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14 Feb 2013

Volume 113, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 064301 (2013); http://dx.doi.org/10.1063/1.4789897 (11 pages)

Y. G. Marinov, G. B. Hadjichristov, A. G. Petrov, S. Marino, C. Versace, and N. Scaramuzza
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back to top Device Physics

Low-temperature indium-bonded alkali vapor cell for chip-scale atomic clocks

R. Straessle, M. Pellaton, C. Affolderbach, Y. Pétremand, D. Briand, G. Mileti, and N. F. de Rooij

J. Appl. Phys. 113, 064501 (2013); http://dx.doi.org/10.1063/1.4789942 (8 pages)

Online Publication Date: 8 February 2013

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A low-temperature sealing technique for micro-fabricated alkali vapor cells for chip-scale atomic clock applications is developed and evaluated. A thin-film indium bonding technique was used for sealing the cells at temperatures of ≤140 °C. These sealing temperatures are much lower than those reported for other approaches, and make the technique highly interesting for future micro-fabricated cells, using anti-relaxation wall coatings. Optical and microwave spectroscopy performed on first indium-bonded cells without wall coatings are used to evaluate the cleanliness of the process as well as a potential leak rate of the cells. Both measurements confirm a stable pressure inside the cell and therefore an excellent hermeticity of the indium bonding. The double-resonance measurements performed over several months show an upper limit for the leak rate of 1.5 × 10−13 mbar·l/s. This is in agreement with additional leak-rate measurements using a membrane deflection method on indium-bonded test structures.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Hybrid diodes based on n-type Ge and conductive polymer doped by graphene oxide sheets with and without reduction treatment

Jian-Jhou Zeng (曾建洲) and Yow-Jon Lin (林祐仲)

J. Appl. Phys. 113, 064502 (2013); http://dx.doi.org/10.1063/1.4790889 (5 pages) | Cited 1 time

Online Publication Date: 11 February 2013

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The authors present a hybrid diode based on n-type Ge and poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) having the reduced graphene oxide (RGO) or graphene oxide (GO) sheets. It is found that conductivity of RGO-doped PEDOT:PSS films increases with increasing the reduction temperature of GO sheets. The improvement of electrical conductivity is considered to mainly come from the carrier mobility enhancement. In addition, the ideality factor of n-type Ge/RGO-doped PEDOT:PSS diodes decreases with increasing the reduction temperature of GO sheets. The device-performance improvement originates from high-mobility hole transport combined with long-lifetime electron trapping in the RGO-doped PEDOT:PSS film. However, GO doping may lead to decreased conductivity, owing to the large number of the oxygen-related defects in GO sheets. The device-performance degradation originates from low-mobility hole transport combined with short-lifetime electron trapping in the GO-doped PEDOT:PSS film.
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85.30.Kk Junction diodes

Qualitative and quantitative evaluation of thin-film solar cells using solar cell local characterization

J.-M. Wagner, J. Carstensen, A. Schütt, and H. Föll

J. Appl. Phys. 113, 064503 (2013); http://dx.doi.org/10.1063/1.4790479 (4 pages)

Online Publication Date: 11 February 2013

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The light-beam-induced current-based CELLO measurement technique (solar CELl LOcal characterization), originally developed for wafer-based silicon solar cells, can successfully be applied to thin-film solar cells, provided that contacting of a single cell is possible. This is shown exemplarily for several crystalline silicon on glass samples, having varying quality with respect to photocurrent extraction, series resistance, and power losses. For the latter, a comparison with results obtained from dark lock-in thermography gives quantitative agreement, provided that the cells are not severely shunted.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Optimization of Hall bar response to localized magnetic and electric fields

