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8 Oct 2007

Volume 91, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages)

B. J. Lee, K. Park, and Z. M. Zhang
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Reduction of impact-ionization threshold energies for performance enhancement of complementary impact-ionization metal-oxide-semiconductor transistors

Eng-Huat Toh, Grace Huiqi Wang, Lap Chan, Ganesh Samudra, and Yee-Chia Yeo

Appl. Phys. Lett. 91, 153501 (2007); http://dx.doi.org/10.1063/1.2798064 (3 pages) | Cited 1 time

Online Publication Date: 8 October 2007

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We explore the improvement of electrical performance of impact-ionization metal-oxide-semiconductor (I-MOS) transistors by the reduction of impact-ionization threshold energy through incorporation of materials with smaller bandgaps. Silicon-germanium (SiGe) I-MOS transistors were demonstrated. The lower bandgap of SiGe, as compared to Si, contributes to lower electron and hole impact-ionization threshold energies, leading to avalanche breakdown at a much reduced source voltage and enhanced device performance. Both n- and p-channel I-MOS devices were fabricated on Si0.60Ge0.40-on-insulator substrates using a complementary metal-oxide-semiconductor compatible process flow. Excellent subthreshold swings as low as 5 mV/decade were achieved for the SiGe I-MOS devices. Reduction in breakdown voltage VBD was as large as 1.3 and 1.6 V, respectively, for the n- and p-channel Si0.60Ge0.40 I-MOS devices.
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85.30.Tv Field effect devices

Structure-function relationships of conjugated polyelectrolyte electron injection layers in polymer light emitting diodes

Andres Garcia, Renqiang Yang, Youngeup Jin, Bright Walker, and Thuc-Quyen Nguyen

Appl. Phys. Lett. 91, 153502 (2007); http://dx.doi.org/10.1063/1.2794422 (3 pages) | Cited 19 times

Online Publication Date: 8 October 2007

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The characteristics of conjugated polymer light-emitting diodes containing poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) as the emissive layer and cationic or anionic conjugated polyelectrolytes (CPEs) as the electron injection layer are reported. Structure variations involving backbone, type of counterion, and charge were used to establish structure-function relationships. More efficient electron injection from Al and better device performance are attained with CPEs bearing negative charges. For cationic CPEs having the same counterion but different conjugated structures, one observes better device efficiency using the material with higher electron mobility. Thus, both charge and backbone are important for optimizing device performance.
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85.60.Jb Light-emitting devices

Suppression of interface state generation upon electron injection in nitrided oxides grown on 4H-SiC

John Rozen, Sarit Dhar, S. T. Pantelides, L. C. Feldman, Sanwu Wang, J. R. Williams, and V. V. Afanas’ev

Appl. Phys. Lett. 91, 153503 (2007); http://dx.doi.org/10.1063/1.2790374 (3 pages) | Cited 10 times

Online Publication Date: 9 October 2007

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The flatband voltage stability of SiO2/SiC metal-oxide-semiconductor capacitors upon electron injection can be enhanced by the introduction of nitrogen in a thermal gate oxide. We show that it is due to the suppression of negative charge buildup in interface states during injection. We discuss the role of nitrogen in this effect and how it might be linked to the passivation of interface defects.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Efficient green organic light-Emitting devices with a nondoped dual-functional electroluminescent material

Qing-Xiao Tong, Shiu-Lun Lai, Mei-Yee Chan, Ka-Ho Lai, Jian-Xin Tang, Hoi-Lun Kwong, Chun-Sing Lee, and Shuit-Tong Lee

Appl. Phys. Lett. 91, 153504 (2007); http://dx.doi.org/10.1063/1.2795339 (3 pages) | Cited 15 times

Online Publication Date: 9 October 2007

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An efficient nondoped green organic light-emitting device was demonstrated by using a dual-functional electroluminescent material, 4,4′,4″-tris[8-(7,10-diphenylfluoranthenyl)] phenylamine (TDPFPA). TDPFPA was shown to be a good hole transporting [with a mobility of (1.1–1.2)×10−4 cm2 V−1 s−1 at (1.8–5.6)×105 V cm−1] and efficient fluorescent material with an exceptionally high glass transition temperature of 237 °C. The device with a simple structure of indium tin oxide/TDPFPA/4,7-diphenyl-1,10-phenanthroline/LiF/Al showed green emission with Commission Internationale de L’Eclairage coordinates of (0.24, 0.54), a current efficiency of 9.9 cd/A, and power efficiency of 10.6 lm/W.
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85.60.Jb Light-emitting devices

