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16 Aug 2010

Volume 97, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 073101 (2010); http://dx.doi.org/10.1063/1.3478515 (3 pages)

Hon-Way Lin (林弘偉), Yu-Jung Lu (呂宥蓉), Hung-Ying Chen (陳虹穎), Hong-Mao Lee (李弘貿), and Shangjr Gwo (果尚志)
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Role of twin boundaries in semiconductor to metal transition characteristics of VO2 films

Tsung-Han Yang, Chunming Jin, Honghui Zhou, Roger J. Narayan, and J. Narayan

Appl. Phys. Lett. 97, 072101 (2010); http://dx.doi.org/10.1063/1.3481075 (3 pages) | Cited 6 times

Online Publication Date: 16 August 2010

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Epitaxial (002) VO2 films were grown on c-sapphire with Ga:ZnO and ZnO buffer layers. We investigated the influence of twin boundaries on the semiconductor-to-metal transition (SMT) characteristics of VO2, when current flows parallel and perpendicular to the twin boundaries. The structure of the twin boundary was kept the same for these two configurations. The hysteresis in SMT characteristics is considerably reduced when current flows parallel to the boundaries compared to that in the normal direction of the boundaries. We present a model to explain these observations and discuss the role of these boundaries on the SMT characteristics, and the importance of grain boundary engineering in the design of VO2 based devices.
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61.72.Mm Grain and twin boundaries
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.A- Nucleation and growth
81.05.Dz II-VI semiconductors

Evolution of pyramid morphology during InAs(001) homoepitaxy

J. Bubesh Babu and Kanji Yoh

Appl. Phys. Lett. 97, 072102 (2010); http://dx.doi.org/10.1063/1.3481077 (3 pages) | Cited 2 times

Online Publication Date: 16 August 2010

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Growth of InAs(001) homoepitaxial layer has been carried out especially at the bistable region, where the coexistence of both In-stabilized (4×2) and As-stabilized (2×4) surface reconstruction are found to be predominant. The observation of pyramid morphology in this bistable region is reported here. Atomic force microscopy studies have been performed on such pyramids. The heights of the observed pyramids vary from 12 to 26 nm with their bases from 3.6×1.2 to 18×6.3 μm2. Formation of such pyramids in the bistable region is attributed to the unique anomalous As-desorption observed during the surface reconstruction.
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81.05.Ea III-V semiconductors
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
68.35.bg Semiconductors
68.43.Nr Desorption kinetics

High electron mobility In2O3(001) and (111) thin films with nondegenerate electron concentration

Oliver Bierwagen and James S. Speck

Appl. Phys. Lett. 97, 072103 (2010); http://dx.doi.org/10.1063/1.3480416 (3 pages) | Cited 12 times

Online Publication Date: 16 August 2010

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Temperature dependent Hall measurements were applied to demonstrate, semiconducting n-type high-quality In2O3(001) and (111) thin films with nondegenerate unintentionally doped (UID) electron concentrations on the order of 1017 cm−3 at room temperature, which is below those of bulk single crystals. The freeze-out of the electron concentration in all samples suggests a shallow UID donor with ionization energy in the 17 meV range. Postgrowth annealing in oxygen allowed to further decrease the UID electron concentration with simultaneous mobility increase, suggesting oxygen vacancies to be the shallow UID donors. Hall mobilities above 200 cm2/V s at room temperature and 1000 cm2/V s at low temperatures exceed those of bulk single crystals and demonstrate high material quality and purity.
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72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.jd Vacancies

Experimental determination of wave function spread in Si inversion layers

Amlan Majumdar

Appl. Phys. Lett. 97, 072104 (2010); http://dx.doi.org/10.1063/1.3473771 (3 pages)

