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26 Nov 2012

Volume 101, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 221101 (2012); http://dx.doi.org/10.1063/1.4767646 (5 pages)

Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso
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Conductance modulation of Si nanowire arrays

Chuanbo Li, Emiljana Krali, Kristel Fobelets, Buwen Cheng, and Qiming Wang

Appl. Phys. Lett. 101, 222101 (2012); http://dx.doi.org/10.1063/1.4768692 (3 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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The conductance modulation of vertically aligned Si nanowire arrays with ammonia is investigated. Ammonia adsorption on the surface of the nanowires (NWs) in the array greatly increases the electrical conductivity of n-type NWs. This effect can be potentially applied to boost figure of merit for thermoelectric applications by combining the phonon confinement effect of NWs with the electrical conductivity increase. By using 1/f noise measurements, the mechanism of conduction modulation is investigated. The enhancement of the electrical conduction is interpreted in terms of electron trap filling of the native oxide via ammonia adsorption.
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73.63.Nm Quantum wires
72.70.+m Noise processes and phenomena
68.43.Mn Adsorption kinetics

Flexible cobalt-phthalocyanine thin films with high charge carrier mobility

Ajay Singh, Arvind Kumar, Ashwini Kumar, Soumen Samanta, Anil K. Debnath, Purushottam Jha, Rajeshwar Prasad, Zakaria Salmi, Sophie Nowak, Mohamed M. Chehimi, Dinesh K. Aswal, and Shiv K. Gupta

Appl. Phys. Lett. 101, 222102 (2012); http://dx.doi.org/10.1063/1.4767990 (5 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of ∼118 cm2 V−1 s−1 (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J–V) to trap-free space-charge limited conduction (J–V2). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.
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68.55.ag Semiconductors
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Fq High-field and nonlinear effects
81.40.Lm Deformation, plasticity, and creep
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Effects of hydrogen on the electronic properties of Ga(AsBi) alloys

G. Pettinari, A. Patanè, A. Polimeni, M. Capizzi, Xianfeng Lu, and T. Tiedje

Appl. Phys. Lett. 101, 222103 (2012); http://dx.doi.org/10.1063/1.4768237 (5 pages)

Online Publication Date: 26 November 2012

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The effects of hydrogen incorporation on the electronic properties of Ga(AsBi) alloys are investigated in a wide range of Bi-concentration (0.6% ≤ x ≤ 10.6%) by Hall effect measurements in magnetic fields up to 14 T and by photoluminescence spectroscopy. For all the investigated Bi-concentrations, we report the passivation of Bi-induced shallow acceptor levels—responsible for the native p-type conductivity in Ga(AsBi)—and a tenfold increase of the hole mobility upon hydrogen incorporation in the host lattice. The emission energy is, instead, negligibly affected by hydrogenation, indicating that the narrowing of the band-gap energy with Bi and the native p-type conductivity are two uncorrelated effects arising from different Bi-induced electronic levels. Passivation by hydrogen of the shallow Bi-acceptor levels makes also possible to identify deep Bi-acceptor states.
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71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials
72.80.Sk Insulators
71.20.-b Electron density of states and band structure of crystalline solids
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

A combined first principle calculations and experimental study on the spin-polarized band structure of Co-doped PbPdO2

S. W. Chen, S. C. Huang, G. Y. Guo, S. Chiang, J. M. Lee, S. A. Chen, S. C. Haw, K. T. Lu, and J. M. Chen

Appl. Phys. Lett. 101, 222104 (2012); http://dx.doi.org/10.1063/1.4768293 (4 pages)

Online Publication Date: 26 November 2012

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With x-ray spectroscopy and first-principles calculations, we expose the electronic structure, near the Fermi level, of Co-doped PbPdO2 composed of O 2p-Pd 4d hybridized states with an additional contribution of a spin-polarized Co 3d state at either a greater or smaller energy. The spin-polarized Co 3d states interacting with O 2p-Pd 4d hybridized states cause spin splitting at the band edge. Fascinating physical properties such as high-temperature ferromagnetism thus arise in Co-doped PbPdO2. Results will help in the design of materials with desired electronic structures and the control of spin polarization with chemical doping.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra
75.50.Dd Nonmetallic ferromagnetic materials
61.72.up Other materials
71.15.-m Methods of electronic structure calculations

Influence of Ni impurities on the thermoelectric properties of Ca-partially filled skutterudites CaxCo4Sb12

