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31 Aug 2009

Volume 95, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 95, 091901 (2009); http://dx.doi.org/10.1063/1.3212896 (3 pages)

Noy Bassik, George M. Stern, and David H. Gracias
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Microscale inverse acoustic band gap structure in aluminum nitride

Nai-Kuei Kuo, Chengjie Zuo, and Gianluca Piazza

Appl. Phys. Lett. 95, 093501 (2009); http://dx.doi.org/10.1063/1.3213345 (3 pages) | Cited 5 times

Online Publication Date: 2 September 2009

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This work presents the design and demonstration of a microscale inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) with a frequency stop band for bulk acoustic waves in the very high frequency range. Conversely to conventional microscale acoustic band gaps, the IABG is formed by a two-dimensional periodic array of unit cells consisting of a high acoustic velocity material cylinder surrounded by a low acoustic velocity medium. The periodic arrangement of the IABG array induces scattering of incident acoustic waves and generates a stop band, whose center frequency is primarily determined by the lattice constant of the unit cell and whose bandwidth depends on the cylinder radius, the film thickness, and the size of the tethers that support the cylinder. A wide band gap (>13% of the center frequency) is formed by the IABG even when thin AlN films are used. The experimental response of an IABG structure having a unit cell of 8.6 μm and an AlN film thickness of 2 μm confirms the existence of a frequency band gap between 185 MHz and 240 MHz.
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68.55.jd Thickness
68.60.Bs Mechanical and acoustical properties
62.65.+k Acoustical properties of solids
71.20.Nr Semiconductor compounds

Gain-length scaling in quantum dot/quantum well infrared photodetectors

T. Yamanaka, B. Movaghar, S. Tsao, S. Kuboya, A. Myzaferi, and M. Razeghi

Appl. Phys. Lett. 95, 093502 (2009); http://dx.doi.org/10.1063/1.3222856 (3 pages)

Online Publication Date: 2 September 2009

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The gain in quantum dot/quantum well infrared photodetectors is investigated. The scaling of the gain with device length has been analyzed, and the behavior agrees with the previously proposed model. We conclude that we understand the gain in the low bias region, but in the high field region, discrepancies remain. An extension of the gain model is presented to cover the very high electric field region. The high field data are compared to the extended model and discussed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Room temperature negative differential resistance of a monolayer molecular rotor device

Mei Xue, Sanaz Kabehie, Adam Z. Stieg, Ekaterina Tkatchouk, Diego Benitez, Rachel M. Stephenson, William A. Goddard, Jeffrey I. Zink, and Kang L. Wang

Appl. Phys. Lett. 95, 093503 (2009); http://dx.doi.org/10.1063/1.3222861 (3 pages) | Cited 1 time

Online Publication Date: 2 September 2009

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An electrically driven molecular rotor device comprised of a monolayer of redox-active ligated copper compounds sandwiched between a gold electrode and a highly doped P+Si substrate was fabricated. Current-voltage spectroscopy revealed a temperature-dependent negative differential resistance (NDR) associated with the device. Time-dependent density functional theory suggests the source of the observed NDR to be redox-induced ligand rotation around the copper metal center, an explanation consistent with the proposed energy diagram of the device. An observed temperature dependence of the NDR behavior further supports this hypothesis.
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85.65.+h Molecular electronic devices
73.61.Ng Insulators
72.20.Ht High-field and nonlinear effects

A study on the temperature dependence of characteristics of phase change memory devices

Suyoun Lee, Doo Seok Jeong, Jeung-hyun Jeong, Wu Zhe, Young-Wook Park, Hyung-Woo Ahn, Won Mok Kim, and Byung-ki Cheong

Appl. Phys. Lett. 95, 093504 (2009); http://dx.doi.org/10.1063/1.3211872 (3 pages) | Cited 2 times

Online Publication Date: 2 September 2009

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We investigated the temperature dependence of characteristics of phase change memory devices composed of Ge2Sb2Te5 (GST). We found that the RESET resistance (RR), SET resistance (RS), and SET time (tSET) decreased with increasing ambient temperature (Tamb.) while RESET current (IR) increased with Tamb. These results were explained in terms of the enhanced thermal activation of electrical conduction in GST and the increased thermal conductivity of the bottom electrode with Tamb.. Besides, threshold voltage (Vth) was found to decrease linearly with Tamb., seemingly in support of the relaxation semiconductor model and hopping-dominated transport model both of which predicted the existence of critical conductivity for threshold switching in chalcogenide glasses.
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84.30.Sk Pulse and digital circuits

