Size-, shape-, and position-controlled GaAs nano-whiskers

Ohlsson, Björn; Björk, Mikael; Magnusson, Martin H.; Deppert, Knut; Samuelson, Lars; Wallenberg, L. Reine

doi:10.1063/1.1418446

Cited by 267 publications

(192 citation statements)

References 10 publications

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“…The NWs are preferred to grow along the [111] direction in the case of ZB phase and along the [0001] in the case of WZ. Subsequently, the Aucatalyzed VLS method was successfully used to grow III-V NWs by other techniques, including molecular beam epitaxy (MBE) [63,64] and chemical beam epitaxy (CBE) [65,66].…”

Section: Nw Growth Mechanismsmentioning

confidence: 99%

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

et al. 2014

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This thesis deals with the growth of GaAs nanowires (NWs) by molecular beam epitaxy (MBE) using vapor-liquid-solid method on various substrates including GaAs(111)B, Si(111) and graphene. The growth of the NWs on GaAs substrates was carried out by Au-catalyzed technique, whereas the growths on Si and graphene substrates were carried out using self-catalyzed technique that has been the main focus of this thesis. The long-term goal of this work was to produce p-n radial junction GaAs NWs for solar cell applications.Necessary conditions were established for obtaining vertical self-catalyzed GaAs NWs on Si(111), which is reproducible from run-to-run. One of the major issues in these NWs grown by both Au-and self-catalyzed techniques is their crystal structure. The Au-catalyzed GaAs NWs usually adopt a wurtzite (WZ) crystal phase, whereas the self-catalyzed NWs a zinc blende (ZB) phase. However, in both the cases the NWs contain stacking faults, rotational twins or/and a mixed crystal phase. The ZB and WZ phases show different optical properties, and one phase might be favored over other for certain applications. Therefore the crystal phase was controlled within single NWs by tuning the V/III ratio and introducing GaAsSb inserts. The change of the crystal phases was correlated with the change in the contact angle of the Ga droplet.Since the discovery of graphene, an ultra-thin two-dimensional material, the research on graphene has become an active field in recent years due to its remarkable properties including excellent electrical and thermal conductivities, mechanical strength and flexibility, and optical transparency. By growing the semiconductor NWs on graphene, a completely new hybrid system can be envisioned where the unique properties of both NWs and graphene can be utilized. Therefore we established a method for the growth of semiconductor NWs on graphene by demonstrating epitaxial growth of vertical GaAs and InAs NWs on different graphitic substrates.Core-shell heterostructure, doping, optical properties, and position controlled growth of self-catalyzed GaAs NWs were investigated. Growth of GaAs/GaAsSb coreshell NWs where the Sb content was tuned from about 10% -70% was studied. The effect of growth temperature and the Sb flux on the morphology of GaAsSb shell was investigated. In addition, by utilizing the core-shell geometry where the shell copies the crystal phase of the core, WZ phase of GaAsSb was demonstrated. Successful p-type doping of GaAs core using Be as dopant, and n-type doping of GaAs shell using Si and Te as dopants were achieved. To investigate the optical properties, GaAs/AlGaAs coreshell NWs were grown with different V/III ratios during the core growth. The NWs grown with high V/III ratio, despite containing a higher density of twinned ZB and WZ GaAs with SFs, were found to have superior optical quality as compared to the NWs grown with low V/III ratio that contain pure ZB GaAs. The observed V/III ratio dependent optical quality was correlated to the intrinsic defects such as As vac...

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Section: Nw Growth Mechanismsmentioning

confidence: 99%

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

et al. 2014

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“…A broad range of semiconductor nanowires, including Si, Ge [13,14], III-Vs [15,16] and II-VIs [17][18][19][20][21], have been grown using chemical vapor deposition (CVD), thermal evaporation, solvothermal synthesis and molecular-beam exitaxy (MBE) based on the metal-catalyzed vaporliquid-solid (VLS) mechanism [22]. However, only a few reports on the synthesis of tellurium-based NWs have been published so far.…”

mentioning

confidence: 99%

MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

Wójtowicz¹,

Janik²,

Zaleszczyk³

et al. 2008

J. Korean Phy. Soc.

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We review our results on the growth of ZnTe-and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)-and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was 111 , and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe-and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn 2+ transition between crystal-field-split energy levels ( 4 T1 → 6 A1) was observed in the ZnMnTe nanowires.

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“…However, in-situ heating of nanowires shows a solid state gold/gallium particle at the growth temperature indicating that nanowires can be grown catalyzed by a solid particle instead of a liquid droplet. [1] GaAs nanowires were grown in a chemical beam epitaxy (CBE) system at 540ºC with gold nano particles as growth catalysts [2]. After growth, the wires were removed from the substrate and deposited onto a carbon lacy grid.…”

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confidence: 99%

Solid-phase Diffusion Mechanism for GaAs Nanowire Growth

Larsson

Persson

Wallenberg

et al. 2005

MAM

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In-situ heating of nanowires has been performed in order to understand the process of catalysed nanowire growth. The proposed growth process has been described as the vapour-liquid-solid (VLS) mechanism, where the epitaxial crystal growth is catalysed by a molten gold droplet in a vapour of the reagents onto a solid substrate surface. However, in-situ heating of nanowires shows a solid state gold/gallium particle at the growth temperature indicating that nanowires can be grown catalyzed by a solid particle instead of a liquid droplet. [1] GaAs nanowires were grown in a chemical beam epitaxy (CBE) system at 540ºC with gold nano particles as growth catalysts [2]. After growth, the wires were removed from the substrate and deposited onto a carbon lacy grid. The wires were heated in a heating stage and images were acquired at different temperatures with a transmission electron microscope (TEM) and analyzed with energy dispersive spectrometry (EDS).The nanowire growth takes place at the surface between the gold seed particle and the crystalline surface forming a wire with the same diameter as the gold particle. At the end of the growth process the temperature is lowered and the gallium supply is terminated while keeping the arsenic pressure constant. The last part of the growth will then form a characteristic 'neck' right below the gold particle (Fig. 1a). To investigate the origin of the neck the wires were re-heated to probe whether we could re-alloy the material of the neck with the metal particle. In the first experiment nanowires were slowly heated up to 470ºC over a four-hour period while continuously observing them in the TEM. The wires were then kept above 400ºC for another four hours and then finally cooled down to room temperature (Fig. 1a-c). Several very clear observations were made. There was a noticeable alloying between the gold particle and the wire already at temperatures around 350ºC. We also observed that keeping the wires at temperatures above 400ºC lead to a continuing decomposition of the nanowires (Fig. 1b-c). No change in appearance, i.e. no new neck formation was observed on cooling down the wires to room temperature, indicating that the arsenic was not stored in the gold particle and the reversed reaction could evidently not take place.This result was also confirmed by EDS line scans (Fig. 2a-b) comparing nanowires before and after the heating experiments. The measurements showed both gallium and arsenic to be absent in the seed particle before heating, whereas gallium was present in the seed particles after heating. From these results we conclude that the neck in the nanowires was created after the gallium source had been switched off allowing the gallium inside the gold particle to react with the arsenic still present in the growth chamber.A second heating experiment was carried out, where nanowires were heated to above 600 C in the TEM. Images and diffraction patterns acquired at 540°C, which is equivalent to the growth temperature, showed crystallinity of the seed particle (Fig. 3). This...

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Size-, shape-, and position-controlled GaAs nano-whiskers

Cited by 267 publications

References 10 publications

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

Solid-phase Diffusion Mechanism for GaAs Nanowire Growth

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