M. Puyet, B. Lenoir, A. Dauscher, C. Candolfi, J. Hejtmanek, C. Stiewe, and E. Müller

Appl. Phys. Lett. 101, 222105 (2012); http://dx.doi.org/10.1063/1.4768439 (4 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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Polycrystalline samples of the skutterudite compounds CaxCo4Sb12 were synthesized and investigated by means of electrical resistivity, thermal conductivity, and thermopower in the 300–800 K temperature range. Additional Hall effect measurements were performed between 2 and 300 K. Both Ni-free and Ni-containing Co powders were used as starting materials to elucidate the impact of Ni impurities at the ppm level on the thermoelectric properties. The presence of minute amounts of Ni atoms in the crystal structure leads to enhanced thermopower values with respect to the Ni-free samples, likely associated with the development of additional electron pockets near the Fermi level. Ni impurities, thus, play a significant role on the transport properties and lead to a spectacular increase in the dimensionless thermoelectric figure of merit ZT of up to 150% at 800 K.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
61.66.Dk Alloys
61.72.S- Impurities in crystals

Femtosecond laser direct hard mask writing for selective facile micron-scale inverted-pyramid patterning of silicon

K. Kumar, K. K. C. Lee, P. R. Herman, J. Nogami, and N. P. Kherani

Appl. Phys. Lett. 101, 222106 (2012); http://dx.doi.org/10.1063/1.4768689 (5 pages) | Cited 1 time

Online Publication Date: 27 November 2012

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We report on the fabrication of high-fidelity inverted-pyramids in crystalline silicon (c-Si) at the 1 μm scale through the selective removal of a silicon nitride (SiNx) hard-mask with a 522 nm femtosecond (fs) laser and subsequent alkaline potassium hydroxide (KOH) etching. Through a series of systematic experiments on a range of hard-mask thicknesses, the use of 20 nm thick SiNx film yielded a 0.6 μm diameter laser-ejected aperture in the hard-mask at a single pulse fluence of 0.45 J cm−2, resulting in 1 μm wide inverted-pyramid structure in c-Si after KOH etching. Anisotropic KOH etching of the partially amorphized c-Si underlying the fs-laser patterned hard mask was found to render clean (111) planes of c-Si. An array of inverted-pyramids on c-Si surfaces as large as 4 cm2 was produced with a defect density of less than 1 in 104. This facile, non-contact, and cleanroom-independent technique serves a variety of applications including anti-reflective texturing of thin c-Si for photovoltaics, wafer marking, labeling, and fabrication of microfluidic and optical devices or laboratories on silicon wafers.
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81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
78.47.J- Ultrafast spectroscopy (<1 psec)

Deep level transient spectroscopy and minority carrier lifetime study on Ga-doped continuous Czochralski silicon

Yohan Yoon, Yixin Yan, Nels P. Ostrom, Jinwoo Kim, and George Rozgonyi

Appl. Phys. Lett. 101, 222107 (2012); http://dx.doi.org/10.1063/1.4766337 (4 pages)

Online Publication Date: 27 November 2012

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Continuous-Czochralski (c-Cz) crystal growth has been suggested as a viable technique for the fabrication of photovoltaic Si wafers due to its low resistivity variation of any dopant, independent of segregation, compared to conventional Cz. In order to eliminate light induced degradation due to boron-oxygen traps in conventional p-type silicon wafers, gallium doped wafers have been grown by c-Cz method and investigated using four point probe, deep level transient spectroscopy (DLTS), and microwave-photoconductance decay. Iron-gallium related electrically active defects were identified using DLTS as the main lifetime killers responsible for reduced non-uniform lifetimes in radial and axial positions of the c-Cz silicon ingot. A direct correlation between minority carrier lifetime and the concentration of electrically active Fe-Ga pairs was established.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors
81.10.Fq Growth from melts; zone melting and refining
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors

Tunable Dirac cone in the rectangular symmetrical semiconductor quantum dots array

Juan Peng, Zhen-Guo Fu, and Shu-Shen Li

Appl. Phys. Lett. 101, 222108 (2012); http://dx.doi.org/10.1063/1.4768939 (4 pages)

Online Publication Date: 27 November 2012

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We studied the electronic properties of a two-dimensional (2D) rectangular symmetrical semiconductor quantum dots (QD) lattice and found a type of tunable Dirac cone structure in its energy spectrum by using tight-binding method. We show that, by tuning the parameters of the QD lattice, the energy gap could be closed and form the Dirac cone. A phase diagram of transition from the gap opening to the gapless state is also obtained. Furthermore, we found the Dirac cone is anisotropic, implying direction-dependent electronic properties and conductivities. These findings may be useful for the development and application of high-speed semiconductor QD devices.
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68.65.Hb Quantum dots (patterned in quantum wells)
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Nr Semiconductor compounds
73.21.La Quantum dots
81.07.Ta Quantum dots
64.70.-p Specific phase transitions

Impurity-limited lattice disorder recovery in ion-implanted ZnO

A. Yu. Azarov, B. G. Svensson, and A. Yu. Kuznetsov

Appl. Phys. Lett. 101, 222109 (2012); http://dx.doi.org/10.1063/1.4768289 (4 pages) | Cited 1 time

