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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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Cracking in hydrogen ion-implanted Si/Si0.8Ge0.2/Si heterostructures

Lin Shao, Y. Q. Wang, J. G. Swadener, M. Nastasi, Phillip E. Thompson, and N. David Theodore

Appl. Phys. Lett. 92, 061904 (2008); http://dx.doi.org/10.1063/1.2838338 (3 pages) | Cited 1 time

Online Publication Date: 12 February 2008

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We demonstrate that a controllable cracking can be realized in Si with a buried strain layer when hydrogen is introduced using traditional H-ion implantation techniques. However, H stimulated cracking is dependent on H projected ranges; cracking occurs along a Si0.8Ge0.2 strain layer only if the H projected range is shallower than the depth of the strained layer. The absence of cracking for H ranges deeper than the strain layer is attributed to ion-irradiation induced strain relaxation, which is confirmed by Rutherford-backscattering-spectrometry channeling angular scans. The study reveals the importance of strain in initializing continuous cracking with extremely low H concentrations.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
61.72.uf Ge and Si
61.82.Fk Semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Structural and optical investigations of Nd-doped fluorozirconate-based glass ceramics for enhanced upconverted fluorescence

Bernd Ahrens, Christian Eisenschmidt, Jacqueline A. Johnson, Paul T. Miclea, and Stefan Schweizer

Appl. Phys. Lett. 92, 061905 (2008); http://dx.doi.org/10.1063/1.2837542 (3 pages) | Cited 15 times

Online Publication Date: 12 February 2008

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We found enhanced upconverted fluorescence in Nd3+-doped fluorozirconate glasses which were additionally doped with chlorine ions. Upon annealing between 240 and 290°C, hexagonal phase BaCl2 nanocrystals between 20 and 180 nm in diameter were formed in the glass. During the thermal processing, some of the Nd3+ ions enter the nanocrystals leading to additional splitting of the infrared fluorescence spectra and to increased upconverted fluorescence intensities. The optimum value was found for the 270°C sample where the upconverted fluorescence intensity is approximately a factor of 60 stronger than the one found for the as-made glass.
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61.46.Hk Nanocrystals
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.43.Fs Glasses

Effect of interstitial C incorporation on the Raman scattering of Si1−x−yGexCy epitaxial layer

Suk Choi, Hyun Woo Kim, Hee Jin Kim, Sukwon Hong, Gun-Do Lee, and Euijoon Yoon

Appl. Phys. Lett. 92, 061906 (2008); http://dx.doi.org/10.1063/1.2842419 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2008

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We performed Raman spectroscopy on the Si1−x−yGexCy epitaxial layers grown on Si substrates by ultrahigh vacuum chemical vapor deposition. The incorporation of substitutional C atoms reduces the Si–Si mode frequency of Si1−x−yGexCy, whereas the interstitial C incorporation shifts it up. The ab initio phonon frequency calculation considering the most stable interstitial C site was performed to verify our results and we showed that the V-shaped behavior, showing the decrease and increase of Si–Si mode frequency as the amount of C, originated from the effect of interstitial C incorporation and proposed that the Si–Si Raman vibrational mode frequency shift can be used as a tool to observe interstitial C atoms.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Hv Other nonmetallic inorganics
61.72.jj Interstitials
68.55.-a Thin film structure and morphology

Screening dynamics of intrinsic electric field in AlGaN quantum wells

A. Pinos, S. Marcinkevičius, K. Liu, M. S. Shur, E. Kuokštis, G. Tamulaitis, R. Gaska, J. Yang, and W. Sun

Appl. Phys. Lett. 92, 061907 (2008); http://dx.doi.org/10.1063/1.2857467 (3 pages) | Cited 11 times

