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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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Experimental, finite element, and density-functional theory study of inorganic nanotube compression

Estelle Kalfon-Cohen, Ohad Goldbart, Roy Schreiber, Sidney R. Cohen, David Barlam, Tommy Lorenz, Jan-Ole Joswig, and Gotthard Seifert

Appl. Phys. Lett. 98, 081908 (2011); http://dx.doi.org/10.1063/1.3556679 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2011

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Interactions between the walls in multiwalled nanotubes are key to determining their mechanical properties. Here, we report studies of radial deformation of multiwalled WS2 nanotubes in an atomic force microscope. The experimental results were fitted to a finite element model to determine the radial modulus. These results are compared with density-functional tight-binding calculations of a double-walled tube. Good agreement was obtained between experiment and calculations. The results indicate the importance of the sliding between layers in moderating the radial modulus. A plateau in the deformation curves is seen to have atomistic origins.
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81.07.De Nanotubes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

sp2-like hybridization of silicon valence orbitals in silicene nanoribbons

Paola De Padova, Claudio Quaresima, Bruno Olivieri, Paolo Perfetti, and Guy Le Lay

Appl. Phys. Lett. 98, 081909 (2011); http://dx.doi.org/10.1063/1.3557073 (3 pages) | Cited 14 times

Online Publication Date: 23 February 2011

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Silicene nanoribbons grown on a silver (110) substrate have been studied by reflection electron energy loss spectroscopy as a function of the electron beam incidence angle α. The spectra, taken at the Si K absorption edge (1.840 keV), reveal the presence of two distinct loss structures attributed to transitions 1s→π∗ and 1s→σ∗, according to their intensity dependence on α. Such behavior, when compared to graphite, attests the sp2-like hybridization of the silicon valence orbitals in the silicene nanoribbons as is, indeed, for carbon atomic bonds of graphene.
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79.20.Uv Electron energy loss spectroscopy
73.22.-f Electronic structure of nanoscale materials and related systems

Theory of ionic polymer conductor network composite

Xiao Wang (王宵) and Wei Hong (洪伟)

Appl. Phys. Lett. 98, 081910 (2011); http://dx.doi.org/10.1063/1.3555437 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2011

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Ionic polymer conductor network composite (IPCNC) is a mixed conductor consisting of a network of loaded ionomer and another network of metallic particles. It is known that the microstructure of the composite, especially that of the electrodes, plays a dominating role in the performance of an IPCNC. However, the microstructure of IPCNC has seldom been addressed in theoretical models. This letter formulates a continuum field theory for IPCNC by considering a supercapacitorlike microstructure with a large distributed interfacial area. The theory is then applied to the study of the equilibrium deformation and electrochemistry in a thin-sheet IPCNC actuator.
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66.30.Dn Theory of diffusion and ionic conduction in solids
82.45.Fk Electrodes
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Optically detected nuclear magnetic resonance in n-GaAs using an on-chip microcoil

Y. S. Chen, J. Huang, D. Reuter, A. Ludwig, A. D. Wieck, and G. Bacher

Appl. Phys. Lett. 98, 081911 (2011); http://dx.doi.org/10.1063/1.3553503 (3 pages)

Online Publication Date: 24 February 2011

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Optically detected nuclear magnetic resonance (NMR) with micrometer resolution is demonstrated in n-GaAs using an on-chip microcoil. To trace the Overhauser field, the electron Larmor frequency is monitored via time-resolved magneto-optical Kerr rotation. Sweeping the frequency of the rf magnetic field induced by an on-chip microscale current loop, nuclear spin depolarization is achieved for each isotope species. The experimental data indicate an impact of a local quadrupole field, most likely caused by ionized donors, on the amplitude and linewidth of the NMR spectrum. By applying rf pulse sequences, the Rabi oscillation of 75As nuclear spins is obtained with an effective dephasing time of ∼ 200 μs.
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76.70.Hb Optically detected magnetic resonance (ODMR)
78.47.D- Time resolved spectroscopy (>1 psec)
78.66.Fd III-V semiconductors
71.70.Jp Nuclear states and interactions
78.20.Ls Magneto-optical effects
76.60.-k Nuclear magnetic resonance and relaxation

Raman scattering from Ti3SiC2 single crystals

Frédéric Mercier, Odette Chaix-Pluchery, Thierry Ouisse, and Didier Chaussende

Appl. Phys. Lett. 98, 081912 (2011); http://dx.doi.org/10.1063/1.3558919 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2011

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The lack of single crystalline Ti3SiC2 samples is currently limiting the accurate measurement of its basic properties as its layered crystalline structure presents a very strong anisotropy. In this letter, we report the growth of pure Ti3SiC2 single crystals after a careful study of the Ti3SiC2 liquidus surface extent through thermodynamical calculations. From a Raman scattering study on those single crystals, an unambiguous assignment of most of the phonon modes has been established, giving an answer to the discrepancies existing in the literature.
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78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
65.40.G- Other thermodynamical quantities
81.10.Fq Growth from melts; zone melting and refining

