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11 Feb 2008

Volume 92, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 063101 (2008); http://dx.doi.org/10.1063/1.2839572 (3 pages)

M. N. Ou, T. J. Yang, S. R. Harutyunyan, Y. Y. Chen, C. D. Chen, and S. J. Lai
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Selective etching of independent contacts in a double quantum-well structure: Quantum-gate transistor

S. Lang, L. Worschech, M. Emmerling, M. Strauß, S. Höfling, and A. Forchel

Appl. Phys. Lett. 92, 062101 (2008); http://dx.doi.org/10.1063/1.2841662 (3 pages)

Online Publication Date: 11 February 2008

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Double GaAs quantum wells (QWs) embedded between modulation-doped AlGaAs barriers with different aluminium (Al) contents were grown by molecular beam epitaxy. Independent electric contacts to each well were realized by applying different etching techniques without substrate removal. In particular, the lower quantum well was electrically pinched off by a local undercut of the lower AlGaAs barrier exploiting an Al selective etching process. In contrast, the upper quantum well was locally depleted by top etched trenches. Transistor operation of quantum wires defined in such bilayers is demonstrated at room temperature with one GaAs layer used as conducting channel controlled by the other nearby GaAs layer as efficient quantum gate.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Sz Deposition technology
85.40.Ls Metallization, contacts, interconnects; device isolation

Lack of charge offset drift is a robust property of Si single electron transistors

Emmanouel Hourdakis, Jeremy A. Wahl, and Neil M. Zimmerman

Appl. Phys. Lett. 92, 062102 (2008); http://dx.doi.org/10.1063/1.2841659 (3 pages) | Cited 4 times

Online Publication Date: 12 February 2008

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One of the challenges that single-electron transistors (SETs) face before they can be considered technologically useful is the charge offset drift. Recently, two different types of Si SETs were shown to have a drift of only 0.01e (the fundamental charge) over several days. Those devices came from one fabrication source. Here, we present the results for Si SETs fabricated by our group (a different source) demonstrating their operation as SETs. We confirm that the charge offset drift is less than 0.01e, demonstrating the lack of charge offset drift is generic to Si devices and not dependent on the fabrication source.
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85.35.Gv Single electron devices

Lower current operation of phase change memory cell with a thin TiO2 layer

Cheng Xu, Zhitang Song, Bo Liu, Songlin Feng, and Bomy Chen

Appl. Phys. Lett. 92, 062103 (2008); http://dx.doi.org/10.1063/1.2841655 (3 pages) | Cited 22 times

Online Publication Date: 12 February 2008

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The phase change memory cell with 8 nm TiO2 layer inserted between phase change material Ge2Sb2Te5 and bottom heating electrode tungsten was fabricated. It showed an advanced electrical threshold switching characteristics in the dc current-voltage measurement with the much lower value of threshold voltage of 1.5 V. The reset current of the device cell decreased 68% compared with that without TiO2 layer. These results will contribute to the lower power consumption of the phase change memory. Besides that, the device cell showed good endurance characteristics, demonstrating the capability of random access memory application.
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84.30.Sk Pulse and digital circuits

Atomic size mismatch strain induced surface reconstructions

Jessica E. Bickel, Normand A. Modine, Anton Van der Ven, and Joanna Mirecki Millunchick

Appl. Phys. Lett. 92, 062104 (2008); http://dx.doi.org/10.1063/1.2841846 (3 pages) | Cited 4 times

Online Publication Date: 13 February 2008

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The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs/GaAs surfaces.
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68.35.bg Semiconductors
68.35.Md Surface thermodynamics, surface energies
81.65.-b Surface treatments
68.35.Dv Composition, segregation; defects and impurities

Stochastic data processing circuit based on single electrons using nanoscale field-effect transistors

K. Nishiguchi, Y. Ono, A. Fujiwara, H. Inokawa, and Y. Takahashi

Appl. Phys. Lett. 92, 062105 (2008); http://dx.doi.org/10.1063/1.2870199 (3 pages) | Cited 8 times

Online Publication Date: 13 February 2008

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A circuit utilizing single electrons is demonstrated at room temperature using a silicon-on-insulator metal-oxide-semiconductor field-effect transistor (MOSFET). Individual electrons randomly passing through the nanoscale MOSFET, which are the origin of shot noise, are monitored by an electrometer in real time. This random behavior of single electrons is used as a random number for a stochastic associative memory for image-pattern matching, in which the most preferable pattern is extracted with the largest probability. The use of electron transport in the MOSFET provides high controllability of the randomness as well as fast generation of random numbers. The present result promises single-electron applications using nanoscale MOSFETs.
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85.30.Tv Field effect devices

Spin separation via a three-terminal Aharonov–Bohm interferometers

Feng Chi and Jun Zheng

Appl. Phys. Lett. 92, 062106 (2008); http://dx.doi.org/10.1063/1.2857471 (3 pages) | Cited 32 times

