electron-channeling-contrast-imaging-for-rapid-iii-v-heteroepitaxial

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

The Ohio State University

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&#x4E09;&#x7EF4;&#x7518;/AlN &#x7EB3;&#x7C73;&#x7EBF;&#x5F02;&#x8D28;&#x5206;&#x9694;&#x6210;&#x6838;&#x4E0E;&#x751F;&#x957F;&#x7684;&#x8FC7;&#x7A0B;&#x3002;

Bottom-up nanostructure assembly has been a central theme of materials synthesis over the past few decades. Semiconductor quantum dots and nanowires provide additional degrees of freedom for charge confinement, strain engineering, and surface sensitivity-properties that are useful to a wide range of solid state optical and electronic technologies. A central challenge is to understand and manipulate nanostructure assembly to reproducibly generate emergent structures with the desired properties. However, progress is hampered due to the interdependence of nucleation and growth phenomena. Here we show that by dynamically adjusting the growth kinetics, it is possible to separate the nucleation and growth processes in spontaneously formed GaN nanowires using a two-step molecular beam epitaxy technique. First, a growth phase diagram for these nanowires is systematically developed, which allows for control of nanowire density over three orders of magnitude. Next, we show that by first nucleating nanowires at a low temperature and then growing them at a higher temperature, height and density can be independently selected while maintaining the target density over long growth times. GaN nanowires prepared using this two-step procedure are overgrown with three-dimensionally layered and topologically complex heterostructures of (GaN/AlN). By adjusting the growth temperature in the second growth step either vertical or coaxial nanowire superlattices can be formed. These results indicate that a two-step method allows access to a variety of kinetics at which nanowire nucleation and adatom mobility are adjustable.

Three-dimensional GaN/AlN nanowire heterostructures by separating nucleation and growth processes.

Assembl&eacute;e de nanostructure ascendante a &eacute;t&eacute; un th&egrave;me central de la synth&egrave;se de mat&eacute;riaux dans les derni&egrave;res d&eacute;cennies. Nanofils et points quantiques semi-conducteurs fournissent des autres degr&eacute;s de libert&eacute; pour le confinement de la charge, la souche engineering et surfaces sensibilit&eacute;-propri&eacute;t&eacute;s qui sont utiles &agrave; un large &eacute;ventail de technologies optiques et &eacute;lectroniques de l&#39;&eacute;tat solide. Un d&eacute;fi essentiel est de comprendre et de manipuler la nanostructure Assembl&eacute;e pour g&eacute;n&eacute;rer des structures &eacute;mergentes avec les propri&eacute;t&eacute;s d&eacute;sir&eacute;es de fa&ccedil;on reproductible. Cependant, le progr&egrave;s sont entrav&eacute; en raison de l&#39;interd&eacute;pendance des ph&eacute;nom&egrave;nes de nucl&eacute;ation et de croissance. Nous d&eacute;montrons qu&#39;en ajustant dynamiquement la cin&eacute;tique de croissance, il est possible de s&eacute;parer les processus de nucl&eacute;ation et croissance de nanofils de GaN spontan&eacute;ment form&eacute; &agrave; l&#39;aide d&#39;une technique d&#39;&eacute;pitaxie de faisceau mol&eacute;culaire en deux &eacute;tapes. Tout d&#39;abord, un diagramme de phase de croissance pour ces nanofils est syst&eacute;matiquement mis au point, qui permet un contr&ocirc;le de la densit&eacute; de nanofils de trois ordres de grandeur. Ensuite, nous montrons que par nucl&eacute;ation tout d&#39;abord les nanofils &agrave; basse temp&eacute;rature et ensuite leur culture &agrave; des temp&eacute;ratures sup&eacute;rieures, hauteur et la densit&eacute; peuvent &ecirc;tre ind&eacute;pendamment s&eacute;lectionn&eacute;s tout en maintenant la densit&eacute; de la cible au cours de longs temps de croissance. GaN nanofils pr&eacute;par&eacute;s &agrave; l&#39;aide de cette proc&eacute;dure en deux &eacute;tapes sont envahis par les h&eacute;t&eacute;rostructures tridimensionnellement en couches et topologiquement complexes de (GaN/AlN). En r&eacute;glant la temp&eacute;rature de croissance dans l&#39;&eacute;tape de la seconde venue soit superr&eacute;seaux NANOFIL vertical ou coaxial peut &ecirc;tre form&eacute;. Ces r&eacute;sultats indiquent qu&#39;une m&eacute;thode en deux &eacute;tapes permet d&#39;acc&eacute;der &agrave; une vari&eacute;t&eacute; de cin&eacute;tique &agrave; laquelle NANOFIL nucl&eacute;ation et la mobilit&eacute; de l&#39;atome adsorb&eacute; sont r&eacute;glables.