Online Publication Date: 17 August 2010

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We have experimentally determined the extent of wave function spread TQM in Si inversion layers on (100)-oriented surface in metal-oxide-semiconductor field-effect transistors (MOSFETs) using the back gate bias sensitivity of front gate threshold voltage of planar fully depleted silicon-on-insulator (SOI) MOSFETs. We show that the sum of TQM for large positive and negative F is an electrically determined value of the SOI thickness TSI. We find that the electric field dependence of TQM for electrons and holes is given by TQM ∼ F−0.4 and F−0.6, respectively, at high electric fields with TQM being larger for holes at a given F. Larger TQM for holes can be explained by the fact that holes have a smaller effective mass along the confinement direction than electrons in (100) Si. The field dependences of TQM are, however, not consistent with the results of variational calculations that assume single-subband occupancy and predict TQM ∼ F−1/3. The discrepancy likely indicates that the effects of multiple-subband occupation are significant at room temperature, especially for holes.
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85.30.Tv Field effect devices
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Impact of solid-phase crystallization of amorphous silicon on the chemical structure of the buried Si/ZnO thin film solar cell interface

M. Bär, M. Wimmer, R. G. Wilks, M. Roczen, D. Gerlach, F. Ruske, K. Lips, B. Rech, L. Weinhardt, M. Blum, S. Pookpanratana, S. Krause, Y. Zhang, C. Heske, W. Yang, et al.

Appl. Phys. Lett. 97, 072105 (2010); http://dx.doi.org/10.1063/1.3462316 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2010

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The chemical interface structure between phosphorus-doped hydrogenated amorphous silicon and aluminum-doped zinc oxide thin films is investigated with soft x-ray emission spectroscopy (XES) before and after solid-phase crystallization (SPC) at 600 °C. In addition to the expected SPC-induced phase transition from amorphous to polycrystalline silicon, our XES data indicates a pronounced chemical interaction at the buried Si/ZnO interface. In particular, we find an SPC-enhanced formation of Si–O bonds and the accumulation of Zn in close proximity to the interface. For an assumed closed and homogeneous SiO2 interlayer, an effective thickness of (5±2) nm after SPC could be estimated.
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88.40.H- Solar cells (photovoltaics)
68.35.Ct Interface structure and roughness

High temperature Luttinger liquid conductivity in carbon nanotube bundles

B. A. Danilchenko, L. I. Shpinar, N. A. Tripachko, E. A. Voitsihovska, S. E. Zelensky, and B. Sundqvist

Appl. Phys. Lett. 97, 072106 (2010); http://dx.doi.org/10.1063/1.3467464 (3 pages) | Cited 4 times

Online Publication Date: 17 August 2010

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The conductance and the current-voltage characteristics of metallic single wall carbon nanotube bundles have been measured between 4.2 and 330 K using 10–30 ns electric pulses to avoid overheating. The current-voltage characteristics at different temperatures collapse to a single curve when plotted in the specific coordinates following from the Tomonaga–Luttinger (T–L) liquid concept. Direct evidence is obtained for the existence of a T–L liquid phase up to 190 K and the system shows a transition between the T–L liquid state and a Mott insulating phase below 25 K.
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81.07.De Nanotubes
73.63.Fg Nanotubes
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)
61.46.Fg Nanotubes

A study on the modulation of the electrical transport by mechanical straining of individual titanium dioxide nanotube

A. Asthana, T. Shokuhfar, Q. Gao, P. Heiden, C. Friedrich, and R. S. Yassar

Appl. Phys. Lett. 97, 072107 (2010); http://dx.doi.org/10.1063/1.3466663 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2010

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We report here, the deformation driven modulation of the electrical transport properties of an individual TiO2 nanotube via in situ transmission electron microscopy (TEM) using a scanning tunneling microscopy system. The current-voltage characteristics of each individual TiO2 nanotube revealed that under bending deformation within the elastic limit, the electrical conductivity of a TiO2 nanotube can be enhanced. High resolution TEM and electron diffraction pattern reveal that TiO2 nanotubes have tetragonal structure (a = 0.378 nm, c = 0.9513 nm, I41/amd). Analysis based on a metal-semiconductor-metal model suggests that in-shell, surface defect-driven conduction modes and electron–phonon coupling effect are responsible for the modulated semiconducting behaviors.
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72.80.-r Conductivity of specific materials
62.20.F- Deformation and plasticity
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
73.40.Sx Metal-semiconductor-metal structures

