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12 May 2008

Volume 92, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 92, 193301 (2008); http://dx.doi.org/10.1063/1.2920199 (3 pages)

Wei Chen, Hong Liang Zhang, Han Huang, Lan Chen, and Andrew Thye Shen Wee
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Ultrafast electron emission from metallic nanotip arrays induced by near infrared femtosecond laser pulses

S. Tsujino, P. Beaud, E. Kirk, T. Vogel, H. Sehr, J. Gobrecht, and A. Wrulich

Appl. Phys. Lett. 92, 193501 (2008); http://dx.doi.org/10.1063/1.2924290 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2008

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The authors explore the impact of femtosecond light pulses on the field-emission properties of single-gate molybdenum field-emitter arrays with nanometer scale tip apex. Despite the small fraction of the emission area, we observed a single-photon photoelectric current from the emitter tips on top of the dc field-emission current under the irradiation of 50 fs laser pulses at a wavelength of 800 nm with an external quantum efficiency up to ∼ 2×10−7 and the emitter tip quantum efficiency of ∼ 10−2. The result indicates that metallic field-emitter arrays are promising for applications that require high-brightness short electron beams.
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85.45.Db Field emitters and arrays, cold electron emitters
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Enhancement of electron field emission property with silver incorporation into diamondlike carbon matrix

Sk. Faruque Ahmed, Myoung-Woon Moon, and Kwang-Ryeol Lee

Appl. Phys. Lett. 92, 193502 (2008); http://dx.doi.org/10.1063/1.2926676 (3 pages) | Cited 11 times

Online Publication Date: 12 May 2008

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Effects of silver doping on the electron field emission properties of diamondlike carbon films deposited on silicon substrates by the rf reactive sputtering technique were studied in detail. It was found that the threshold field and effective emission barrier were reduced by Ag doping and the emission current strongly depends on the Ag doping percentage. The threshold field was found to decrease from 6.8 to 2.6 V/μm with a variation of Ag at. % from 0 to 12.5. The field enhancement factor was calculated and we have explained the emission mechanism.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.U- Doping and impurity implantation

Indistinguishable photons from a diode

A. J. Bennett, R. B. Patel, A. J. Shields, K. Cooper, P. Atkinson, C. A. Nicoll, and D. A. Ritchie

Appl. Phys. Lett. 92, 193503 (2008); http://dx.doi.org/10.1063/1.2918841 (3 pages) | Cited 14 times

Online Publication Date: 13 May 2008

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We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.
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78.67.Hc Quantum dots
42.79.Fm Reflectors, beam splitters, and deflectors
42.25.Hz Interference

Silicon nanowire tunneling field-effect transistors

M. T. Björk, J. Knoch, H. Schmid, H. Riel, and W. Riess

Appl. Phys. Lett. 92, 193504 (2008); http://dx.doi.org/10.1063/1.2928227 (3 pages) | Cited 30 times

Online Publication Date: 13 May 2008

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We demonstrate the implementation of tunneling field-effect transistors (TFETs) based on silicon nanowires (NWs) that were grown using the vapor-liquid-solid growth method. The Si NWs contain p-i-n+ segments that were achieved by in situ doping using phosphine and diborane as the n- and p-type dopant source, respectively. Electrical measurements of the TFETs show a band-to-band tunneling branch in the transfer characteristics. Furthermore, an increase in the on-state current and a decrease in the inverse subthreshold slope upon reducing the gate oxide thickness are measured. This matches theoretical calculations using a Wenzel Kramer Brillouin approximation with nanowire diameter and oxide thickness as input parameters.
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85.30.Tv Field effect devices

Prepassivation surface treatment effects on pulsed and dc I-V performance of AlGaN/GaN high-electron-mobility transistors

David J. Meyer, Joseph R. Flemish, and Joan M. Redwing

Appl. Phys. Lett. 92, 193505 (2008); http://dx.doi.org/10.1063/1.2928236 (3 pages)

