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25 Apr 2011

Volume 98, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 98, 171102 (2011); http://dx.doi.org/10.1063/1.3582035 (3 pages)

Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa
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Interface model for HfO2 gate stack from first principles calculations and its application to nanoscale device simulations

Mincheol Shin, Yongjin Park, Ki-jeong Kong, and Hyunju Chang

Appl. Phys. Lett. 98, 173501 (2011); http://dx.doi.org/10.1063/1.3575570 (3 pages) | Cited 2 times

Online Publication Date: 25 April 2011

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Rigorous first-principles calculations are performed to address the interface properties of HfO2 gate stacks with interlayer (IL). The band-gap and dielectric constant change nonabruptly at the HfO2/IL and IL/Si interfaces with transition regions of a few angstrom wide. Device-level simulations are then performed with the interface properties reflected, and electrostatics, gate-leakage and drain currents are found to be substantially influenced by the presence of the transition regions. Based on the findings, the equivalent single-layer model as a practical guide to the modeling and simulation of HfO2 gate stacks is proposed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Ch Permittivity (dielectric function)
71.15.-m Methods of electronic structure calculations

Mechanical analysis and optimization of a microcantilever sensor coated with a solid receptor film

Genki Yoshikawa

Appl. Phys. Lett. 98, 173502 (2011); http://dx.doi.org/10.1063/1.3583451 (3 pages) | Cited 1 time

Online Publication Date: 25 April 2011

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This letter presents an analytical model for the static deflection and optimization of a nanomechanical cantilever sensor coated with a solid receptor film. All relevant physical parameters of both cantilever and coating film are included; Young’s modulus, Poisson’s ratio, and geometrical parameters (length, width, and thickness). This model provides accurate values verified by a good agreement with those simulated by finite element analysis, while the Stoney’s equation [ G. G. Stoney, Proc. R. Soc. London, Ser. A 82, 172 (1909)] and Sader’s model [ J. E. Sader, J. Appl. Phys. 89, 2911 (2001)] which assume ideal surface stress without a solid coating film, result in significant deviation under some conditions. Mechanical analysis and optimization based on experimental results are also demonstrated as an example.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
46.25.Cc Theoretical studies
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
02.70.Dh Finite-element and Galerkin methods
02.60.Pn Numerical optimization

Atomistic approach to alloy scattering in Si1−xGex

Saumitra R. Mehrotra, Abhijeet Paul, and Gerhard Klimeck

Appl. Phys. Lett. 98, 173503 (2011); http://dx.doi.org/10.1063/1.3583983 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2011

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SiGe alloy scattering is of significant importance with the introduction of strained layers and SiGe channels into complementary metal-oxide semiconductor technology. However, alloy scattering has till now been treated in an empirical fashion with a fitting parameter. We present a theoretical model within the atomistic tight-binding representation for treating alloy scattering in SiGe. This approach puts the scattering model on a solid atomistic footing with physical insights. The approach is shown to inherently capture the bulk alloy scattering potential parameters for both n-type and p-type carriers and matches experimental mobility data.
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72.20.Dp General theory, scattering mechanisms
72.20.Fr Low-field transport and mobility; piezoresistance

In-line absorption sensor based on coiled optical microfiber

Roberto Lorenzi, Yongmin Jung, and Gilberto Brambilla

Appl. Phys. Lett. 98, 173504 (2011); http://dx.doi.org/10.1063/1.3582924 (3 pages) | Cited 3 times

Online Publication Date: 27 April 2011

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We fabricated and tested an evanescent-wave absorption sensor consisting of an optical microfiber coil resonator embedded in fluidic channel walls. Low concentrations of flowing analyte show optical losses in agreement with a modified Beer–Lambert law. Higher concentration causes a limit value of the measured optical losses arising from adsorption mechanisms.
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42.81.Pa Sensors, gyros
42.81.Dp Propagation, scattering, and losses; solitons
42.81.Bm Fabrication, cladding, and splicing

Crystallized HfLaO embedded tetragonal ZrO2 for dynamic random access memory capacitor dielectrics

Yunsang Shin, Kyung Kyu Min, Seok-Hee Lee, Sung Kyu Lim, Jae Sub Oh, Kee-Jeung Lee, Kwon Hong, and Byung Jin Cho

Appl. Phys. Lett. 98, 173505 (2011); http://dx.doi.org/10.1063/1.3583590 (3 pages)

