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5 Apr 2010

Volume 96, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 96, 143103 (2010); http://dx.doi.org/10.1063/1.3378684 (3 pages)

Joshua A. Kellar, Justice M. P. Alaboson, Qing Hua Wang, and Mark C. Hersam
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Enhanced thermoelectric performance of (Sb0.75Bi0.25)2Te3 compound from first-principles calculations

H. Y. Lv, H. J. Liu, L. Pan, Y. W. Wen, X. J. Tan, J. Shi, and X. F. Tang

Appl. Phys. Lett. 96, 142101 (2010); http://dx.doi.org/10.1063/1.3372636 (3 pages) | Cited 11 times

Online Publication Date: 5 April 2010

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The electronic properties of (Sb0.75Bi0.25)2Te3 compound are examined by using the full-potential linearized augmented plane-wave method. The transport coefficients are then calculated within the semiclassical Boltzmann theory, and further evaluated as a function of chemical potential assuming a rigid band picture and constant relaxation time. The ZT value is thus estimated by inserting an averaged thermal conductivity. Our theoretical calculations give a valuable insight on how to enhance the thermoelectric performance of this compound, and many potential doping elements and their optimal concentrations are suggested.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
71.15.-m Methods of electronic structure calculations
05.60.-k Transport processes

Impact of defect distribution on transport properties for Au/ZnO Schottky contacts formed with H2O2-treated unintentionally doped n-type ZnO epilayers

Sejoon Lee, Youngmin Lee, Deuk Young Kim, and Tae Won Kang

Appl. Phys. Lett. 96, 142102 (2010); http://dx.doi.org/10.1063/1.3374890 (3 pages) | Cited 10 times

Online Publication Date: 5 April 2010

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The Au/ZnO Schottky contacts fabricated using H2O2-treated unintentionally doped ZnO epilayers showed an abnormal behavior in their transport properties; i.e., the background carrier density-dependent trade-off relation between the barrier height and the ideality factor was observed. This result is attributed to the difference in carrier transport mechanisms for each sample fabricated using ZnO epilayers with different background carrier concentrations; namely, the observed trade-off relation originates from a result that the difference in the distribution of oxygen vacancies near the surface and depletion regions, which depends on the initial background carrier concentration of each sample, causes the different carrier transport mechanism.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.jd Vacancies
81.65.-b Surface treatments
73.50.Dn Low-field transport and mobility; piezoresistance

Charge transport in flat and nanorod structured ruthenium thin films

M. M. Steeves, D. Deniz, and R. J. Lad

Appl. Phys. Lett. 96, 142103 (2010); http://dx.doi.org/10.1063/1.3377006 (3 pages) | Cited 4 times

Online Publication Date: 5 April 2010

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Resistivities and Hall coefficients of flat and nanorod-structured Ru thin films were investigated from 295 to 600 K. Resistivities decreased upon first heating due to defect annealing, but Hall coefficients were found to be independent of temperature and defect content. The error in the Hall coefficient due to the Ettingshausen effect is shown to be negligible. Although resistivities and Hall coefficients of flat films are determined by a nominal film thickness, resistivities of nanorod-structured films are dominated by an ultrathin polycrystalline layer at the film-substrate interface and Hall coefficients appear to depend on an effective thickness determined by nanorod size and spacing.
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73.61.At Metal and metallic alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.15.Jf Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials

Evidence of electrical activity of extended defects in 3C–SiC grown on Si

X. Song, J. F. Michaud, F. Cayrel, M. Zielinski, M. Portail, T. Chassagne, E. Collard, and D. Alquier

Appl. Phys. Lett. 96, 142104 (2010); http://dx.doi.org/10.1063/1.3383233 (3 pages) | Cited 8 times

