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8 Mar 2010

Volume 96, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 96, 101501 (2010); http://dx.doi.org/10.1063/1.3352316 (3 pages)

Bomi Gweon, Daeyeon Kim, Dan Bee Kim, Heesoo Jung, Wonho Choe, and Jennifer H. Shin
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Effects of barrier layers on device performance of high mobility In0.7Ga0.3As metal-oxide-semiconductor field-effect-transistors

Han Zhao, Yen-Ting Chen, Jung Hwan Yum, Yanzhen Wang, Fei Zhou, Fei Xue, and Jack C. Lee

Appl. Phys. Lett. 96, 102101 (2010); http://dx.doi.org/10.1063/1.3350893 (3 pages) | Cited 26 times

Online Publication Date: 8 March 2010

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We have applied single InP barrier layer with different thicknesses and InP/In0.52Al0.48As double-barrier layer to In0.7Ga0.3As Al2O3 metal-oxide-semiconductor field-effect-transistors (MOSFETs) and investigated their effects on device performance. In0.7Ga0.3As MOSFETs with 3 nm InP single-barrier attain 22% higher peak effective mobility while devices with 5 nm InP attain 58% higher peak mobility than the ones without barrier. Devices using InP/In0.52Al0.48As double-barrier achieve mobility enhancement at both low-field (68% at peak mobility) and high-field (55%) compared to ones without barrier. High channel mobility of 4729 cm2/V s has been obtained using InP/In0.52Al0.48As barrier and atomic-layer-deposited Al2O3 gate oxide.
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85.30.Tv Field effect devices
81.05.Ea III-V semiconductors

Multiband quantum transport simulations of ultimate p-type double-gate transistors: Influence of the channel orientation

Nicolas Cavassilas, Nicolas Pons, Fabienne Michelini, and Marc Bescond

Appl. Phys. Lett. 96, 102102 (2010); http://dx.doi.org/10.1063/1.3352558 (3 pages) | Cited 3 times

Online Publication Date: 8 March 2010

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We present a ballistic real-space six-band k.p transport model to study the influence of the channel orientation in double-gate p-type metal-oxide-semiconductor (pMOS) transistors. The six-band k.p Hamiltonian is integrated into a self-consistent two-dimensional ballistic transport simulator based on the nonequilibrium Green’s function formalism. The impact of the transport direction is analyzed as a function of the Si transistor channel length. We show that direct source-drain tunneling strongly degrades the subthreshold behavior in short [110]-oriented transistors. This result contradicts the commonly accepted idea that [110] channel orientation provides the best performances for pMOS devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Investigating the origin of Fermi level pinning in Ge Schottky junctions using epitaxially grown ultrathin MgO films

Yi Zhou, Wei Han, Yong Wang, Faxian Xiu, Jin Zou, R. K. Kawakami, and Kang. L. Wang

Appl. Phys. Lett. 96, 102103 (2010); http://dx.doi.org/10.1063/1.3357423 (3 pages) | Cited 20 times

Online Publication Date: 8 March 2010

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Fermi level (FL) pinning at the Ge valence band results in a high Schottky barrier height for all metal/n-Ge contacts. The origin of this pinning effect has been ascribed to either metal induced gap states or surface states arise from the native defects at the Ge surface, such as dangling bonds. The discrepancy in the reported results/explanations is mainly due to the lack of an explicit characterization of a high quality metal/Ge or metal/ultrathin oxide/Ge junction, which should be ideally single crystalline, atomically smooth and free of process-induced defects or intermixing. We report the Schottky characteristics of high quality metal/MgO/n-Ge junctions with the ultrathin MgO epitaxially grown on Ge. We find the depinning effect displays a weak dependence on the MgO thickness, indicating the interface states due to the native defects on Ge surface are likely to play the dominant role in FL pinning.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
71.55.Cn Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

