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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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Size dependence of the electronic structures and electron-phonon coupling in ZnO quantum dots

S. C. Ray, Y. Low, H. M. Tsai, C. W. Pao, J. W. Chiou, S. C. Yang, F. Z. Chien, W. F. Pong, M.-H. Tsai, K. F. Lin, H. M. Cheng, W. F. Hsieh, and J. F. Lee

Appl. Phys. Lett. 91, 262101 (2007); http://dx.doi.org/10.1063/1.2824396 (3 pages) | Cited 5 times

Online Publication Date: 26 December 2007

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The electronic structures and optical properties of various sizes of ZnO quantum dots (QDs) were studied using x-ray absorption, photoluminescence, and Raman spectroscopy. The increase in the intensity ratio of the second-order Raman spectra of longitudinal optical mode and its fundamental mode, which is related to the strength of the electron-phonon coupling (EPC), is found to increase with the size of QD. The trend of EPC also correlates with the increase of the intensity ratio of the O 2pπ (Iπ) and 2pσ (Iσ) orbital features in the O K-edge x-ray absorption near-edge structure (XANES) as the size of QD increases. The EPC and XANES results suggest that the crystal orientations of ZnO QDs are approximately aligned with the c axis parallel with the polarization of x-ray photons.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.67.Hc Quantum dots

Electron mobility in InGaN channel heterostructure field effect transistor structures with different barriers

J. Xie, J. H. Leach, X. Ni, M. Wu, R. Shimada, Ü. Özgür, and H. Morkoç

Appl. Phys. Lett. 91, 262102 (2007); http://dx.doi.org/10.1063/1.2824461 (3 pages) | Cited 9 times

Online Publication Date: 26 December 2007

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InGaN possesses higher electron mobility and velocity than GaN, and therefore is expected to lead to relatively better performances for heterostructure field effect transistors (HFETs). However, the reported mobilities for AlGaN/InGaN HFETs are lower than GaN channel HFETs. To address this issue, we studied the effect of different barriers on the Hall mobility for InGaN channel HFETs grown by metal organic chemical vapor deposition. Unlike the conventional AlGaN barrier, the AlInN barrier can be grown at the same temperature as the InGaN channel layer, alleviating some of the technological roadblocks. Specifically, this avoids possible degradation of the thin InGaN channel during AlGaN growth at high temperatures; and paves the way for better interfaces. An undoped In0.18Al0.82N/AlN/In0.04Ga0.96N HFET structure exhibited a μH = 820 cm2/V s, with a ns = 2.12×1013 cm−2 at room temperature. Moreover, with an In-doped AlGaN barrier, namely, Al0.24In0.01Ga0.75N, grown at 900 °C, the μH increased to 1230 cm2/V s with a ns of 1.09×1013 cm−2 for a similar InGaN channel. Furthermore, when the barrier was replaced by Al0.25Ga0.75N grown at 1030 °C, μH dropped to 870 cm2/V s with ns of 1.26×1013 cm−2 at room temperature. Our results suggest that to fully realize the potential of the InGaN channel HFETs, AlInN or AlInGaN should be used as the barrier instead of the conventional AlGaN barrier.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Thickness dependence of the electronic properties in V2O3 thin films

C. Grygiel, Ch. Simon, B. Mercey, W. Prellier, R. Frésard, and P. Limelette

Appl. Phys. Lett. 91, 262103 (2007); http://dx.doi.org/10.1063/1.2824465 (3 pages) | Cited 13 times

Online Publication Date: 26 December 2007

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High quality vanadium sesquioxide V2O3 films (170–1100 Å) were grown using the pulsed laser deposition technique on (0001)-oriented sapphire substrates, and the effects of film thickness on the lattice strain and electronic properties were examined. X-ray diffraction indicates that there is an in-plane compressive lattice parameter (a), close to −3.5% with respect to the substrate and an out-of-plane tensile lattice parameter (c). The thin film samples display metallic character between 2 and 300 K, and no metal-to-insulator transition is observed. At low temperature, the V2O3 films behave as a strongly correlated metal, and the resistivity (ρ) follows the equation ρ = ρ0+AT2, where A is the transport coefficient in a Fermi liquid. Typical values of A have been calculated to be 0.14 μΩ cm K−2, which is in agreement with the coefficient reported for V2O3 single crystals under high pressure. Moreover, a strong temperature dependence of the Hall resistance confirms the electronic correlations of these V2O3 thin film samples.
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73.20.At Surface states, band structure, electron density of states
73.61.-r Electrical properties of specific thin films
71.27.+a Strongly correlated electron systems; heavy fermions
72.20.My Galvanomagnetic and other magnetotransport effects
68.60.Bs Mechanical and acoustical properties

Cerium oxide nanocrystals for nonvolatile memory applications

Shao-Ming Yang, Chao-Hsin Chien, Jiun-Jia Huang, Tan-Fu Lei, Ming-Jinn Tsai, and Lurng-Shehng Lee

Appl. Phys. Lett. 91, 262104 (2007); http://dx.doi.org/10.1063/1.2821367 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2007

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The characteristics of silicon-oxide-nitride-oxide-silicon-type memories embedded with cerium oxide nanocrystals were demonstrated. They were fabricated by depositing a thin CeO2 film on the SiO2 tunneling layer and subsequently rapid-thermal annealing process. The mean size and aerial density of the CeO2 nanocrystals embedded in SiO2 are estimated to be about 8–10 nm and (3–7)×1011/cm−2 after a high-temperature annealing with different ambients on 900 °C. The program/erase behaviors and data retention characteristics were described to demonstrate its advantages for nonvolatile memory device applications.
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84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices
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