Online Publication Date: 6 April 2010

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In this paper, we demonstrate the high electrical activity of extended defects found in 3C–SiC heteroepitaxially grown layer on (100) silicon substrates. Cross-sectional scanning transmission electron microscopy analysis was performed to reveal the defects while scanning spreading resistance microscopy aimed to study their electrical behavior. Using this technique, complete layer resistance cartography was done. The electrical activity of the extended defects in 3C–SiC was clearly evidenced. Furthermore, the defect activity was estimated to be higher than that of heavily nitrogen doped (5×1018 cm−3) 3C–SiC layer.
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73.61.Le Other inorganic semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ma Scanning transmission electron microscopy (STEM)

Local electronic properties and magnetism of (Cd,Mn)Te quantum wells

L. Sangaletti, M. C. Mozzati, G. Drera, V. Aguekian, L. Floreano, A. Morgante, A. Goldoni, and G. Karczewski

Appl. Phys. Lett. 96, 142105 (2010); http://dx.doi.org/10.1063/1.3378811 (3 pages)

Online Publication Date: 7 April 2010

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The electronic properties of heterostructures containing (Cd,Mn)Te quantum wells are probed by soft x-ray spectroscopies. We provide experimental evidence that Mn ions are in the Mn2+ (3d5) electronic configuration, and rule out the possibility that charge transfer and crystal field effects can reduce the magnetic moment of each Mn ion to the value (0.61) extracted from the fitting of the magnetization curve with a Brillouin function. These results confirm that the observed magnetic behavior can be correctly explained by assuming an antiferromagnetic coupling between nearest-neighbor S = 5/2 Mn2+ ions, rather than a paramagnetic response from an ensemble of low-spin Mn ions.
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73.21.Fg Quantum wells
71.70.Ch Crystal and ligand fields
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
78.70.Dm X-ray absorption spectra
75.50.Pp Magnetic semiconductors

III-V-semiconductor-on-insulator n-channel metal-insulator-semiconductor field-effect transistors with buried Al2O3 layers and sulfur passivation: Reduction in carrier scattering at the bottom interface

Masafumi Yokoyama, Tetsuji Yasuda, Hideki Takagi, Noriyuki Miyata, Yuji Urabe, Hiroyuki Ishii, Hisashi Yamada, Noboru Fukuhara, Masahiko Hata, Masakazu Sugiyama, Yoshiaki Nakano, Mitsuru Takenaka, and Shinichi Takagi

Appl. Phys. Lett. 96, 142106 (2010); http://dx.doi.org/10.1063/1.3374447 (3 pages) | Cited 18 times

Online Publication Date: 7 April 2010

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We have developed III-V-semiconductor-on-insulator (III-V-OI) structures on Si wafers with excellent bottom interfaces between In0.53Ga0.47As-OI channel layers and atomic-layer-deposited Al2O3 (ALD-Al2O3) buried oxides (BOXs). A surface activated bonding process and the sulfur passivation pretreatment have realized the excellent In0.53Ga0.47As-OI/ALD-Al2O3 BOX bottom interface properties. As a result, the III-V-OI n-channel metal-insulator-semiconductor field-effect transistors under the back-gate configuration showed the peak mobility of 1800 cm2/V s and the higher electron mobility than the Si universal one even in the high effective electric field range because of the reduction in the surface roughness and fixed charges.
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85.30.Tv Field effect devices
81.65.Rv Passivation
72.20.Fr Low-field transport and mobility; piezoresistance
68.35.B- Structure of clean surfaces (and surface reconstruction)

Singlet-triplet transition in a few-electron lateral In0.75Ga0.25As/In0.75Al0.25As quantum dot

F. Deon, V. Pellegrini, F. Carillo, F. Giazotto, G. Biasiol, L. Sorba, and F. Beltram

Appl. Phys. Lett. 96, 142107 (2010); http://dx.doi.org/10.1063/1.3380821 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2010

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The magnetic-field evolution of Coulomb blockade peaks in lateral In0.75Ga0.25As/In0.75Al0.25As quantum dots in the few-electron regime is reported. Quantum dots are defined by gates evaporated onto a 60-nm-thick hydrogen silsesquioxane insulating film. A gyromagnetic factor g∗ ≈ 4.4 is measured via zero-bias spin spectroscopy and a transition from singlet to triplet spin configuration is found at an in-plane magnetic field B = 0.7 T. This observation opens the way to the manipulation of singlet and triplet states at moderate fields and its relevance for quantum information applications will be discussed.
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73.21.La Quantum dots
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
71.35.-y Excitons and related phenomena
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
03.67.-a Quantum information

