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28 Feb 2011

Volume 98, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 98, 093502 (2011); http://dx.doi.org/10.1063/1.3531756 (3 pages)

Marina S. Leite, Robyn L. Woo, William D. Hong, Daniel C. Law, and Harry A. Atwater
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Probability of divacancy trap production in silicon diodes exposed to focused ion beam irradiation

Željko Pastuović, Ettore Vittone, Ivana Capan, and Milko Jakšić

Appl. Phys. Lett. 98, 092101 (2011); http://dx.doi.org/10.1063/1.3559000 (3 pages) | Cited 6 times

Online Publication Date: 28 February 2011

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We present ion beam induced charge (IBIC) measurements of the critical displacement damage dose Dd values and modeling of the probability of divacancy trap production in p+−n−n+ silicon diodes exposed to megaelectron volt energy ion beam irradiation. The normalized induced charge (Q0/Q) measured by He ion probe in tested silicon diodes irradiated by focused He, Li, O, and Cl ion beams with energies of about 0.3 MeV/u increases linearly with Dd according to the modified radiation damage function and nonionizing energy loss (NIEL) theory. A simple IBIC model based on Gunn theorem showed clear dependence of the induced charge Q and corresponding equivalent damage factor Ked value on both a depth profile of charge created by ionizing particle (probe) and a depth distribution of stable defects created from primary defects produced by damaging ions. The average probability of the divacancy production (defined as the ratio of the final electrical active defect quantity and primary ion induced vacancy quantity for each impinging ion) of 0.18 (18%) was calculated by the IBIC modeling for all damaging ions.
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85.30.Kk Junction diodes

Current rectification induced by asymmetrical electrode materials in a molecular device

J. B. Pan, Z. H. Zhang, K. H. Ding, X. Q. Deng, and C. Guo

Appl. Phys. Lett. 98, 092102 (2011); http://dx.doi.org/10.1063/1.3556278 (3 pages) | Cited 16 times

Online Publication Date: 28 February 2011

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Molecular devices are constructed based on a molecule connected into both electrodes with different metal materials, and their transport properties are investigated by the first-principles method. The result shows that such devices can generate two asymmetrical Schottky barriers at contacts; the current rectification thus is created. This rectification is also fully rationalized by the calculated transmission spectra and the spatial distribution of the lowest unoccupied molecular orbital and highest occupied molecular orbital states. Our study suggests that it might be a very important way for both electrodes using different materials to realize a molecular rectification.
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85.65.+h Molecular electronic devices

Terahertz optical-Hall effect characterization of two-dimensional electron gas properties in AlGaN/GaN high electron mobility transistor structures

S. Schöche, Junxia Shi, A. Boosalis, P. Kühne, C. M. Herzinger, J. A. Woollam, W. J. Schaff, L. F. Eastman, M. Schubert, and T. Hofmann

Appl. Phys. Lett. 98, 092103 (2011); http://dx.doi.org/10.1063/1.3556617 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2011

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The free-charge carrier mobility, sheet density, and effective mass of a two-dimensional electron gas are exemplarily determined in the spectral range from 640 GHz to 1 THz in a AlGaN/GaN heterostructure using the optical-Hall effect at room temperature. Complementary midinfrared spectroscopic ellipsometry measurements are performed for analysis of heterostructure constituents layer thickness, phonon mode, and free-charge carrier parameters. The electron effective mass is determined to be (0.22±0.04)m0. The high-frequency sheet density and carrier mobility parameters are in good agreement with results from dc electrical Hall effect measurements, indicative for frequency-independent carrier scattering mechanisms of the two-dimensional carrier distribution.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Shallow donor and DX states of Si in AlN

N. T. Son, M. Bickermann, and E. Janzén

Appl. Phys. Lett. 98, 092104 (2011); http://dx.doi.org/10.1063/1.3559914 (3 pages) | Cited 2 times

Online Publication Date: 28 February 2011

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In unintentionally Si-doped AlN, the electron paramagnetic resonance (EPR) spectrum of the Si shallow donor (g = 1.9905) was observed in darkness at room temperature. The temperature dependence of the EPR signal suggests that Si in AlN is a DX center with the DX− state lying at ∼ 78 meV below the neutral shallow donor state. With such relatively small thermal activation energy, Si is expected to behave as a shallow dopant in AlN at normal device operating temperatures.
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71.55.Eq III-V semiconductors
76.30.Lh Other ions and impurities

Light-induced long-ranged disorder effect in ultradilute two-dimensional holes in GaAs heterojunction-insulated-gate field-effect-transistors

Jian Huang, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 98, 092105 (2011); http://dx.doi.org/10.1063/1.3560061 (3 pages)