Tridimensionnelles GaN/AlN NANOFIL h&eacute;t&eacute;rostructures en s&eacute;parant les processus de nucl&eacute;ation et de croissance.

Bottom-up-Nanostruktur-Versammlung wurde ein zentrales Thema der Materialsynthese in den vergangenen Jahrzehnten. Halbleiter-Quantenpunkte und Nanodr&auml;hte bieten zus&auml;tzliche Freiheitsgrade f&uuml;r kostenlos Beengtheit, Stamm engineering und Oberfl&auml;che Empfindlichkeit-Eigenschaften, die f&uuml;r eine Vielzahl von solid-State-optische und elektronische Technologien nutzen sind. Eine zentrale Herausforderung ist zu verstehen und manipulieren Nanostruktur Versammlung um reproduzierbar emergente Strukturen mit den gew&uuml;nschten Eigenschaften zu generieren. Allerdings ist aufgrund der Interdependenz der Keimbildung und Wachstum Ph&auml;nomene Fortschritt behindert. Hier zeigen wir, dass durch dynamische Anpassung der Wachstums-Kinetics, die Keimbildung und Wachstum Prozesse in spontan gebildeten GaN Nanowires mit einer zweistufigen Molekulare Beam Epitaxie-Technik zu trennen kann. Zun&auml;chst wird ein Wachstum-Phasendiagramm f&uuml;r diese Nanowires systematisch entwickelt, erm&ouml;glicht die Kontrolle der drei Gr&ouml;&szlig;enordnungen Nanodraht-Dichte. Als N&auml;chstes zeigen wir, dass zuerst Nukleierungsmittel Nanodr&auml;hte bei niedrigen Temperaturen und dann wachsen sie bei einer h&ouml;heren Temperatur, H&ouml;he und Dichte unabh&auml;ngig ausgew&auml;hlt werden k&ouml;nnen und gleichzeitig die Ziel-Dichte &uuml;ber lange Wachstum Zeiten. GaN Nanowires vorbereitet, dieses Zweischrittverfahren sind mit dreidimensional vielschichtig und topologisch komplexe Heterostrukturen von (GaN/AlN) bewachsen. Durch die Anpassung der Temperatur Wachstum im zweiten Wachstum Schritt k&ouml;nnen entweder senkrecht oder Koaxial Nanodraht Superlattices gebildet werden. Diese Ergebnisse zeigen, dass eine zweistufige Methode Zugang zu einer Vielzahl von Kinetik erlaubt, auf welche Nanodraht Keimbildung und Adatom Mobilit&auml;t einstellbar sind.

Dreidimensionale GaN/AlN-Nanodraht-Heterostrukturen durch die Trennung von Keimbildung und Wachstums-Prozessen.

Assembly nanostruttura bottom-up &egrave; stato un tema centrale della sintesi di materiali negli ultimi decenni. Nanofili e punti quantici semiconduttore forniscono ulteriori gradi di libert&agrave; per confinamento carica, ceppo ingegneria superficiale sensibilit&agrave;-propriet&agrave; e che sono utili per una vasta gamma di tecnologie ottiche ed elettroniche allo stato solido. Una sfida centrale &egrave; quello di comprendere e manipolare nanostruttura assieme per generare reproducibly strutture emergenti con le propriet&agrave; desiderate. Tuttavia, il progresso &egrave; ostacolata a causa dell&#39;interdipendenza dei fenomeni di nucleazione e crescita. Qui vi mostriamo che regolando dinamicamente la cinetica di crescita, &egrave; possibile separare i processi di nucleazione e crescita di nanofili di GaN spontaneamente formate utilizzando una tecnica di epitassia di fasci molecolari in due fasi. In primo luogo, un diagramma di fase di crescita per questi nanofili &egrave; sistematicamente sviluppato, che consente un controllo della densit&agrave; nanofilo sopra tre ordini di grandezza. Successivamente, ci mostra che in primo luogo nucleare nanofili a bassa temperatura e poi li cresce ad una temperatura superiore, altezza e densit&agrave; pu&ograve; essere indipendente selezionate mantenendo la densit&agrave; target sopra lunghi tempi di crescita. GaN nanofili preparati usando questa procedura in due fasi sono ricoperti di eterostrutture topologicamente complessa e tridimensionale stratificata di (GaN/AlN). Regolando la temperatura di crescita nel passaggio seconda crescita possono essere formati sia superreticoli nanofilo verticale o coassiale. Questi risultati indicano che un metodo in due fasi consente l&#39;accesso a una variet&agrave; di cinetica alla quale nanofilo nucleazione e adatom mobilit&agrave; sono regolabili.

