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9 Feb 2009

Volume 94, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 94, 062105 (2009); http://dx.doi.org/10.1063/1.3079078 (3 pages)

Ikai Lo, Chia-Ho Hsieh, Yu-Chi Hsu, Wen-Yuan Pang, and Ming-Chi Chou
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Dependence of energy band offsets at Ge2Sb2Te5/SiO2 interface on nitrogen concentration

Lina Wei-Wei Fang, Zhang Zheng, Ji-Sheng Pan, Rong Zhao, Minghua Li, Luping Shi, Tow-Chong Chong, and Yee-Chia Yeo

Appl. Phys. Lett. 94, 062101 (2009); http://dx.doi.org/10.1063/1.3079396 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2009

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The electronic property for a series of nitrogen-doped Ge2Sb2Te5 phase change material was characterized using high-resolution x-ray photoelectron spectroscopy. The Te 3d5/2 and Si 2p core-level spectra as well as valence band spectra were used in the analysis. As the nitrogen content increases, the valence band offset also decreases, while that of the conduction band increases. Our results show that the valence band and conduction band offsets of nitrogen-doped Ge2Sb2Te5 on silicon oxide exhibit a linear dependence on nitrogen content in the film, for nitrogen content of up to 8.4 at. %.
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71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.up Other materials

NiSiGe nanocrystals for nonvolatile memory devices

Chih-Wei Hu, Ting-Chang Chang, Chun-Hao Tu, Cheng-Neng Chiang, Chao-Cheng Lin, Simon M. Sze, and Tseung-Yuen Tseng

Appl. Phys. Lett. 94, 062102 (2009); http://dx.doi.org/10.1063/1.3080201 (3 pages) | Cited 1 time

Online Publication Date: 9 February 2009

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In this work, charge-storage characteristics of NiSiGe nanocrystal memory device have been studied. Transmission electron microscope shows that the annealed NiSiGe film has higher nanocrystal size and density distribution. Related material analyses such as x-ray photoelectron spectroscopy, Raman spectroscopy, and energy dispersive spectrometer were used to confirm that the Ge elements provide the additional nucleation centers and enhance the nanocrystals aggregation during thermal process. With the improved nanocrystal formation process, a remarkable improvement of the memory effect is observed by comparing the NiSi and NiSiGe nanocrystals. In addition, the retention characteristics of the nanocrystals memory devices have been discussed.
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84.30.Sk Pulse and digital circuits
78.66.Nk Insulators
79.60.-i Photoemission and photoelectron spectra
78.30.Hv Other nonmetallic inorganics

Point defects in sputtered NiO films

Wei-Luen Jang, Yang-Ming Lu, Weng-Sing Hwang, Tung-Li Hsiung, and H. Paul Wang

Appl. Phys. Lett. 94, 062103 (2009); http://dx.doi.org/10.1063/1.3081025 (3 pages) | Cited 10 times

Online Publication Date: 10 February 2009

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The dominant point defects in p-type NiO films were determined by analyzing the coordination number (CN) change with various annealing temperatures and the composition profile of double-layer films deposited individually in oxygen and in argon atmospheres. The results show that the nonstoichiometry of sputtered NiO film is determined by the number of nickel atoms rather than by the number of oxygen atoms. It is concluded that nickel vacancies are the dominant point defects that result in the electrical conductivity of NiO films.
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61.72.jd Vacancies
68.55.ag Semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
73.61.Le Other inorganic semiconductors
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Electronic properties of dislocations in GaN investigated by scanning tunneling microscopy

Ph. Ebert, L. Ivanova, S. Borisova, H. Eisele, A. Laubsch, and M. Dähne

Appl. Phys. Lett. 94, 062104 (2009); http://dx.doi.org/10.1063/1.3073741 (3 pages) | Cited 12 times

Online Publication Date: 10 February 2009

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We investigated the type, spatial distribution, line direction, and electronic properties of dislocations in n-type GaN by scanning tunneling microscopy. We found uncharged perfect dislocations with a/3{11math0} Burgers vectors and negatively charged Shockley partial dislocations with a/3{1math00} Burgers vectors interconnected by a negatively charged stacking fault. The charges are traced to different charge transfer levels associated with the particular core structure.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.20.Nr Semiconductor compounds

Self-assembled GaN hexagonal micropyramid and microdisk

Ikai Lo, Chia-Ho Hsieh, Yu-Chi Hsu, Wen-Yuan Pang, and Ming-Chi Chou

Appl. Phys. Lett. 94, 062105 (2009); http://dx.doi.org/10.1063/1.3079078 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2009

