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16 Mar 2009

Volume 94, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 111101 (2009); http://dx.doi.org/10.1063/1.3097278 (3 pages)

Ling Lu, Adam Mock, Tian Yang, Min Hsiung Shih, Eui Hyun Hwang, Mahmood Bagheri, Andrew Stapleton, Stephen Farrell, John O’Brien, and P. Daniel Dapkus
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Carrier transport mechanisms of nonvolatile write-once-read-many-times memory devices with InP–ZnS core-shell nanoparticles embedded in a polymethyl methacrylate layer

Jung Hoon Ham, Do Hyun Oh, Sung Hwan Cho, Jae Hun Jung, Tae Whan Kim, Eui Dock Ryu, and Sang Wook Kim

Appl. Phys. Lett. 94, 112101 (2009); http://dx.doi.org/10.1063/1.3097805 (3 pages) | Cited 9 times

Online Publication Date: 16 March 2009

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Current-voltage (I-V) curves at 300 K for Al/InP–ZnS nanoparticles embedded in a polymethyl methacrylate layer/Al devices showed electrical bistability for write-once-read-many-times (WORM) memory devices. From the I-V curves, the ON/OFF ratio for the device with InP–ZnS nanoparticles was significantly larger than that for the device without InP–ZnS nanoparticles, indicative of the existence of charge capture in the InP nanoparticles. The estimated retention time of the ON state for the WORM memory device was more than 10 years. The carrier transport mechanisms for the WORM memory devices are described by using several models to fit the experimental I-V data.
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84.30.Sk Pulse and digital circuits
81.07.Bc Nanocrystalline materials

Dislocation core effect scattering in a quasitriangle potential well

Xiaoqing Xu, Xianglin Liu, Shaoyan Yang, Jianming Liu, Hongyuan Wei, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 94, 112102 (2009); http://dx.doi.org/10.1063/1.3098356 (3 pages) | Cited 5 times

Online Publication Date: 16 March 2009

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A theory of scattering by charged dislocation lines in a quasitriangle potential well of AlxGa1−xN/GaN heterostructures is developed. The dependence of mobility on carrier sheet density and dislocation density is obtained. The results are compared with those obtained from a perfect two-dimensional electron gas and the reason for discrepancy is given.
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61.72.Bb Theories and models of crystal defects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Dp General theory, scattering mechanisms
72.20.Ee Mobility edges; hopping transport

Cathodoluminescence study of dislocation-related luminescence from small-angle grain boundaries in multicrystalline silicon

Woong Lee, Jun Chen, Bin Chen, Jiho Chang, and Takashi Sekiguchi

Appl. Phys. Lett. 94, 112103 (2009); http://dx.doi.org/10.1063/1.3099001 (3 pages)

Online Publication Date: 16 March 2009

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Dislocation-related luminescence from small-angle grain boundaries (SA-GBs) in multicrystalline Si was investigated by cathodoluminescence. D3 and D4 emissions were detected at SA-GBs with a misorientation angle of around 1°–1.5°, and D1 and D2 at SA-GBs with a misorientation angle of around 2°–2.5°. Electron beam-induced current investigations indicate that the former SA-GBs possess only shallow energy levels, while the latter possess both deep and shallow levels. The origins of D-line luminescence at SA-GBs are discussed in terms of dislocation structures.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Mm Grain and twin boundaries
78.55.Ap Elemental semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors

Improved Ni/3C-SiC contacts by effective contact area and conductivity increases at the nanoscale

Jens Eriksson, Fabrizio Roccaforte, Filippo Giannazzo, Raffaella Lo Nigro, Vito Raineri, Jean Lorenzzi, and Gabriel Ferro

Appl. Phys. Lett. 94, 112104 (2009); http://dx.doi.org/10.1063/1.3099901 (3 pages) | Cited 2 times

Online Publication Date: 16 March 2009

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We report on the evolution of the electrical and structural properties of Ni/3C-SiC contacts during annealing in the temperature range of 600–950 °C. A structural analysis showed the formation of different nickel silicide phases upon annealing. A combination of transmission line model and conductive atomic force microscopy measurements demonstrated a correlation between the macroscale specific contact resistance and the nanoscale resistance, measured locally across the sample. These results further revealed that the structural evolution is accompanied by an increased uniformity of the local current distribution, indicating that an increase of the effective contact area contributes to the improvement of the contact properties.
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73.40.Cg Contact resistance, contact potential
81.40.Gh Other heat and thermomechanical treatments
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.ag Semiconductors
68.37.Ps Atomic force microscopy (AFM)
73.40.Ns Metal-nonmetal contacts

Spatially resolved doping concentration measurement in semiconductors via spin noise spectroscopy

M. Römer, J. Hübner, and M. Oestreich

Appl. Phys. Lett. 94, 112105 (2009); http://dx.doi.org/10.1063/1.3098074 (3 pages) | Cited 6 times

