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15 Apr 2008

Volume 103, Issue 8, Articles (08xxxx)

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Effect of the evanescent modes on ballistic thermal transport in quantum structures

Fang Xie, Ke-Qiu Chen, Y. G. Wang, and Yan Zhang

J. Appl. Phys. 103, 084501 (2008); http://dx.doi.org/10.1063/1.2904883 (5 pages) | Cited 9 times

Online Publication Date: 16 April 2008

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Using the scattering matrix method, we investigate the effect of the evanescent modes on ballistic transport probability and thermal conductance in T-shaped and concavity-shaped quantum structures at low temperatures. The results show that the evanescent modes play different roles in the transport possibility and the thermal conductance in both T-shaped and concavity-shaped quantum structures. The evanescent modes can enhance thermal conductance in the concavity-shaped structure and suppress thermal conductance in the T-shaped structure. A brief analysis of these results is given.
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73.23.Ad Ballistic transport
73.21.Hb Quantum wires
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Combined optical and electrical modeling of polymer:fullerene bulk heterojunction solar cells

Jan D. Kotlarski, Paul W. M. Blom, Lambert. J. A. Koster, Martijn Lenes, and Lenneke H. Slooff

J. Appl. Phys. 103, 084502 (2008); http://dx.doi.org/10.1063/1.2905243 (5 pages) | Cited 29 times

Online Publication Date: 16 April 2008

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Optical interference effects are important for the total absorption as well as the profile of the exciton generation rate in polymer:fullerene bulk heterojunction solar cells. For solar cells with an active layer of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] as electron donor and [6,6]-phenyl C61 butyric acid methyl ester as electron acceptor, the total exciton generation rate can be directly extracted from the saturated photocurrent. It is demonstrated that for solar cells with an active layer thickness smaller than 250 nm, a constant exciton generation profile, based on this extracted total rate, gives identical electrical characteristics as compared to exciton generation profiles from an optical model. For thicker cells interference effects have to be taken into account, since a uniform generation profile leads to an overestimation of recombination losses and space-charge formation.
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84.60.Jt Photoelectric conversion

Silicon thickness fluctuation scattering dependence of electron mobility in ultrathin body silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors

Yong-Seon Lee, Tae-Hun Shim, Sang-Dong Yoo, and Jea-Gun Park

J. Appl. Phys. 103, 084503 (2008); http://dx.doi.org/10.1063/1.2902951 (5 pages) | Cited 2 times

Online Publication Date: 18 April 2008

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A matrix element for thickness fluctuation (δTSOI) scattering was derived to demonstrate the mobility dependence on Eeff, especially at a low inversion charge concentration, with an ultrathin channel thickness below 7 nm. This case contrasts other research with a lack of such dependence on either thick silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) or bulk MOSFETs. Our matrix element implies that the quantized energy fluctuation associated with δTSOI varies with the average distance of electrons from the surface interface. In particular, it implies the effects of the change in transverse potential on the subband energy fluctuation for each subband, which results in a different matrix element for each applied gate bias. By using this matrix element model, the low-field electron mobility was shown to depend not only on TSi but also on Eeff. Furthermore, the results of a simulation of electron mobility degradation as a function of TSi at low Eeff agreed well with previous experimental results.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.De Semiconductor-device characterization, design, and modeling

Optical and electrical study of deformed hydrogenated bulk Cd0.96Zn0.04Te single crystal

F. Lmai, N. Brihi, Z. Takkouk, K. Guergouri, F. Bouzerara, and M. Hage-Ali

J. Appl. Phys. 103, 084504 (2008); http://dx.doi.org/10.1063/1.2836483 (5 pages) | Cited 4 times

Online Publication Date: 21 April 2008

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The effect of hydrogenation on defects associated with dislocations has been studied in the p-type Cd0.96Zn0.04Te (CZT) semiconductor, grown by the horizontal Bridgman method, with the help of current I(V), capacity C(V) measurements, photoluminescence spectra, and cathodoluminescence imaging. To generate dislocations by plastic deformation we have used a Vickers microhardness instrument on several cadmium (Cd)(111) and telluride (Te)(mathmathmath)CZT faces. Hydrogenation was carried out by exposure of the samples to hydrogen plasma at 150 °C and 3 mbar for 3 h. The analysis of the results obtained confirms both the reduction of the acceptor concentration, that acceptors may be passivated by formation of neutral complexes with hydrogen, and that the majority defect on each face is the tellurium vacancy, VTe. A reduction of the broadband at 1.547 eV (VCd2−−D) is observed, while the donor bound exciton D0X is increased on the Cd face and finally, it seems that the hydrogen stabilizes dislocations and prevents their removal.
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71.55.Gs II-VI semiconductors
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
81.10.Fq Growth from melts; zone melting and refining
62.20.Qp Friction, tribology, and hardness