Online Publication Date: 13 May 2008

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This study has examined the effects that various prepassivation plasma surface treatments had on pulsed and dc I-V characteristics of AlGaN/GaN high-electron-mobility transistors. Pulsed I-V current recovery data indicates that C2F6, NH3, O2, and Cl2 plasma treatments can be used in conjunction with plasma-enhanced chemical vapor deposited silicon nitride to significantly reduce rf dispersion. The different prepassivation surface treatments, however, produced little variation in dc I-V parameters such as gate leakage current, interdevice isolation current, and off-state breakdown voltage as compared to untreated passivated samples.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
81.65.Rv Passivation

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer

H. S. Ling, S. Y. Wang, C. P. Lee, and M. C. Lo

Appl. Phys. Lett. 92, 193506 (2008); http://dx.doi.org/10.1063/1.2926663 (3 pages) | Cited 20 times

Online Publication Date: 13 May 2008

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We demonstrate the high quantum efficiency InAs/In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also improves the escape probability of the photoelectrons. Compared with the conventional DWELL QDIPs, the quantum efficiency increases more than 20 times and the detectivity is about an order of magnitude higher at 77 K.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Effects of well thickness on the spectral properties of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors

G. Jolley, L. Fu, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 92, 193507 (2008); http://dx.doi.org/10.1063/1.2927487 (3 pages) | Cited 13 times

Online Publication Date: 14 May 2008

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We report on the effects of the quantum well (QW) thickness on the spectral response and other characteristics of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. The main device properties are observed to have a strong dependence on the QW parameters.
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81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.De Quantum wells
85.60.Gz Photodetectors (including infrared and CCD detectors)

Transversely tapered hybrid electro-optic polymer/sol-gel Mach–Zehnder waveguide modulators

Y. Enami, D. Mathine, C. T. DeRose, R. A. Norwood, J. Luo, A. K.-Y. Jen, and N. Peyghambarian

Appl. Phys. Lett. 92, 193508 (2008); http://dx.doi.org/10.1063/1.2927489 (3 pages) | Cited 4 times

Online Publication Date: 15 May 2008

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We show results of a proposed hybrid modulator structure that reduces both the optical loss and half wave voltage (Vπ). A sol-gel waveguide core transversely sandwiched between two Mach–Zehnder arms of electro-optic (EO) polymer cores enables an adiabatic transverse transition between the sol-gel and the EO polymer cores without the need for Y branches. The undercladding thickness is reduced to 3.7 μm with negligible further optical loss from the bottom electrode. EO modulation with Vπ of 1.8 V at 1550 nm is demonstrated using a guest-host EO polymer, with an optical insertion loss of 13.7 dB in the transverse magnetic mode.
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42.79.Hp Optical processors, correlators, and modulators

Low-noise wideband ultrasound detection using polymer microring resonators

Sheng-Wen Huang, Sung-Liang Chen, Tao Ling, Adam Maxwell, Matthew O’Donnell, L. Jay Guo, and Shai Ashkenazi

Appl. Phys. Lett. 92, 193509 (2008); http://dx.doi.org/10.1063/1.2929379 (3 pages) | Cited 12 times

Online Publication Date: 15 May 2008

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Polymer microring resonators for low-noise, wideband ultrasound detection are presented. Using a nanoimprinting technique, we fabricated polymer microring resonators with a quality factor of 6000 resulting in high sensitivity to ultrasound. A noise-equivalent pressure of 0.23 kPa over 1–75 MHz and a detection bandwidth of over 90 MHz at −3 dB were measured. These results demonstrate the potential of polymer microring resonators for high-frequency ultrasound and photoacoustic imaging. For a typical photoacoustic imaging test case, the high sensitivity demonstrated in these devices would increase imaging depth by a factor of 3 compared to state-of-the-art polyvinylidene fluoride detectors.
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43.58.-e Acoustical measurements and instrumentation
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

