analysis-of-contact-interfaces-for-single-gan-nanowire-devices

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

National Institute of Standards and Technology 

Stable optical trapping and manipulation of high-index particles in low-index host media is often impossible due to the dominance of scattering forces over gradient forces. Here we explore optical manipulation in liquid crystalline structured hosts and show that robust optical manipulation of high-index particles, such as GaN nanowires, is enabled by laser-induced distortions in long-range molecular alignment, via coupling of translational and rotational motions due to helicoidal molecular arrangement, or due to elastic repulsive interactions with confining substrates. Anisotropy of the viscoelastic liquid crystal medium and particle shape give rise to a number of robust unconventional trapping capabilities, which we use to characterize defect structures and study rheological properties of various thermotropic liquid crystals.

Unconventional structure-assisted optical manipulation of high-index nanowires in liquid crystals.

We demonstrate a new method for tailoring the selectivity of chemical sensors using semiconductor nanowires (NWs) decorated with metal and metal oxide multicomponent nanoclusters (NCs). Here we present the change of selectivity of titanium dioxide (TiO(2)) nanocluster-coated gallium nitride (GaN) nanowire sensor devices on the addition of platinum (Pt) nanoclusters. The hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO(2) and/or Pt nanoclusters (NCs) using the sputtering technique. This paper present the sensing characteristics of GaN/(TiO(2)-Pt) nanowire-nanocluster (NWNC) hybrids and GaN/(Pt) NWNC hybrids, and compare their selectivity with that of the previously reported GaN/TiO(2) sensors. The GaN/TiO(2) NWNC hybrids showed remarkable selectivity to benzene and related aromatic compounds, with no measurable response for other analytes. Addition of Pt NCs to GaN/TiO(2) sensors dramatically altered their sensing behavior, making them sensitive only to methanol, ethanol and hydrogen, but not to any other chemicals we tested. The GaN/(TiO(2)-Pt) hybrids were able to detect ethanol and methanol concentrations as low as 100 nmol mol(-1) (ppb) in air in approximately 100 s, and hydrogen concentrations from 1 µmol mol(-1) (ppm) to 1% in nitrogen in less than 60 s. However, GaN/Pt NWNC hybrids showed limited sensitivity only towards hydrogen and not towards any alcohols. All these hybrid sensors worked at room temperature and are photomodulated, i.e. they responded to analytes only in the presence of ultraviolet (UV) light. We propose a qualitative explanation based on the heat of adsorption, ionization energy and solvent polarity to explain the observed selectivity of the different hybrids. These results are significant from the standpoint of applications requiring room-temperature hydrogen sensing and sensitive alcohol monitoring. These results demonstrate the tremendous potential for tailoring the selectivity of the hybrid nanosensors for a multitude of environmental and industrial sensing applications.

Methanol, ethanol and hydrogen sensing using metal oxide and metal (TiO(2)-Pt) composite nanoclusters on GaN nanowires: a new route towards tailoring the selectivity of nanowire/nanocluster chemical sensors.

Effects of design and materials on the dielectrophoretic self-assembly of individual gallium nitride nanowires (GaN NWs) onto microfabricated electrodes have been experimentally investigated. The use of TiO(2) surface coating generated by atomic layer deposition (ALD) improves dielectrophoretic assembly yield of individual GaN nanowires on microfabricated structures by as much as 67%. With a titanium dioxide coating, individual nanowires were placed across suspended electrode pairs in 46% of tests (147 out of 320 total), versus 28% of tests (88 out of 320 total tests) that used uncoated GaN NWs. An additional result from these tests was that suspending the electrodes 2.75 μm above the substrate corresponded with up to 15.8% improvement in overall assembly yield over that of electrodes fabricated directly on the substrate.

Controlled dielectrophoretic nanowire self-assembly using atomic layer deposition and suspended microfabricated electrodes.

The development of Ni/Au contacts to Mg-doped GaN nanowires (NWs) is examined. Unlike Ni/Au contacts to planar GaN, current-voltage (I-V) measurements of Mg-doped nanowire devices frequently exhibit a strong degradation after annealing in N(2)/O(2). This degradation originates from the poor wetting behavior of Ni and Au on SiO(2) and the excessive void formation that occurs at the metal/NW and metal/oxide interfaces. The void formation can cause cracking and delamination of the metal film as well as reduce the contact area at the metal/NW interface, which increases the resistance. The morphology and composition of the annealed Ni/Au contacts on SiO(2) and the p-GaN films were investigated by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) measurements. Adhesion experiments were performed in order to determine the degree of adhesion of the Ni/Au films to the SiO(2) as well as observe and analyze the morphology of the film's underside by SEM. Device degradation from annealing was prevented through the use of a specific adhesion layer of Ti/Al/Ni deposited prior to the nanowire dispersal and Ni/Au deposition. I-V measurements of NW devices fabricated using this adhesion layer showed a decrease in resistance after annealing, whereas all others showed an increase in resistance. Transmission electron microscopy (TEM) on a cross-section of a NW with Ni/Au contacts and a Ti/Al/Ni adhesion layer showed a lack of void formation at the contact/NW interface. Results of the XRD and TEM analysis of the NW contact structure using a Ti/Al/Ni adhesion layer suggests Al alloying of the Ni/Au contact increases the adhesion and stability of the metal film as well as prevents excessive void formation at the contact/NW interface.

Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires.

The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm(2)/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth.

Noncontact measurement of charge carrier lifetime and mobility in GaN nanowires.

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In this Letter we report on the fabrication, device characteristics, and optical coupling of a two-nanowire device comprising GaN nanowires with light-emitting and photoconductive capabilities. Axial p-n junction GaN nanowires were grown by molecular beam epitaxy, transferred to a non-native substrate, and selectively contacted to form discrete optical source or detector nanowire components. The optical coupling demonstrated for this device may provide new opportunities for integration of optical interconnects between on-chip electrical subsystems.

On-chip optical interconnects made with gallium nitride nanowires.

Dans cette lettre, nous rapportons sur la fabrication, caract&eacute;ristiques du dispositif et couplage optique d&#39;un dispositif de deux-NANOFIL comprenant des nanofils de GaN avec capacit&eacute;s photoconducteurs et luminescent. Nanofils GaN axial jonction p-n ont &eacute;t&eacute; cultiv&eacute;es par &eacute;pitaxie par jet mol&eacute;culaire, transf&eacute;r&eacute;s &agrave; un substrat non indig&egrave;nes et s&eacute;lectivement contact&eacute;s &agrave; forme optiques source ou d&eacute;tecteur de nanofils composants discrets. Le couplage optique d&eacute;montr&eacute;e pour cet appareil peut-&ecirc;tre offrir des possibilit&eacute;s nouvelles pour l&#39;int&eacute;gration des optiques d&#39;interconnexions entre les sous-syst&egrave;mes &eacute;lectriques sur puce.

Sur puce optique d&#39;interconnexions avec les nanofils de nitrure de gallium.

In diesem Brief berichten wir &uuml;ber die Fabrikation, Ger&auml;teeigenschaften und optische Kopplung von einem zwei-Nanodraht-Ger&auml;t bestehend aus GaN Nanowires mit leuchtende und photoleitende F&auml;higkeiten. Axiale p-n-&Uuml;bergang GaN Nanowires wurden durch Molekularstrahlepitaxie geworden, auf eine nicht-Native-Substrat &uuml;bertragen und selektiv in Form diskreter Quelle oder Detektor Nanodraht Optikkomponenten kontaktiert. Die optische Kopplung demonstrierte f&uuml;r dieses Ger&auml;t kann neue M&ouml;glichkeiten bieten, f&uuml;r die Integration von optischen Verbindungen zwischen on-Chip-elektrische-Subsystemen.

Auf dem Chip optische Verbindungen mit Gallium-Nitrid-Nanodr&auml;hte.

In questa lettera riportiamo la fabbricazione, le caratteristiche del dispositivo e accoppiamento ottico di un dispositivo di due-nanowire nanofili GaN con capacit&agrave; illuminante e fotoconduttiva. Assiale giunzione p-n GaN nanofili erano cresciuti per Epitassia da fasci molecolari, trasferiti in un substrato non-native e selettivamente contattati in forma discrete fonte o rivelatore nanofilo componenti ottici. L&#39;accoppiamento ottico ha dimostrato per questo dispositivo pu&ograve; fornire nuove opportunit&agrave; per integrazione dell&#39;ottica interconnessioni tra sottosistemi elettrici on-chip.

On-chip ottico interconnessioni realizzati con nanofili di nitruro di gallio.