UV-blue photoluminescence from close-packed SiC nanocrystal film

J. Y. Fan, H. X. Li, Q. J. Wang, D. J. Dai, and P. K. Chu

Appl. Phys. Lett. 98, 081913 (2011); http://dx.doi.org/10.1063/1.3556657 (3 pages) | Cited 7 times

Online Publication Date: 24 February 2011

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We observed stable photoluminescence from close-packed cubic SiC nanocrystals that are self-assembled into thin solid film. The peak wavelength shifts from blue to near UV with increasing excitation energy and follows well the quantum-confinement effect. The photoluminescence excitation spectrum indicates a 3.47 eV bandgap corresponding to a particle size of 2.3 nm. The nanocrystal film shows triple-exponential photoluminescence decay with lifetimes of 2.3, 8.5, and 36.9 ns. The results open the possibility of the solid state UV-blue light emitting by use of the SiC nanocrystals in photonics and photonics/electronics integration.
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78.66.Li Other semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Hk Nanocrystals
71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials
73.63.Bd Nanocrystalline materials

Thermally driven isotropic crystallinity breaking of nanocrystals: Insight into the assembly of EuS nanoclusters and nanorods with oleate ligands

Weidong He and James H. Dickerson

Appl. Phys. Lett. 98, 081914 (2011); http://dx.doi.org/10.1063/1.3560460 (3 pages) | Cited 5 times

Online Publication Date: 24 February 2011

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Clusters of EuS nanocrystals formed through the thermal assembly of 2.5 nm nanocrystal monomers by varying the annealing temperature from 300 to 340 °C. Below 310 °C, oleate ligands stabilized on the surface of the EuS nanocrystals, giving rise to their low solubility in triethanolamine while facilitating monomer–monomer oriented attachment into short-chain structures. Above 320 °C, the oleate ligands thermally detached from the surface and were replaced by oleyamine. This reaction mechanism was a multilevel oriented attachment, based on calculations of the nanocrystal growth kinetics, whose evolution gave rise to the formation of EuS nanorods at 340 °C.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments

Thermal rectification in bulk materials with asymmetric shape

D. Sawaki, W. Kobayashi, Y. Moritomo, and I. Terasaki

Appl. Phys. Lett. 98, 081915 (2011); http://dx.doi.org/10.1063/1.3559615 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2011

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We investigate thermal rectification in a bulk material with a pyramid shape to elucidate shape dependence of the thermal rectification, and find that rectifying coefficient R is 1.35 for this shape, which is smaller than R = 1.43 for a rectangular shape. This result is fully duplicated by our numerical calculation based on Fourier’s law. We also apply this calculation to a given shape, and show a possible way to increase R depending on the shape.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
02.30.Nw Fourier analysis

 Static and ultrafast dynamics of defects of SrTiO3 in LaAlO3/SrTiO3 heterostructures

X. Wang, J. Q. Chen, A. Roy Barman, S. Dhar, Q.-H. Xu, T. Venkatesan, and Ariando

Appl. Phys. Lett. 98, 081916 (2011); http://dx.doi.org/10.1063/1.3554705 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2011

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A detailed defect energy level map was investigated for heterostructures of 26 unit cells of LaAlO3 on SrTiO3 prepared at a low oxygen partial pressure of 10−6 mbar. The origin is attributed to the presence of dominating oxygen defects in SrTiO3 substrate. Using femtosecond laser spectroscopy, the transient absorption and relaxation times for various transitions were determined. An ultrafast relaxation process of 2–3 ps from the conduction band to the closest defect level and a slower process of 70–92 ps from conduction band to intraband defect level were observed. The results are discussed on the basis of the proposed defect-band diagram.
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71.55.Ht Other nonmetals
78.47.jb Transient absorption
61.72.jd Vacancies

A host sensitized reddish-orange Gd2MoO6:Sm3+ phosphor for light emitting diodes

Yan Chen, Jing Wang, Chunmeng Liu, Xiaojun Kuang, and Qiang Su

Appl. Phys. Lett. 98, 081917 (2011); http://dx.doi.org/10.1063/1.3557065 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2011

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An intense reddish-orange phosphor, Gd2MoO6:Sm3+, was developed by solid state chemistry. The photoluminescence excitation and emission spectra, concentration effect are investigated. The results show an efficient energy transfer from MoO66− group to Sm3+ occurs and Sm3+ ion emits an intense reddish-orange light with high color purity and an excellent reproduction quality of optical properties. These results demonstrate that Sm3+ ion with low 4f–4f absorption efficiency in near ultraviolet region can play a role of activator in narrow reddish-orange emitting phosphor potentially useful in ∼ 370 nm GaN-based light emitting diode through efficient energy feeding by charge transfer absorption of MoO66− group.
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85.60.Jb Light-emitting devices
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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.
Show PACS
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
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