Highly ordered catalyst-free InGaN/GaN core–shell architecture arrays with expanded active area region

Jung, Byung Oh,Bae, Si-Young,Kim, Sang Yun,Lee, Seunga,Lee, Jeong Yong,Lee, Dong-Seon,Kato, Yoshihiro,Honda, Yoshio,Amano, Hiroshi Elsevier 2015 Nano energy Vol.11 No.-

<P><B>Abstract</B></P> <P>Highly ordered, position-controlled gallium nitride (GaN) nanowire based multiple-quantum-wells (MQWs) core–shell architecture arrays are synthesized by metalorganic chemical vapor deposition (MOCVD). We investigate the possibility of using GaN nanowire arrays as a basal template for the growth of In<SUB> <I>x</I> </SUB>Ga<SUB>1−<I>x</I> </SUB>N/GaN MQWs. The MQWs on three different crystal facets (<I>c</I>-, <I>m</I>-, and <I>semipolar</I>-plane) of GaN nanowire exhibit dissimilar structural properties. The structural characteristics of InGaN/GaN core–shell arrays are inspected by cross-sectional high-resolution transmission electron microscopy (HR-TEM). We also investigate the optical properties of MQW core–shell structure nanoarrays. The luminescent characteristics of InGaN/GaN core–shell structure arrays are determined by photoluminescence (PL) and cathodoluminescence (CL) measurements. The monochromatic CL images clearly show the light emission behavior of InGaN/GaN MQW coaxial structure. Two distinguishable light emission peaks were observed in the GaN nanowire based core–shell structure. The characteristic of light emission mainly depends on the properties of MQWs, which are generated from different crystal facets of GaN. In addition, the light emission intensity shows different behaviors depending on the area of the GaN nanowire <I>m</I>-plane. The results of this study suggest that GaN nanowire arrays can be used as a good alternative basal template for next-generation light-emitting diodes (LEDs).</P> <P><B>Highlights</B></P> <P> <UL> <LI> This research describes a scalable process for the precise position-controlled selective area growth of GaN nanoarchitecture and its based InGaN/GaN MQWs core–shell arrays. </LI> <LI> The InGaN/GaN MQWs on three different crystal facets of GaN nanowire exhibit dissimilar structural and optical properties. </LI> <LI> The light emission mainly comes from MQWs on nonpolar { 1 1 ̄ 00 } <I>m</I>-plane sidewalls. </LI> <LI> The Fill factor (FF) is markedly increased up to 204.2% according to the <I>m</I>-plane height of the GaN nanowire. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Source와 기판 거리에 따른 GaN nanowires의 합성 mode 변화 제어

신동익,이호준,강삼묵,윤대호,Shin, T.I.,Lee, H.J.,Kang, S.M.,Yoon, D.H. 한국결정성장학회 2008 韓國結晶成長學會誌 Vol.18 No.1

GaN nanowires는 수평 VPE법으로 합성 되었다. 본 실험에서는 source와 기판과의 거리가 합성된 GaN nanowires의 형상에 미치는 영향에 대하여 실험하였다. GaN nanowires는 $950^{\circ}C$ 온도에서 Ar 과 $NH_3$ 가스가 각각 1000, 50 sccm 의 유량에서 합성되었다. 합성된 GaN nanowires의 단면형태는 삼각형의 모양을 가졌으며, GaN nanowires의 길이는 200에서 500 nm 정도 였다. 합성된 GaN nanowires의 모양은 FESEM 으로 확인하였고, XRD 분석을 통하여 그 구조가 wurzite 구조인 것을 확인하였다. 또한, HRTEM 사진과 SAED 패턴을 통하여 합성된 GaN nanowires의 표면과 구조를 분석하였다. 성장된 GaN nanowires의 광학적 특성은 PL분석을 통하여 이루어졌다. We synthesized GaN nanowires with high quality using the vapor phase epitaxy technique. The GaN nanowires were obtained at a temperature of $950^{\circ}C$. The Ar and $NH_3$ flow rates were 1000 sccm and 50 sccm, respectively. The shape of the GaN nanowires was confirmed through FESEM analysis. We were able to conclude that the GaN nanowires synthesized via vapor-solid (VLS) mechanism when the source was closed to the substrate. On the other side, the VS mechanism changed to vapor-liquid-solid (VLS) as the source and the substrate became more distant. Therefore, we can suggest that the large amount of Ga source from initial growth interrupt the role of catalyst on the substrate.