Effect of size polydispersity in polymer-dispersed liquid-crystal films

José A. Ferrari, Enrique A. Dalchiele, Erna M. Frins, Juan A. Gentilini, César D. Perciante, and Elizabeth Scherschener

J. Appl. Phys. 103, 084505 (2008); http://dx.doi.org/10.1063/1.2903063 (4 pages) | Cited 4 times

Online Publication Date: 21 April 2008

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The electro-optical effect of size polydispersity in polymer-dispersed liquid-crystal (PDLC) films is investigated. Liquid crystal (LC) droplets of different sizes require different electric field amplitudes for director reorientation, which will produce a mismatch of effective refractive indices. This, in turn, will produce an increase in interdroplet scattering (i.e., decrease in the direct transmitted light) within a specific range of electric field amplitudes. We propose a phenomenological “two-size” model describing this enhanced “pseudo-off-state” achieved under application of an electrical field and present validation experiments. Our approach may be used to get more insight into the transmittance behavior of PDLCs affecting the contrast ratio.
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61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
68.15.+e Liquid thin films
78.20.Jq Electro-optical effects

Realization, characterization, and optical modeling of inverted bulk-heterojunction organic solar cells

Tayebeh Ameri, Gilles Dennler, Christoph Waldauf, Patrick Denk, Karen Forberich, Markus C. Scharber, Christoph J. Brabec, and Kurt Hingerl

J. Appl. Phys. 103, 084506 (2008); http://dx.doi.org/10.1063/1.2902804 (6 pages) | Cited 32 times

Online Publication Date: 22 April 2008

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Inverted bulk-heterojunction organic solar cells (OSCs) using solution-processed layers possess significant advantages compared to the usual noninverted devices. To investigate the full potential of this type of OSC, we have carried out some optical modeling by rigorous coupled wave analysis. The influence of the thickness of several different layers in the device has been quantified, as well as the maximum possible number of photons absorbed in the poly(3-hexyltiophene):[6,6]-phenyl-C61-butyric acid methyl ester active layer for both conventional and inverted structures. It appears that the thickness of the hole injecting layer placed in front of the metallic mirror can influence the electromagnetic field distribution in the OSC, but no additional beneficial optical spacer effect is observed. The thickness of the electron injecting layer deposited on the semitransparent electrode also has a negligible influence on the photons absorbed in the active layer for the inverted structure.
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84.60.Jt Photoelectric conversion

A compact quantum model for fin-shaped field effect transistors valid from dc to high frequency and noise simulations

A. Lázaro, B. Nae, B. Iñiguez, F. Garcia, I. M. Tienda-Luna, and A. Godoy

J. Appl. Phys. 103, 084507 (2008); http://dx.doi.org/10.1063/1.2907720 (9 pages) | Cited 2 times

Online Publication Date: 22 April 2008

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Fin-shaped field effect transistors (FinFETs) are considered to be a very attractive option to improve the performance of complementary metal-oxide-semiconductor devices into the sub-50‐nm gate length regime. However, for those dimensions, quantum effects must be considered in order to develop accurate compact models useful for circuit simulations. In this paper, we study the influence of the quantum effects on dc, Radio frequency (rf), and microwave noise for nanoscale FinFET transistors including nonstationary effects. We present an analytical charge model to adjust the charge control computed from the self-consistent solution of the two-dimensional Schrödinger and Poisson equations. rf and noise performances are calculated using the active transmission line method. Comparison between classical and quantum charge control and between drift-diffusion and hydrodynamic models is carried out.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Admittance characterization of semiconductor junctions