Single-electron transistors based on self-assembled silicon-on-insulator quantum dots

Conrad R. Wolf, Klaus Thonke, and Rolf Sauer

Appl. Phys. Lett. 96, 142108 (2010); http://dx.doi.org/10.1063/1.3383235 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2010

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We present an approach to fabricate single-electron devices consisting of a silicon quantum dot (QD) between metallic leads. Silicon QDs are obtained by reactive ion etching into a silicon-on-insulator substrate partially protected by a self-assembled etch mask. Electrodes are fabricated and aligned to the QDs by an electromigration process whereby their native oxide serves as tunneling barrier. The devices show Coulomb blockade corresponding to a charging energy of 19.4 meV and can be switched from the nonconducting to a conducting state giving rise to Coulomb diamonds. The behavior is well reproduced by a numerical orthodox theory calculation.
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85.35.Gv Single electron devices
81.16.Dn Self-assembly
85.40.Hp Lithography, masks and pattern transfer
85.35.Ds Quantum interference devices
81.65.Cf Surface cleaning, etching, patterning

Scanning nanoelectrometer based on a two-dimensional electron gas transistor with a probe-integrated gate electrode

Yukio Kawano and Koji Ishibashi

Appl. Phys. Lett. 96, 142109 (2010); http://dx.doi.org/10.1063/1.3371766 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2010

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We report a scanning nanoelectrometer based on a two-dimensional electron gas (2DEG) transistor in GaAs/AlGaAs, whose gate electrode is combined with a metal-coated cantilever probe. In this system, local electric potential is detected through gate effects for the 2DEG detector caused by electrical polarization of the probe. Using this technique, we have demonstrated mapping of the electric potential distribution for 2DEG samples in a GaAs/AlGaAs interface and in a graphene surface. Time-resolved measurements of local potential are also presented.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices
07.68.+m Photography, photographic instruments; xerography

Characterization of fast charge trapping in bias temperature instability in metal-oxide-semiconductor field effect transistor with high dielectric constant

Minseok Jo, Seonghyun Kim, Joonmyoung Lee, Seungjae Jung, Ju-Bong Park, Hyung-Suk Jung, Rino Choi, and Hyunsang Hwang

Appl. Phys. Lett. 96, 142110 (2010); http://dx.doi.org/10.1063/1.3384999 (3 pages) | Cited 5 times

Online Publication Date: 7 April 2010

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We used pulse bias temperature instability measurements to investigate the energy distributions of fast charge trapping sources to understand the origin of fast charge traps in an HfO2 device. The trap energy level was extracted using a trap-to-band tunneling model by changing the measurement delay time. The fast electron traps in an n-channel metal oxide semiconductor field effect transistors (MOSFET) exist in a 1 eV range below the bottom of the HfO2 conduction band. In the case of a p-channel MOSFET, the fast hole traps exist in the range 1–2 eV above the top of the HfO2 valence band, which could be attributed to a formation of negatively charged NO defects.
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85.30.Tv Field effect devices

Dual functional modification by N doping of Ta2O5: p-type conduction in visible-light-activated N-doped Ta2O5

Takeshi Morikawa, Shu Saeki, Tomiko Suzuki, Tsutomu Kajino, and Tomoyoshi Motohiro

Appl. Phys. Lett. 96, 142111 (2010); http://dx.doi.org/10.1063/1.3386532 (3 pages) | Cited 11 times