Comparative study of trap densities of states in CdTe/CdS solar cells

Y. Y. Proskuryakov, J. D. Major, K. Durose, V. Barrioz, S. J. C. Irvine, E. W. Jones, and D. Lamb

Appl. Phys. Lett. 91, 153505 (2007); http://dx.doi.org/10.1063/1.2790778 (3 pages) | Cited 5 times

Online Publication Date: 9 October 2007

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Density of deep and shallow states has been investigated in three different kinds of CdTe/CdS samples, two of which were grown by metal-organic chemical vapor deposition (MOCVD) and one by close-space sublimation (CSS) methods. The MOCVD samples were p doped by As and grown either with or without a ZnO buffer layer between the transparent conductor and CdS layers. Capacitance-voltage, admittance spectroscopy, and quantum efficiency measurements show pronounced effects of As doping and ZnO incorporation. It is found that A centers and vacancies of Cd, usually observed in CSS devices, are absent in the defect spectra of MOCVD samples.
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84.60.Jt Photoelectric conversion
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.70.Hz Solid-vapor transitions
61.72.J- Point defects and defect clusters
61.72.up Other materials

Nonvolatile nanocrystal charge trap flash memory devices using a micellar route to ordered arrays of cobalt nanocrystals

Chiyoung Lee, Jeong-Hwa Kwon, Jang-Sik Lee, Yong-Mu Kim, Yoojung Choi, Hyunjung Shin, Jaegab Lee, and Byeong-Hyeok Sohn

Appl. Phys. Lett. 91, 153506 (2007); http://dx.doi.org/10.1063/1.2798502 (3 pages) | Cited 19 times

Online Publication Date: 9 October 2007

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This study demonstrates that self-assembled diblock copolymer micelles can be used as a template to assemble cobalt (Co) nanocrystal (NC) arrays for use as charge storage layers in charge trap flash memory devices. Diblock copolymer micelles embedded with Co were synthesized on p-Si substrates having a thin tunneling oxide of HfO2. The micelle templates were completely removed by oxygen plasma treatment and reduction procedures, resulting in ordered arrays of Co NCs. The nonvolatile memory devices exhibit program/erase characteristics, as confirmed by their capacitance-voltage responses, current-voltage responses, endurance characterization, and nanoscale device measurement using scanning nonlinear dielectric microscopy.
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84.30.Sk Pulse and digital circuits
81.07.Bc Nanocrystalline materials

Three-dimensional microphotonic crystals of ZrO2 toughened Al2O3 for terahertz wave applications

Weiwu Chen, Soshu Kirihara, and Yoshinari Miyamoto

Appl. Phys. Lett. 91, 153507 (2007); http://dx.doi.org/10.1063/1.2783199 (3 pages) | Cited 7 times

Online Publication Date: 10 October 2007

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This letter reports an approach, based on microstereolithography, to create three-dimensional photonic crystals of microscale structure made of ceramic-resin composite (before sintering) and dense ceramics (after sintering). For ZrO2 toughened Al2O3 ceramic-resin photonic crystals (with a lattice constant of 500 μm), the forming resolution was around 10 μm and the measured band gap appeared between 350 and 400 GHz in the Γ-X ⟨100⟩ direction, 350 and 400 GHz in the Γ-K ⟨110⟩ direction, and 270 and 360 GHz in the Γ-L ⟨111⟩ direction. After sintering, the lattice constant shrunk to 380 μm and the band gap was between 320 and 420 GHz in the Γ-X ⟨100⟩ direction, 330 and 400 GHz in the Γ-K ⟨110⟩ direction, and 260 and 355 GHz in the Γ-L ⟨111⟩ direction.
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42.70.Qs Photonic bandgap materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Electrical properties in vanadyl-phthalocyanine-based metal-insulator-semiconductor devices

Lijuan Wang, Guojun Liu, Haibo Wang, De Song, Bo Yu, and Donghang Yan

Appl. Phys. Lett. 91, 153508 (2007); http://dx.doi.org/10.1063/1.2798585 (3 pages) | Cited 7 times

Online Publication Date: 10 October 2007

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We investigated electrical properties of vanadyl phthalocyanine (VOPc) metal-insulator-semiconductor (MIS) devices by the measurement of capacitance and conductance, which were fabricated on ordered para-sexiphenyl (p-6P) layer by weak epitaxy growth method. The VOPc/p-6P MIS diodes showed a negligible hysteresis effect at a gate voltage of ±20 V and small hysteresis effect at a gate voltage of ±40 V due to the low interface trap state density of about 1×1010 eV−1 cm−2. Furthermore, a high transition frequency of about 10 kHz was also observed under their accumulation mode. The results indicated that VOPc was a promising material and was suitable to be applied in active matrix liquid crystal displays and organic logic circuits.
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85.30.Kk Junction diodes
85.30.Tv Field effect devices
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