Online Publication Date: 28 February 2011

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Comparing the results of transport measurements of strongly correlated two-dimensional holes in a GaAs heterojunction-insulated-gate field-effect-transistor obtained before and after a brief photoillumination, the light-induced disorder is found to cause qualitative changes suggesting altered carrier states. For charge concentrations ranging from 3×1010 down to 7×108 cm−2, the post-illumination hole mobility exhibits a severe suppression for charge densities below 2×1010 cm−2 while almost no change for densities above. The long-ranged nature of the disorder is identified. The temperature dependence of the conductivity is also drastically modified by the disorder reconfiguration from being nonactivated to activated.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects

Charge carrier velocity distributions in field-effect transistors

Chen-Guan Lee, Brian Cobb, Laura Ferlauto, and Ananth Dodabalapur

Appl. Phys. Lett. 98, 092106 (2011); http://dx.doi.org/10.1063/1.3558910 (3 pages) | Cited 1 time

Online Publication Date: 28 February 2011

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The measurement of the distribution of charge carrier velocities in a field-effect transistor can provide considerable insight into charge transport mechanisms and structure-property relationships. We have developed such a method and have applied it to study temperature-dependent velocity distributions in solution-processed zinc-tin oxide thin-film transistors. Two distinct transport pathways, each with a different activation energy, have been observed, in contrast to a single activation energy yielded by steady-state measurements. Our results show that more insight into charge transport behavior and phenomena can be obtained with such time-resolved transport measurements.
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85.30.Tv Field effect devices

Order-of-magnitude reduction of carrier lifetimes in [100] n-type GaAs shock-compressed to 4 GPa

P. Grivickas, M. D. McCluskey, and Y. M. Gupta

Appl. Phys. Lett. 98, 092107 (2011); http://dx.doi.org/10.1063/1.3561019 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2011

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Dynamics of excess carriers, following a short excitation pulse, were recorded in shock-compressed [100] GaAs:Te to 4 GPa using time- and spectral-resolved photoluminescence (PL) measurements. PL signals extending over five orders of magnitude and comprising several recombination mechanisms were detected in single-event experiments. In marked contrast to earlier hydrostatic pressure results, a linear lifetime reduction was observed under uniaxial strain. The present results suggest that the lifetime reaches a minimum at the direct-to-indirect transition.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence
62.50.Ef Shock wave effects in solids and liquids

Doped, porous iron oxide films and their optical functions and anodic photocurrents for solar water splitting

Coleman X. Kronawitter, Samuel S. Mao, and Bonnie R. Antoun

Appl. Phys. Lett. 98, 092108 (2011); http://dx.doi.org/10.1063/1.3552711 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2011

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The fabrication and morphological, optical, and photoelectrochemical characterization of doped iron oxide films is presented. The complex index of refraction and absorption coefficient of polycrystalline films are determined through measurement and modeling of spectral transmission and reflection data using appropriate dispersion relations. Photoelectrochemical characterization for water photo-oxidation reveals that the conversion efficiencies of electrodes are strongly influenced by substrate temperature during their oblique-angle physical vapor deposition. These results are discussed in terms of the films’ morphological features and the known optoelectronic limitations of iron oxide films for application in solar water splitting devices.
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78.66.Nk Insulators
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.50.-m Photochemistry
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
78.56.-a Photoconduction and photovoltaic effects

Transport limited interfacial carrier relaxation in a double-layer device investigated by time-resolved second harmonic generation and impedance spectroscopy

Le Zhang, Dai Taguchi, Jun Li, Takaaki Manaka, and Mitsumasa Iwamoto

Appl. Phys. Lett. 98, 092109 (2011); http://dx.doi.org/10.1063/1.3560054 (3 pages) | Cited 6 times

Online Publication Date: 1 March 2011

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The interfacial carrier relaxation in an indium tin oxide/polyimide/pentacene/Au double-layer device was studied in both time and frequency domains by using time-resolved second harmonic generation (TR-SHG) and impedance spectroscopy (IS), respectively. Although both hole and electron injection into the pentacene layer and their accumulation at the pentacene/polyimide interface were revealed in TR-SHG, it was only observed in IS under the hole injection condition. The “contradiction” between the two methods for the same carrier relaxation process was explained on the basis of a model, transport limited interfacial carrier relaxation, in which the quasistatic state governs the one-directional carrier transport.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Ns Metal-nonmetal contacts
78.47.D- Time resolved spectroscopy (>1 psec)
78.47.N- High resolution nonlinear optical spectroscopy

Graphene-based spin logic gates

Minggang Zeng, Lei Shen (沈雷), Haibin Su, Chun Zhang, and Yuanping Feng

Appl. Phys. Lett. 98, 092110 (2011); http://dx.doi.org/10.1063/1.3562320 (3 pages) | Cited 5 times