Tridimensionale GaN/AlN nanofilo eterostrutture separando i processi di nucleazione e crescita.

&#x30DC;&#x30C8;&#x30E0;&#x30A2;&#x30C3;&#x30D7;&#x578B;&#x30CA;&#x30CE;&#x69CB;&#x9020;&#x30A2;&#x30BB;&#x30F3;&#x30D6;&#x30EA;&#x6750;&#x6599;&#x5408;&#x6210;&#x306E;&#x4E2D;&#x5FC3;&#x30C6;&#x30FC;&#x30DE;&#x306F;&#x3001;&#x904E;&#x53BB;&#x6570;&#x5341;&#x5E74;&#x9593;&#x3055;&#x308C;&#x3066;&#x3044;&#x307E;&#x3059;&#x3002;&#x534A;&#x5C0E;&#x4F53;&#x91CF;&#x5B50;&#x30C9;&#x30C3;&#x30C8; &#x30FB; &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x96FB;&#x8377;&#x306E;&#x9589;&#x3058;&#x8FBC;&#x3081;&#x306A;&#x81EA;&#x7531;&#x5EA6;&#x3092;&#x63D0;&#x4F9B;&#x3057;&#x3001;&#x30A8;&#x30F3;&#x30B8;&#x30CB;&#x30A2; &#x30EA;&#x30F3;&#x30B0;&#x3001;&#x304A;&#x3088;&#x3073;&#x8868;&#x9762;&#x611F;&#x5EA6; - &#x56FA;&#x4F53;&#x5149;&#x30FB;&#x96FB;&#x5B50;&#x6280;&#x8853;&#x306E;&#x5E83;&#x3044;&#x7BC4;&#x56F2;&#x306B;&#x6709;&#x7528;&#x306A;&#x7279;&#x6027;&#x306E;&#x3072;&#x305A;&#x307F;&#x3002;&#x4E2D;&#x592E;&#x306E;&#x8AB2;&#x984C;&#x3092;&#x7406;&#x89E3;&#x3057;&#x3001;&#x518D;&#x73FE;&#x53EF;&#x80FD;&#x306A;&#x5275;&#x767A;&#x7684;&#x69CB;&#x9020;&#x3067;&#x3001;&#x76EE;&#x7684;&#x306E;&#x30D7;&#x30ED;&#x30D1;&#x30C6;&#x30A3;&#x3092;&#x751F;&#x6210;&#x3059;&#x308B;&#x30CA;&#x30CE;&#x69CB;&#x9020;&#x30A2;&#x30BB;&#x30F3;&#x30D6;&#x30EA;&#x3092;&#x64CD;&#x4F5C;&#x3059;&#x308B;&#x3053;&#x3068;&#x3067;&#x3059;&#x3002;&#x305F;&#x3060;&#x3057;&#x3001;&#x9032;&#x884C;&#x72B6;&#x6CC1;&#x306E;&#x6838;&#x751F;&#x6210;&#x3068;&#x6210;&#x9577;&#x73FE;&#x8C61;&#x306E;&#x76F8;&#x4E92;&#x4F9D;&#x5B58;&#x95A2;&#x4FC2;&#x306B;&#x3088;&#x308A;&#x59A8;&#x3052;&#x3089;&#x308C;&#x3066;&#x3044;&#x307E;&#x3059;&#x3002;&#x3053;&#x3053;&#x3067;&#x6210;&#x9577;&#x30AB;&#x30A4;&#x30CD;&#x30C6;&#x30A3;&#x30AF;&#x30B9;&#x3092;&#x52D5;&#x7684;&#x306B;&#x8ABF;&#x6574;&#x3059;&#x308B;&#x3053;&#x3068;&#x306B;&#x3088;&#x308A;&#x3001;2 &#x6BB5;&#x968E;&#x5206;&#x5B50;&#x7DDA;&#x30A8;&#x30D4;&#x30BF;&#x30AD;&#x30B7;&#x30FC;&#x6CD5;&#x306B;&#x3088;&#x308B;&#x81EA;&#x767A;&#x7684;&#x306B;&#x5F62;&#x6210;&#x3055;&#x308C;&#x305F; GaN &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC;&#x306B;&#x304A;&#x3051;&#x308B;&#x6838;&#x751F;&#x6210;&#x3068;&#x6210;&#x9577;&#x306E;&#x30D7;&#x30ED;&#x30BB;&#x30B9;&#x3092;&#x5206;&#x96E2;&#x3059;&#x308B;&#x3053;&#x3068;&#x304C;&#x53EF;&#x80FD;&#x3067;&#x3059;.