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2 Oct 2006

Volume 89, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 89, 142101 (2006); http://dx.doi.org/10.1063/1.2358202 (3 pages)

H. C. Lin, P. D. Ye, Y. Xuan, G. Lu, A. Facchetti, and T. J. Marks
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High-performance GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

H. C. Lin, P. D. Ye, Y. Xuan, G. Lu, A. Facchetti, and T. J. Marks

Appl. Phys. Lett. 89, 142101 (2006); http://dx.doi.org/10.1063/1.2358202 (3 pages) | Cited 9 times

Online Publication Date: 2 October 2006

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High-performance GaAs metal-insulator-semiconductor field-effect-transistors (MISFETs) fabricated with very thin self-assembled organic nanodielectrics (SANDs), deposited from solution at room temperature, are demonstrated. A submicron gate-length depletion-mode n-channel GaAs MISFET with SAND thicknesses ranging from 5.5 to 16.5 nm exhibit a gate leakage current density <10−5 A/cm2 at a gate bias smaller than 3 V, a maximum drain current of 370 mA/mm at a forward gate bias of 2 V, and a maximum intrinsic transconductance of 170 mS/mm. The importance of appropriate GaAs surface chemistry treatments on SAND/GaAs interface properties is also presented. Application of SANDs to III-V compound semiconductors affords more opportunities to manipulate the complex III-V surface chemistry with broad materials options.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Ballistic admittance: Periodic variation with frequency

A. P. Dmitriev and M. S. Shur

Appl. Phys. Lett. 89, 142102 (2006); http://dx.doi.org/10.1063/1.2357933 (3 pages) | Cited 1 time

Online Publication Date: 2 October 2006

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The authors show that both real and imaginary parts of the admittance of short (ballistic or quasiballistic) semiconductor structures are oscillatory functions of the frequency with the period determined by the inverse electron transit time with the Fermi velocity. This oscillatory dependence is caused by the phase difference between the electrons injected from the opposite contacts.
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73.23.Ad Ballistic transport
72.20.Fr Low-field transport and mobility; piezoresistance
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Optical signatures of asymmetric fractal diffusion of electron-hole plasma in semiconductor quantum wells

J. B. Borges, S. W. da Silva, P. C. Morais, and A. F. G. Monte

Appl. Phys. Lett. 89, 142103 (2006); http://dx.doi.org/10.1063/1.2358842 (3 pages) | Cited 1 time

Online Publication Date: 2 October 2006

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The lateral electron-hole transport in intrinsic In0.53Ga0.47As/InP quantum well, grown on tilted InP substrate, was investigated by scanning the photoluminescence intensity profile on the sample’s surface. Simulations of the asymmetric carrier density profile, using a non-Fickian diffusion equation described by the Lévy statistics [ S. I. Denisov et al., Phys. Rev. E 73, 036120 (2006) ], show that anomalous diffusion observed along the y direction (perpendicular to the terrace edges) is associated with the presence of Auger recombination, more likely induced by the fractal interface morphology.
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78.67.De Quantum wells
73.63.Hs Quantum wells
72.30.+q High-frequency effects; plasma effects
78.55.Cr III-V semiconductors
66.30.-h Diffusion in solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Room temperature electron spin coherence in telecom-wavelength quaternary quantum wells

W. H. Lau, V. Sih, N. P. Stern, R. C. Myers, D. A. Buell, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 89, 142104 (2006); http://dx.doi.org/10.1063/1.2358931 (3 pages) | Cited 8 times

Online Publication Date: 3 October 2006

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Time-resolved Kerr rotation spectroscopy is used to monitor the room temperature electron spin dynamics of optical telecommunication wavelength AlInGaAs multiple quantum wells lattice matched to InP. The authors found that electron spin coherence times and effective g factors vary as a function of aluminum concentration. The measured electron spin coherence times of these multiple quantum wells, with wavelengths ranging from 1.26 to 1.53 μm, reach approximately 100 ps at room temperature, and the measured electron effective g factors are in the range from −2.3 to −1.1.
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78.47.-p Spectroscopy of solid state dynamics
78.67.De Quantum wells
78.66.Fd III-V semiconductors
72.25.Dc Spin polarized transport in semiconductors
78.20.Ls Magneto-optical effects
78.20.Ek Optical activity

Electrical transport properties of ferromagnetic GaxCr1−xN thin films

Stephen Y. Wu and N. Newman

Appl. Phys. Lett. 89, 142105 (2006); http://dx.doi.org/10.1063/1.2357603 (3 pages) | Cited 11 times