Growth of GaN Nanowires on Si Substrate Using Ni Catalyst in Vertical Chemical Vapor Deposition Reactor

Kim, Tae Yun,Lee, Sang Hyun,Mo, Young Hwan,Shim, Hyun Wook,Nahm, Kee Suk,Suh, Eun-Kyung,Park, Gyung Soo 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.1

GaN nanowires were successfully grown on Ni-coated Si substrate by direct reaction of gallium with ammonia gas in a home-made vertical tubular chemical vapor deposition reactor. The growth of GaN nanowires was uniformly observed across the Si substrate surface, but the density and average diameter of the nanowires varied along the position of the substrate surface. At the position of 5㎝ above Ga source surface, the growth of GaN crystal grains was observed with few nanowires. The length of the nanowires reached several micrometers. The clear lattice fringes in HRTEM image revealed the growth of good quality hexagonal single-crystal GaN nanowires. Photoluminescence of the GaN nanowires showed a strong band edge emission at the energy position of ∼3.4eV with negligible deep level yellow emission. Field emission characteristics of the GaN nanowires showed that the turn-on field of GaN nanowires was ∼7.4V/um with a field enhancing factor β of∼555. The catalytic growth mechanism of the GaN nanowires was discussed on the basis of experimental results in this work.

Effect of crystal orientation of GaN/V₂O₅ core-shell nanowires on piezoelectric nanogenerators

Waseem, Aadil,Johar, Muhammad Ali,Hassan, Mostafa Afifi,Bagal, Indrajit V.,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan Elsevier 2019 Nano energy Vol.60 No.-

<P><B>Abstract</B></P> <P>GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell nanowire (NW) piezoelectric generators of controlled crystallographic orientations were fabricated, and the device performance was characterized. Catalyst-assisted c- and m-axis GaN NWs were grown on a c-plane GaN thin film by varying the NH<SUB>3</SUB> flow rate and reactor pressure. The grown NWs were then utilized to fabricate the flexible piezoelectric nanogenerators (PNGs) to practically investigate the impact of the c- and m-axis GaN NWs on the piezoelectric response. The c-axis GaN NWs exhibited a higher piezoelectric output than m-axis GaN NWs. Furthermore, the GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell structure was utilized in the NWs to suppress the internal carrier screening that degrades the piezoelectric output. The maximum output voltage (27 V) exhibited by core-shell c-axis NWs was thrice the voltage exhibited by pristine c-axis GaN NWs (9 V). A stability test was performed for one hour to verify the feasibility of using flexible PNGs for real applications. The high stability of PNGs was attributed to the flexibility and high crystallinity of the NWs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> C- & m-axis GaN NWs are grown by MOCVD for piezoelectric generators. </LI> <LI> The piezoelectric output for pristine c-axis NWs is twice the output of m-axis NWs. </LI> <LI> The piezoelectric output of the GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell NWs is three times of pristine NWs. </LI> <LI> PNGs exhibited long-term stability due to excellent mechanical properties of NWs. </LI> <LI> GaN/V<SUB>2</SUB>O<SUB>5</SUB> heterojunction suppressed the junction current screening effect. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell nanowire (NW) piezoelectric generators of controlled crystallographic orientations are reported. Catalyst-assisted c- and m-axis GaN NWs grown by MOCVD are utilized to fabricate the flexible piezoelectric nanogenerators to investigate the impact of the c- and m-axis GaN NWs on the piezoelectric response. The c-axis GaN NWs exhibited the higher piezoelectric output than m-axis GaN NWs. The GaN/V<SUB>2</SUB>O<SUB>5</SUB> core-shell structure is utilized in the NWs which further enhanced the output voltage to 27 V and output current to 590 nA.</P> <P>[DISPLAY OMISSION]</P>

Growth of GaN Nanowires on Si Substrate Using Ni Catalyst in Vertical Chemical Vapor Deposition Reactor

남기석,서은경,박경수,Tae Yun Kim,Sang Hyun Lee,Young Hwan Mo,Hyun Wook Shim 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.1

GaN nanowires were successfully grown on Ni-coated Si substrate by direct reaction of gallium with ammonia gas in a home-made vertical tubular chemical vapor deposition reactor. The growth of GaN nanowires was uniformly observed across the Si substrate surface, but the density and average diameter of the nanowires varied along the position of the substrate surface. At the position of 5 cm above Ga source surface, the growth of GaN crystal grains was observed with few nanowires. The length of the nanowires reached several micrometers. The clear lattice fringes in HRTEM image revealed the growth of good quality hexagonal single-crystal GaN nanowires. Photoluminescence of the GaN nanowires showed a strong band edge emission at the energy position of ~3.4 eV with negligible deep level yellow emission. Field emission characteristics of the GaN nanowires showed that the turn-on field of GaN nanowires was ~7.4 V/um with a field enhancing factor b of ~555. The catalytic growth mechanism of the GaN nanowires was discussed on the basis of experimental results in this work.

Metal catalyst-assisted growth of GaN nanowires on graphene films for flexible photocatalyst applications

Park, J.B.,Kim, N.J.,Kim, Y.J.,Lee, S.H.,Yi, G.C. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.11

We report the growth of high-areal-density GaN nanowires on large-size graphene films using a nickel (Ni) catalyst-assisted vapor-liquid-solid (VLS) method. Before the nanowire growth, the graphene films were prepared on copper foils using hot-wall chemical vapor deposition and transferred onto SiO<SUB>2</SUB>/Si substrates. Then, for catalyst-assisted VLS growth, Ni catalyst layers with thickness of a few nanometers were deposited on the graphene-coated substrates using a thermal evaporator. We investigated the effect of the Ni catalyst thickness on the formation of GaN nanowires. Furthermore, the structural and optical characteristics of GaN nanowires were investigated using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The GaN nanowires grown on graphene films were transferred onto polymer substrates using a simple lift-off method for applications as flexible photocatalysts. Photocatalysis activities of the GaN nanowires prepared on the flexible polymer substrates were investigated under bending conditions.