&#x307E;&#x305A;&#x3001;&#x3053;&#x308C;&#x3089;&#x306E;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x306E;&#x6210;&#x9577;&#x76F8;&#x56F3;&#x304C;&#x4F53;&#x7CFB;&#x7684;&#x306B;&#x958B;&#x767A;&#x3055;&#x308C;&#x306F; 3 &#x6841;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x5BC6;&#x5EA6;&#x306E;&#x5236;&#x5FA1;&#x304C;&#x53EF;&#x80FD;&#x3067;&#x3059;&#x3002;&#x6B21;&#x306B;&#x3001;&#x307E;&#x305A;&#x4F4E;&#x6E29;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x3092;&#x6838;&#x3057;&#x3001;&#x305D;&#x308C;&#x3089;&#x306F;&#x3088;&#x308A;&#x9AD8;&#x3044;&#x6E29;&#x5EA6;&#x3067;&#x6210;&#x9577;&#x306B;&#x3088;&#x3063;&#x3066;&#x9AD8;&#x3055;&#x3068;&#x5BC6;&#x5EA6;&#x72EC;&#x7ACB;&#x3057;&#x3066;&#x9577;&#x3044;&#x6210;&#x9577;&#x56DE;&#x4EE5;&#x4E0A;&#x30BF;&#x30FC;&#x30B2;&#x30C3;&#x30C8;&#x5BC6;&#x5EA6;&#x3092;&#x7DAD;&#x6301;&#x3057;&#x306A;&#x304C;&#x3089;&#x9078;&#x629E;&#x306A;&#x3044;&#x3067;&#x304D;&#x308B;&#x3053;&#x3068;&#x3092;&#x793A;&#x3057;&#x307E;&#x3059;&#x3002;&#x3053;&#x306E; 2 &#x6BB5;&#x968E;&#x306E;&#x624B;&#x9806;&#x3092;&#x4F7F;&#x7528;&#x3057;&#x3066;&#x4F5C;&#x88FD;&#x3057;&#x305F; GaN &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC; (Gan/aln) &#x306E;&#x4E09;&#x6B21;&#x5143;&#x5C64;&#x72B6;&#x3068;&#x4F4D;&#x76F8;&#x7684;&#x306B;&#x8907;&#x96D1;&#x306A;&#x30D8;&#x30C6;&#x30ED;&#x69CB;&#x9020;&#x3068;&#x751F;&#x3044;&#x8302;&#x3063;&#x305F;&#x3002;2 &#x756A;&#x76EE;&#x306E;&#x6210;&#x9577;&#x30B9;&#x30C6;&#x30C3;&#x30D7;&#x306E;&#x6210;&#x9577;&#x6E29;&#x5EA6;&#x3092;&#x8ABF;&#x6574;&#x3059;&#x308B;&#x3053;&#x3068;&#x306B;&#x3088;&#x3063;&#x3066;&#x3069;&#x3061;&#x3089;&#x304B;&#x5782;&#x76F4;&#x307E;&#x305F;&#x306F;&#x540C;&#x8EF8;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC;&#x8D85;&#x683C;&#x5B50;&#x3092;&#x5F62;&#x6210;&#x3067;&#x304D;&#x307E;&#x3059;&#x3002;2 &#x6BB5;&#x968E;&#x6CD5;&#x304C;&#x3069;&#x306E;&#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x3067;&#x6838;&#x751F;&#x6210;&#x3068;&#x30A2;&#x30C9;&#x30A2;&#x30C8;&#x30E0; &#x30E2;&#x30D3;&#x30EA;&#x30C6;&#x30A3;&#x8ABF;&#x6574;&#x3067;&#x304D;&#x307E;&#x3059;&#x30AB;&#x30A4;&#x30CD;&#x30C6;&#x30A3;&#x30AF;&#x30B9;&#x306E;&#x69D8;&#x3005; &#x306A;&#x3078;&#x306E;&#x30A2;&#x30AF;&#x30BB;&#x30B9;&#x3092;&#x3067;&#x304D;&#x308B;&#x3053;&#x3068;&#x304C;&#x793A;&#x5506;&#x3055;&#x308C;&#x307E;&#x3057;&#x305F;&#x3002;

