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28 May 2012

Volume 100, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 100, 222402 (2012); http://dx.doi.org/10.1063/1.3700809 (4 pages)

Felix Balhorn, Simon Jeni, Wolfgang Hansen, Detlef Heitmann, and Stefan Mendach
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Second harmonic generation in phase matched aluminum nitride waveguides and micro-ring resonators

W. H. P. Pernice, C. Xiong, C. Schuck, and H. X. Tang

Appl. Phys. Lett. 100, 223501 (2012); http://dx.doi.org/10.1063/1.4722941 (4 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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We demonstrate second order optical nonlinearity in aluminum nitride on insulator substrates. Using sputter-deposited aluminum nitride thin films, we realize nanophotonic waveguides and critically coupled micro-ring resonators that simultaneously support high Q cavity resonant modes for both visible and infrared light. Using phase matched devices, we achieve efficient second-harmonic generation and produce up to 0.55 μW of visible light on the chip with a conversion efficiency of −46 dB with 22 mW input waveguide pump power. From the measured response, we obtain a second order nonlinear susceptibility (χ2) of 4.7 pm/V. Our platform provides a viable route for realizing wideband linear and nonlinear optical devices on a chip.
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42.65.Wi Nonlinear waveguides
42.82.Et Waveguides, couplers, and arrays
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
42.79.Wc Optical coatings
81.15.Cd Deposition by sputtering

Off-state breakdown and dispersion optimization in AlGaN/GaN heterojunction field-effect transistors utilizing carbon doped buffer

S. A. Chevtchenko, E. Cho, F. Brunner, E. Bahat-Treidel, and J. Würfl

Appl. Phys. Lett. 100, 223502 (2012); http://dx.doi.org/10.1063/1.4723719 (3 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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An example of GaN buffer structure optimization in AlGaN/GaN heterojunction field-effect transistors is demonstrated. Transistors fabricated on four epitaxial structures with buffer consisting of unintentionally doped GaN channel (35 nm or 100 nm) and carbon doped GaN:C layers (∼1 × 1018 cm−3 or ∼1 × 1017 cm−3) are compared. As the criteria for optimization off-state breakdown voltage (Vbr) and drain current dispersion are used. The observed trade-off between the two parameters and dependency of Vbr on the carbon concentration and on the channel thickness are explained by a potential barrier formed due to GaN:C part of the buffer.
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85.30.Tv Field effect devices

Detection of filament formation in forming-free resistive switching SrTiO3 devices with Ti top electrodes

S. Stille, Ch. Lenser, R. Dittmann, A. Koehl, I. Krug, R. Muenstermann, J. Perlich, C. M. Schneider, U. Klemradt, and R. Waser

Appl. Phys. Lett. 100, 223503 (2012); http://dx.doi.org/10.1063/1.4724108 (4 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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We investigated the influence of Ti top electrodes on the resistive switching properties of SrTiO3 thin film devices. Above a Ti layer thickness of 5 nm, the initial resistance is strongly reduced, giving rise to forming-free devices. Hard x-ray photoemission experiments reveal the Ti layer to be composed of several oxide phases, induced by the redox-reaction at the Ti/SrTiO3 interface. Grazing incidence small angle x-ray scattering measurements indicate that the reduction of the SrTiO3 thin film occurs in a filamentary way. We attribute this behavior to the preferential reduction of SrTiO3 thin films along highly defective areas.
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68.55.-a Thin film structure and morphology
82.30.-b Specific chemical reactions; reaction mechanisms
82.45.Mp Thin layers, films, monolayers, membranes
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Evidence of space charge limited flow in the gate current of AlGaN/GaN high electron mobility transistors

Weikai Xu, Hemant Rao, and Gijs Bosman

Appl. Phys. Lett. 100, 223504 (2012); http://dx.doi.org/10.1063/1.4724207 (4 pages)

Online Publication Date: 1 June 2012

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Room temperature gate leakage current measurements as a function of gate bias voltage are reported for different AlGaN/GaN high electron mobility transistors and interpreted in terms of space charge limited flow in the presence of shallow traps through very small area conductive leakage paths already present or formed under electrical stress in the gate stack device area. Transport parameters for electrons following these paths are extracted, and the observation of gate electron velocity saturation in stressed devices indicates that newly created leakage paths form predominantly in high electric field gate edge regions.
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85.30.Tv Field effect devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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