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21 Feb 2011

Volume 98, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 081101 (2011); http://dx.doi.org/10.1063/1.3555489 (3 pages)

B. Cluzel, K. Foubert, L. Lalouat, J. Dellinger, D. Peyrade, E. Picard, E. Hadji, and F. de Fornel
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Defects in ZnO transparent conductors studied by capacitance transients at ZnO/Si interface

Baoe Li, Yutaka Adachi, Jianyong Li, Hedeyo Okushi, Isao Sakaguchi, Shigenori Ueda, Hideki Yoshikawa, Yoshiyuki Yamashita, Shoichi Senju, Keisuke Kobayashi, Masatomo Sumiya, Hajime Haneda, and Naoki Ohashi

Appl. Phys. Lett. 98, 082101 (2011); http://dx.doi.org/10.1063/1.3556440 (3 pages) | Cited 1 time

Online Publication Date: 22 February 2011

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Deep levels in heavily aluminum-doped zinc oxide (AZO) thin film were studied by transient capacitance (C-t) measurements and photoemission spectroscopy (PES). To study degenerated AZO by C-t measurements, AZO films were deposited on a p-type silicon (p-Si) substrate to form a depletion layer at the AZO/p-Si interface. Analyses of C-t behavior revealed that concentration of a trap level 0.3 eV below the bottom of the conduction was on the order of 1019 cm−3, which is 20%–50% of the shallow donor concentration. Such a high concentration of the trap level in AZO was evidenced by subsequent PES measurements.
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71.55.Gs II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors

On the kinetics of platinum silicide formation

Erik J. Faber, Rob A. M. Wolters, and Jurriaan Schmitz

Appl. Phys. Lett. 98, 082102 (2011); http://dx.doi.org/10.1063/1.3556563 (3 pages) | Cited 3 times

Online Publication Date: 22 February 2011

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In this work, the kinetics of platinum silicide formation for thin Pt films (50 nm) on monocrystalline 〈100〉 silicon is investigated via in situ resistance measurements under isothermal (197–275 °C) conditions. For Pt2Si diffusion limited growth was observed. For PtSi formation, however, no linear relation between silicide thickness and √t was found. PtSi growth over time could be described using the Avrami relation rendering Avrami exponent n = 1.4±0.1. Additionally, an effective activation energy EA = 1.7±0.1 eV was derived using the Avrami k values. The findings are important for obtaining well defined silicide films and silicide-to-silicon contacts.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
66.30.Dn Theory of diffusion and ionic conduction in solids
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Carbon doped InAlAs/InGaAs/InAs heterostructures: Tuning from n- to p-doping

M. Hirmer, D. Schuh, and W. Wegscheider

Appl. Phys. Lett. 98, 082103 (2011); http://dx.doi.org/10.1063/1.3557026 (3 pages) | Cited 1 time

Online Publication Date: 22 February 2011

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We fabricated carbon doped InAs/InxGa1−xAs/InxAl1−xAs heterostructures, which show p-type and n-type conductivity for different In contents. Two-dimensional hole gas in a structure with x = 0.75 has been prepared in the ternary compound, despite the fact that carbon as an n-type dopant in InAs exhibits electron conductivity in InxGa1−xAs and InxAl1−xAs compounds with high indium content. A special doping design has been employed to obtain hole conductivity. As a result, the conductivity can be tuned from n-type to p-type with the In content and with different doping profiles in these structures.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Schottky contacts on differently grown n-type ZnO single crystals

Vl. Kolkovsky, L. Scheffler, E. Hieckmann, E. V. Lavrov, and J. Weber

Appl. Phys. Lett. 98, 082104 (2011); http://dx.doi.org/10.1063/1.3558728 (3 pages) | Cited 8 times

Online Publication Date: 22 February 2011

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The preparation and characterization of Schottky contacts on differently grown n-type ZnO crystals was studied. We demonstrate that depending on the crystal growth process different procedures of surface treatment should be used to achieve good Schottky contacts. A treatment in a dc-hydrogen plasma enables us to fabricate Schottky contacts on hydrothermally grown ZnO, whereas a similar treatment of the vapor phase and melt grown ZnO resulted in the reduction in the diode rectification ratio. In the later samples a treatment in H2O2 significantly improves the quality of Schottky contacts. The origin of the different behavior will be discussed.
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices

Local piezoelectric effect on single crystal ZnO microbelt transverse I-V characteristics