SiN-passivated Γ-gate Al0.27Ga0.73N/GaN high electron mobility transistors by using a shifted exposure method

Ching-Sung Lee and An-Yung Kao

Appl. Phys. Lett. 95, 093505 (2009); http://dx.doi.org/10.1063/1.3224182 (3 pages) | Cited 2 times

Online Publication Date: 3 September 2009

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Effective gate-length reduction, surface passivation, and a field-plate structure upon the gate-drain region of a Γ-gate Al0.27Ga0.73N/GaN high electron mobility transistor (HEMT) have been achieved at the same time. The present SiN-passivated device with a 0.6 μm gate length and a 0.6 μm long field plate has demonstrated superior dc and rf characteristics as compared to a conventional-gated structure. Physical insights of device performance with respect to different SiN layer thicknesses are also investigated.
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85.30.Tv Field effect devices
81.05.Ea III-V semiconductors

Scanning capacitance microscopy investigation on InGaAs/InP avalanche photodiode structures: Light-induced polarity reversal

Hao Yin, Tianxin Li, Wenjuan Wang, Weida Hu, Le Lin, and Wei Lu

Appl. Phys. Lett. 95, 093506 (2009); http://dx.doi.org/10.1063/1.3216847 (3 pages) | Cited 4 times

Online Publication Date: 3 September 2009

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Cross-sectional scanning capacitance microscopy is applied to study the carrier distribution as well as its variation under irradiation in an InGaAs/InP avalanche photodiode. The photocarriers excited by the stray light of atomic force microscope laser beam lead to a dramatic deviation of the dC/dV profile in the unintended-doped absorption layer, and even cause the reversal of signal polarity. The existence of surface potential and its impact on the spreading of photocarriers near the cleaved face are demonstrated as the main origins of the light-induced dC/dV reversal. The effect provides experimental information on the distribution property of photoelectric process in devices.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Hysteretic bipolar resistive switching characteristics in TiO2/TiO2−x multilayer homojunctions

Young Ho Do, June Sik Kwak, Yoon Cheol Bae, Kyooho Jung, Hyunsik Im, and Jin Pyo Hong

Appl. Phys. Lett. 95, 093507 (2009); http://dx.doi.org/10.1063/1.3224179 (3 pages) | Cited 10 times

Online Publication Date: 4 September 2009

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TiO2 (oxygen rich, region 1)/TiO2−x (oxygen poor, region 2) multilayer homojunctions were studied as alternative resistive switching structures for both high and low resistance transitions. Stable bipolar resistive switching characteristics, including stable switching speeds (microseconds) and endurance behaviors, as well as long retention times (>104 s) were demonstrated. The nature of the resistive switching phenomenon in multilayer structures seems to be a combination of the conduction path and the redox reaction, resulting from the oxygen ions drifting between the oxygen rich and poor regions of the multilayer structures. A possible conduction sketch for bipolar switching behaviors is also discussed.
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68.65.Ac Multilayers
68.55.-a Thin film structure and morphology
81.65.Mq Oxidation

Multilevel unipolar resistance switching in TiO2 thin films

S. C. Chae (채승철), J. S. Lee, W. S. Choi, S. B. Lee, S. H. Chang, H. Shin, B. Kahng, and T. W. Noh

Appl. Phys. Lett. 95, 093508 (2009); http://dx.doi.org/10.1063/1.3224185 (3 pages) | Cited 8 times

Online Publication Date: 4 September 2009

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We report on multilevel switching behavior in the unipolar resistance switching of TiO2 thin films. Multiple metastable states were observed during the reset process by measuring I-V curves. As observed using a conducting atomic force microscope, the multilevel resistance switching was accompanied by decreases in area and in the conductance of the top surface conducting regions. These experimental observations at both the macroscopic and microscopic levels could be explained by using the “random circuit breaker network” model, which is a dynamic bond percolation model.
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68.55.aj Insulators
68.37.Ps Atomic force microscopy (AFM)
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
73.25.+i Surface conductivity and carrier phenomena
73.61.Ng Insulators
72.20.Dp General theory, scattering mechanisms
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