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28 Jan 2013

Volume 102, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 102, 041101 (2013); http://dx.doi.org/10.1063/1.4777564 (5 pages)

K. Winkler, C. Schneider, J. Fischer, A. Rahimi-Iman, M. Amthor, A. Forchel, S. Reitzenstein, S. Höfling, and M. Kamp
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Atom probe study of Cu2ZnSnSe4 thin-films prepared by co-evaporation and post-deposition annealing

T. Schwarz, O. Cojocaru-Mirédin, P. Choi, M. Mousel, A. Redinger, S. Siebentritt, and D. Raabe

Appl. Phys. Lett. 102, 042101 (2013); http://dx.doi.org/10.1063/1.4788815 (4 pages) | Cited 2 times

Online Publication Date: 28 January 2013

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We use atom probe tomography (APT) for resolving nanometer scale compositional fluctuations in Cu2ZnSnSe4 (CZTSe) thin-films prepared by co-evaporation and post-deposition annealing. We detect a complex, nanometer–sized network of CZTSe and ZnSe domains in these films. Some of the ZnSe domains contain precipitates having a Cu- and Sn-rich composition, where the composition cannot be assigned to any of the known equilibrium phases. Furthermore, Na impurities are found to be segregated at the CZTSe/ZnSe interface. The insights given by APT are essential for understanding the growth of CZTSe absorber layers for thin-film solar cells and for optimizing their optoelectronic properties.
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81.15.Dj E-beam and hot filament evaporation deposition
64.75.-g Phase equilibria
68.55.ag Semiconductors

Defect enhanced funneling of diffusion current in silicon

S. Azimi, Z. Y. Dang, J. Song, M. B. H. Breese, E. Vittone, and J. Forneris

Appl. Phys. Lett. 102, 042102 (2013); http://dx.doi.org/10.1063/1.4789849 (5 pages) | Cited 1 time

Online Publication Date: 29 January 2013

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We report a current transport mechanism observed during electrochemical anodization of ion irradiated p-type silicon, in which a hole diffusion current is highly funneled along the gradient of modified doping profile towards the maximum ion induced defect density, dominating the total current flowing and hence the anodization behaviour. This study is characterized within the context of electrochemical anodization but relevant to other fields where any residual defect density may result in similar effects, which may adversely affect performance, such as in wafer gettering or satellite-based microelectronics. Increased photoluminescence intensity from localized buried regions of porous silicon is also shown.
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66.30.Lw Diffusion of other defects
78.55.Ap Elemental semiconductors
81.65.-b Surface treatments

Resistive switching mechanism in silicon highly rich SiOx (x < 0.75) films based on silicon dangling bonds percolation model

Yuefei Wang, Xinye Qian, Kunji Chen, Zhonghui Fang, Wei Li, and Jun Xu

Appl. Phys. Lett. 102, 042103 (2013); http://dx.doi.org/10.1063/1.4776695 (5 pages)

Online Publication Date: 29 January 2013

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The unipolar resistive switches are investigated in silicon highly rich SiOx (x < 0.75) films. The as-deposited SiO0.73 films contain high concentration (1.0 × 1019 cm−3) of silicon dangling bonds (Si-DBs) and are rich in SiO2≡Si–Si and O3≡Si–Si configurations. Unlike the currently reported normal silicon-rich SiOx (x > 1.8) based devices, our Pt/SiO0.73/Pt devices operate at lower voltage regime (<2.0 V) and exhibit much lower resistance (∼30 Ω). The reset voltage (∼0.7 V) is lower than set voltage (∼1.7 V) and the performance is reduced in the vacuum environment. We propose a Si-DBs percolation model to explain the above characteristics. The experimental evidences for supporting our model are presented and discussed.
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72.60.+g Mixed conductivity and conductivity transitions
77.55.-g Dielectric thin films
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High mobility ambipolar MoS2 field-effect transistors: Substrate and dielectric effects

Wenzhong Bao, Xinghan Cai, Dohun Kim, Karthik Sridhara, and Michael S. Fuhrer

Appl. Phys. Lett. 102, 042104 (2013); http://dx.doi.org/10.1063/1.4789365 (4 pages) | Cited 7 times

Online Publication Date: 29 January 2013

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We fabricate MoS2 field effect transistors on both SiO2 and polymethyl methacrylate (PMMA) dielectrics and measure charge carrier mobility in a four-probe configuration. For multilayer MoS2 on SiO2, the mobility is 30–60 cm2/Vs, relatively independent of thickness (15–90 nm), and most devices exhibit unipolar n-type behavior. In contrast, multilayer MoS2 on PMMA shows mobility increasing with thickness, up to 470 cm2/Vs (electrons) and 480 cm2/Vs (holes) at thickness ∼50 nm. The dependence of the mobility on thickness points to a long-range dielectric effect of the bulk MoS2 in increasing mobility.
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85.30.Tv Field effect devices

On the mechanism of recombination at oxide precipitates in silicon

J. D. Murphy, K. Bothe, V. V. Voronkov, and R. J. Falster

Appl. Phys. Lett. 102, 042105 (2013); http://dx.doi.org/10.1063/1.4789858 (5 pages)