M. Nardone and V. G. Karpov

J. Appl. Phys. 103, 084508 (2008); http://dx.doi.org/10.1063/1.2903142 (9 pages) | Cited 1 time

Online Publication Date: 23 April 2008

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We propose a phenomenological theory of admittance characterization of diode structures with resistive electrodes, including photovoltaic cells and Schottky junctions. The concept of decay length is introduced which describes how far an ac signal propagates through the resistive electrode in the lateral direction. The measured capacitance and conductance strongly depend on the decay length and the electrode configuration of the device. We show that properly arranged admittance circuitry and adequate characterization allow one to extract much more information from the data than previously believed.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
85.60.-q Optoelectronic devices

Transition edge sensors for bolometric applications: responsivity and saturation

D. J. Goldie, M. D. Audley, D. M. Glowacka, V. N. Tsaneva, and S. Withington

J. Appl. Phys. 103, 084509 (2008); http://dx.doi.org/10.1063/1.2909981 (8 pages) | Cited 2 times

Online Publication Date: 24 April 2008

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Microstrip-coupled transition edge sensors (TESs) combined with waveguide-horn technology produce sensitive bolometric detectors with well-defined, single-mode beam patterns and excellent polarization characteristics. These devices are now being deployed for astronomical observations. In bolometric applications, where power levels are monitored, the critical parameter that characterizes the detection is the power-to-current responsivity sI(ω), where ω is the postdetection angular frequency. In real applications, such as on a ground-based telescope, the signal of interest is superimposed on a background such as the thermal emission from the atmosphere. The power emitted by the atmosphere changes slowly in time and these changes may change the responsivity of the detector. A detailed understanding of how sI(ω) changes as a function of applied power levels and how the TES response saturates is vital for accurate calibration of astronomical data. In this paper we describe measurements of the changes in the current flowing through a TES as a function of the circuit bias and the applied power. From these measurements we calculate the efficiency of the coupling of power into the TES from a closely thermally coupled microstrip termination resistor and we determine the zero frequency responsivity sI(0) as a function of both the circuit bias and power. The variation of the responsivity is compared with predictions of a small-signal model: for the case when the loop gain LI is high, when simplifying approximations to the full solution to the electrothermal equations apply; and using the electrothermal parameters of the TES, determined by impedance measurements, as inputs to the full model solution. We find good agreement between theory and measurement in both cases in the relevant regimes.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.20.Fw Calorimeters
06.20.fb Standards and calibration

Spin cast thin polymer interlayers in polymer light-emitting diodes: Thickness control through use of cross-linkable polymers

Gabriel Bernardo, Ana Charas, Luís Alcácer, and Jorge Morgado

J. Appl. Phys. 103, 084510 (2008); http://dx.doi.org/10.1063/1.2896452 (7 pages) | Cited 6 times

Online Publication Date: 24 April 2008

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The effect of very thin polymer interlayers made of either acid-initiated cross-linkable polyfluorenes or the parent non-cross-linkable polyfluorenes, on top of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, on the efficiency of light-emitting diodes based on three different electroluminescent (EL) polymers is studied. We find that the use of non-cross-linkable polymers leads to the formation of interlayers with a thickness not exceeding 1 nm and their effect on the light-emitting diode characteristics is not directly correlated with the energetic position of the frontier levels, indicating that other effects, such as interfacial morphology and contact area, which may depend on the specific interlayer/EL polymer combination, play a significant role. When cross-linkable polymers are used, thicker interlayers are formed (up to about 7 nm), and their effect is better related to their frontier level energy. In particular, we found that with these interlayers, a quite significant EL efficiency increase can be obtained.
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85.60.Jb Light-emitting devices

One dimensional plasmons in pyroelectric-semiconductor composites

A. P. Dmitriev and M. S. Shur

J. Appl. Phys. 103, 084511 (2008); http://dx.doi.org/10.1063/1.2903296 (5 pages)

Online Publication Date: 24 April 2008

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We show that the spontaneous and piezoelectric polarization fields inside semiconductor wires embedded into a pyroelectric matrix induce thin mobile electron and/or hole stripes at the wire surfaces. These charged stripes of mobile carriers support longitudinal and transverse plasma waves with typical frequencies in the terahertz range. The longitudinal waves are conventional one-dimensional plasma waves with the frequency approximately proportional to the wave vector. The transverse waves are optical plasma waves with the frequency being nearly independent of the wave vector for the wave vectors approaching zero. The optical plasma branch is expected to strongly interact with the terahertz radiation.
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77.65.-j Piezoelectricity and electromechanical effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.70.+a Pyroelectric and electrocaloric effects