V. Nabaei, R. K. Rajkumar, A. Manzin, O. Kazakova, and A. Tzalenchuk

J. Appl. Phys. 113, 064504 (2013); http://dx.doi.org/10.1063/1.4790508 (8 pages)

Online Publication Date: 11 February 2013

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The present paper investigates the influence of localized magnetic and electric fields, produced by a magnetic scanning tip, on the response of high-mobility two-dimensional electron gas in a Hall bar geometry. We have developed a comprehensive numerical model, validated it by experiment and found the optimal design for magnetic sensing and limitation of perturbing effects due to electric field. This approach can be straightforwardly extended to the design of sensors for the detection of charged magnetic nanoparticles.
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72.20.My Galvanomagnetic and other magnetotransport effects
85.30.De Semiconductor-device characterization, design, and modeling
02.70.Dh Finite-element and Galerkin methods
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Extraordinary magnetoresistance in two and three dimensions: Geometrical optimization

Lisa M. Pugsley, L. R. Ram-Mohan, and S. A. Solin

J. Appl. Phys. 113, 064505 (2013); http://dx.doi.org/10.1063/1.4790503 (9 pages)

Online Publication Date: 12 February 2013

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The extraordinary magnetoresistance (EMR) in metal-semiconductor hybrid structures was first demonstrated using a van der Pauw configuration for a circular semiconductor wafer with a concentric metallic inclusion in it. This effect depends on the orbital motion of carriers in an external magnetic field, and the remarkably high magnetoresistance response observed suggests that the geometry of the metallic inclusion can be optimized to further significantly enhance the EMR. Here, we consider the theory and simulations to achieve this goal by comparing both two-dimensional (2D) and three-dimensional (3D) structures in an external magnetic field to evaluate the EMR in them. New results for 3D structures are presented to show the feasibility of such modeling. Examples of structures that are compatible with present day technological capabilities are given together with their expected responses in terms of EMR. For a 10 μm 2D square structure with a square metallic inclusion, we find an MR up to 107 percent for an applied magnetic field of 1 T. In 3D, for a 10 μm cube with a 5 μm centered metallic inclusion, we obtain an MR of ∼ 104 percent, which is comparable with the 2D structure of equivalent dimensions. The results presented here for specific geometries are scalable to smaller dimensions down to the onset of ballistic effects in the transport. The present calculations open up the possibility of 3D magnetic field sensors capable of determining the magnitude and also direction of the magnetic field once a full characterization of the sensor response is performed.
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73.40.Ns Metal-nonmetal contacts
75.47.Pq Other materials
73.23.Ad Ballistic transport

Multiscale model for phonon-assisted band-to-band tunneling in semiconductors

Arvind Ajoy, S. E. Laux, Kota V. R. M. Murali, and Shreepad Karmalkar

J. Appl. Phys. 113, 064506 (2013); http://dx.doi.org/10.1063/1.4790628 (9 pages)

Online Publication Date: 12 February 2013

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We present a TCAD (Technology Computer Aided Design) compatible multiscale model of phonon-assisted band-to-band tunneling in semiconductors, which incorporates the non-parabolic nature of complex bands within the bandgap of the material. This model is shown capture the measured current-voltage data in silicon, for current transport along the [100], [110], and [111] directions. Our model will be useful to predict band-to-band tunneling phenomena to quantify on and off currents in tunnel FETs and in small geometry MOSFETs and FINFETs.
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73.40.Gk Tunneling
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.20.Mq Elemental semiconductors

Joule's law for organic transistors exploration: Case of contact resistance

Yong Xu, Chuan Liu, Yun Li, Takeo Minari, Peter Darmawan, Francis Balestra, Gerard Ghibaudo, and Kazuhito Tsukagoshi

J. Appl. Phys. 113, 064507 (2013); http://dx.doi.org/10.1063/1.4792066 (5 pages) | Cited 2 times

Online Publication Date: 12 February 2013

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Joule's law opens a straightforward way to explore the operating mechanism of organic field-effect transistors, from the angle of inner transported heating. The microscopic dissipated power is calculated from the local conductivity and electric field, which solves the widespread difficulties in building a macroscopic model to determine the contact resistance. The result quantitatively discloses the correlation between the contact resistance and the charge transport properties covering energetic disorder, band-like and hopping transport as well as carrier mobility anisotropy. It turns out that in a staggered configuration with ideal Ohmic contact, the contact resistance is highly affected by the charge transport.
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73.40.Cg Contact resistance, contact potential
85.30.Tv Field effect devices