Doping- and size-dependent photovoltaic properties of p-type Si-quantum-dot heterojunction solar cells: correlation with photoluminescence

Seung Hui Hong, Jae Hee Park, Dong Hee Shin, Chang Oh Kim, Suk-Ho Choi, and Kyung Joong Kim

Appl. Phys. Lett. 97, 072108 (2010); http://dx.doi.org/10.1063/1.3480609 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2010

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Boron-doped SiOx/SiO2 superlattices have been prepared on n-type Si (100) wafers by ion beam sputtering and subsequently annealed to form p-type Si quantum dots (QDs)/n-type Si-wafer heterojunction solar cells. Systematic studies on photoluminescence (PL) and photovoltaic effects show that optimum formation of Si QDs, proper doping concentration (nB), and minimization of defects are crucial factors for enhancing energy-conversion efficiency of the solar cells. Highest efficiency of 9.5% is obtained under the conditions of x = 1.0 (QD size: ∼ 5 nm) and nB = 6.3×1020 cm−3. Possible physical mechanisms are discussed to explain the correlation of the photovoltaic parameters and the QD-/defect-PL intensities. The demonstration of the photovoltaic effects in the Si-QD heterojunction solar cells is promising for the development of next-generation all-Si-QD solar cells.
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73.50.Pz Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
88.40.jj Silicon solar cells
61.72.uf Ge and Si

Bipolar resistance switching driven by tunnel barrier modulation in TiOx/AlOx bilayered structure

Seung Jae Baik and Koeng Su Lim

Appl. Phys. Lett. 97, 072109 (2010); http://dx.doi.org/10.1063/1.3481076 (3 pages) | Cited 2 times

Online Publication Date: 18 August 2010

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A TiOx/AlOx resistance switching device was investigated as a prototype of a bilayered structure composed of a “transport layer” and a “tunnel layer.” Study of its carrier transport led to the conclusion that resistance switching is driven by the modulation of the AlOx tunnel barrier. Redox in the AlOx layer causes the decrease in tunneling resistance that scales with the inverse of the area. The appropriate switching characteristics in a bilayered structure can be obtained by adopting a tunnel layer that has a higher lattice binding energy than the transport layer.
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84.32.Dd Connectors, relays, and switches

Influence of doping at the nanoscale at LaAlO3/SrTiO3 interfaces

T. Fix, F. Schoofs, J. L. MacManus-Driscoll, and M. G. Blamire

Appl. Phys. Lett. 97, 072110 (2010); http://dx.doi.org/10.1063/1.3481353 (3 pages) | Cited 7 times

Online Publication Date: 18 August 2010

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The origin of the free charge layer which forms at the LaAlO3/SrTiO3 interface is still uncertain. By varying the doping concentration and the nature of the dopant in SrTiO3 at the LaAlO3/SrTiO3 interface, we show the extreme sensitivity of the system and confirm that the underlying phenomenon accounting for the conduction is most likely an electronic reconstruction. We explain that although doping these interfaces might be useful to induce additional properties such as ferromagnetism or useful to probe the electronic reconstruction, undoped interfaces provide the highest carrier density.
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73.63.Rt Nanoscale contacts
73.40.-c Electronic transport in interface structures
61.72.sd Impurity concentration
75.50.Dd Nonmetallic ferromagnetic materials

Sputtering formation of p-type SnO thin-film transistors on glass toward oxide complimentary circuits

Hisato Yabuta, Nobuyuki Kaji, Ryo Hayashi, Hideya Kumomi, Kenji Nomura, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 97, 072111 (2010); http://dx.doi.org/10.1063/1.3478213 (3 pages) | Cited 13 times

Online Publication Date: 18 August 2010

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Thin film transistors (TFTs) using polycrystalline tin oxides (SnO–SnO2) channels were formed on glass by a conventional sputtering method and subsequent annealing treatments. SnO-channel TFTs showed p-type operation with on/off current ratios of ∼ 102 and field-effect mobilities of 0.24 cm2 V−1 s−1. Incorporation of excess oxygen to SnO channel layers did not generate holes but did electrons, which in turn led to n-type operation. This result is explained by transformation to a local SnO2-like structure and finally to SnO2. We propose a simple method to fabricate complimentary circuits by simultaneous selective formation of p- and n-channel TFTs.
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85.30.Tv Field effect devices