&#x3053;&#x306E;&#x624B;&#x7D19;&#x3067;&#x4F5C;&#x88FD;&#x3001;&#x30C7;&#x30D0;&#x30A4;&#x30B9;&#x7279;&#x6027;&#x3068;&#x5149;&#x7D50;&#x5408;&#x306E; GaN &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC;&#x767A;&#x5149;&#x304A;&#x3088;&#x3073;&#x5149;&#x5C0E;&#x96FB;&#x6027;&#x6A5F;&#x80FD;&#x3092;&#x69CB;&#x6210;&#x3059;&#x308B; 2 &#x3064;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4; &#x30C7;&#x30D0;&#x30A4;&#x30B9;&#x3092;&#x5831;&#x544A;&#x3057;&#x307E;&#x3059;&#x3002;&#x8EF8;&#x306E; pn &#x63A5;&#x5408;&#x306E; GaN &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC;&#x5206;&#x5B50;&#x7DDA;&#x30A8;&#x30D4;&#x30BF;&#x30AD;&#x30B7;&#x30FC;&#x6210;&#x9577;&#x3001;&#x975E;&#x30CD;&#x30A4;&#x30C6;&#x30A3;&#x30D6;&#x306E;&#x57FA;&#x6750;&#x306B;&#x79FB;&#x52D5;&#x3001;&#x30D5;&#x30A9;&#x30FC;&#x30E0;&#x96E2;&#x6563;&#x5149;&#x30BD;&#x30FC;&#x30B9;&#x307E;&#x305F;&#x306F;&#x691C;&#x51FA;&#x5668;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4; &#x30B3;&#x30F3;&#x30DD;&#x30FC;&#x30CD;&#x30F3;&#x30C8;&#x3092;&#x9078;&#x629E;&#x7684;&#x306B;&#x9023;&#x7D61;&#x3002;&#x5149;&#x306E;&#x7D71;&#x5408;&#x30C1;&#x30C3;&#x30D7;&#x306B;&#x96FB;&#x6C17;&#x306E;&#x30B5;&#x30D6;&#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x9593;&#x306E;&#x76F8;&#x4E92;&#x63A5;&#x7D9A;&#x306E;&#x305F;&#x3081;&#x3001;&#x5149;&#x306E;&#x3053;&#x306E;&#x30C7;&#x30D0;&#x30A4;&#x30B9;&#x306E;&#x5B9F;&#x8A3C;&#x7D50;&#x5408;&#x5EA6;&#x65B0;&#x3057;&#x3044;&#x6A5F;&#x4F1A;&#x3092;&#x63D0;&#x4F9B;&#x53EF;&#x80FD;&#x6027;&#x304C;&#x3042;&#x308A;&#x307E;&#x3059;&#x3002;

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&#xC774; &#xD3B8;&#xC9C0;&#xC5D0;&#xC11C; &#xC6B0;&#xB9AC;&#xAC00; &#xC81C;&#xC870; &#xC7A5;&#xCE58; &#xD2B9;&#xC131;&#xACFC; &#xBC1C;&#xAD11; &#xBC0F; photoconductive &#xAE30;&#xB2A5;&#xC744; &#xAC04; &#xC815;&#xC744; 2 &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4; &#xC18C;&#xC790;&#xC758; &#xAD11;&#xD559; &#xCEE4;&#xD50C;&#xB9C1;&#xC5D0; &#xB300; &#xD55C; &#xBCF4;&#xACE0;&#xC11C;. &#xCD95; p-n &#xC811;&#xD569; GaN &#xC815; &#xD588;&#xB2E4; &#xBD84;&#xC790; &#xBE54; &#xD53C;&#xC5D0; &#xC758;&#xD574; &#xC131;&#xC7A5; &#xB418; &#xACE0; &#xAE30;&#xBCF8;&#xC774; &#xC544;&#xB2CC; &#xAE30;&#xD310;&#xC5D0; &#xC804;&#xC1A1; &#xC591;&#xC2DD; &#xC774;&#xC0B0; &#xAD11; &#xC18C;&#xC2A4; &#xB610;&#xB294; &#xAC80;&#xCD9C;&#xAE30; &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4; &#xAD6C;&#xC131; &#xC694;&#xC18C;&#xB97C; &#xC120;&#xD0DD;&#xC801;&#xC73C;&#xB85C; &#xC5F0;&#xB77D;. &#xAD11; &#xCEE4;&#xD50C;&#xB9C1;&#xC774; &#xC7A5;&#xCE58;&#xC5D0; &#xB300; &#xD55C; &#xAC80;&#xC99D; &#xB41C; &#xAD11;&#xC758; &#xD1B5;&#xD569; &#xCE69;&#xC5D0; &#xC804;&#xAE30; &#xD558;&#xC704; &#xC2DC;&#xC2A4;&#xD15C; &#xC0AC;&#xC774;&#xC758; &#xC0C1;&#xD638; &#xC5F0;&#xACB0;&#xC744; &#xC704;&#xD55C; &#xC0C8;&#xB85C;&#xC6B4; &#xAE30;&#xD68C;&#xB97C; &#xC81C;&#xACF5;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.

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En esta carta nos informe sobre el acoplamiento &oacute;ptico de un dispositivo de dos-Nanocable GaN nanocables con capacidades fotoconductora y emisi&oacute;n de luz, fabricaci&oacute;n y caracter&iacute;sticas del dispositivo. Axial p-n GaN nanohilos fueron cultivadas por epitaxia de haces moleculares, transferidos a un sustrato no nativos y selectivamente contact&oacute; a forma discretos fuente o detector Nanocable componentes &oacute;pticos. El acoplamiento &oacute;ptico demostrada para este dispositivo puede proporcionar nuevas oportunidades para la integraci&oacute;n de los medios &oacute;pticos interconexiones entre subsistemas el&eacute;ctricos en el chip.

Kris A. Bertness

Quantum Electronics and Photonics Division

National Institute of Standards and Technology

Analysis of Contact Interfaces for Single GaN Nanowire Devices