Online Publication Date: 3 October 2006

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The authors report the transport properties of ferromagnetic Ga0.97Cr0.03N films with a Curie temperature of over 900 K. Samples synthesized under conditions that produce the maximum occupancy of Cr atoms on the Ga site ( ∼ 90%) and the maximum ferromagnetic moment of ∼ 0.6μB/Cr (775 °C growth temperature) exhibit a T−1/4 dependence of resistivity, indicative of Mott [J. Non-Cryst. Solids 1, 1 (1968) ] phonon-assisted variable range hopping between deep level defects. The observation of variable range hopping in ferromagnetic films indicates that ferromagnetism results from a double-exchange-type mechanism. Films grown at higher temperatures (>800 °C) show enhanced Cr segregation, properties associated with percolative transport, and very small, if any, ferromagnetic moments.
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73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
73.50.Dn Low-field transport and mobility; piezoresistance
64.75.-g Phase equilibria

Dependence of carrier lifetime in germanium on resisitivity and carrier injection level

E. Gaubas and J. Vanhellemont

Appl. Phys. Lett. 89, 142106 (2006); http://dx.doi.org/10.1063/1.2358967 (3 pages) | Cited 7 times

Online Publication Date: 3 October 2006

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The dependence of carrier lifetime on resistivity and carrier injection level in germanium crystals is studied using microwave probing of optically excited samples. Bulk lifetimes in the range between 30 ns and 500 μs are measured. The carrier lifetime decreases with decreasing resistivity and increases with increasing excitation level. Possible mechanisms are discussed and it is shown that the carrier recombination transients are driven by a system of recombination and trapping centers.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Doping dependence of the carrier lifetime crossover point upon dissociation of iron-boron pairs in crystalline silicon

D. Macdonald, T. Roth, P. N. K. Deenapanray, T. Trupke, and R. A. Bardos

Appl. Phys. Lett. 89, 142107 (2006); http://dx.doi.org/10.1063/1.2358126 (3 pages) | Cited 19 times

Online Publication Date: 4 October 2006

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The excess carrier density at which the carrier lifetime in crystalline silicon remains unchanged after dissociating iron-boron pairs, known as the crossover point, is reported as a function of the boron dopant concentration. Modeling this doping dependence with the Shockley-Read-Hall model does not require knowledge of the iron concentration and suggests a possible refinement of reported values of the capture cross sections for electrons and holes of the acceptor level of iron-boron pairs. In addition, photoluminescence-based measurements were found to offer some distinct advantages over traditional photoconductance-based techniques in determining recombination parameters from low-injection carrier lifetimes.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.uf Ge and Si
61.72.S- Impurities in crystals
78.55.Ap Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects

Combinatorial study of Ni–Ti–Pt ternary metal gate electrodes on HfO2 for the advanced gate stack

K.-S. Chang, M. L. Green, J. Suehle, E. M. Vogel, H. Xiong, J. Hattrick-Simpers, I. Takeuchi, O. Famodu, K. Ohmori, P. Ahmet, T. Chikyow, P. Majhi, B.-H. Lee, and M. Gardner

Appl. Phys. Lett. 89, 142108 (2006); http://dx.doi.org/10.1063/1.2357011 (3 pages) | Cited 11 times

Online Publication Date: 4 October 2006

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The authors have fabricated combinatorial Ni–Ti–Pt ternary metal gate thin film libraries on HfO2 using magnetron co-sputtering to investigate flatband voltage shift (ΔVfb), work function (Φm), and leakage current density (JL) variations. A more negative ΔVfb is observed close to the Ti-rich corner than at the Ni- and Pt-rich corners, implying smaller Φm near the Ti-rich corners and higher Φm near the Ni- and Pt-rich corners. In addition, measured JL values can be explained consistently with the observed Φm variations. Combinatorial methodologies prove to be useful in surveying the large compositional space of ternary alloy metal gate electrode systems.
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84.32.Tt Capacitors
81.15.Cd Deposition by sputtering

Mechanisms for current-induced conductivity changes in a conducting polymer

Xin Xu, Richard A. Register, and Stephen R. Forrest

Appl. Phys. Lett. 89, 142109 (2006); http://dx.doi.org/10.1063/1.2358309 (3 pages) | Cited 17 times

Online Publication Date: 4 October 2006

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A layer of polyethylene dioxythiophene:polystyrene sulfonic acid (PEDT:PSS) spun onto the surface of an inorganic semiconductor forms a highly asymmetric rectifying junction when a small current is applied and can be permanently open circuited with application of a high current density. This allows the polymer/semiconductor junction to function as a write-once-read-many-times memory element. We use x-ray photoelectron spectroscopy and temperature induced conductivity measurements to study the morphological and chemical changes responsible for the large current-induced conductivity changes. It is found that by applying a large current to the organic-inorganic semiconductor rectifying heterojunction structure Au/PEDT:PSS/Si, the ratio of PEDT+ to PSS− near the interface changes due to phase segregation in the presence of both high electric field (>105 V/cm) and temperature. This leads to a decrease in film conductivity by up to six orders of magnitude from its value in the conductive state.
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73.61.Ph Polymers; organic compounds
84.30.Sk Pulse and digital circuits
79.60.Fr Polymers; organic compounds
64.75.-g Phase equilibria