M. Li, Y. J. Su, W. Y. Chu, L. J. Qiao, Alex A. Volinsky, and Grygoriy Kravchenko

Appl. Phys. Lett. 98, 082105 (2011); http://dx.doi.org/10.1063/1.3555456 (3 pages) | Cited 5 times

Online Publication Date: 22 February 2011

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One-dimensional ZnO microbelts were prepared by chemical vapor deposition on Si substrates with sputtered Pt film. Using Pt-coated atomic force microscope (AFM) tip, the belts’ transverse I-V characteristics were measured under varying applied elastic loads. ZnO microbelt conductivity reduced with load, but gradually increased upon unloading. Transverse electrical conductivity decrease at higher loads is attributed to the depletion zone formation induced by local piezoelectric effect in ZnO single crystal belt with (000math) top surface indented by the AFM tip. The observed effect can be utilized in a nanoforce sensor device.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.16.Be Chemical synthesis methods

InAs inserted InGaAs buried channel metal-oxide-semiconductor field-effect-transistors with atomic-layer-deposited gate dielectric

Fei Xue, Han Zhao, Yen-Ting Chen, Yanzhen Wang, Fei Zhou, and Jack C. Lee

Appl. Phys. Lett. 98, 082106 (2011); http://dx.doi.org/10.1063/1.3559609 (3 pages) | Cited 7 times

Online Publication Date: 23 February 2011

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Performance improvement of InGaAs buried channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) has been achieved by inserting InAs layer and properly designing the inserted layer position. In0.7Ga0.3As and InAs channel buried channel MOSFETs were fabricated and analyzed including drive current, transconductance, effective mobility, and subthreshold swing. All InAs buried channel devices show good off-state and saturation property. By inserting InAs in the middle of InGaAs channel (InGaAs/InAs/InGaAs channel), 37% enhancement of high field effective channel mobility was achieved over devices with pure InGaAs channel. Devices with InAs inserted in the middle exhibits peak effective channel mobility around 6140 cm2/V s and subthreshold swing of 107 mV/dec.
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85.30.Tv Field effect devices

Multiple phosphorus chemical sites in heavily phosphorus-doped diamond

Hiroyuki Okazaki, Rikiya Yoshida, Takayuki Muro, Tetsuya Nakamura, Takanori Wakita, Yuji Muraoka, Masaaki Hirai, Hiromitsu Kato, Satoshi Yamasaki, Yoshihiko Takano, Satoshi Ishii, Tamio Oguchi, and Takayoshi Yokoya

Appl. Phys. Lett. 98, 082107 (2011); http://dx.doi.org/10.1063/1.3554699 (3 pages) | Cited 3 times

Online Publication Date: 23 February 2011

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We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors

Strain-induced negative differential resistance in armchair-edge graphene nanoribbons

Hui Fang, Ru-Zhi Wang, Si-Ying Chen, Mi Yan, Xue-Mei Song, and Bo Wang

Appl. Phys. Lett. 98, 082108 (2011); http://dx.doi.org/10.1063/1.3556637 (3 pages) | Cited 6 times

Online Publication Date: 23 February 2011

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The transport properties of graphene strips under tensile strain have been theoretically investigated. For the armchair-edge graphene nanoribbons (GNRs) with width N = 3m−1, the additional negative differential resistance (NDR) undergoes a process from occurring to enhancement and then disappearance with increasing tensile strain. The changes in the additional NDR may be originated from the suppression of strain-mediated channel states for the variations in degenerate energy bands near Fermi level. The strain-induced NDR behaviors of the GNRs present the possibility of the potential applications in electromechanical nanodevices such as stress-controlled Goto pair for digital signal restoration.
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72.20.Ht High-field and nonlinear effects
72.80.Vp Electronic transport in graphene
73.22.Pr Electronic structure of graphene
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Influence of the p-type doping concentration on reflection-mode GaN photocathode

Xiaohui Wang, Benkang Chang, Ling Ren, and Pin Gao

Appl. Phys. Lett. 98, 082109 (2011); http://dx.doi.org/10.1063/1.3556656 (3 pages) | Cited 4 times

Online Publication Date: 23 February 2011

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Four different p-type doping GaN photocathodes are activated by Cs/O, and the quantum efficiency (QE) curves are obtained. According to the QE equation, the curves are fitted. Both the QE curves and the fitting results show that the optimal p-type doping concentration is at 1017 cm−3. The electron diffusion length and surface-electron escape probability can be balanced well at 1017 cm−3. To a certain degree, thick emission layer is conducive to improving the QE, which is more obvious with the long wavelength.
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71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
85.60.Ha Photomultipliers; phototubes and photocathodes
61.72.uj III-V and II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology

Spectroscopic measurements of the surface stoichiometry of chemical vapor deposited GaN

H. S. Craft, A. L. Rice, R. Collazo, Z. Sitar, and J.-P. Maria

Appl. Phys. Lett. 98, 082110 (2011); http://dx.doi.org/10.1063/1.3554762 (3 pages)

Online Publication Date: 23 February 2011

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We report on the surface stoichiometry of Ga-polar GaN films grown by metalorganic chemical vapor deposition as studied by x-ray photoelectron spectroscopy. GaN film surfaces are found to be Ga-rich, with Ga:N ratios ranging from 1.3:1 to 3.2:1. In vacuo ion-beam sputter/annealing studies show that these treatments drive the apparent Ga:N surface composition farther from unity, either through a decrease in surface contamination, oxidation of the surface, or both. Simple annealing experiments decrease the Ga:N ratio. The measured GaN ratio is correlated with the GaN growth time, suggesting that residual Ga precursor after growth interacts with the GaN surface as it cools.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.ag Semiconductors
81.65.Mq Oxidation

The effect of ZnO surface conditions on the electronic structure of the ZnO/CuPc interface

Sang Han Park, Hyo Jin Kim, Mann-Ho Cho, Yeonjin Yi, Sang Wan Cho, Jaehyun Yang, and Hyoungsub Kim

Appl. Phys. Lett. 98, 082111 (2011); http://dx.doi.org/10.1063/1.3555440 (3 pages) | Cited 4 times

Online Publication Date: 23 February 2011

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The interfacial electronic structures of zinc oxide (ZnO)/copper-phthalocyanine (CuPc) were investigated by in situ x-ray and ultraviolet photoelectron spectroscopy (UPS) to determine the effects of air contamination on the ZnO substrate. UPS spectra showed that the 0.2 eV of the interface dipole is generated at the interface of the air exposed ZnO/CuPc while the interface of the annealed ZnO/CuPc generated −0.2 eV. In both cases, no band bending was observed. On the other hand, band bending at 0.3 eV and an interface dipole of 0.2 eV were observed at the interface of the sputter cleaned ZnO/CuPc. The energy offset between the conduction band maximum of ZnO and the highest occupied molecular orbital of CuPc was determined to be 0.6–0.7 eV for the contaminated ZnO interface while the offset was 1.0 eV for the cleaned ZnO interface. Contaminating moisture has little effect on the offset while the charge transfer was blocked and the offset was decreased in the presence of hydrocarbons.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.72.Cc Kinetics of defect formation and annealing
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.15.Cd Deposition by sputtering

Improved germanium n+/p junction diodes formed by coimplantation of antimony and phosphorus

Jeehwan Kim, Stephen W. Bedell, and Devendra K. Sadana

Appl. Phys. Lett. 98, 082112 (2011); http://dx.doi.org/10.1063/1.3558715 (3 pages) | Cited 9 times

Online Publication Date: 24 February 2011

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Obtaining heavily-doped n-type germanium (Ge) is difficult since n-type dopant activation in Ge is limited to less than 5×1019 cm−3 which is far below the solid solubility limit of phosphorus (P) in Ge. Such poor activation has limited the rectifying properties of n+/p Ge diodes. This work is aimed at understanding the challenge of forming highly rectifying n+/p diode as well as enhancing rectification of n+/p diode by using antimony (Sb) and P coimplantation process. Enhanced n+ doping of greater than 1020 cm−3 in Ge obtained by Sb/P codoping results in enhanced rectification in Ge n+/p junction diode.
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85.30.Kk Junction diodes

Strain relief and AlSb buffer layer morphology in GaSb heteroepitaxial films grown on Si as revealed by high-angle annular dark-field scanning transmission electron microscopy

S. Hosseini Vajargah, M. Couillard, K. Cui, S. Ghanad Tavakoli, B. Robinson, R. N. Kleiman, J. S. Preston, and G. A. Botton

Appl. Phys. Lett. 98, 082113 (2011); http://dx.doi.org/10.1063/1.3551626 (3 pages) | Cited 13 times