Online Publication Date: 1 March 2011

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Logic operation is the key of digital electronics and spintronics. Based on spin-dependent transport property of zigzag graphene nanoribbons studied using nonequilibrium Green’s function method and density functional theory, we propose a complete set of all-carbon spin logic gates, in which the spin-polarized current can be manipulated by the source-drain voltage and magnetic configuration of the electrodes. These logic gates allow further designs of complex spin logic operations and pave the way for full implementation of spintronics computing devices.
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72.25.-b Spin polarized transport
82.45.-h Electrochemistry and electrophoresis
61.48.Gh Structure of graphene
84.30.-r Electronic circuits
61.46.-w Structure of nanoscale materials
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Random telegraph-signal noise in junctionless transistors

A. N. Nazarov, I. Ferain, N. Dehdashti Akhavan, P. Razavi, R. Yu, and J. P. Colinge

Appl. Phys. Lett. 98, 092111 (2011); http://dx.doi.org/10.1063/1.3557505 (3 pages) | Cited 4 times

Online Publication Date: 1 March 2011

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Random telegraph-signal noise (RTN) is measured in junctionless metal-oxide-silicon field-effect transistors (JL MOSFETs) as a function of gate and drain voltage and temperature. It is shown that the RTN in JL MOSFETs increases significantly when an accumulation layer is formed. The amplitude of RTN is considerably smaller in JL devices than in inversion-mode MOSFET fabricated using similar fabrication parameters. A measurement technique is developed to extract the main parameters of the traps, including the average charge capture and emission time from the traps.
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85.30.Tv Field effect devices

Impact of static and dynamic stress on threshold voltage instability in high-k/metal gate n-channel metal-oxide-semiconductor field-effect transistors

Chih-Hao Dai, Ting-Chang Chang, Ann-Kuo Chu, Yuan-Jui Kuo, Wen-Hung Lo, Szu-Han Ho, Ching-En Chen, Jou-Miao Shih, Hua-Mao Chen, Bai-Shan Dai, Guangrui Xia, Osbert Cheng, and Cheng Tung Huang

Appl. Phys. Lett. 98, 092112 (2011); http://dx.doi.org/10.1063/1.3560463 (3 pages) | Cited 9 times

Online Publication Date: 2 March 2011

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This letter investigates the impact of static and dynamic stress on threshold voltage (Vth) instability in ultrathin n-channel metal-oxide-semiconductor field-effect transistors with hafnium-based gate stacks. Experimental results indicate Vth shift under dynamic stress is more serious than that under static stress due to charge trapping within the high-k dielectric. Capacitance-voltage techniques demonstrated that electron trapping under dynamic stress was located in the high-k dielectric near the source/drain overlap region rather than throughout the overall dielectric layer. This implies in real circuit operation, the phenomenon of electrons trapped in high-k near the source/drain overlap is the main issue affecting Vth instability.
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85.30.Tv Field effect devices

Increase in current density for metal contacts to n-germanium by inserting TiO2 interfacial layer to reduce Schottky barrier height

J.-Y. Jason Lin, Arunanshu M. Roy, Aneesh Nainani, Yun Sun, and Krishna C. Saraswat

Appl. Phys. Lett. 98, 092113 (2011); http://dx.doi.org/10.1063/1.3562305 (3 pages) | Cited 11 times

Online Publication Date: 3 March 2011

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Metal contacts to n-type Ge have poor performance due to the Fermi level pinning near the Ge valence band at metal/Ge interfaces. The electron barrier height can be reduced by inserting ultrathin dielectrics at the metal-semiconductor interface. However, this technique introduces tunneling resistance from the large conduction band offset (CBO) between the insulator and Ge. In this work, the CBO between TiO2 and Ge is estimated to range from −0.06 to −0.26 eV so tunneling resistance can be reduced. By inserting 7.1 nm TiO2 between Al and n-Ge, current densities increased by about 900× at 0.1 V and 1200× at −0.1 V compared to contacts without TiO2.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
73.21.Ac Multilayers

Electric field dependent activation energy of electron transport in fullerene diodes and field effect transistors: Gill’s law

A. Pivrikas, Mujeeb Ullah, H. Sitter, and N. S. Sariciftci

Appl. Phys. Lett. 98, 092114 (2011); http://dx.doi.org/10.1063/1.3557503 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2011

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The electric field and temperature dependence of the electron mobility is studied comparatively in the bulk of fullerene (C60) diodes and at the interface with dielectric of organic field effect transistors (OFETs). Electron mobility values follow a Poole–Frenkel-type electric field dependence in both types of devices. The activation energy for electron transport is electric field dependent and follows the square root law of field in both devices as predicted by Gill’s law. The same Gill’s energy EGill = 34 meV is measured in diodes and OFETs, which corresponds well to Meyer–Neldel energy (EMN = 35 meV). It is shown that both the electric field and charge carrier concentration must be accounted for the description of disordered charge transport.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
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