Online Publication Date: 9 April 2010

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We report dual functional modulation, both p-type conduction and band gap narrowing, of Ta2O5 semiconductor induced by heavy doping of nitrogen in films sputtered in N2/Ar mixture and ammonia-treated powders. The N doping induced a redshift in the optical absorption edge from 320 to 500 nm, resulting in the absorption of visible light. Simultaneously, the N doping caused a change in the conduction from n-type to p-type. As a result, the N–Ta2O5 photoelectrode containing 7.6 or 16.1 at. % of N exhibited a distinct cathodic photocurrent (due to p-type conduction) in solutions under visible light irradiation (>410 nm).
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73.61.Le Other inorganic semiconductors
73.50.Pz Photoconduction and photovoltaic effects
71.20.Nr Semiconductor compounds
78.66.Li Other semiconductors
61.72.up Other materials
82.45.Fk Electrodes

Improved thermal stability of Al2O3/HfO2/Al2O3 high-k gate dielectric stack on GaAs

Dong Chan Suh, Young Dae Cho, Sun Wook Kim, Dae-Hong Ko, Yongshik Lee, Mann-Ho Cho, and Jungwoo Oh

Appl. Phys. Lett. 96, 142112 (2010); http://dx.doi.org/10.1063/1.3377915 (3 pages) | Cited 14 times

Online Publication Date: 9 April 2010

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Thermal stability of HfO2 high-k gate dielectric on GaAs is investigated. Compared to HfO2 gate dielectric, significant improvements in interfacial properties as well as electrical characteristics were found by constructing a Al2O3/HfO2/Al2O3 dielectric stack. At elevated temperatures, the amorphous Al2O3 layers were effective in inhibiting crystallization of HfO2. Since the passivating Al2O3 layers prevent interfacial oxide and trap charge formation, it aids in reducing the increasing rate of equivalent oxide thickness as well as capacitance-voltage hysteresis. Transmission electron microscopy and x-ray photoelectron spectroscopy data supported the improved electrical characteristic of GaAs metal-oxide-semiconductor capacitors with Al2O3/HfO2/Al2O3 gate dielectric stack.
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77.55.F- High-permittivity capacitive films
84.32.Tt Capacitors
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Lp Transmission electron microscopy (TEM)
68.60.Dv Thermal stability; thermal effects
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)

Simultaneous nickel silicidation and silicon crystallization induced by excimer laser annealing on plastic substrate

A. Alberti, A. La Magna, M. Cuscunà, G. Fortunato, and V. Privitera

Appl. Phys. Lett. 96, 142113 (2010); http://dx.doi.org/10.1063/1.3377916 (3 pages) | Cited 4 times

Online Publication Date: 9 April 2010

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Ni–Si reaction and α-Si crystallization on polyimide were simultaneously induced by excimer laser annealing. A ∼ 8 nm Ni film was deposited on Si in such a way that Ni atoms were also distributed within the α-Si layer. The role of Ni atoms during crystallization and surface silicidation was studied in the submelting regime and modeled by diffusion-reaction equations. It has been found that the starting Ni distribution in α-Si and the thermal gradient due to the plastic were crucial to induce Si crystallization. At a threshold of ∼ 0.2 J/cm2 melting is induced in the polycrystalline silicon layer and in the residual α-Si.
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64.70.kg Semiconductors
64.70.dj Melting of specific substances
82.20.-w Chemical kinetics and dynamics
81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids

Dual nature of acceptors in GaN and ZnO: The curious case of the shallow MgGa deep state

Stephan Lany and Alex Zunger

Appl. Phys. Lett. 96, 142114 (2010); http://dx.doi.org/10.1063/1.3383236 (3 pages) | Cited 10 times

Online Publication Date: 9 April 2010

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Employing a Koopmans corrected density functional method, we find that the metal-site acceptors Mg, Be, and Zn in GaN and Li in ZnO bind holes in deep levels that are largely localized at single anion ligand atoms. In addition to this deep ground state (DGS), we observe an effective-masslike delocalized state that can exist as a short lived shallow transient state (STS). The Mg dopant in GaN represents the unique case where the ionization energy of the localized deep level exceeds only slightly that of the shallow effective-mass acceptor, which explains why Mg works so exceptionally well as an acceptor dopant.
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71.55.Eq III-V semiconductors
71.55.Gs II-VI semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors
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