Effect of the Coating on the Structure and Optical Properties of GaN Nanowires

Jong-Soo Lee,민병돈,조경아,김상식,Sung-Kyu Sim,Hyun-Suk Kim 한국전기전자재료학회 2004 Transactions on Electrical and Electronic Material Vol.5 No.3

Structural and optical properties of as-synthesized, Ga2O3-coated, and Al2O3-coated GaN nanowires are examined in this paper. GaN nanowires were synthesized by thermal evaporation of ball-milled GaN powders in an NH3 atmosphere. The thermal annealing of the as-synthesized GaN nanowires in an argon atmosphere allows their surfaces to be oxidized, leading to the formation of 2nm-thick Ga2O3 layers. For the oxidized GaN nanowires, the distances between the neighboring lattice planes are shortened, and an excitonic emission band is remarkably enhanced in intensity, compared with the as-synthesized GaN nanowires. In addition, the as-synthesized GaN nanowires were coated cylindrically with Al2O3 by atomic layer deposition technique. Our study suggests that the Al2O3-coating passivates some of surface states in the GaN nanowires.

Effect of the Coating on the Structure and Optical Properties of GaN Nanowires

Lee, Jong-Soo,Sim, Sung-Kyu,Min, Byung-Don,Cho, Kyoung-Ah,Kim, Hyun-Suk,Kim, Sang-Sig The Korean Institute of Electrical and Electronic 2004 Transactions on Electrical and Electronic Material Vol.5 No.3

Structural and optical properties of as-synthesized, Ga$_2$O$_3$-coated, and Al$_2$O$_3$-coated GaN nanowires are examined in this paper. GaN nanowires were synthesized by thermal evaporation of ball-milled GaN powders in an NH$_3$ atmosphere. The thermal annealing of the as-synthesized GaN nanowires in an argon atmosphere allows their surfaces to be oxidized, leading to the formation of 2nm-thick Ga$_2$O$_3$ layers. For the oxidized GaN nanowires, the distances between the neighboring lattice planes are shortened, and an excitonic emission band is remarkably enhanced in intensity, compared with the as-synthesized GaN nanowires. In addition, the as-synthesized GaN nanowires were coated cylindrically with Al$_2$O$_3$ by atomic layer deposition technique. Our study suggests that the Al$_2$O$_3$-coating passivates some of surface states in the GaN nanowires.

Metal catalyst-assisted growth of GaN nanowires on graphene films for flexible photocatalyst applications

박준범,김남정,김용진,이상협,이규철 한국물리학회 2014 Current Applied Physics Vol.14 No.11

We report the growth of high-areal-density GaN nanowires on large-size graphene films using a nickel (Ni) catalyst-assisted vapor-liquid-solid (VLS) method. Before the nanowire growth, the graphene films were prepared on copper foils using hot-wall chemical vapor deposition and transferred onto SiO2/Si substrates. Then, for catalyst-assisted VLS growth, Ni catalyst layers with thickness of a few nanometers were deposited on the graphene-coated substrates using a thermal evaporator. We investigated the effect of the Ni catalyst thickness on the formation of GaN nanowires. Furthermore, the structural and optical characteristics of GaN nanowires were investigated using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The GaN nanowires grown on graphene films were transferred onto polymer substrates using a simple lift-off method for applications as flexible photocatalysts. Photocatalysis activities of the GaN nanowires prepared on the flexible polymer substrates were investigated under bending conditions.

Enhanced near-UV emission from self-catalytic brush-like GaN nanowires

Kim, S.,Park, S.,Ko, H.,Jeong, B.Y.,Lee, C. North-Holland 2014 Materials letters Vol.116 No.-

Recently, the enhanced field emission, photocatalytic activity and blue shift in UV emission of branched GaN nanowire structures were reported. Nevertheless, enhanced luminescence in branched GaN nanowires have not been reported despite the importance of short-wavelength emission. This paper reports synthesis of self-catalytic brush-like GaN nanowires exhibiting enhanced near-ultraviolet (NUV) emission. The diameters of the branches in the brush-like nanowires ranged from 3 to 14nm, whereas those of backbones ranged from 30 to 80nm. In contrast, the diameters of pristine nanowires were in a similar range to those of the backbones in the brush-like nanowires. The brush-like GaN nanowires showed significantly enhanced NUV emission compared to pristine GaN nanowires. This enhanced NUV emission might be due to the quantum confinement of excitons caused by the branches in the brush-like nanowires with diameters smaller than the Bohr exciton radius.