&#x6838;&#x751F;&#x6210;&#x3068;&#x6210;&#x9577;&#x306E;&#x30D7;&#x30ED;&#x30BB;&#x30B9;&#x306E;&#x5206;&#x96E2;&#x306B;&#x3088;&#x308B;&#x4E09;&#x6B21;&#x5143; Gan/aln &#x30CA;&#x30CE;&#x30EF;&#x30A4;&#x30E4;&#x30FC; &#x30FB; &#x30D8;&#x30C6;&#x30ED;&#x69CB;&#x9020;&#x3002;

&#xC0C1;&#xD5A5;&#xC2DD; nanostructure &#xC5B4;&#xC148;&#xBE14;&#xB9AC; &#xC9C0;&#xB09C; &#xBA87; &#xB144;&#xAC04; &#xC7AC;&#xB8CC; &#xD569;&#xC131;&#xC758; &#xC911;&#xC2EC; &#xC8FC;&#xC81C; &#xB418;&#xC5C8;&#xC2B5;&#xB2C8;&#xB2E4;. &#xBC18;&#xB3C4;&#xCCB4; &#xC591;&#xC790; &#xC810; &#xBC0F; &#xC815; &#xCDA9;&#xC804; &#xAC10; &#xAE08;&#xC5D0; &#xB300; &#xD55C; &#xCD94;&#xAC00; &#xC790;&#xC720;&#xB3C4; &#xC81C;&#xACF5;, &#xC2A4;&#xD2B8;&#xB808;&#xC778; &#xC5D4;&#xC9C0;&#xB2C8;&#xC5B4;&#xB9C1; &#xBC0F; &#xD45C;&#xBA74; &#xAC10;&#xB3C4;-&#xC18D;&#xC131;&#xC740; &#xB2E4;&#xC591; &#xD55C; &#xACE0;&#xCCB4; &#xAD11;&#xD559; &#xBC0F; &#xC804;&#xC790; &#xAE30;&#xC220; &#xD558;&#xB294; &#xB370; &#xC720;&#xC6A9; &#xD569;&#xB2C8;&#xB2E4;. &#xC911;&#xC559; &#xB3C4;&#xC804;&#xC744; &#xC774;&#xD574; &#xD558; &#xACE0; &#xC870;&#xC791; nanostructure &#xC5B4;&#xC148;&#xBE14;&#xB9AC; &#xC815;&#xC758;&#xC0C1; &#xC6D0;&#xD558;&#xB294; &#xC18D;&#xC131;&#xC73C;&#xB85C; &#xAE34;&#xAE09; &#xAD6C;&#xC870;&#xB97C; &#xC0DD;&#xC131; &#xD558;&#xB294;. &#xADF8;&#xB7EC;&#xB098;, &#xC9C4;&#xD589; nucleation &#xBC0F; &#xC131;&#xC7A5; &#xD604;&#xC0C1;&#xC758; &#xC0C1;&#xD638; &#xC758;&#xC874;&#xC73C;&#xB85C; &#xC778;&#xD574; &#xBC29;&#xD574;. &#xC5EC;&#xAE30; &#xC6B0;&#xB9AC; &#xC131;&#xC7A5; &#xC18D;&#xB3C4; &#xB3D9;&#xC801;&#xC73C;&#xB85C; &#xC870;&#xC815; &#xD558; &#xC5EC; &#xAD6C;&#xBD84; nucleation &#xBC0F; &#xC131;&#xC7A5; &#xD504;&#xB85C;&#xC138;&#xC2A4; 2 &#xB2E8;&#xACC4; &#xBD84;&#xC790; &#xBE54; &#xD53C; &#xAE30;&#xC220;&#xC744; &#xC0AC;&#xC6A9; &#xD558; &#xC5EC; &#xC790;&#xBC1C;&#xC801;&#xC73C;&#xB85C; &#xD615;&#xC131;&#xB41C; &#xB41C; GaN &#xC815;&#xC5D0; &#xC218;&#xB294; &#xBCF4;&#xC5EC;&#xC90D;&#xB2C8;&#xB2E4;. &#xCCAB;&#xC9F8;,&#xC774; &#xC815;&#xC5D0; &#xB300; &#xD55C; &#xC131;&#xC7A5; &#xB2E8;&#xACC4; &#xB2E4;&#xC774;&#xC5B4;&#xADF8;&#xB7A8;&#xC744; &#xCCB4;&#xACC4;&#xC801;&#xC73C;&#xB85C; &#xAC1C;&#xBC1C;, &#xC138; &#xBC30;&#xB098; &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4; &#xBC00;&#xB3C4; &#xC81C;&#xC5B4;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xB2E4;&#xC74C;&#xC73C;&#xB85C;, &#xC6B0;&#xB9AC; &#xBA3C;&#xC800; &#xB0AE;&#xC740; &#xC628;&#xB3C4;&#xC5D0;&#xC11C; &#xC815; nucleating &#xACE0; &#xB2E4;&#xC74C; &#xB354; &#xB192;&#xC740; &#xC628;&#xB3C4;&#xC5D0;&#xC11C; &#xC131;&#xC7A5;, &#xB192;&#xC774; &#xBC00;&#xB3C4; &#xC120;&#xD0DD;&#xD560; &#xC218; &#xC788;&#xB294; &#xB3C5;&#xB9BD;&#xC801;&#xC73C;&#xB85C; &#xC548; &#xAE34; &#xC131;&#xC7A5; &#xC2DC;&#xAC04;&#xC744; &#xD1B5;&#xD574; &#xB300;&#xC0C1; &#xBC00;&#xB3C4; &#xC720;&#xC9C0; &#xD558;&#xBA74;&#xC11C; &#xBCF4;&#xC5EC;&#xC90D;&#xB2C8;&#xB2E4;. &#xAC04; &#xC815;&#xC774; 2 &#xB2E8;&#xACC4; &#xC808;&#xCC28;&#xB97C; &#xC0AC;&#xC6A9; &#xD558; &#xC5EC; &#xC900;&#xBE44; (GaN/AlN)&#xC758; 3 &#xCC28;&#xC6D0;&#xC73C;&#xB85C; &#xACC4;&#xCE35;&#xD654; &#xBC0F; &#xD1A0;&#xD3F4;&#xB85C;&#xC9C0;&#xAC00; &#xBCF5;&#xC7A1; &#xD55C; heterostructures&#xC640; &#xD568;&#xAED8; &#xC790;&#xB780; &#xC788;&#xB2E4;. &#xB450; &#xBC88;&#xC9F8; &#xC131;&#xC7A5; &#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xC131;&#xC7A5; &#xC628;&#xB3C4; &#xC870;&#xC815; &#xD558; &#xC5EC; &#xC138;&#xB85C; &#xB610;&#xB294; &#xB3D9;&#xCD95; &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4; superlattices &#xC911; &#xD558;&#xB098;&#xB97C; &#xD615;&#xC131; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xC774;&#xB7EC;&#xD55C; &#xACB0;&#xACFC; 2 &#xB2E8;&#xACC4; &#xBA54;&#xC11C;&#xB4DC;&#xB294; &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4;&#xC5D0;&#xC11C; nucleation &#xBC0F; adatom &#xC774;&#xB3D9;&#xC131;&#xC740; &#xAC00;&#xBCC0; &#xC18D;&#xB3C4;&#xC758; &#xB2E4;&#xC591; &#xD55C;&#xC5D0; &#xC561;&#xC138;&#xC2A4;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4; &#xB098;&#xD0C0;&#xB0C5;&#xB2C8;&#xB2E4;.