Alternative sources of p-type conduction in acceptor-doped ZnO

Sukit Limpijumnong, Luke Gordon, Maosheng Miao, Anderson Janotti, and Chris G. Van de Walle

Appl. Phys. Lett. 97, 072112 (2010); http://dx.doi.org/10.1063/1.3481069 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2010

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We report first-principles calculations and interface simulations for Zn3P2, a compound that may form during doping of ZnO with phosphorous. While P is a deep acceptor in ZnO and thus unable to produce p-type conductivity, we show that hole accumulation can occur at ZnO/Zn3P2 interfaces due to the unusual valence-band alignment between the two materials. This provides an explanation for the hole conductivity that has been observed in Hall measurements on phosphorous-doped ZnO.
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71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors

Highly conductive ZnO grown by pulsed laser deposition in pure Ar

Robin C. Scott, Kevin D. Leedy, Burhan Bayraktaroglu, David C. Look, and Yong-Hang Zhang

Appl. Phys. Lett. 97, 072113 (2010); http://dx.doi.org/10.1063/1.3481372 (3 pages) | Cited 8 times

Online Publication Date: 19 August 2010

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Ga-doped ZnO was deposited by pulsed laser deposition at 200 °C on SiO2/Si, Al2O3, or quartz in 10 mTorr of pure Ar. The as-grown, bulk resistivity at 300 K is 1.8×10−4 Ω cm, three-times lower than that of films deposited at 200 °C in 10 mTorr of O2 followed by an anneal at 400 °C in forming gas. Furthermore, depth uniformity of the electrical properties is much improved. Mobility analysis shows that this excellent resistivity is mostly due to an increase in donor concentration, rather than a decrease in acceptor concentration. Optical transmittance is approximately 90% in the visible and near-IR spectral regions.
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81.15.Fg Pulsed laser ablation deposition
78.40.Fy Semiconductors
73.61.Ga II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.sd Impurity concentration
68.55.ag Semiconductors

Determination of diffusion lengths in nanowires using cathodoluminescence

Anders Gustafsson, Jessica Bolinsson, Niklas Sköld, and Lars Samuelson

Appl. Phys. Lett. 97, 072114 (2010); http://dx.doi.org/10.1063/1.3473829 (3 pages) | Cited 6 times

Online Publication Date: 19 August 2010

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We used cathodoluminescence imaging to determine diffusion lengths in III-V semiconductor nanowires, grown by metal-organic chemical vapor deposition seeded by gold nanoparticles. Intensity profiles were recorded either from the interface between the substrate and homogeneous nanowires, or from segments in nanowires containing axial heterostructures to determine the diffusion length. We determined diffusion lengths of 0.10 to 0.90 μm, the shortest for uncapped wires. The reduction is attributed largely to surface recombination.
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78.67.Lt Quantum wires
78.67.Uh Nanowires
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
73.25.+i Surface conductivity and carrier phenomena

Impact of nitrogen incorporation on pseudomorphic site-controlled quantum dots grown by metalorganic vapor phase epitaxy

V. Dimastrodonato, L. O. Mereni, G. Juska, and E. Pelucchi

Appl. Phys. Lett. 97, 072115 (2010); http://dx.doi.org/10.1063/1.3481675 (3 pages) | Cited 4 times

Online Publication Date: 20 August 2010

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We report on some surprising optical properties of diluted nitride InGaAs1−εNε/GaAs (ε⪡1) pyramidal site-controlled quantum dots, grown by metalorganic vapor phase epitaxy on patterned GaAs (111)B substrates. Microphotoluminescence characterizations showed antibinding exciton/biexciton behavior, a spread of exciton lifetimes in an otherwise very uniform sample, with unexpected long neutral exciton lifetimes (up to 7 ns) and a nearly zero fine structure splitting on a majority of dots.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
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