TEM characterization of catalyst- and mask-free grown GaN nanorods

Schowalter, Marco; Aschenbrenner, T.; Kruse, C.; Hommel, D.; Rosenauer, A.

doi:10.1088/1742-6596/209/1/012020

Cited by 8 publications

(7 citation statements)

References 11 publications

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“…Due to the high temperature and the comparatively large amount of ammonia in the MOVPE reactor, roughly half of the Al 2 O 3 surface was converted into AlN, as can be estimated from the XPS O1s intensity reduction between untreated and nitridated sapphire. A TEM investigation of these AlN islands has been published elsewhere [17]. Note that the same nitridation process results in a different impact on a c-plane sapphire substrate (not shown here): After nitridation a much weaker change in the surface morphology is observed.…”

Section: Resultsmentioning

confidence: 87%

“…7(b) and (c) a thin interface layer with a lower intensity (dark line indicated by the black and white dashed lines) is visible between the aplane GaN and the sapphire substrate. Energy filtered TEM (EFTEM) measurements show the presence of an AlGaN layer [17]. Neither EFTEM nor HAADF images show any significant fluctuations within the AlGaN.…”

Section: Nucleationmentioning

confidence: 98%

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Catalyst free self‐organized grown high‐quality GaN nanorods

Aschenbrenner

Kunert

Freund

et al. 2011

Physica Status Solidi (b)

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Highly ordered GaN nanorods were grown self-organized and without catalyst on r-plane sapphire by molecular beam epitaxy while the AlN nucleation sites for the nanorods were provided by a nitridation process using a metal-organic vapor-phase epitaxy system. The growth window for the nanorod formation was analysed in detail and turned out to be very sensitive with respect to the growth temperature. The nanorods are symmetrically tilted with an inclination angle of 628 between the substrate and the nanorods. The mirror axis is the c-direction of the compact GaN layer surrounding the roots of the nanocolumns. Methods for the control of the nanorod density and the suppression of one nanorod growth direction are presented. The results indicate a diffusion based growth mechanism. Transmission electron microscopy studies and high resolution X-ray diffraction (HRXRD) polar plots reveal the epitaxial relationship between substrate, compact GaN layer and nanorods. The nanorods grow in c-direction and the side facets are m-planes. Transmission electron microscopic and optical analysis of the nanorods reveal the good structural and optical properties, respectively. A full width at half maximum (FWHM) of 1.2 meV of the donor-bound exciton emission was measured for both the ensemble and single free-standing nanorods. Successful n-and Mg-doping of nanorods was verified by a strong increase of the micro-photoluminescence intensity of the respective donor-bound and acceptor-bound exciton emission peak in comparison to an undoped sample.The background shows a secondary electron microscope image (angle of 108 between sample surface and electron beam) of the nanorods. Superimposed to the SEM image, a typical microphotoluminescence spectrum of the excitonic emission of an ensemble at 25 K is presented. The donor-bound, acceptorbound and free exciton lines are labelled with D 0 X, A 0 X and FX, respectively.

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Section: Resultsmentioning

confidence: 87%

Section: Nucleationmentioning

confidence: 98%

Catalyst free self‐organized grown high‐quality GaN nanorods

Aschenbrenner

Kunert

Freund

et al. 2011

Physica Status Solidi (b)

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“…To estimate the numerical values of the physical quantities entering the pre-exponential factors in eqs 2 and 18 for the incubation times, we first need to convert the incoming gallium flux I (nm −2 min −1 ) into the nm × min −1 units by multiplying it to the elementary volume of solid GaN of 0.023 nm 3 . Then the fits shown in Figure 3 yield Dσ 0 t A = 3 × 10 −4 nm 2 for heterogeneous nucleation on a-Al x O y and (Dσ 1 ) 2 t A 3 = 10 −6 nm 4 min for homogeneous nucleation on SiN x .…”