Nucleation &#xBC0F; &#xC131;&#xC7A5; &#xD504;&#xB85C;&#xC138;&#xC2A4;&#xB97C; &#xAD6C;&#xBD84; &#xD558; &#xC5EC; 3 &#xCC28;&#xC6D0; GaN/AlN &#xB098;&#xB178;&#xC640;&#xC774;&#xC5B4; heterostructures.

Nanoestructura ascendente Asamblea ha sido un tema central de la s&iacute;ntesis de materiales en las &uacute;ltimas d&eacute;cadas. Nanohilos y puntos cu&aacute;nticos de semiconductor proporcionar m&aacute;s grados de libertad para el confinamiento de la carga, tensi&oacute;n superficiales e ingenier&iacute;a sensibilidad-propiedades que son &uacute;tiles para una amplia gama de tecnolog&iacute;as &oacute;pticas y electr&oacute;nicas de estado s&oacute;lido. Un desaf&iacute;o central es entender y manipular la nanoestructura Asamblea para generar reproducible estructuras emergentes con las propiedades deseadas. Sin embargo, el progreso se ve obstaculizado debido a la interdependencia de los fen&oacute;menos de nucleaci&oacute;n y crecimiento. Aqu&iacute; mostramos que ajustando din&aacute;micamente la cin&eacute;tica de crecimiento, es posible separar los procesos de nucleaci&oacute;n y crecimiento en nanohilos de GaN espont&aacute;neamente formados utilizando una t&eacute;cnica de epitaxia de haces moleculares de dos etapas. En primer lugar, un diagrama de fase de crecimiento para estos nanohilos se desarrolla sistem&aacute;ticamente, que permite el control de densidad de Nanocable sobre tres &oacute;rdenes de magnitud. A continuaci&oacute;n, te mostramos que primero nucleaci&oacute;n nanocables a baja temperatura y luego cultivarlas en una temperatura m&aacute;s alta, altura y densidad independientemente seleccionables manteniendo la densidad objetivo durante largos periodos de crecimiento. GaN nanohilos preparados con este procedimiento de dos etapas son cubiertos con capas tridimensionalmente y topol&oacute;gicamente complejas heteroestructuras de (GaN/AlN). Ajustando la temperatura de crecimiento en el crecimiento del segundo paso pueden moldearse bien superredes de Nanocable coaxial o vertical. Estos resultados indican que un m&eacute;todo de dos etapas permite el acceso a una variedad de cin&eacute;tica en que Nanocable nucleaci&oacute;n y adatom movilidad son ajustables.

Tridimensional GaN/AlN Nanocable heteroestructuras separando los procesos de nucleaci&oacute;n y crecimiento.

Almost all electronic devices utilize a pn junction formed by random doping of donor and acceptor impurity atoms. We developed a fundamentally new type of pn junction not formed by impurity-doping, but rather by grading the composition of a semiconductor nanowire resulting in alternating p and n conducting regions due to polarization charge. By linearly grading AlGaN nanowires from 0% to 100% and back to 0% Al, we show the formation of a polarization-induced pn junction even in the absence of any impurity doping. Since electrons and holes are injected from AlN barriers into quantum disk active regions, graded nanowires allow deep ultraviolet LEDs across the AlGaN band-gap range with electroluminescence observed from 3.4 to 5 eV. Polarization-induced p-type conductivity in nanowires is shown to be possible even without supplemental acceptor doping, demonstrating the advantage of polarization engineering in nanowires compared with planar films and providing a strategy for improving conductivity in wide-band-gap semiconductors. As polarization charge is uniform within each unit cell, polarization-induced conductivity without impurity doping provides a solution to the problem of conductivity uniformity in nanowires and nanoelectronics and opens a new field of polarization engineering in nanostructures that may be applied to other polar semiconductors.

Polarization-induced pn diodes in wide-band-gap nanowires with ultraviolet electroluminescence.