Online Publication Date: 13 February 2008

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Shift of the transition energy after pulsed optical excitation in Al0.35Ga0.65N/Al0.49Ga0.51N quantum well (QW) structures with varying well width has been studied by time-resolved photoluminescence. The shift dynamics, which is due to descreening of the intrinsic electric field, has characteristic times similar to carrier lifetimes revealing negligible influence of trapped carriers on screening. Comparison of the experimental spectral shifts with the calculations has shown that the intrinsic field in our AlGaN QWs is about 0.4–0.5 MV/cm, which is about a factor of two smaller than the value calculated using the theoretical polarization constants.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors

Picosecond photoexcitation of acoustic waves in locally canted gold films

T. Pezeril, F. Leon, D. Chateigner, S. Kooi, and Keith A. Nelson

Appl. Phys. Lett. 92, 061908 (2008); http://dx.doi.org/10.1063/1.2841823 (3 pages) | Cited 4 times

Online Publication Date: 13 February 2008

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The laser photoacoustic technique is used to generate and detect picosecond coherent acoustic vibrations in gold film media deposited on Si substrates. As a consequence of the gold crystallites’ canted orientation, the pump-probe picosecond transient reflectivity shows oscillations at the fundamental shear mode frequency. The shear character of the mode is suggested by its dispersion, by the dependence of the signal on the probe laser wavelength, and by x-ray texture analysis.
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78.66.Bz Metals and metallic alloys
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Molecular simulation strategy for mechanical modeling of amorphous/porous low-dielectric constant materials

Cadmus A. Yuan, Olaf van der Sluis, G. Q. Zhang, Leo J. Ernst, Willem D. van Driel, Amy E. Flower, and Richard B. R. van Silfhout

Appl. Phys. Lett. 92, 061909 (2008); http://dx.doi.org/10.1063/1.2832639 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2008

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We propose an amorphous/porous molecular connection network generation algorithm for simulating the material stiffness of a low-k material (SiOC:H). Based on a given concentration of the basic building blocks, this algorithm will generate an approximate and large amorphous network. The molecular topology is obtained by distributing these blocks randomly into a predefined framework. Subsequently, a structural relaxation step including local and global perturbations is applied to achieve the most likely stereochemical structure. Thus, the obtained mechanical properties of the low-k materials have been verified with the experimental data.
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61.43.Gt Powders, porous materials
61.43.Bn Structural modeling: serial-addition models, computer simulation
77.22.Ch Permittivity (dielectric function)

Investigation of phase transition of Ge2Sb2Te5 and N-incorporated Ge2Sb2Te5 films using x-ray absorption spectroscopy

Youngkuk Kim, M. H. Jang, K. Jeong, M.-H. Cho, K. H. Do, D.-H. Ko, H. C. Sohn, and Min Gyu Kim

Appl. Phys. Lett. 92, 061910 (2008); http://dx.doi.org/10.1063/1.2844878 (3 pages) | Cited 12 times

Online Publication Date: 14 February 2008

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For this study, the phase-change materials Ge2Sb2Te5 and N-doped Ge2Sb2Te5 films were investigated using x-ray absorption near-edge structure and extended x-ray absorption fine structure. During the phase transition, change in electronic structure is observed by the shift of the absorption edge energy, i.e., structural coordination of Ge–Te changes from tetrahedral to octahedral coordination, of which the interatomic distances are 3.12 and 2.83 Å, respectively. In addition, nitrogen incorporation into the film led to a p-p orbital hybridization and a different crystallization behavior. The hybridization caused by the formation of a Ge–N bond was related to suppression of the phase transition.
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64.70.K- Solid-solid transitions
78.70.Dm X-ray absorption spectra
78.66.Bz Metals and metallic alloys
71.20.Gj Other metals and alloys
68.55.-a Thin film structure and morphology

Time resolved magneto-optical studies of ferromagnetic InMnSb films

M. Frazier, R. N. Kini, K. Nontapot, G. A. Khodaparast, T. Wojtowicz, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 92, 061911 (2008); http://dx.doi.org/10.1063/1.2842423 (3 pages)

