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15 Aug 2011

Volume 110, Issue 4, Articles (04xxxx)

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back to top Device Physics

Patterned electrode vertical field effect transistor: Theory and experiment

Ariel J. Ben-Sasson and Nir Tessler

J. Appl. Phys. 110, 044501 (2011); http://dx.doi.org/10.1063/1.3622291 (12 pages) | Cited 1 time

Online Publication Date: 16 August 2011

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We present a theoretical and experimental investigation of the recently reported new architecture of a patterned electrode vertical field effect transistor (PE-VFET). The investigation focuses on the role of the embedded source electrode architecture in the device behavior. Current-voltage characteristics was unraveled through the use of a self-consistent numerical simulation resulting in guidelines for the PE-VFET architecture regarding the On/Off current ratio, output current density, and apparent threshold voltage. Current modulation characteristics are obtained through the formation of virtual contacts at the PE nano-features (i.e., perforations) under gate bias, which lead to the formation of vertical channels under drain bias. As the vertical channel is formed the device characteristics change from contact-limited to space-charge-limited. The analytical model strength is shown with the parameter extraction procedure applied to a measured PE-VFET device fabricated using block copolymer lithography and with the appropriate simulation results.
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85.30.Tv Field effect devices

Frequency hopping due to acousto-electric interaction in ZnO based surface acoustic wave oscillator

Daipayan Dasgupta and K. Sreenivas

J. Appl. Phys. 110, 044502 (2011); http://dx.doi.org/10.1063/1.3622327 (8 pages) | Cited 1 time

Online Publication Date: 18 August 2011

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A 36 MHz surface acoustic wave delay line based oscillator has been used to study the effect of acousto-electric interaction due to photo generated charge carriers in rf sputtered ZnO film under UV illumination (λ = 365 nm, 20–100 μW/cm2). Design aspects for developing a delay line based SAW oscillator are specified. The observed linear downshift in frequency (2.2 to 19.0 kHz) with varying UV intensity (20–100 μW/cm2) is related to the fractional velocity change due to acousto-electric interaction. UV illumination level of 100 μW/cm2 leads to a characteristic frequency hopping behavior arising due to a change in the oscillation criteria, and is attributed to the complex interplay between the increased attenuation and velocity shift.
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43.58.Wc Electrical and mechanical oscillators
81.15.Cd Deposition by sputtering
84.30.Ng Oscillators, pulse generators, and function generators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators

Fabrication and characterization of Na0.5K0.5NbO3-CuNb2O6 lead-free step-down piezoelectric transformers

Ming-Ru Yang, Sheng-Yuan Chu, I-Hao Chan, and Sheng-Kai Huang

J. Appl. Phys. 110, 044503 (2011); http://dx.doi.org/10.1063/1.3624579 (6 pages)

Online Publication Date: 19 August 2011

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Lead-free (Na0.5K0.5)NbO3 (NKN) ceramics doped with 1 mol% CuNb2O6 (01CN) ceramics were prepared using the conventional mixed oxide method at a sintering temperature of 1075 °C. NKN + 1 mol% CuTa2O6 (NKN-01CN) ceramics sintered at 1075 °C exhibit excellent “hard” piezoelectric properties of kp = 40%, kt = 45%, and k33 = 57%, with ferroelectric property Ec = 23 kV/cm. The mechanical quality factor (Qm) is extraordinarily high (1933) and the temperature stability is excellent (Temperature coefficient of frequency (TCF) = −154 ppm/°C). The piezoelectric transformer (PT) was fabricated on NKN-01CN lead-free substrates, and the electrical characteristics were investigated. The devices were simplified into an equivalent circuit and analyzed using the MATLAB software package. The simulation results matched the experimental results. By reversing the input and the output, the step-down PT can be easily fabricated using a simple disk-type structure. A maximum efficiency of 93% with a voltage gain of 0.12 was measured, which was in good agreement with the simulation results (a maximum efficiency of 98.7% with a voltage gain of 0.13) for the step-down mode.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
84.30.Jc Power electronics; power supply circuits

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

Eralci M. Therézio, Erick Piovesan, Marco Anni, R. A. Silva, Osvaldo N. Oliveira, Jr., and Alexandre Marletta