Online Publication Date: 30 January 2013

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Oxide precipitates are well known to degrade minority carrier lifetime in silicon, but the mechanism by which they act as recombination centres is not fully understood. We report minority carrier lifetime measurements on oxide precipitate-containing silicon which has been intentionally contaminated with iron. Analysis of the injection-dependence of lifetime demonstrates the same recombination centres exist in iron-contaminated and not intentionally contaminated samples, with the state density scaling with iron loss from the bulk. This shows that recombination activity arises from impurity atoms segregated to oxide precipitates and/or surrounding crystallographic defects.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
81.30.Mh Solid-phase precipitation
61.72.sh Impurity distribution
64.75.Qr Phase separation and segregation in semiconductors

Mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi

G. Vardar, S. W. Paleg, M. V. Warren, M. Kang, S. Jeon, and R. S. Goldman

Appl. Phys. Lett. 102, 042106 (2013); http://dx.doi.org/10.1063/1.4789369 (4 pages)

Online Publication Date: 30 January 2013

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We have examined the mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi. We consider the role of the transition from group-V-rich to group-III-rich conditions, i.e., the stoichiometry threshold, in the presence of Bi. For As-rich GaAsBi growth, Bi acts as a surfactant, leading to the formation of droplet-free GaAsBi films. For films within 10% of the stoichiometric GaAsBi growth regime, surface Ga droplets are observed. However, for Ga-rich GaAsBi growth, Bi acts as an anti-surfactant, inducing Ga-Bi droplet formation. We propose a growth mechanism based upon the growth-rate-dependence of the stoichiometry threshold for GaAsBi.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
81.05.Ea III-V semiconductors

Orbital structure of FeTiO3 ilmenite investigated with polarization-dependent X-ray absorption spectroscopy and band structure calculations

S. W. Chen, M. J. Huang, P. A. Lin, H. T. Jeng, J. M. Lee, S. C. Haw, S. A. Chen, H. J. Lin, K. T. Lu, D. P. Chen, S. X. Dou, X. L. Wang, and J. M. Chen

Appl. Phys. Lett. 102, 042107 (2013); http://dx.doi.org/10.1063/1.4789992 (4 pages)

Online Publication Date: 30 January 2013

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We explored the orbital structure of FeTiO3 with polarization-dependent x-ray absorption spectra complemented with electronic structure calculations. The electronic structure, near the bottom of conduction band, is composed of O 2p and Ti 3d orbitals. Ti 3d/4p hybridization dominantly lies on the ab plane. The highly delocalized Ti 4p orbital might hybridize with O 2p orbital and even extend to the next-neighbor Fe atom whereby establishing a linear orbital combination of Ti-O-Fe. A clear picture of the orbital construction in FeTiO3 will help to elucidate the paths of pressure-induced charge transfer and other physical or magnetic characteristics.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra

The role of the products of the decay of optical phonons

A. Dyson and B. K. Ridley

Appl. Phys. Lett. 102, 042108 (2013); http://dx.doi.org/10.1063/1.4790280 (3 pages)

Online Publication Date: 1 February 2013

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The decay of nonequilibrium longitudinal optical phonons is investigated by abandoning the usual assumption that the decay products remain in thermodynamic equilibrium. The case when only the grand-daughter modes remain in thermodynamic equilibrium is studied. The effective lifetime of the LO mode, which is the one that would be measured by experiment, is found to decrease with increasing occupancy of the LO mode.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
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Detecting p-type conduction in Ba-doped InN

Q. Y. Xie, W. M. Xie, J. L. Wang, H. P. Zhu, J. H. Yang, L. Sun, and X. S. Wu

Appl. Phys. Lett. 102, 042109 (2013); http://dx.doi.org/10.1063/1.4790281 (4 pages)

Online Publication Date: 1 February 2013

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The buried p-type conduction is demonstrated in InN with Ba ion implantation dose increases up to 1 × 1015 ions/cm−2. The in-plane lattice parameter increases by about 1.2% deep in the film due to larger Ba replacing smaller indium (In). The n-type conductivity is also detected at the surface, which may results from the N-deficiency. First-principles calculations show that holes at the surface, induced by Ba ion implantation, are compensated by extra electrons from the In adlayer. The p-type carriers dominate in the bulk layers, which is in good agreement with the experimental results.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
73.25.+i Surface conductivity and carrier phenomena

Schottky barrier height extraction from forward current-voltage characteristics of non-ideal diodes with high series resistance

Khaled Ahmed and Tony Chiang

Appl. Phys. Lett. 102, 042110 (2013); http://dx.doi.org/10.1063/1.4789989 (3 pages)

Online Publication Date: 1 February 2013

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Forward bias current-voltage (I-V) characteristics measured at room temperature were used to extract Schottky barrier heights in sulfur-implanted PtSi/n-Si and NiGe/n-Ge contacts. It is found that I-V data claimed to support barrier height reductions of ∼700 meV and ∼500 meV are more consistent with ∼300 meV and 100 meV reductions, respectively. These estimates should better guide attempts aiming at finding physical models for the observed reductions.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
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