AlGaN-based ultraviolet photodetector with micropillar structures

Wei-Chih Lai, Li-Chi Peng, Chien-Chun Chen, Jinn-Kong Sheu, and Shih-Chang Shei

Appl. Phys. Lett. 96, 102104 (2010); http://dx.doi.org/10.1063/1.3354018 (3 pages)

Online Publication Date: 9 March 2010

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We demonstrated a single AlGaN layer with two different Al contents on the GaN μ-pillars template. It was found by the selective wavelength spatial cathodoluminescence images that the emission wavelengths of the AlGaN layer were at 345 and 325 nm on the side of the cone and on the top and valley surface of pillars, respectively. The Schottky-type photodetectors were also demonstrated on double Al contents of deposited AlGaN on GaN micropillar templates. The three steps of responses occurred at about 326, 346, and 356 nm with responsivities of 1.1×10−2, 5.9×10−3, and 4.04×10−3 A/W, respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.60.Hk Cathodoluminescence, ionoluminescence

Single-electron pumping from a quantum dot into an electrode

Kenji Sasaoka, Takahiro Yamamoto, and Satoshi Watanabe

Appl. Phys. Lett. 96, 102105 (2010); http://dx.doi.org/10.1063/1.3319497 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2010

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The transient current dynamics of a quantum capacitor consisting of a quantum dot connected to a single electrode has been theoretically investigated by the nonequilibrium Green’s function method. We have clarified the influence of dot-electrode coupling strength on the transient current behavior of the quantum capacitor. Our simulation reproduces very well the behaviors seen in recent experimental results by Fève et al., [Science 316, 1169 (2007)] , such as the increase in maximum value of instantaneous current and the decrease in total amount of electrons pumped from the dot when the dot-electrode coupling increases.
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85.35.Gv Single electron devices
84.32.Tt Capacitors
73.21.La Quantum dots

Low subthreshold slope in junctionless multigate transistors

Chi-Woo Lee, Alexei N. Nazarov, Isabelle Ferain, Nima Dehdashti Akhavan, Ran Yan, Pedram Razavi, Ran Yu, Rodrigo T. Doria, and Jean-Pierre Colinge

Appl. Phys. Lett. 96, 102106 (2010); http://dx.doi.org/10.1063/1.3358131 (3 pages) | Cited 17 times

Online Publication Date: 10 March 2010

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The improvement of subthreshold slope due to impact ionization is compared between “standard” inversion-mode multigate silicon nanowire transistors and junctionless transistors. The length of the region over which impact ionization takes place, as well as the amplitude of the impact ionization rate are found to be larger in the junctionless devices, which reduces the drain voltage necessary to obtain a sharp subthreshold slope.
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85.30.Tv Field effect devices
72.20.Ht High-field and nonlinear effects

Effects of ambient atmosphere on the transfer characteristics and gate-bias stress stability of amorphous indium-gallium-zinc oxide thin-film transistors

Sang-Yun Sung, Jun Hyuk Choi, Un Bin Han, Ki Chang Lee, Joon-Hyung Lee, Jeong-Joo Kim, Wantae Lim, S. J. Pearton, D. P. Norton, and Young-Woo Heo

Appl. Phys. Lett. 96, 102107 (2010); http://dx.doi.org/10.1063/1.3357431 (3 pages) | Cited 25 times

Online Publication Date: 10 March 2010

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We investigated the transfer characteristics and the gate-bias stability of amorphous indium-gallium-zinc oxide thin-film transistors when the channel layer was exposed to hydrogen, oxygen, air, or vacuum at room temperature during measurements. The threshold voltage and the drain current were changed by the ambient atmospheres. The threshold voltage shift (ΔVth) under gate-bias stress was faster in hydrogen than in oxygen and vacuum. It is suggested that hydrogen exposure degrades the gate-bias stress stability due to surface accumulation layer creation. The characteristic trapping times, τ, in H2, O2, air, and vacuum were 5×103, 1.5×104, 2×104, and 6.3×104 s, respectively.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
73.61.Jc Amorphous semiconductors; glasses