Section: ■ Discussionmentioning

confidence: 99%

“…Despite many efforts, self-induced nucleation of GaN NWs on bare crystalline sapphire substrates has not been achieved so far. Therefore, GaN NWs are formed on sapphire by using either AlN buffers (created by sapphire nitridation or grown intentionally , ) or external catalysts. − The latter approach, however, seriously impedes the crystalline quality and luminescence properties of the resulting NWs compared to those typically achieved in the self-induced approach. , …”

Section: Introductionmentioning

confidence: 99%

Analysis of Incubation Times for the Self-Induced Formation of GaN Nanowires: Influence of the Substrate on the Nucleation Mechanism

Sobanska

Dubrovskiı̆

Tchutchulashvili

et al. 2016

Crystal Growth & Design

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Surprisingly long incubation times for the self-induced formation of GaN nanowires on different substrates can reach hundreds of minutes and remain a mystery in GaN crystal growth. Herein, we examine the incubation times of GaN islands that subsequently give rise to nanowires on amorphous Al x O y /Si and SiN x /Si substrates versus the temperature and gallium flux. Experimental data are obtained by in situ monitoring of the surface morphology by reflection high energy electron diffraction during plasma-assisted molecular beam epitaxy. We develop a model that confirms an inverse power-law dependence of the incubation time on the gallium flux and the Arrhenius-type temperature dependence. The power exponent p and the activation energy E inc are related to the nucleation mechanism and the island growth regime. We find the values p ≅ 1, E inc = 6.0 eV for Al x O y , and p ≅ 2, E inc = 10.2 eV for SiN x buffer. The dominant nucleation mechanism on amorphous Al x O y should be heterogeneous. Homogeneous nucleation dominates on SiN x , while the diffusion growth regime of GaN islands occurs in both cases. Overall, the long incubation times are attributed to extremely low effective diffusion lengths of gallium adatoms such that the squared diffusion length times the gallium bonding rate ranges from 10–4 to 1 nm2 in typical cases.

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“…Also for catalyst-free growth of GaN NWs on sapphire by metal-organic vapor phase epitaxy, special preparation of substrate surface is required. 5 Therefore, either AlN buffers created by sapphire nitridation 6 or grown intentionally, 2,7 or catalyst-assisted growth 4,8,9 are commonly applied to overcome a barrier for GaN nucleation. It is noteworthy that GaN NWs grown by a catalyst-free way are of much higher structural and optical quality than those grown with the use of Ni as an external catalyst.…”

Section: Introductionmentioning

confidence: 99%

Enhanced catalyst-free nucleation of GaN nanowires on amorphous Al2O3 by plasma-assisted molecular beam epitaxy

Sobanska

Kłosek

Borysiuk

et al. 2014

Journal of Applied Physics

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We report on plasma-assisted molecular beam epitaxial growth of GaN nanowires (NWs) on Si(111) substrates with a thin amorphous Al2O3 buffer layer deposited by atomic layer deposition. Comparison of nucleation kinetics shows that presence of amorphous Al2O3 buffer significantly enhances spontaneous nucleation of GaN NWs. Slower nucleation was observed on partially amorphous silicon nitride films. No growth of NWs was found on sapphire substrate under the same growth conditions which we explain by a low density of defects on monocrystalline substrate surface where NWs may nucleate. Our finding shows that tuning of substrate microstructure is an efficient tool to control rate of self-induced nucleation of GaN NWs.

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TEM characterization of catalyst- and mask-free grown GaN nanorods

Cited by 8 publications

References 11 publications

Catalyst free self‐organized grown high‐quality GaN nanorods

Catalyst free self‐organized grown high‐quality GaN nanorods

Analysis of Incubation Times for the Self-Induced Formation of GaN Nanowires: Influence of the Substrate on the Nucleation Mechanism

Enhanced catalyst-free nucleation of GaN nanowires on amorphous Al2O3 by plasma-assisted molecular beam epitaxy

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