J. Appl. Phys. 110, 044504 (2011); http://dx.doi.org/10.1063/1.3622143 (6 pages) | Cited 1 time

Online Publication Date: 19 August 2011

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The importance of interface effects for organic devices has long been recognized, but getting detailed knowledge of the extent of such effects remains a major challenge because of the difficulty in distinguishing from bulk effects. This paper addresses the interface effects on the emission efficiency of poly(p-phenylene vinylene) (PPV), by producing layer-by-layer (LBL) films of PPV alternated with dodecylbenzenesulfonate. Films with thickness varying from ∼15 to 225 nm had the structural defects controlled empirically by converting the films at two temperatures, 110 and 230 °C, while the optical properties were characterized by using optical absorption, photoluminescence (PL), and photoluminescence excitation spectra. Blueshifts in the absorption and PL spectra for LBL films with less than 25 bilayers (<40–50 nm) pointed to a larger number of PPV segments with low conjugation degree, regardless of the conversion temperature. For these thin films, the mean free-path for diffusion of photoexcited carriers decreased, and energy transfer may have been hampered owing to the low mobility of the excited carriers. The emission efficiency was then found to depend on the concentration of structural defects, i.e., on the conversion temperature. For thick films with more than 25 bilayers, on the other hand, the PL signal did not depend on the PPV conversion temperature. We also checked that the interface effects were not caused by waveguiding properties of the excited light. Overall, the electronic states at the interface were more localized, and this applied to film thickness of up to 40–50 nm. Because this is a typical film thickness in devices, the implication from the findings here is that interface phenomena should be a primary concern for the design of any organic device.
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78.66.Sq Composite materials
85.60.Jb Light-emitting devices
68.37.-d Microscopy of surfaces, interfaces, and thin films
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.At Surface states, band structure, electron density of states
78.55.Kz Solid organic materials

A general and precise method to evaluate the series resistance of photovoltaic cells from I-V characteristics

C. Chibbaro, M. Zimbone, G. Litrico, P. Baeri, M. L. Lo Trovato, and F. Aleo

J. Appl. Phys. 110, 044505 (2011); http://dx.doi.org/10.1063/1.3622617 (9 pages)

Online Publication Date: 19 August 2011

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This paper presents a general method for extracting solar cell parameters from current- voltage characteristics obtained under illumination. In particular, it focuses on the problem of measuring very low values of series resistance with sufficient precision. The method makes use of two different sets of experimental data: a cell current-voltage characteristic measured at a fixed sun irradiance level and a set of short circuit current and open circuit voltage value pairs measured at various sun irradiance levels. The method involves an interplay of different fitting procedures iteratively performed to these two data sets. The method is tested on two single junction silicon cells with the same very low series resistance however, having two very different values of shunt resistance. It is shown that in both cases this method is much more precise and reproducible than other conventional methods.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Analysis on switching mechanism of graphene oxide resistive memory device

Seul Ki Hong, Ji Eun Kim, Sang Ouk Kim, and Byung Jin Cho

J. Appl. Phys. 110, 044506 (2011); http://dx.doi.org/10.1063/1.3624947 (5 pages) | Cited 2 times

Online Publication Date: 22 August 2011

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Recently, a flexible resistive switching memory device using graphene oxide was successfully demonstrated. In this work, the new findings on the switching mechanism of the graphene oxide memory are presented through a comprehensive study on the switching phenomena. It has been found that the switching operation of graphene oxide resistive switching memory (RRAM) is governed by dual mechanism of oxygen migration and Al diffusion. However, the Al diffusion into the graphene oxide is the main factor to determine the switching endurance property which limits the long term lifetime of the device. The electrode dependence on graphene oxide RRAM operation has been analyzed as well and is attributed to the difference in surface roughness of graphene oxide for the different bottom electrodes.
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84.30.Sk Pulse and digital circuits

Electronic transport in doped pyrenyl carbazole

Farman Ali, N. Periasamy, Meghan P. Patankar, and K. L. Narasimhan

J. Appl. Phys. 110, 044507 (2011); http://dx.doi.org/10.1063/1.3626046 (6 pages)

Online Publication Date: 25 August 2011

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In this paper, we report on electronic transport and impedance measurements on thin films of unintentionally hole doped 3,6-dipyrenyl-N-hexylcarbazole. Evidence for doping from dc conductivity, ESR, and capacitance measurements is presented. From a study of the bias, temperature and frequency dependence of capacitance, we estimate the integrated density of states above the Fermi level to be 1017/cm3. This is also the doping concentration in these samples.
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73.61.Ph Polymers; organic compounds
76.30.-v Electron paramagnetic resonance and relaxation
61.72.sd Impurity concentration
61.72.up Other materials
81.05.Fb Organic semiconductors
71.20.Rv Polymers and organic compounds

Passivation and activation of Mg acceptors in heavily doped GaN

M. E. Zvanut, Y. Uprety, J. Dashdorj, M. Moseley, and W. Alan Doolittle

J. Appl. Phys. 110, 044508 (2011); http://dx.doi.org/10.1063/1.3626461 (5 pages)

Online Publication Date: 29 August 2011

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Electron paramagnetic resonance measurements are used to monitor the passivation and activation of the Mg-related acceptor in GaN doped with different concentrations of Mg, up to 2 × 1020 cm−3. Samples were annealed in either forming gas (H2:N2) or pure N2 between 200 and 900 °C. As expected, the Mg-related EPR signal is reduced by at least a factor of ten during the forming gas treatment; while the pure N2 environment revives the signal. However, the study also shows that reactions between Mg and hydrogen occur at a temperature as low as 525 °C in the 1020 cm−3 Mg doped samples; while in more lightly doped samples, temperatures greater than 700 °C are required to observe changes in the Mg signal intensity. While the observations support the model in which a hydrogen atom ionizes at the Mg impurity and the remaining proton bonds at a near neighbor, the different temperature dependence suggests that hydrogen diffusion is affected by the increased Mg concentration.
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81.65.Rv Passivation
76.30.Lh Other ions and impurities
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors

In-Situ growth of cadmium telluride nanocrystals in poly(3-hexylthiophene) matrix for photovoltaic application

Mohd Taukeer Khan, Amarjeet Kaur, S. K. Dhawan, and Suresh Chand

J. Appl. Phys. 110, 044509 (2011); http://dx.doi.org/10.1063/1.3626464 (7 pages) | Cited 1 time

Online Publication Date: 29 August 2011

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In the present study, nanocrystals of cadmium telluride (CdTe) have been directly synthesized in poly(3-hexylthiophene) (P3HT) matrix without use of any surfactant. In situ synthesis of nanoparticles in polymer matrix improves the polymer-nanoparticles interface, which facilitates efficient electronic interaction between them. Spectral results suggest that CdTe nanocrystals are bound with P3HT via dipole-dipole interaction and form a charge transfer complex. Structural and morphological studies reveal that CdTe works as transport media along/between the polymer chains, which facilitate percolation pathways for charge transport. Therefore, enhancement in current density has been observed for the bulk heterojunction (BHJ) device of P3HT-CdTe nanocomposites blended with PCBM. An open circuit voltage (VOC) of 0.80 V was obtained from the BHJ device due to the increase in the energy level offset between the donor and acceptor. This new photovoltaic element could provide a new nanoscale criterion for the investigation of photoinduced energy/charge transport in organic-inorganic interfaces.
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81.16.-c Methods of micro- and nanofabrication and processing
72.40.+w Photoconduction and photovoltaic effects
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Qk Reinforced polymers and polymer-based composites

Characterization and modeling of structural properties of SiGe/Si superlattices upon annealing

M. Py, J. P. Barnes, P. Rivallin, A. Pakfar, T. Denneulin, D. Cooper, and J. M. Hartmann

J. Appl. Phys. 110, 044510 (2011); http://dx.doi.org/10.1063/1.3622622 (12 pages) | Cited 2 times

Online Publication Date: 30 August 2011

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Stacked multichannel or nanowire CMOS transistors are foreseen as viable options in future technology nodes. Superior electric performances and a relative immunity to short channel effects have already been demonstrated in such devices. They rely on (i) the epitaxy of SiGe/Si superlattices, (ii) the anisotropic etching of the source and drain (S/D) blocks and the channels, and (iii) the high degree of selectivity that can be achieved when laterally etching the SiGe sacrificial layers. The voids left by the removal of SiGe are then conformally filled by HfO2/TiN/poly-Si gates, leading to the formation of multichannel devices. Doping elements can be included in situ in the SiGe layers during the epitaxial step in order to achieve a proper S/D doping after annealing. Precise knowledge of the diffusion behavior of all species is then crucial to understand and tailor final device performance. In this work, we investigated the properties of intrinsic or in situ doped (with B, C, or P) SiGe/Si superlattices upon annealing, using several characterization techniques, such as x-ray diffraction, x-ray reflectivity, time-of-flight-secondary ion mass spectrometry, and dark-field electron holography; as well as diffusion simulation tools such as S-Process. The combined analysis and simulation approaches allowed a complete characterization of the studied structures upon annealing. In the first step, the diffusion of both germanium and dopants was observed experimentally and quantified with simulation. Their diffusion mechanisms were also studied. In the second step, the evolution of the strain distribution upon annealing was experimentally monitored and simulated to quantify the strain relaxation in such structures.
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68.65.Cd Superlattices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
66.30.J- Diffusion of impurities

Low energy Xe milling for the quantitative profiling of active dopants by off-axis electron holography

David Cooper, Jean-Michel Hartmann, and Narciso Gambacorti

J. Appl. Phys. 110, 044511 (2011); http://dx.doi.org/10.1063/1.3625262 (5 pages) | Cited 1 time

Online Publication Date: 31 August 2011

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Off-axis electron holography is a powerful technique that can be used to measure the active dopants in semiconductors. The preparation of thin transmission electron microscopy specimens containing nm-scale regions of interest is extremely challenging and as a consequence ion milling is an essential tool. The exposure of doped specimens to energetic ions creates defects deep in the specimens that trap the active dopants, being the principle cause of what is known as the inactive region. The inactive thickness leads to an underestimation of the dopant potential in the specimens. Here we show that this artifact can be significantly reduced from 140 nm for specimens prepared using only Ga ions at 30 kV to only 10 nm by preparing specimens using 1.5 keV Xe ions for specimens containing p-n junctions with dopant concentrations of 2 × 1018 cm−3.
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61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.72.uf Ge and Si
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