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15 Oct 2007

Volume 91, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 91, 162101 (2007); http://dx.doi.org/10.1063/1.2794995 (3 pages)

D. J. Reilly, C. M. Marcus, M. P. Hanson, and A. C. Gossard
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Humidity-dependent stability of amorphous germanium nitrides fabricated by plasma nitridation

Katsuhiro Kutsuki, Gaku Okamoto, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 91, 163501 (2007); http://dx.doi.org/10.1063/1.2799260 (3 pages) | Cited 7 times

Online Publication Date: 15 October 2007

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We have investigated the stability of amorphous germanium nitride (Ge3N4) layers formed by plasma nitridation of Ge(100) surfaces using x-ray photoelectron spectroscopy and atomic force microscopy. We have found that humidity in the air accelerates the degradation of Ge3N4 layers and that under 80% humidity condition, most of the Ge–N bonds convert to Ge–O bonds, producing a uniform GeO2 layer, within 12 h even at room temperature. After this conversion of nitrides to oxides, the surface roughness drastically increased by forming GeO2 islands on the surfaces. These findings indicate that although Ge3N4 layers have superior thermal stability compared to the GeO2 layers, Ge3N4 reacts readily with hydroxyl groups and it is therefore essential to take the best care of the moisture in the fabrication of Ge-based devices with Ge3N4 insulator or passivation layers.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.65.Rv Passivation
52.77.-j Plasma applications
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Ps Atomic force microscopy (AFM)
68.55.-a Thin film structure and morphology

Efficient surface-conducted field emission from ZnO nanotetrapods

Chi Li, Kai Hou, Wei Lei, Xiaobing Zhang, Baoping Wang, and X. W. Sun

Appl. Phys. Lett. 91, 163502 (2007); http://dx.doi.org/10.1063/1.2798255 (3 pages) | Cited 16 times

Online Publication Date: 16 October 2007

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We report a surface-conducted field emission cathode using ZnO nanotetrapods as the surface conduction emitter. The dependences of electron emission efficiency on ZnO nanotetrapod film thickness and the spacing between adjacent electrodes of surface emitter were studied. A maximum electron emission efficiency of 60% was obtained for an optimal device with film thickness of 8 μm and electrode spacing of 0.1 mm. A low turn-on voltage of about 100 V (corresponding to a field of 1 V/μm) at an emission current density of 0.6 mA/cm2 was obtained which is good enough for field emission displays. Good stability and uniformity were also demonstrated.
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79.70.+q Field emission, ionization, evaporation, and desorption

Intermediate-band solar cells based on quantum dot supracrystals

Q. Shao, A. A. Balandin, A. I. Fedoseyev, and M. Turowski

Appl. Phys. Lett. 91, 163503 (2007); http://dx.doi.org/10.1063/1.2799172 (3 pages) | Cited 29 times

Online Publication Date: 16 October 2007

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The authors show that the ordered three-dimensional arrays of quantum dots, i.e., quantum dot supracrystals, can be used to implement the intermediate-band solar cell with the efficiency exceeding the Shockley-Queisser limit for a single junction cell. The strong electron wave function overlap resulting in minibands formation allows one to tune the band structure and enhance the light absorption and carrier transport. A first-principles semianalytical approach was used to determine the optimum dimensions of the quantum dots and the interdot spacing to achieve a maximum efficiency in the InAs0.9N0.1/GaAs0.98Sb0.02 quantum dot supracrystal photovoltaic cells.
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84.60.Jt Photoelectric conversion

Thin film crystal growth template removal: Application to stress reduction in lead zirconate titanate microstructures

P. Gkotsis, P. B. Kirby, F. Saharil, J. Oberhammer, and G. Stemme

Appl. Phys. Lett. 91, 163504 (2007); http://dx.doi.org/10.1063/1.2801386 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2007

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A key issue for the design and reliability of microdevices is process related; residual stresses in the thin films from which they are composed, especially for sol-gel deposited Pb(Zrx,Ti1−x)O3 ceramics, where use of Pt as a template layer, though essential for the nucleation of the perovskite phase, results in structures with high levels of stress largely fixed by the thermal expansion coefficient mismatch between Pt and Si. Here a technique for the elimination of this stress is presented, involving the use of adhesive wafer bonding and bulk micromachining procedures to remove the Pt layer following the Pb(Zrx,Ti1−x)O3 deposition.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.65.-j Piezoelectricity and electromechanical effects
68.60.Bs Mechanical and acoustical properties

Experimental investigation of bubble formation during capillary filling of SiO2 nanoslits

Lasse Højlund Thamdrup, Fredrik Persson, Henrik Bruus, Anders Kristensen, and Henrik Flyvbjerg

