than approximately 25 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
78.40.Ha Other nonmetallic inorganics
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