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The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO2 by plasma-assisted molecular-beam epitaxy. It was found that the (000math) disk was established with the capture of N atoms by most-outside Ga atoms as the (1×1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Improved reliability of Mo nanocrystal memory with ammonia plasma treatment

Chao-Cheng Lin, Ting-Chang Chang, Chun-Hao Tu, Wei-Ren Chen, Chih-Wei Hu, Simon M. Sze, Tseung-Yuen Tseng, Sheng-Chi Chen, and Jian-Yang Lin

Appl. Phys. Lett. 94, 062106 (2009); http://dx.doi.org/10.1063/1.3081021 (3 pages) | Cited 5 times

Online Publication Date: 12 February 2009

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We investigated ammonia plasma treatment influence on the nonvolatile memory characteristics of the charge storage layer composed of Mo nanocrystals embedded in nonstoichiometry oxide (SiOx). X-ray photoelectron spectra analyses revealed that nitrogen was incorporated into the charge storage layer. Electric analyses indicated that the memory window was reduced and the retention and the endurance improved after the treatment. The reduction in the memory window and the improvement in retention were interpreted in terms of the nitrogen passivation of traps in the oxide around Mo nanocrystals. The robust endurance characteristic was attributed the improvement of the quality of the surrounding oxide by nitrogen passivation.
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84.30.Sk Pulse and digital circuits
52.77.-j Plasma applications
79.60.Jv Interfaces; heterostructures; nanostructures
81.65.Rv Passivation

Realization of a high mobility dual-gated graphene field-effect transistor with Al2O3 dielectric

Seyoung Kim, Junghyo Nah, Insun Jo, Davood Shahrjerdi, Luigi Colombo, Zhen Yao, Emanuel Tutuc, and Sanjay K. Banerjee

Appl. Phys. Lett. 94, 062107 (2009); http://dx.doi.org/10.1063/1.3077021 (3 pages) | Cited 134 times

Online Publication Date: 12 February 2009

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We fabricate and characterize dual-gated graphene field-effect transistors using Al2O3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al2O3. Our devices show mobility values of over 8000 cm2/V s at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering and consequently degrade the device characteristics. We propose a device model to fit the experimental data using a single mobility value.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Superlinear photovoltaic effect in Si nanocrystals based metal-insulator-semiconductor devices

S. Prezioso, S. M. Hossain, A. Anopchenko, L. Pavesi, M. Wang, G. Pucker, and P. Bellutti

Appl. Phys. Lett. 94, 062108 (2009); http://dx.doi.org/10.1063/1.3081410 (3 pages) | Cited 13 times

Online Publication Date: 12 February 2009

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Superlinear-variation in short circuit photocurrent with increasing incident optical power has been observed in metal-insulator-semiconductor structures having a silicon rich oxinitride active layer containing silicon nanocrystals. A model has been elaborated where an internal gain mechanism explains the superlinear photovoltaic effect. The internal gain mechanism is due to secondary carrier generation (SCG) from sub-bandgap levels in the nanocrystal. SCG is caused by impact excitation from the photogenerated conduction band electrons. The sub-bandgap levels are associated to traps formed at the dielectric/Si-nanocrystals interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.40.+w Photoconduction and photovoltaic effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Strain-controlled electronic properties and magnetorelaxor behaviors in electron-doped CaMnO3 thin films

P.-H. Xiang, H. Yamada, A. Sawa, and H. Akoh

Appl. Phys. Lett. 94, 062109 (2009); http://dx.doi.org/10.1063/1.3082091 (3 pages) | Cited 6 times

Online Publication Date: 13 February 2009

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We have fabricated epitaxial thin films of electron-doped manganite Ca1−xCexMnO3 (CCMO) with 0 ≤ x ≤ 0.08. The transport properties of CCMO films are very sensitive to substrate-controlled epitaxial strain. For the CCMO(x = 0.05) film, the metallic transport characteristic is observed only on a nearly lattice-matched NdAlO3 (NAO) substrate, while tensilely and compressively stressed films are insulating. The CCMO(x = 0.06) film on the NAO substrate shows a large magnetoresistance characteristic of a magnetorelaxor. This behavior can be explained in terms of the phase separation and the irreversible growth of the metallic domain in antiferromagnetic insulating matrix.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.50.Ee Antiferromagnetics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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