Online Publication Date: 24 February 2011

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The interfacial misfit (IMF) dislocation array of an epitaxial GaSb film on a Si substrate has been imaged with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The mismatch strain accommodation through dislocation formation has been investigated using geometric phase analysis (GPA) on HAADF-STEM images with atomic resolution to probe the defects’ local strain distribution. These measurements indicate that the lattice parameter of the epitaxial film recovers its bulk value within three unit cells from the interface due to the relaxation through IMF dislocations. The atomic number contrast of the HAADF-STEM images and energy dispersive x-ray spectrometry illustrate the formation of islands of AlSb buffer layer along the interface. The role of the AlSb buffer layer in facilitating the GaSb film growth on Si is further elucidated by investigating the strain field of the islands with the GPA.
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68.55.ag Semiconductors
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
68.55.J- Morphology of films

Transient photocurrent and photovoltage studies on charge transport in dye sensitized solar cells made from the composites of TiO2 nanofibers and nanoparticles

Xiaoxu Wang, Sudeep Karanjit, Lifeng Zhang, Hao Fong, Qiquan Qiao, and Zhengtao Zhu

Appl. Phys. Lett. 98, 082114 (2011); http://dx.doi.org/10.1063/1.3560057 (3 pages) | Cited 5 times

Online Publication Date: 25 February 2011

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Herein, we report the transient photocurrent and photovoltage studies on the charge transport in dye sensitized solar cells (DSSCs) made from the composites of electrospun titanium oxide (TiO2) nanofibers, and conventional TiO2 nanoparticles. The results on charge transport parameters (including the charge recombination lifetime, the electron transport lifetime, and the diffusion length) indicated that the addition of TiO2 nanofibers into composite photoanodes led to substantial improvement on the efficiency of charge collection, suggesting that the composites of nanoparticles and one-dimensional nanostructures are promising materials for the development of DSSCs with high efficiency.
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88.40.H- Solar cells (photovoltaics)

Hole diffusivity in GaAsBi alloys measured by a picosecond transient grating technique

S. Nargelas, K. Jarašiūnas, K. Bertulis, and V. Pačebutas

Appl. Phys. Lett. 98, 082115 (2011); http://dx.doi.org/10.1063/1.3557047 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2011

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We applied a time-resolved transient grating technique for investigation of nonequilibrium carrier dynamics in GaAs1−xBix alloys with x = 0.025–0.063. The observed decrease in carrier bipolar diffusivity with lowering temperature and its saturation below 80 K revealed a strong localization of nonequilibrium holes. Thermal activation energy ΔEa = 46 meV of diffusivity and low hole mobility value μh = 10–20 cm2/V s at room temperature confirmed the hybridization model of the localized Bi states with the valence band of GaAs. Nonlinear increase in carrier recombination rate with the Bi content, 1/τR∝Bi(x)3.2 indicated an increasing structural disorder in the alloy.
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78.47.J- Ultrafast spectroscopy (<1 psec)
71.20.Lp Intermetallic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
66.30.-h Diffusion in solids

Observation of anomalous Hall effect in EuO epitaxial thin films grown by a pulse laser deposition

T. Yamasaki, K. Ueno, A. Tsukazaki, T. Fukumura, and M. Kawasaki

Appl. Phys. Lett. 98, 082116 (2011); http://dx.doi.org/10.1063/1.3557050 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2011

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We have found that there is a narrow but distinct window in oxygen pressure for growing phase-pure epitaxial EuO films by a pulsed laser deposition. With finely decreasing the oxygen pressure, the electrical property is varied from insulating to metallic with an enhancement in Curie temperature from 70 to 120 K. The anomalous Hall contribution was clearly observed in Hall resistance at 5 K in the highest electron density sample. The saturated anomalous Hall conductivity (0.2 S/cm) is rather high in comparison with those of the other ferromagnetic oxides, probably due to strong spin-orbit coupling in EuO.
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72.20.My Galvanomagnetic and other magnetotransport effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Fg Pulsed laser ablation deposition

Electronic fiber in graphene

Zhenhua Wu

Appl. Phys. Lett. 98, 082117 (2011); http://dx.doi.org/10.1063/1.3557500 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2011

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We investigate theoretically the transmission properties through a p-n-p junction on graphene. Here, we show that the electronic transport property presents deep analogies with light propagation. It originates from the similarity between the linear spectra of the Dirac fermions and photons that obey the Maxwell’s equations. We demonstrate that the p-n-p channel acts as an electronic fiber in which electrons propagate along the channel without dissipation.
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72.80.Vp Electronic transport in graphene
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