Appl. Phys. Lett. 91, 163505 (2007); http://dx.doi.org/10.1063/1.2801397 (3 pages) | Cited 17 times

Online Publication Date: 17 October 2007

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Experimental results are presented regarding the influence of bubble formation on the capillary filling speed of water in SiO2 nanoslits with heights ranging from 33 to 158 nm. The formation of an isolated pinned bubble in a nanoslit with a height of 111 nm causes an immediate decrease in the filling speed. In nanoslits with heights below 100 nm, pinned bubbles are continuously formed at the advancing liquid meniscus. This observed increase in bubble density, which increases the fluidic resistance, quantitatively coincides with an observed reduction of the filling speed during filling of nanoslits with heights below 100 nm.
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47.55.db Drop and bubble formation
47.55.nb Capillary and thermocapillary flows
47.61.Jd Multiphase flows

A bistable liquid-crystal display mode based on electrically driven smectic A layer reorientation

Hui-Yu Chen, Renfan Shao, Eva Korblova, Wei Lee, David Walba, and Noel A. Clark

Appl. Phys. Lett. 91, 163506 (2007); http://dx.doi.org/10.1063/1.2799742 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2007

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We describe a device geometry using interdigital electrodes that enables the electrically driven reorientation of smectic A layers from a homeotropic state (dark between crossed polarizers) to a planar state (bright between crossed polarizers) and back again. The resulting electro-optic effect is strongly bistable and gives high contrast ratio and fast response, rendering it a potential candidate for flexible-display applications.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
42.79.Ci Filters, zone plates, and polarizers
78.20.Jq Electro-optical effects
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Terahertz plasmon photoresponse in a density modulated two-dimensional electron channel of a GaAs/AlGaAs field-effect transistor

G. R. Aizin, D. V. Fateev, G. M. Tsymbalov, and V. V. Popov

Appl. Phys. Lett. 91, 163507 (2007); http://dx.doi.org/10.1063/1.2800369 (3 pages) | Cited 9 times

Online Publication Date: 17 October 2007

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We present a theory of dc photoresponse, change in device conductance, at the plasmon resonance in the density modulated two-dimensional electron channel of the grating-gated GaAs/AlGaAs field-effect transistor irradiated by an electromagnetic wave of terahertz frequency. An equilibrium density modulation is shown to give rise to a specific mechanism of photoresponse due to a plasma electrostriction effect. In strongly modulated systems, this effect dominates the photoresponse and results in a strong increase of the resonant peak amplitudes and photoresponse sign reversal dependent on the modulation depth and the equilibrium density profile. These results are in good qualitative agreement with recent experiments.
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85.30.Tv Field effect devices

Nanocrystalline diamond films as UV-semitransparent Schottky contacts to 4H-SiC

Marko J. Tadjer, Karl D. Hobart, Joshua D. Caldwell, James E. Butler, Kendrick X. Liu, Charles R. Eddy, Jr., D. Kurt Gaskill, K. K. Lew, Brenda L. VanMil, Rachael L. Myers-Ward, Mario G. Ancona, Fritz J. Kub, and Tatyana I. Feygelson

Appl. Phys. Lett. 91, 163508 (2007); http://dx.doi.org/10.1063/1.2800886 (3 pages) | Cited 8 times

Online Publication Date: 17 October 2007

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A heterojunction between thin films of nanocrystalline diamond (NCD) and 4H-SiC has been developed. Undoped and B-doped NCDs were deposited on both n− and p− SiC epilayers. I-V measurements on p+ NCD/n− SiC indicated Schottky rectifying behavior with a turn-on voltage of around 0.2 V. The current increased over eight orders of magnitude with an ideality factor of 1.17 at 30 °C. Ideal energy-band diagrams suggested a possible conduction mechanism for electron transport from the SiC conduction band to either the valence band or acceptor level of the NCD film. Applications as an UV semitransparent electrical contact to 4H-SiC are discussed.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Cw Elemental semiconductors

Anisotropic ambipolar carrier transport and high bipolar mobilities up to 0.1 cm2 V−1 s−1 in aligned liquid-crystal glass films of oligofluorene

Li-Yin Chen, Tung-Huei Ke, Chung-Chih Wu, Teng-Chih Chao, Ken-Tsung Wong, and Ching-Chao Chang

Appl. Phys. Lett. 91, 163509 (2007); http://dx.doi.org/10.1063/1.2801360 (3 pages) | Cited 7 times