Electrical bistability in a xanthene class molecule: Conduction mechanisms

Arup K. Rath, Satyajit Sahu, and Amlan J. Pal

Appl. Phys. Lett. 89, 142110 (2006); http://dx.doi.org/10.1063/1.2358946 (3 pages) | Cited 5 times

Online Publication Date: 4 October 2006

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The author study conduction mechanism in two conducting states of a bistable device at 10–300 K range. They find that in the electrical bistable devices, electrical switching is associated with a change in the conduction mechanism. Device current in the low-conducting state follows an injection-limited mechanism. The current in the high-conducting state conforms a bulk-dominated mechanism, namely, space-charge limited conduction with an exponential distribution of traps. The bistability has an associated memory phenomenon. The devices exhibit read-only and random-access memory applications for several hours.
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85.65.+h Molecular electronic devices
84.30.Sk Pulse and digital circuits

Bipolar transport observed through extraction currents on organic photovoltaic blend materials

L. Mattias Andersson, Fengling Zhang, and Olle Inganäs

Appl. Phys. Lett. 89, 142111 (2006); http://dx.doi.org/10.1063/1.2360199 (3 pages) | Cited 11 times

Online Publication Date: 5 October 2006

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Both electron and hole mobilities have been simultaneously measured through charge extraction by linearly increasing voltage on polymer heterojunction solar cells with varying stoichiometry of polymer and acceptor. The polymer is a low band gap copolymer of fluorene, thiophene, and electron accepting groups named APFO-Green 5, and the acceptor is [6,6]-phenyl-C61-butyric acid methylester. Results are correlated to field effect transistor measurements on the same material system. A monotonous increase in mobility for both carrier types is observed with increased acceptor loading.
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84.60.Jt Photoelectric conversion
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds

Internal and external polarization memory loss in single semiconductor quantum dots

Q. Q. Wang, A. Muller, P. Bianucci, C. K. Shih, M. T. Cheng, H. J. Zhou, and J. B. Han

Appl. Phys. Lett. 89, 142112 (2006); http://dx.doi.org/10.1063/1.2360202 (3 pages) | Cited 4 times

Online Publication Date: 5 October 2006

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By using nonlinear resonant optical control and polarized photoluminescence, the authors studied the intensity dependence of exciton spin relaxation and photoluminescence polarization in single self-assembled InGaAs quantum dots. Data from dots with different dipole moments reveal two distinctive channels for polarization memory loss: (i) an external pathway due to carrier escape and capture to and from the wetting layer that is responsible for memory loss increasing with intensity and (ii) an internal loss channel due to intrinsic spin relaxation. The values obtained rule out a universal freezing of exciton spin relaxation in single self-assembled quantum dots related to the wetting layer.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.65.-k Nonlinear optics
71.35.-y Excitons and related phenomena
68.08.Bc Wetting

Nonradiative traps in InGaN/GaN multiple quantum wells revealed by two wavelength excitation

I. J. Chen, T. T. Chen, Y. F. Chen, and T. Y. Lin

Appl. Phys. Lett. 89, 142113 (2006); http://dx.doi.org/10.1063/1.2360221 (3 pages) | Cited 4 times

Online Publication Date: 5 October 2006

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The authors report an investigation of two wavelength excited photoluminescence on InGaN/GaN multiple quantum wells. It is found that with an addition below-gap excitation the photoluminescence intensity can be quenched by up to 50%. In addition, the decay time of localized carriers changes from 173.9 to 7.9 ns. The experimental results can be well explained in terms of the electronic transitions involving deep defect states in the GaN barrier. Based on the variation of the photon energy of the below-gap excitation, the origin of the deep trap can be identified. The authors point out here that two wavelength excitation spectroscopy is a powerful tool to reveal nonradiative defects in optoelectronic devices.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
73.21.Fg Quantum wells
73.63.Hs Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Influence of electron injection on the photoresponse of ZnO homojunction diodes

O. Lopatiuk-Tirpak, L. Chernyak, L. J. Mandalapu, Z. Yang, J. L. Liu, Konstantin Gartsman, Yishay Feldman, and Zinovy Dashevsky

Appl. Phys. Lett. 89, 142114 (2006); http://dx.doi.org/10.1063/1.2360233 (3 pages) | Cited 6 times