Online Publication Date: 27 April 2011

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Cubic-structured HfLaO embedded tetragonal ZrO2 is investigated for application to a dynamic random access memory capacitor dielectric. It is found that hole injection is the determining factor of the leakage current in the ZrO2–HfLaO stack and thus HfLaO should be kept away from the electrode interface due to its smaller valance band offset than that of ZrO2. The insertion of cubic-structured HfLaO into tetragonal ZrO2 with an optimized thickness combination can effectively reduce the equivalent oxide thickness without increasing the leakage current.
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84.30.Sk Pulse and digital circuits
84.32.Tt Capacitors
77.55.F- High-permittivity capacitive films
71.20.Ps Other inorganic compounds

23 GHz ferroelectric electron gun based gyrotron

R. Ben-Moshe and M. Einat

Appl. Phys. Lett. 98, 173506 (2011); http://dx.doi.org/10.1063/1.3583597 (3 pages)

Online Publication Date: 27 April 2011

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Ferroelectric cathodes have been explored as an alternative electron source for microwave tubes. Past experiments have demonstrated operation at frequencies of 2–10 GHz. Since the ferroelectric cathode is based on surface plasma, the relatively high energy spread limits the tube operation frequency. Hence, the possibility to obtain higher frequencies remained questionable. In this experimental work a gyrotron oscillator was designed with the operation frequency increased toward that of millimeter waves. A cylindrical tube with a cutoff frequency of ∼ 22 GHz was integrated to a ferroelectric electron gun. Pulses of ∼ 0.5 μs duration with a frequency of 23 GHz were obtained.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.47.+w Vacuum tubes

Resistance switching and white-light photovoltaic effects in BiFeO3/Nb–SrTiO3 heterojunctions

T. L. Qu, Y. G. Zhao, D. Xie, J. P. Shi, Q. P. Chen, and T. L. Ren

Appl. Phys. Lett. 98, 173507 (2011); http://dx.doi.org/10.1063/1.3584031 (3 pages) | Cited 13 times

Online Publication Date: 28 April 2011

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BiFeO3/Nb–SrTiO3 heterojunctions with room-temperature resistance switching (RS) and white-light photovoltaic (PV) effects were fabricated by pulsed laser deposition. The current-voltage characteristics of these heterojunctions show a good rectifying property with a large rectifying ratio of 104. Nonvolatile bipolar RS effect was observed with an ON/OFF-state current ratio of about 102. The heterojunctions also exhibit a substantial white-light PV effect. Both the RS and PV behaviors can be modulated by additional pulsed voltages, which control the electric polarization of the heterojunctions. This letter is helpful for exploring the multifunctional heterojunctions and their applications in memory devices and solar cells.
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73.40.Ei Rectification
73.50.Pz Photoconduction and photovoltaic effects
77.55.-g Dielectric thin films
72.60.+g Mixed conductivity and conductivity transitions
77.22.Ej Polarization and depolarization

Field-dependent carrier trapping induced kink effect in AlGaN/GaN high electron mobility transistors

Lihua Fu, Hai Lu, Dunjun Chen, Rong Zhang, Youdou Zheng, Tangsheng Chen, Ke Wei, and Xinyu Liu

Appl. Phys. Lett. 98, 173508 (2011); http://dx.doi.org/10.1063/1.3584861 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2011

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An anomalous kink effect featuring an abrupt recovery of drain current following current collapse is observed in the room-temperature output characteristics of AlGaN/GaN high electron mobility transistors. The kink is largely caused by trapping electrons from the gate leakage current by deep levels within the AlGaN barrier at high drain bias, resulting in a positive shift in threshold voltage and a reduction in reverse gate leakage current. The release of the trapped electrons is likely due to impact ionization of traps by hot electrons, which starts to play a role at relatively lower drain bias. Both sub-bandgap illumination and temperature rise could reduce the kink.
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85.30.Tv Field effect devices

Influence of anisotropic light-hole band structure on indirect tunneling in silicon

Edward Chen and Dee-Son Pan

Appl. Phys. Lett. 98, 173509 (2011); http://dx.doi.org/10.1063/1.3584868 (3 pages)

Online Publication Date: 29 April 2011

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In this letter, we have clarified the physics of indirect interband tunneling in silicon. By considering the detailed anisotropic light-hole band structure, the magnitude of the current densities shows J〈110〉 ≈ J〈111〉 ≈ 10×J〈100〉 under the low electric field and J〈110〉 ≈ J〈111〉 ≈ 3×J〈100〉 under the high electric field. The quantitative result is consistent with the recent experimental data. The study also indicates that the indirect tunneling current in strain silicon or Si1−xGex can be changed a lot by the highly anisotropic valence band structure.
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71.20.Mq Elemental semiconductors
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling
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