Online Publication Date: 17 October 2007

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By taking advantage of the rich morphological characteristics of oligofluorenes and the mesophase-mediated molecular assembly/alignment, we studied carrier-transport properties of solid-state oligofluorenes in different morphologies and orientations. Compared to the amorphous phase, the uniaxially aligned liquid-crystal glass of oligofluorenes could give up to 100-fold enhancement in bipolar carrier-transport mobilities, bringing both hole and electron mobilities to nearly 0.1 cm2/V s. Furthermore, significant anisotropic bipolar transport, i.e., preferential bipolar carrier transport along the oligomer chain direction is observed.
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73.61.Jc Amorphous semiconductors; glasses
72.20.Fr Low-field transport and mobility; piezoresistance
61.30.-v Liquid crystals

Submicron metal-semiconductor-metal diamond photodiodes toward improving the responsivity

Meiyong Liao, Jose Alvarez, Masataka Imura, and Yasuo Koide

Appl. Phys. Lett. 91, 163510 (2007); http://dx.doi.org/10.1063/1.2800801 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2007

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Metal-semiconductor-metal deep-ultraviolet detectors with electrode spacings from 0.14 to 10 μm have been fabricated on a homoepitaxial diamond thin film grown on a Ib-type diamond substrate. A dramatic increase of the deep ultraviolet responsivity is observed when the electrode spacing is scaled down. The reduction in the electrode spacing enables the full depletion of the spacing at low biases, providing a higher responsivity without sacrification of the response speed.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Dark current suppression in type II InAs/GaSb superlattice long wavelength infrared photodiodes with M-structure barrier

Binh-Minh Nguyen, Darin Hoffman, Pierre-Yves Delaunay, and Manijeh Razeghi

Appl. Phys. Lett. 91, 163511 (2007); http://dx.doi.org/10.1063/1.2800808 (3 pages) | Cited 45 times

Online Publication Date: 18 October 2007

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We presented an alternative design of type II superlattice photodiodes with the insertion of a mid-wavelength infrared M-structure AlSb/GaSb/InAs/GaSb/AlSb superlattice for the reduction of dark current. The M-structure superlattice has a larger carrier effective mass and a greater band discontinuity as compared to the standard type II superlattices at the valence band. It acts as an effective medium that weakens the diffusion and tunneling transport at the depletion region. As a result, a 10.5 μm cutoff type II superlattice with 500 nm M-superlattice barrier exhibited a R0A of 200 Ω cm2 at 77 K, approximately one order of magnitude higher than the design without the barrier. The quantum efficiency of such structures does not show dependence on either barrier thickness or applied bias.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Wc Optical coatings
42.15.Eq Optical system design

Frequency dispersion reduction and bond conversion on n-type GaAs by in situ surface oxide removal and passivation

C. L. Hinkle, A. M. Sonnet, E. M. Vogel, S. McDonnell, G. J. Hughes, M. Milojevic, B. Lee, F. S. Aguirre-Tostado, K. J. Choi, J. Kim, and R. M. Wallace

Appl. Phys. Lett. 91, 163512 (2007); http://dx.doi.org/10.1063/1.2801512 (3 pages) | Cited 34 times

Online Publication Date: 19 October 2007

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The method of surface preparation on n-type GaAs, even with the presence of an amorphous-Si interfacial passivation layer, is shown to be a critical step in the removal of accumulation capacitance frequency dispersion. In situ deposition and analysis techniques were used to study different surface preparations, including NH4OH, Si-flux, and atomic hydrogen exposures, as well as Si passivation depositions prior to in situ atomic layer deposition of Al2O3. As–O bonding was removed and a bond conversion process with Si deposition is observed. The accumulation capacitance frequency dispersion was removed only when a Si interlayer and a specific surface clean were combined.
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81.05.Ea III-V semiconductors
81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
73.61.Ey III-V semiconductors

Current-induced cleaning of graphene

J. Moser, A. Barreiro, and A. Bachtold

Appl. Phys. Lett. 91, 163513 (2007); http://dx.doi.org/10.1063/1.2789673 (3 pages) | Cited 128 times

Online Publication Date: 19 October 2007

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A simple yet highly reproducible method to suppress contamination of graphene at low temperature inside the cryostat is presented. The method consists of applying a current of several milliamperes through the graphene device, which is here typically a few microns wide. This ultrahigh current density is shown to remove contamination adsorbed on the surface. This method is well suited for quantum electron transport studies of undoped graphene devices, and its utility is demonstrated here by measuring the anomalous quantum Hall effect.
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81.05.U- Carbon/carbon-based materials
81.65.Cf Surface cleaning, etching, patterning
68.35.Dv Composition, segregation; defects and impurities
68.43.Mn Adsorption kinetics
73.43.Fj Novel experimental methods; measurements
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