Online Publication Date: 13 February 2008

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We propose a three-terminal ring-type device which contains a single-level quantum dot (QD) to extract or separate the spin-up and the spin-down electrons that are injected into the QD from a middle lead, into the left and the right leads, respectively. This scheme is based on the Rashba spin-orbit interaction (RSOI) in the bridge between the left and the right leads and is free from magnetic field or magnetic material. We find that both the spin directions and the magnitude of the outflow currents in the left and the right leads can be tuned by the RSOI strength and the structure parameters.
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68.65.Hb Quantum dots (patterned in quantum wells)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Metastable behavior of donors in CuGaSe2 under illumination

Susanne Siebentritt and Thorsten Rissom

Appl. Phys. Lett. 92, 062107 (2008); http://dx.doi.org/10.1063/1.2857473 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2008

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Several metastable effects have been observed in chalcopyrite solar cells. Recently, they have been related to the amphoteric behavior of the Se vacancy. We give an independent experimental evidence on this amphoteric behavior. By comparing charge carrier densities obtained from Hall effect measurements under illumination and in the dark, we conclude that illumination removes compensating donors.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Hd Other semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Impact of incomplete set programing on the performance of phase change memory cell

Der-Sheng Chao, Chenhsin Lien, Chain-Ming Lee, Yi-Chan Chen, Jyi-Tyan Yeh, Fred Chen, Ming-Jung Chen, Philip H. Yen, Ming-Jer Kao, and Ming-Jinn Tsai

Appl. Phys. Lett. 92, 062108 (2008); http://dx.doi.org/10.1063/1.2839379 (3 pages) | Cited 14 times

Online Publication Date: 13 February 2008

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Phase change memory (PCM) cells with T-shaped structure using tungsten heater were fabricated and the cell characteristics concerning the programing pulse width were also investigated in this work. The numerical modeling shows the thermal nonuniformity over the active region due to the considerable thermal sink of tungsten heater results in the amorphous-phase residues and the incomplete set programing. The experimental results reveal the existence of residual amorphous phase and indicate that the incomplete set programing is the dominant factor to degrade the PCM cell performances, such as the sensing margin and the endurance. The strategies to eliminate the incomplete set programing are the optimization in programing pulse width and the replacement of the tungsten heater with higher resistivity metal such as TiAlN.
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84.30.Sk Pulse and digital circuits
85.30.De Semiconductor-device characterization, design, and modeling

Pumped pure spin current and shot noise spectra in a two-level Rashba dot

Hai-Feng Lü and Yong Guo

Appl. Phys. Lett. 92, 062109 (2008); http://dx.doi.org/10.1063/1.2838298 (3 pages) | Cited 9 times

Online Publication Date: 14 February 2008

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The authors analyze theoretically the pumped spin current and current noise spectra in a two-level Rashba dot connected to two ferromagnetic electrodes with parallel magnetic configuration. It is found that the interlevel spin flips induced by the Rashba spin-orbit interaction can generate a pure spin current, whose strength is determined by both the energy spacing between two levels and the spin-flip strength. It is further pointed out that the total charge current noise at a finite bias voltage can be used to determine whether the pumped current is a pure spin type or not.
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72.25.Dc Spin polarized transport in semiconductors
73.63.Kv Quantum dots
72.70.+m Noise processes and phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Effect on nitrogen acceptor as Mg is alloyed into ZnO

Y. Q. Gai, B. Yao, Z. P. Wei, Y. F. Li, Y. M. Lu, D. Z. Shen, J. Y. Zhang, D. X. Zhao, X. W. Fan, Jingbo Li, and Jian-Bai Xia

Appl. Phys. Lett. 92, 062110 (2008); http://dx.doi.org/10.1063/1.2857496 (3 pages) | Cited 10 times

Online Publication Date: 14 February 2008

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Our Raman measurement indicates that the intensity of the peaks (510 and 645 cm−1) related to nitrogen concentration is enhanced in MgZnO compared with that in ZnO. Using first-principles band structure methods, we calculated the formation energy and transition energy level for nitrogen acceptor in ZnO and random MgxZn1−xO (with x = 0.25) alloy. Our calculations show that the incorporation of nitrogen can be enhanced as Mg is alloyed into ZnO, which agrees with our experiments. The acceptor energy level deeper in the alloy ascribes to the downward shift of the valence-band maximum edge in the presence of magnesium.
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71.55.Gs II-VI semiconductors
78.30.Hv Other nonmetallic inorganics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

High quality InAsSb grown on InP substrates using AlSb/AlAsSb buffer layers

Bing-Ruey Wu, Chichih Liao, and K. Y. Cheng

Appl. Phys. Lett. 92, 062111 (2008); http://dx.doi.org/10.1063/1.2836947 (3 pages) | Cited 2 times