Online Publication Date: 5 October 2006

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Forward bias electron injection into the p side of a p-n homojunction was shown to result in an improved response of the ZnO photodiodes. Injection of about 25 C of charge yielded a nearly 2.5-fold increase of photocurrent at 350 nm. This improvement was correlated with the increase of the diffusion length of minority electrons in p-type ZnO:Sb as determined by electron beam induced current measurements. It is suggested that the increase of the diffusion length is related to the carrier trapping on nonionized acceptor levels.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Influence of alloy composition on carrier transport and solar cell properties of hydrogenated microcrystalline silicon-germanium thin films

Takuya Matsui, Michio Kondo, Keisuke Ogata, Tsuyoshi Ozawa, and Masao Isomura

Appl. Phys. Lett. 89, 142115 (2006); http://dx.doi.org/10.1063/1.2358318 (3 pages) | Cited 10 times

Online Publication Date: 5 October 2006

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The authors report on carrier transport properties and spectral sensitivities of hydrogenated microcrystalline silicon-germanium (μc-Si1−xGex:H) alloys fabricated by low-temperature ( ∼ 200 °C) plasma-enhanced chemical vapor deposition over the wide compositional range. Hall-effect and conductivity measurements reveal a change from weak n-type to strong p-type conduction for x>0.75 and a monotonic decrease in photoconductivity upon Ge incorporation. In a p-i-n diode structure, the Ge incorporation into i layer reduces quantum efficiencies in the short wavelengths, indicating an increased photocarrier recombination at p/i interface. Nevertheless, under reverse biased condition, a 0.9-μm-thick μc-Si0.6Ge0.4:H absorber yields a large photocurrent of >27 mA/cm2 (air mass 1.5 global) with spectral sensitivities extending into infrared wavelengths, offering a potential advantage over conventional microcrystalline silicon solar cells.
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73.61.Le Other inorganic semiconductors
84.60.Jt Photoelectric conversion
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Carrier transport properties of Al/CdS/GaSb structures

Sujatha Sridaran, Ashonita Chavan, and Partha Dutta

Appl. Phys. Lett. 89, 142116 (2006); http://dx.doi.org/10.1063/1.2356324 (3 pages) | Cited 1 time

Online Publication Date: 5 October 2006

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Low temperature chemical bath deposited cadmium sulfide (CdS) has been used as an interfacial layer on n- and p-GaSb to overcome the limitations posed by the highly unstable GaSb surface. The electrical characteristics of Al/CdS/GaSb structures have been studied. The current transport in these structures is governed by the barriers at the CdS/GaSb interface with an effective series resistance from the bulk of the interfacial CdS layer. Space charge limited current in the interfacial layer gives rise to an increase in the forward turn-on voltages. These structures demonstrate excellent characteristics in the reverse bias region such as high breakdown voltages, low surface leakage current, and good reverse current saturation. Significantly, rectifying junctions on p-GaSb have been achieved with barrier height as high as ∼ 0.6 eV and breakdown voltages of ∼ 4.5 V.
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73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhancement of hole injection in pentacene organic thin-film transistor of O2 plasma-treated Au electrodes

Woong-Kwon Kim, Kihyon Hong, and Jong-Lam Lee

Appl. Phys. Lett. 89, 142117 (2006); http://dx.doi.org/10.1063/1.2360198 (3 pages) | Cited 7 times

Online Publication Date: 6 October 2006

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The effect of oxygen plasma treatment on enhancement of hole mobility was demonstrated using pentacene organic thin-film transistors (OTFTs) with bottom-contact Au electrodes. Linear field-effect mobility increased from 3.2×10−2 to 7.4×10−2 cm2/V s as the Au electrodes were treated with O2 plasma. Secondary electron emission spectra revealed that the work function of oxygen plasma-treated Au is 0.5 eV higher than that of untreated Au. This led to a reduced hole injection barrier at the interface of Au with pentacene, increasing the field-effect mobility of OTFTs.
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85.30.Tv Field effect devices

Fine-feature patterning of self-aligned polymeric thin-film transistors fabricated by digital lithography and electroplating

W. S. Wong, E. M. Chow, R. Lujan, V. Geluz-Aguilar, and M. L. Chabinyc

Appl. Phys. Lett. 89, 142118 (2006); http://dx.doi.org/10.1063/1.2360237 (3 pages) | Cited 5 times

Online Publication Date: 6 October 2006

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Spatially controlled jet-printed etch masks, having a minimum drop size of 40–50 μm, were used to define gap patterns having a minimum feature size of ∼ 10 μm. The defined gaps, in combination with nickel electroplating, were used to create bottom-gate electrode thin-film transistors (TFTs) with gate lengths of 10–20 μm and gate widths of 150 μm. Self-aligned source/drain top contacts were used for fabricating polythiophene-based TFT devices having channel width-to-length ratios of ∼ 4. A typical p-channel TFT device had an on/off ratio of 107, threshold voltage of −1 V, and field-effect mobility of 0.034 cm2/V s.
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85.30.Tv Field effect devices
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