X-ray-excited photoelectron detection using a scanning tunneling microscope

V. Rose, J. W. Freeland, K. E. Gray, and S. K. Streiffer

Appl. Phys. Lett. 92, 193510 (2008); http://dx.doi.org/10.1063/1.2936083 (3 pages) | Cited 9 times

Online Publication Date: 16 May 2008

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Detection of x-ray-enhanced electrons emitted by synchrotron radiation with the tip of a scanning tunneling microscope has the potential to open a path to high-resolution microscopy with chemical sensitivity. Nonresonant photoejected electrons typically yield a current background of a few hundred picoamperes at a bare tip. Coating the tip with an insulating boron nitride film can effectively reduce this background. In this configuration, we have quantitatively studied the bias dependent photoelectron collection for tip/sample separations of 400–1600 nm, where quantum mechanical tunneling does not contribute.
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07.79.Cz Scanning tunneling microscopes
07.85.Qe Synchrotron radiation instrumentation
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Temperature acceleration of structural relaxation in amorphous Ge2Sb2Te5

D. Ielmini, S. Lavizzari, D. Sharma, and A. L. Lacaita

Appl. Phys. Lett. 92, 193511 (2008); http://dx.doi.org/10.1063/1.2930680 (3 pages) | Cited 23 times

Online Publication Date: 16 May 2008

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The structural relaxation (SR) process in an amorphous chalcogenide material (Ge2Sb2Te5) is studied by electrical measurements on phase-change memory devices. SR induces a change in the conduction regime from Poole to Poole–Frenkel transport, evidencing a temperature accelerated defect-annihilation process. Based on an Arrhenius kinetics with distributed activation energies, a temperature-acceleration law is shown, relating the time to reach a specific relaxed state to the temperature during isothermal experiments. This law is demonstrated comparing the time evolution of resistance for different temperatures. These results allow for a significant time reduction in reliability testing of devices and materials affected by SR.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.20.Ht High-field and nonlinear effects

High-Q active ring microwave resonators based on ferrite-ferroelectric layered structures

Alexey B. Ustinov, G. Srinivasan, and Boris A. Kalinikos

Appl. Phys. Lett. 92, 193512 (2008); http://dx.doi.org/10.1063/1.2931085 (3 pages) | Cited 4 times

Online Publication Date: 16 May 2008

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An electric and magnetic field tunable (dual-tunable) microwave active ring resonator is designed and characterized. The device structure is implemented with a microwave amplifier and a ferrite-ferroelectric delay line in the feedback loop. At 8 GHz, an effective Q factor of 50 000 and tuning by 5 MHz with an electric field are achieved. The performance characteristics of the resonator are presented and discussed.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.30.Le Amplifiers
84.40.-x Radiowave and microwave (including millimeter wave) technology

Detection of the valence band in buried Co2MnSi–MgO tunnel junctions by means of photoemission spectroscopy

Gerhard H. Fecher, Benjamin Balke, Andrei Gloskowskii, Siham Ouardi, Claudia Felser, Takayuki Ishikawa, Masafumi Yamamoto, Yoshiyuki Yamashita, Hideki Yoshikawa, Shigenori Ueda, and Keisuke Kobayashi

Appl. Phys. Lett. 92, 193513 (2008); http://dx.doi.org/10.1063/1.2931089 (3 pages) | Cited 19 times

Online Publication Date: 16 May 2008

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This work reports on the detection of the valence band of buried Heusler compounds by means of hard x-ray photoemission spectroscopy. The measurements have been performed on the so-called “half” tunnel junctions that are thin films of Co2MnSi underneath MgO. Starting from the substrate, the structure of the samples is MgO(buffer)–Co2MnSi–MgO(tMgO)–AlOx with a thickness tMgO of the upper MgO layer of 2 and 20 nm. The valence band x-ray photoemission spectra have been excited by hard x rays of about 6 keV energy. The valence band spectra have been used to estimate the mean free path of the electrons through the MgO layer to be 17 nm at kinetic energies of about 6 keV. In particular, it is shown that the buried Co2MnSi films exhibit the same valence density of states as in bulk samples.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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