Online Publication Date: 16 March 2009

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We propose and demonstrate spin noise spectroscopy as an efficient, noncontact method to measure doping concentrations in semiconductors with high accuracy and high spatial resolution. In a proof of concept study, two different doping levels in a silicon-doped GaAs stack are depth resolved with a relative accuracy of up to 5% and a spatial accuracy better than 50 μm. The method promises three-dimensional doping measurements in direct semiconductors with submicrometer resolution even at extremely low doping concentrations.
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61.72.uj III-V and II-VI semiconductors
72.70.+m Noise processes and phenomena
72.25.-b Spin polarized transport

Graphitization process of SiC(0001) studied by electron energy loss spectroscopy

T. Langer, H. Pfnür, H. W. Schumacher, and C. Tegenkamp

Appl. Phys. Lett. 94, 112106 (2009); http://dx.doi.org/10.1063/1.3100776 (3 pages) | Cited 9 times

Online Publication Date: 16 March 2009

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Electron energy loss spectroscopy (EELS) is used to study the transition from the buffer layer to the first graphene layers during graphitization of SiC(0001). Graphene growth is controlled and correlated with spot profile analysis in low energy electron diffraction and x-ray photoelectron spectroscopy. In the EELS data both electronic transitions and plasmon losses are sensitive to the interface. The collective in-plane excitations show a characteristic blueshift upon graphitization, while single electron transitions with dipole moments along the surface normal are suppressed for the buffer layer. These dependencies can be used to control the number of epitaxially grown graphene layers.
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71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
68.35.bg Semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.20.Uv Electron energy loss spectroscopy
79.60.Jv Interfaces; heterostructures; nanostructures

Pulse width controlled resistivity switching at room temperature in Bi0.8Sr0.2MnO3

A. Rebello and R. Mahendiran

Appl. Phys. Lett. 94, 112107 (2009); http://dx.doi.org/10.1063/1.3093673 (3 pages) | Cited 9 times

Online Publication Date: 17 March 2009

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We report pulsed as well as direct current/voltage induced electroresistance in Bi0.8Sr0.2MnO3 at room temperature. It is shown that bilevel and multilevel resistivity switching can be induced by a sequence of pulses of varying pulse width at a fixed voltage amplitude. Resistivity increases abruptly (≈55% at 300 K) upon reducing pulse width from 100 to 25 ms for a fixed electric field (E = 2 V/cm2) of 200 ms pulse period. The resistivity switching is accompanied by a periodic change in temperature, which alone cannot explain the magnitude of the resistivity change.
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72.60.+g Mixed conductivity and conductivity transitions
72.80.Ga Transition-metal compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Growth of AlGaN/GaN heterojunction field effect transistors on semi-insulating GaN using an AlGaN interlayer

Z. Chen (陈振), Y. Pei (裴轶), S. Newman, R. Chu (储荣明), D. Brown, R. Chung, S. Keller, S. P. Denbaars, S. Nakamura, and U. K. Mishra

Appl. Phys. Lett. 94, 112108 (2009); http://dx.doi.org/10.1063/1.3103210 (3 pages) | Cited 9 times

Online Publication Date: 17 March 2009

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Semi-insulating (SI) GaN layers were grown on 4H-SiC substrates by inserting an AlGaN layer between the AlN buffer and the GaN layer. Secondary ion mass spectroscopy measurements showed that the AlGaN layer prevented Si from diffusing from the substrate into the GaN layer. X-ray diffraction and atomic force microscopy analyses showed that an optimized AlGaN interlayer does not degrade the crystal quality or surface morphology of the SI GaN. The room temperature mobility of an AlGaN/GaN heterostructure using this SI GaN was 2200 cm2/V s. High electron mobility transistors (HEMTs) with 0.65 μm long gates were also fabricated on these SI GaN buffers. A power density of 19.0 W/mm with a power added efficiency of 48% was demonstrated at 10 GHz at a drain bias of 78 V. These HEMTs also exhibited sharp pinch off, low leakage, and negligible dispersion.
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85.30.Tv Field effect devices
68.37.Ps Atomic force microscopy (AFM)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance

Observation of stacking faults formed during homoepitaxial growth of p-type 4H-SiC

Ho Keun Song, Jeong Hyun Moon, Hyeong Joon Kim, and Mehran Mehregany

Appl. Phys. Lett. 94, 112109 (2009); http://dx.doi.org/10.1063/1.3089697 (3 pages) | Cited 1 time