Electronic structure and contact resistance at an open-end carbon nanotube and copper interface

Feng Gao, Jianmin Qu, and Matthew Yao

Appl. Phys. Lett. 96, 102108 (2010); http://dx.doi.org/10.1063/1.3354077 (3 pages) | Cited 8 times

Online Publication Date: 11 March 2010

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We report a quantum mechanics study on the electronic structure and contact resistance at an open-end carbon nanotube and copper interface. The local density of states near the carbon nanotube (CNT)/Cu interface are computed using density functional theory (DFT), and the transmission coefficient is calculated using a nonequilibrium Green’s function method in conjunction with DFT. The current-voltage relation of the simulating cell is obtained by using the Landauer–Buttiker formula, from which the contact resistance can be determined. Our results indicate that the contact resistance of the Cu/CNT/Cu system is comparable to that of solder/Cu interface in electronic packaging.
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73.22.-f Electronic structure of nanoscale materials and related systems
73.40.Cg Contact resistance, contact potential
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Carrier velocity in InAlN/AlN/GaN heterostructure field effect transistors on Fe-doped bulk GaN substrates

J. H. Leach, M. Wu, X. Ni, X. Li, J. Xie, Ü. Özgür, H. Morkoç, T. Paskova, E. Preble, K. R. Evans, and Chang-Zhi Lu

Appl. Phys. Lett. 96, 102109 (2010); http://dx.doi.org/10.1063/1.3358192 (3 pages) | Cited 2 times

Online Publication Date: 12 March 2010

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We report microwave characteristics of field effect transistors employing InAlN/AlN/GaN heterostructures grown on low-defect-density bulk Fe-doped GaN substrates. We achieved unity current gain cutoff frequencies of 14.3 and 23.7 GHz for devices with gate lengths of 1 and 0.65 μm, respectively. Measurements as a function of applied bias allow us to estimate the average carrier velocity in the channel to be ∼ 1.0×107 cm/sec for a 1 μm device. Additionally, we found nearly no gate lag in the devices, which is considered a precondition for good performance under large signal operation.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology

Low temperature germanium to silicon direct wafer bonding using free radical exposure

Ki Yeol Byun, Isabelle Ferain, Pete Fleming, Michael Morris, Mark Goorsky, and Cindy Colinge

Appl. Phys. Lett. 96, 102110 (2010); http://dx.doi.org/10.1063/1.3360201 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2010

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A low temperature germanium (Ge) to silicon (Si) wafer bonding method was demonstrated by in situ radical activation bonding in vacuum. In order to gain further insight into the bonding mechanism, the Ge surface chemistry after either oxygen or nitrogen radical activation was analyzed by means of angle-resolved x-ray photoelectron spectroscopy. After low temperature direct bonding of Ge to Si followed by annealing at 200 and 300 °C, advanced imaging techniques were used to characterize the bonded interface.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Low defect-mediated reverse-bias leakage in (0001) GaN via high-temperature molecular beam epitaxy

J. J. M. Law, E. T. Yu, G. Koblmüller, F. Wu, and J. S. Speck

Appl. Phys. Lett. 96, 102111 (2010); http://dx.doi.org/10.1063/1.3360227 (3 pages) | Cited 10 times

Online Publication Date: 12 March 2010

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Conductive atomic force microscopy, scanning electron microscopy, and x-ray diffraction were used to determine the effects of Ga/N flux ratio on the conductivity of current leakage paths in GaN grown by molecular beam epitaxy. Our data reveal a band of fluxes near Ga/N ≈ 1 for which these pathways ceased to be observable. We conclude that changes in surface defects surrounding or impurities along screw-component threading dislocations are responsible for their conductive nature. These observations suggest a method for controlling the primary source of reverse-bias Schottky contact leakage in n-type GaN grown by molecular beam epitaxy.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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