Online Publication Date: 15 February 2008

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We report time resolved magneto-optical measurements in InMnSb ferromagnetic films with 2% and 2.8% Mn contents grown by low temperature molecular beam epitaxy. In order to probe a possible interaction between the spins of photoexcited carriers and the Mn ions, we measured spin dynamics before and after aligning the Mn ions by applying an external magnetic field at temperatures above and below the samples’ Curie temperatures. We observed no significant temperature or magnetic field dependence in the relaxation times and attribute the observed dynamics entirely to the relaxation of photoexcited electrons in the conduction band where the s-d coupling with the localized Mn ions is significantly weaker compared to the p-d exchange coupling. We observed several differences in the optical response of our InMnSb samples which could have been influenced mainly by the samples’ growth conditions.
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78.20.Ls Magneto-optical effects
75.50.-y Studies of specific magnetic materials
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optically induced ultrafast quenching of the semiconductor quantum well luminescence

A. Amo, D. Ballarini, D. Sanvitto, E. Kozhemyakina, L. Viña, A. Lemaître, D. Bajoni, and J. Bloch

Appl. Phys. Lett. 92, 061912 (2008); http://dx.doi.org/10.1063/1.2857494 (3 pages) | Cited 2 times

Online Publication Date: 15 February 2008

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We present an experimental configuration that enables the ultrafast, transient quenching of the excitonic photoluminescence in quantum wells. Our scheme is based on two, delayed, short pulses experiment. A first pulse excites carriers in the system, while a second pulse induces an ultrafast redistribution of excitons that results in abrupt dips in the photoluminescence. We present a model that quantitatively accounts for the measured dip depth. The magnitude of the dip, determined by the temperature change of the carriers, can be controlled by varying the power and delay of the second pulse.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices

Sustained surface wave propagation induced by surface diffusion driven by strain relaxation in a heteroepitaxial film

P. Liu, Y. W. Zhang, H. J. Gao, and K. Y. Lam

Appl. Phys. Lett. 92, 061913 (2008); http://dx.doi.org/10.1063/1.2883938 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2008

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We examine the dynamics of surface pattern formation during both annealing and vapor deposition of a heteroepitaxial thin film on prepatterned substrate surfaces, predicting a sustained propagation of regular surface waves via surface diffusion driven by strain relaxation. Both the wavelength and propagation speed are found to be insensitive to the surface prepatterns, growth rate and film thickness.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.Fx Diffusion; interface formation
68.65.La Quantum wires (patterned in quantum wells)

Nanometer thick single crystal Y2O3 films epitaxially grown on Si (111) with structures approaching perfection

C. W. Nieh, Y. J. Lee, W. C. Lee, Z. K. Yang, A. R. Kortan, M. Hong, J. Kwo, and C.-H. Hsu

Appl. Phys. Lett. 92, 061914 (2008); http://dx.doi.org/10.1063/1.2883939 (3 pages) | Cited 6 times

Online Publication Date: 15 February 2008

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Cubic phase Y2O3 films 1.6–10 nm thick of excellent quality have been epitaxially grown on Si (111) with Y2O3(111)∥Si(111) using electron beam evaporation of Y2O3 in ultrahigh vacuum. Structural and morphological studies were carried out by x-ray scattering and reflectivity and high-resolution transmission electron microscopy, with the growth being in situ monitored by reflection high energy electron diffraction. There are two Y2O3 domains in the initial stage of the oxide growth with equal population, and the B-type domain of Y2O3[2mathmath]∥Si[11math] becomes predominating over the A-type domain of Y2O3[2mathmath]∥Si[2mathmath] with increasing film thickness. Besides the excellent crystallinity of the films as derived from the small ω-rocking curve width of 0.014°, our results also show atomically sharp smooth surface and interfaces.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.aj Insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.70.Ck X-ray scattering
78.66.Nk Insulators
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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
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