III-Nitride semiconductor heterostructures continue to attract a great deal of attention due to the wide range of wavelengths at which they can emit light, and the subsequent desire to employ them in optoelectronic applications. Recently, a new type of pn-junction which relies on polarization-induced doping has shown promise for use as an ultraviolet light emitting diode (UVLED); nanowire growth of this device has been successfully demonstrated. However, as these devices are still in their infancy, in order to more fully understand their physical and electronic properties, they require a multitude of characterization techniques. Specifically, the present contribution will discuss the application of advanced scanning transmission electron microscopy (STEM) to AlxGa1-xN UVLED nanowires. In addition to structural data, chemical and electronic properties will also be probed through various spectroscopy techniques, with the focus remaining on practically applying the knowledge gained via STEM to the growth procedures in order to optimize device peformance.

Full-scale characterization of UVLED Al(x)Ga(1-x)N nanowires via advanced electron microscopy.

Polarization-induced nanowire light emitting diodes (PINLEDs) are fabricated by grading the Al composition along the c-direction of AlGaN nanowires grown on Si substrates by plasma-assisted molecular beam epitaxy (PAMBE). Polarization-induced charge develops with a sign that depends on the direction of the Al composition gradient with respect to the [0001] direction. By grading from GaN to AlN then back to GaN, a polarization-induced p-n junction is formed. The orientation of the p-type and n-type sections depends on the material polarity of the nanowire (i.e., Ga-face or N-face). Ga-face material results in an n-type base and a p-type top, while N-face results in the opposite. The present work examines the polarity of catalyst-free nanowires using multiple methods: scanning transmission electron microscopy (STEM), selective etching, conductive atomic force microscopy (C-AFM), and electroluminescence (EL) spectroscopy. Selective etching and STEM measurements taken in annular bright field (ABF) mode demonstrate that the preferred orientation for catalyst-free nanowires grown by PAMBE is N-face, with roughly 10% showing Ga-face orientation. C-AFM and EL spectroscopy allow electrical and optical differentiation of the material polarity in PINLEDs since the forward bias direction depends on the p-n junction orientation and therefore on nanowire polarity. Specifically, C-AFM reveals that the direction of forward bias for individual nanowire LEDs changes with the polarity, as expected, due to reversal of the sign of the polarization-induced charge. Electroluminescence measurements of mixed polarity PINLEDs wired in parallel show ambipolar emission due to the mixture of p-n and n-p oriented PINLEDs. These results show that, if catalyst-free III-nitride nanowires are to be used to form polarization-doped heterostructures, then it is imperative to understand their mixed polarity and to design devices using these nanowires accordingly.

Mixed polarity in polarization-induced p-n junction nanowire light-emitting diodes.

In this report, we demonstrate band gap tuning of the active region emission wavelength from 365 nm to 250 nm in light emitting diodes fashioned from catalyst-free III-nitride nanowires. Optical characteristics of the nanowire heterostructures and fabricated devices are studied via electroluminescence (EL) and photoluminescence spectroscopy over a wide range of active region compositions. It is observed that for typical nanowire plasma assisted molecular beam epitaxy growth conditions, tuning of emission to wavelengths shorter than 300 nm is hampered by the presence of an optically active defect level. We show that by increasing the AlGaN nanowire growth temperatures this defect emission can be suppressed. These findings are applied to growth of the active region of a nanowire light emitting diode, resulting in a polarization-induced nanowire light emitting diode with peak EL at 250 nm.

Article	Year
Three-dimensional GaN/AlN nanowire heterostructures by separating nucleation and growth processes. Nano letters\| PubMed ID: 21265558	2011
Polarization-induced pn diodes in wide-band-gap nanowires with ultraviolet electroluminescence. Nano letters\| PubMed ID: 22268600	2012
Full-scale characterization of UVLED Al(x)Ga(1-x)N nanowires via advanced electron microscopy. ACS nano\| PubMed ID: 23675609	2013
Mixed polarity in polarization-induced p-n junction nanowire light-emitting diodes. Nano letters\| PubMed ID: 23756087	2013
Deep ultraviolet emitting polarization induced nanowire light emitting diodes with AlxGa₁-xN active regions. Nanotechnology\| PubMed ID: 25327762	2014

Santino D. Carnevale

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