Online Publication Date: 15 February 2008

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High quality InAsSb grown on semi-insulating InP substrates by molecular beam epitaxy was achieved using AlSb/AlAsSb structure as the buffer layer. A 1000 Å InAsSb layer grown on top of 1 μm AlSb/AlAsSb buffer layer showed a room temperature electron mobility of ∼ 12 000 cm2/V s. High structural quality and low misfit defect density were also demonstrated in the InAsSb layer. This novel AlSb/AlAsSb buffer layer structure with the AlAsSb layer lattice matched to InP substrates could enhance the performance of optoelectronic devices utilizing 6.1 Å family of compound semiconductor alloys.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance

Nonvolatile memory characteristics influenced by the different crystallization of Ni–Si and Ni–N nanocrystals

Wei-Ren Chen, Ting-Chang Chang, Jui-Lung Yeh, Chun-Yen Chang, and Shih-Ching Chen

Appl. Phys. Lett. 92, 062112 (2008); http://dx.doi.org/10.1063/1.2841049 (3 pages)

Online Publication Date: 15 February 2008

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The formation of Ni–Si and Ni–N nanocrystals by sputtering a Ni0.3Si0.7 target in argon and nitrogen environment were proposed in this paper. A transmission electron microscope analysis shows the nanocrystals embedded in the nitride layer. X-ray photoelectron spectroscopy and x-ray diffraction also offer the chemical material analysis of nanocrystals with surrounding dielectric and the crystallization of nanocrystals for different thermal annealing treatments. Nonvolatile Ni–Si nanocrystal memories reveal superior electrical characteristics for charge storage capacity and reliability due to the improvement of thermal annealing treatment. In addition, we used energy band diagrams to explain the significance of surrounding dielectric for reliability.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices
81.07.Bc Nanocrystalline materials
64.70.K- Solid-solid transitions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.40.Gh Other heat and thermomechanical treatments

Electroless nickel/gold Ohmic contacts to p-type GaN

L. Lewis, D. P. Casey, A. V. Jeyaseelan, J. F. Rohan, and P. P. Maaskant

Appl. Phys. Lett. 92, 062113 (2008); http://dx.doi.org/10.1063/1.2842425 (3 pages) | Cited 2 times

Online Publication Date: 15 February 2008

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A solution based approach to forming Ohmic contacts to p-type GaN is described. Electroless plated Ni/Au contacts are shown to compare favorably with traditional evaporated contacts, with contact resistivities ρc in the region of 10−2 Ω cm2. These values are readily achieved after a rapid thermal annealing in an O2 atmosphere. The tunneling nature of the contact is confirmed via temperature dependant measurements. X-ray diffraction measurements confirm the similarity between evaporated and plated contacts. Current-photocurrent (I-L) and current-voltage (I-V) measurements from light emitting diodes formed using an electroless p-type contact are shown. Electroless deposition of the contact metals allows for a reduction in processing time and cost.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
72.40.+w Photoconduction and photovoltaic effects
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution

Negative differential mobility in GaAs at ultrahigh fields: Comparison between an experiment and simulations

Sergey Vainshtein, Valentin Yuferev, Vassil Palankovski, Duu-Sheng Ong, and Juha Kostamovaara

Appl. Phys. Lett. 92, 062114 (2008); http://dx.doi.org/10.1063/1.2870096 (3 pages) | Cited 3 times

Online Publication Date: 15 February 2008

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Direct measurement of the electron velocity vn at an extreme electric field E is problematic due to impact ionization. The dependence vn(E) obtained by a Monte Carlo method can be verified, however, by comparing simulated and experimental data on superfast switching in a GaAs bipolar transistor structure, in which the switching transient is very sensitive to this dependence at high electric fields (up to 0.6 MV/cm). Such a comparison allows the conclusion to be made that the change from negative to positive differential mobility predicted earlier at E ∼ 0.3 MV/cm should not happen until the electric field exceeds 0.6 MV/cm.
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85.30.Pq Bipolar transistors
84.32.Dd Connectors, relays, and switches

Platinum thin film–antimony doped barium strontium titanate Schottky barrier diode

N. Sirikulrat

Appl. Phys. Lett. 92, 062115 (2008); http://dx.doi.org/10.1063/1.2883936 (3 pages) | Cited 3 times

Online Publication Date: 15 February 2008

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The Schottky barrier diode of the platinum thin film on the antimony doped barium strontium titanate polycrystalline ceramics was prepared and its electrical conduction was investigated. At the low field forward biasing, the current voltage relationship was Ohmic as expected from the space charge limited conduction (SCLC). Results from the high field biasing indicated that the exponential conduction occurred due to the Schottky emission rather than the trap free square law arising from the SCLC. The barrier height and the ideality factor of 0.87 eV and 1.5 were obtained in the diode with the Pt film thickness of 84 nm.
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85.30.Kk Junction diodes
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Cd Deposition by sputtering
73.61.At Metal and metallic alloys
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