Online Publication Date: 19 March 2009

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Threading dislocations and their transformation into stacking faults (SFs) are observed in p-type 4H-SiC epitaxial layers by high voltage transmission electron microscope. Homoepitaxial growth and in situ aluminum doping of 4H-SiC epitaxial layers are carried out using the organosilicon precursor bistrimethylsilylmethane (C7H20Si2 and the metal-organic precursor trimethylaluminum (C3H9Al), and the free hole concentration of the most heavily aluminum-doped epitaxial layers is >1021 cm−3. Threading dislocations are formed at the interface between the epitaxial layer and the substrate. However, the density of these threading dislocations decreases toward the epitaxial layer surface with their transformations to SFs.
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61.72.Lk Linear defects: dislocations, disclinations
61.72.up Other materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.80.Jc Other crystalline inorganic semiconductors

Nonvolatile memories using deep traps formed in Al2O3 by metal ion implantation

Min Choul Kim, Seung Hui Hong, Hye Ryong Kim, Sung Kim, Suk-Ho Choi, R. G. Elliman, and S. P. Russo

Appl. Phys. Lett. 94, 112110 (2009); http://dx.doi.org/10.1063/1.3097799 (3 pages) | Cited 2 times

Online Publication Date: 19 March 2009

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We demonstrate the feasibility of an approach to nonvolatile memory (NVM) that exploits charge trapping at deep-energy levels formed in Al2O3 by metal doping. Our calculations show that V and Nb are expected to form such deep energy levels in the band gap of Al2O3. To demonstrate the effectiveness of this approach these metal ions were ion-implanted into test structures based on an Al2O3 trapping layer. Several structural analysis techniques and photocurrent spectroscopy show that the doped metal ions are located close to the Al2O3/SiO2 interface and exhibit characteristics consistent with some of the deep levels predicted in calculations. The resulting test devices are shown to exhibit promising NVM characteristics.
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84.30.Sk Pulse and digital circuits
85.40.Ry Impurity doping, diffusion and ion implantation technology

Carrier mobility in a polar semiconductor measured by an optical pump-probe technique

Muneaki Hase

Appl. Phys. Lett. 94, 112111 (2009); http://dx.doi.org/10.1063/1.3103275 (3 pages) | Cited 3 times

Online Publication Date: 19 March 2009

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Ultrafast dephasing of the plasmonlike longitudinal optical phonon-plasmon coupled (LOPC) mode in highly doped n-GaAs has been investigated by using a femtosecond optical pump-probe technique with 40 THz bandwidth as a function of photodoping levels. The direct measurement of plasmon damping with the help of a wavelet analysis enables us to extract carrier (electron) mobility, which decreases with increasing the photodoping levels. It is found that the mobility is suppressed at high photodoping levels due to electron-hole scattering, while it is enhanced near a critical density, being plausibly attributed to the strong coherent coupling of the LO phonon with the plasmon.
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73.61.Ey III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.72.U- Doping and impurity implantation
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.20.Fr Low-field transport and mobility; piezoresistance

Local structure and conduction mechanism in amorphous In–Ga–Zn–O films

Deok-Yong Cho, Jaewon Song, Kwang Duk Na, Cheol Seong Hwang, Jong Han Jeong, Jae Kyeong Jeong, and Yeon-Gon Mo

Appl. Phys. Lett. 94, 112112 (2009); http://dx.doi.org/10.1063/1.3103323 (3 pages) | Cited 17 times

Online Publication Date: 19 March 2009

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The local structures of amorphous In–Ga–Zn–O (InGaZnO4 and In2Ga2ZnO7) films were examined by x-ray absorption spectroscopy and fine structure analysis. The local metal-oxygen coordination in both films indicated bipyramidal GaO5, ZnO5, and trigonal InO6 clusters. Further analyses showed splitting of the Zn–O bond length suggesting distortion of the ZnO5 cluster, which evidenced the existence of localized holes in the Zn atoms. In combination with the abundance of In 5s electrons, this shows that the In–Zn hopping interactions contribute to electrical conduction.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
73.50.Dn Low-field transport and mobility; piezoresistance
78.70.Dm X-ray absorption spectra
71.70.-d Level splitting and interactions

Solid phase epitaxy of amorphous Ge on Si in N2 atmosphere

R. R. Lieten, S. Degroote, M. Leys, N. E. Posthuma, and G. Borghs

Appl. Phys. Lett. 94, 112113 (2009); http://dx.doi.org/10.1063/1.3098075 (3 pages) | Cited 4 times

Online Publication Date: 20 March 2009

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We demonstrate a straightforward and economical way to obtain smooth germanium layers of high quality on silicon. Thin amorphous germanium layers deposited by plasma enhanced chemical vapor deposition on Si(111) substrates are transformed into single crystalline and smooth layers by solid phase epitaxy in N2 atmosphere. The crystal orientation of the substrate has a clear influence on the crystal quality. This is most likely due to a different growth mode, namely, layer-by-layer for Si(111) and three-dimensional growth for Si(001). The amorphous germanium layer can roughen during annealing due to mobile atoms on the surface. This can be effectively suppressed by annealing in N2 ambient. Electrical measurements show high charge mobility.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
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