The role of oxide interlayers in back reflector configurations for amorphous silicon solar cells

V. Demontis, C. Sanna, J. Melskens, R. Santbergen, A. H. M. Smets, A. Damiano, and M. Zeman

J. Appl. Phys. 113, 064508 (2013); http://dx.doi.org/10.1063/1.4790875 (9 pages)

Online Publication Date: 13 February 2013

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Thin oxide interlayers are commonly added to the back reflector of thin-film silicon solar cells to increase their current. To gain more insight in the enhancement mechanism, we tested different back reflector designs consisting of aluminium-doped zinc oxide (ZnO:Al) and/or hydrogenated silicon oxide (SiOx:H) interlayers with different metals (silver, aluminium, and chromium) in standard p-i-n a-Si:H solar cells. We use a unique inverse modeling approach to show that in most back reflectors the internal metal reflectance is lower than expected theoretically. However, the metal reflectance is increased by the addition of an oxide interlayer. Our experiments demonstrate that SiOx:H forms an interesting alternative interlayer because unlike the more commonly used ZnO:Al it can be deposited by plasma-enhanced chemical vapour deposition and it does not reduce the fill factor. The largest efficiency enhancement is obtained with a double interlayer of SiOx:H and ZnO:Al.
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88.40.jj Silicon solar cells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
88.40.hj Efficiency and performance of solar cells

Feasibility studies for filament detection in resistively switching SrTiO3 devices by employing grazing incidence small angle X-ray scattering

S. Stille, C. Baeumer, S. Krannich, C. Lenser, R. Dittmann, J. Perlich, S. V. Roth, R. Waser, and U. Klemradt

J. Appl. Phys. 113, 064509 (2013); http://dx.doi.org/10.1063/1.4792035 (8 pages) | Cited 1 time

Online Publication Date: 14 February 2013

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We report on fundamental studies of grazing incidence small angle X-ray scattering (GISAXS) on resistively switching SrTiO3 thin film metal-insulator-metal (MIM) devices. Different influence factors on the GISAXS scattering pattern, e.g., surface morphology and top electrode material, were evaluated by simulations and compared with subsequent measurements. Pt top electrodes cause a strong background scattering which covers any information from the underlying SrTiO3 layer. In order to reduce this undesired background scattering, the lighter elements Al and Ti have been used. In case of Ti top electrodes, we observed that a laterally formed structure occurs in the SrTiO3 prior to any electrical treatment, which is consistent with the forming-free properties of the MIM structures. For Al top electrodes, we could detect a significant influence of an electroforming step on the scattered intensity.
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84.30.Sk Pulse and digital circuits

Resistive switching mechanisms relating to oxygen vacancies migration in both interfaces in Ti/HfOx/Pt memory devices

Y. S. Lin, F. Zeng, S. G. Tang, H. Y. Liu, C. Chen, S. Gao, Y. G. Wang, and F. Pan

J. Appl. Phys. 113, 064510 (2013); http://dx.doi.org/10.1063/1.4791695 (5 pages)

Online Publication Date: 14 February 2013

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Resistive switching mechanism of Ti/HfOx/Pt memory devices was studied using X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy images. Spatial distributions of valence of Hf demonstrated that the fraction of Hf4+ increased from Ti/HfOx interface to HfOx/Pt interface in high resistance state (HRS), but it maintained a constant level in low resistance state (LRS). Rupture of oxygen vacancies formed conducting paths occurred near the HfOx/Pt interface. The cross sectional images of active switching region also varied with HRS and LRS. A dynamic model of interface processes was proposed to interpret interfaces migration of oxygen vacancies near both the top and bottom electrodes.
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84.30.Sk Pulse and digital circuits
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