Bias temperature instability in metal-oxide-semiconductor field-effect transistors with atomic-layer-deposited Si-nitride/SiO2 stack gate dielectrics

Shiyang Zhu and Anri Nakajima

J. Appl. Phys. 103, 084512 (2008); http://dx.doi.org/10.1063/1.2907768 (7 pages) | Cited 4 times

Online Publication Date: 29 April 2008

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Bias temperature instability (BTI) in p+ poly-Si gated metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited (ALD) Si-nitride/SiO2 stack gate dielectrics was systematically studied using drain current-gate voltage (Id-Vg) and modified direct-current current-voltage (DCIV) measurements. They exhibited quite unique behaviors as compared to the conventional SiON counterpart: turnaround of the threshold voltage shift (ΔVth) during stressing and significant positive BTI in nMOSFETs. The observed phenomena were consistently explained within the framework of conventional reaction-diffusion model for BTI but with two additional assumptions: (1) there exist pre-existing traps in the ALD Si-nitride/SiO2 stack dielectrics and (2) it is the inversion carriers (electrons or holes) rather than the accumulation carriers which effectively dissociate the Si–H bonds at the SiO2/Si interface during BTI stressing. Owing to the absence of nitrogen near the SiO2/Si interface and the compensation effect on ΔVth between the charge trapping in the pre-existing traps and the dissociation of the Si–H bonds under small voltage stress, the ALD Si-nitride/SiO2 stack dielectrics at the operating voltage may have similar or even longer BTI lifetime than the pure SiO2.
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85.30.Tv Field effect devices

Effects of active atomic sinks and reservoirs on the reliability of Cu/low-k interconnects

Frank L. Wei, Christine S. Hau-Riege, Amit P. Marathe, and Carl V. Thompson

J. Appl. Phys. 103, 084513 (2008); http://dx.doi.org/10.1063/1.2907962 (11 pages) | Cited 2 times

Online Publication Date: 29 April 2008

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Electromigration experiments using Cu/low-k interconnect tree structures were carried out in order to study the effects of active atomic sinks and reservoirs on interconnect reliability. In all cases, failures occurred after a long period of void growth. Kinetic parameters were extracted from resistance versus time data, giving (Dz*)0,eff = 3.9×10−10 m2/s and z* = 0.40±0.12. By using these values, the evolution of stress in each of the interconnect tree segments could be calculated and correlated with the rate of void growth and failure times for all test configurations. It is demonstrated that segments that serve as atomic sinks and reservoirs for the failing segments affect the lifetime by modifying the conditions for stress induced migration. Reservoirs can lead to increased lifetimes, while sinks can lead to reduced lifetimes. Quantitative predictions of the times required for failure for Cu/low-k interconnect trees as a function of the effective bulk elastic modulus of the interconnect system, B, are made. As Young’s modulus of the interlevel dielectric films decreases, B decreases, and the positive effects of reservoirs are diminished and the negative effects of sinks are amplified.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Stability of n-channel a‐Si:H/nc‐Si:H bilayer thin-film transistors under dynamic stress

A. T. Hatzopoulos, D. H. Tassis, N. Arpatzanis, C. A. Dimitriadis, F. Templier, M. Oudwan, and G. Kamarinos

J. Appl. Phys. 103, 084514 (2008); http://dx.doi.org/10.1063/1.2903445 (5 pages)

Online Publication Date: 29 April 2008

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The stability of n-channel bottom-gated thin-film transistors (TFTs), fabricated using as channel material hydrogenated amorphous silicon∕nanocrystalline silicon bilayers, is investigated by applying on the gate pulses in the on-state and off-state regions of operation and dc bias on the drain electrode. Dynamic gate stress, with the source and drain electrodes grounded, were also performed to avoid the effect of dc stress during the dynamic stress. The degradation mechanisms are thoroughly studied for each type of stress conditions, including carrier injection in the SiNx gate insulator and generation of traps at the gate insulator∕channel interface and in the active channel material. The common features and the differences in the TFT degradation behavior under different bias stress conditions are discussed.
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85.30.Tv Field effect devices
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