Online Publication Date: 27 November 2012

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The presence of implanted impurities can affect intrinsic defect annihilation or, in macroscopic terms, so-called lattice recovery, specifically in high dose implantation experiments typically applied to radiation hard materials, e.g., ZnO. Correlating diffusion and lattice recovery data, we demonstrate that F bombardment of ZnO results in a unique situation when implantation induced disorder anneals at anomalously low temperatures, specifically due to the F outdiffusion from the disordered region. Control F + B implants resulted in the suppression of F diffusion and stabilization of the lattice disorder providing the evidence for impurity-limited lattice recovery.
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61.72.uj III-V and II-VI semiconductors
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

Band alignment in Ge/GeOx/HfO2/TiO2 heterojunctions as measured by hard x-ray photoelectron spectroscopy

A. K. Rumaiz, J. C. Woicik, C. Weiland, Q. Xie, D. P. Siddons, G. H. Jaffari, and C. Detavernier

Appl. Phys. Lett. 101, 222110 (2012); http://dx.doi.org/10.1063/1.4768947 (4 pages)

Online Publication Date: 27 November 2012

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We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bilayer metal-oxide-semiconductor sandwich with an amorphous plasma enhanced atomic layer deposited (PE-ALD) HfO2 IL and PE-ALD grown TiO2 high k gate dielectric using hard x-ray photoelectron spectroscopy. The native Ge oxide shifts to higher oxidation state as the thickness of the IL layer was increased. The Hf 4f core line shows a broadening with increasing thickness, indicating the formation of Hf-Ge germanate. We observed a deviation from the bulk offset for films with ultra thin layers of HfO2.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
77.55.D- High-permittivity gate dielectric films
73.20.At Surface states, band structure, electron density of states

Observation of the generation of stacking faults and active degradation measurements on off-axis and on-axis 4H-SiC PiN diodes

N. Thierry-Jebali, J. Hassan, M. Lazar, D. Planson, E. Bano, A. Henry, E. Janzén, and P. Brosselard

Appl. Phys. Lett. 101, 222111 (2012); http://dx.doi.org/10.1063/1.4768440 (4 pages)

Online Publication Date: 27 November 2012

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PiN diodes have been fabricated on nominally on-axis Si-face 4H-SiC material and their electrical characteristics are compared to PiN diodes processed with exactly the same device process recipe on 8°-off 4H-SiC material. Some diodes had an optical window on the top metal contact to observe the possible stacking faults generation and motion with photo emission microscopy. The diodes were electrically characterized in forward voltage to test their stability. Electrical characterizations demonstrate that there is no noticeable degradation for the diodes processed on on-axis 4H-SiC substrate and with optical characterization the formation of stacking faults was not observed.
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85.30.Kk Junction diodes
61.72.Nn Stacking faults and other planar or extended defects

High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy

Naoya Miyashita, Nazmul Ahsan, Makoto Inagaki, Muhammad Monirul Islam, Masafumi Yamaguchi, and Yoshitaka Okada

Appl. Phys. Lett. 101, 222112 (2012); http://dx.doi.org/10.1063/1.4768949 (4 pages)

Online Publication Date: 28 November 2012

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We report the highest mobility values above 2000 cm2/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.
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73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Carrier multiplication in bulk indium nitride

S. A. Jensen, J. Versluis, E. Cánovas, J. J. H. Pijpers, I. R. Sellers, and M. Bonn

Appl. Phys. Lett. 101, 222113 (2012); http://dx.doi.org/10.1063/1.4766738 (4 pages)

Online Publication Date: 30 November 2012

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Carrier multiplication (CM) is the process of generating multiple electron-hole pairs from one absorbed photon. Narrow-gap InN is a material that has been proposed for achieving efficient CM. We quantify the CM efficiency in bulk InN using terahertz time-domain spectroscopy. While the CM onset occurs at relatively low photon energies in InN (1.7 ± 0.2 eV), corresponding to 2.7 ± 0.3 times its bandgap, the excitation efficiency above the onset increases linearly with a slope of only ∼13%/Eg. Based on these numbers, the efficiency increase of an InN based photovoltaic device owing to CM is limited to maximum 1% point.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions

Low-voltage zinc oxide thin-film transistors with solution-processed channel and dielectric layers below 150 °C

Xiaoli Xu, Qingyu Cui, Yizheng Jin, and Xiaojun Guo

Appl. Phys. Lett. 101, 222114 (2012); http://dx.doi.org/10.1063/1.4769091 (3 pages)

Online Publication Date: 30 November 2012

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In this letter, solution processed low voltage (<3 V) zinc oxide (ZnO) thin-film transistors with the maximum process temperature not exceeding 150 °C were achieved. In the devices, an ultra-thin zirconium oxide layer was formed as the gate dielectric via ultraviolet irradiation assisted sol-gel processes, and the ZnO channel was processed from an aqueous precursor of ammine-hydroxo zinc complex. The devices can be operated under a voltage of 3 V, and show decent device performance with the field effect mobility of 0.45 cm2/V · s and an ON/OFF current ratio of 105.
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85.30.Tv Field effect devices
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