| 1. |
- Hsu, Chih-Wei, et al.
(författare)
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Controlled Growth of GaN Pyramidal template hosting InGaN Quantum Dots
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The emission properties of InGaN grown on hexagonal GaN pyramids with various pitch distances (PD) are studied. Emissions associated with InGaN quantum wells (QWs) and InGaN quantum dots (QDs) can be identified. The emission energies of InGaN QWs and QDs shift toward opposite directions with increasing PD; red-shift for QWs and blue-shift for QDs. Based on the source supply mechanism in a selective area growth process, the formation of InGaN QDs on GaN pyramids is believed to be a combined effect of Stranski-Krastanow growth mode and spinodal decomposition taking place at the microscopic (0001) surfaces on GaN pyramids.
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| 2. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Epitaxial growth of AlN layers on SiC substrates in a hot-wall MOCVD system
- 2002
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Ingår i: Phys. Stat. Sol. (c), Vol. 0, Issue 1. - : Wiley. ; , s. 205-208
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Konferensbidrag (refereegranskat)abstract
- In this study we report the successful growth of AlN and AlN/GaN on SiC substrates in a MOCVD process based on a hot-wall susceptor design. Different features of AlN growth are established depending on the total reactor pressure, temperature, off-cut SiC substrate orientation and V-to-III gas-flow ratio. The feasibility of the hot-wall MOCVD concept is demonstrated by the performance of AlN/GaN structures with state-of-the-art properties with strong potential for further optimization. A narrower X-ray rocking curve over the asymmetric 10.4 than the symmetric 00.2 reflection clearly underlines the high overall crystal quality of the GaN layers on AlN buffers grown in this type of MOCVD reactor.
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| 3. |
- Kakanakova-Georgieva, A, et al.
(författare)
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Implementation of hot-wall MOCVD in the growth of high-quality GaN on SiC
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. - : Trans Tech Publications. ; , s. 991-994
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Konferensbidrag (refereegranskat)abstract
- This paper reports on the growth of high-quality GaN layers on SiC substrates by hotwall MOCVD. Use of AlN buffer with a thickness exceeding 50 nm is employed for the GaN deposition and it is found to encompass most of the misfit defects. A narrower X-ray rocking curve over asymmetric than over symmetric reflection is measured - full width at a half maximum (FWHM) of 350 arcsec vs. FWHM of 490 arcsec for 10.4 and 00.2 peaks, respectively, indicating high overall quality of the film. The free exciton photoluminescence emission peak has rather narrow FWHM of 5 meV. The typical thickness of the GaN layers is about 2 mum and they are completely depleted according to the capacitance-voltage profiling, which corresponds to estimated residual doping of less than 5x10(14) cm(-3). Only in some cases when the GaN layer is not depleted, deep level transient spectroscopy is performed and two deep traps with activation energies of 0.26 and 0.59 eV below the conduction band are measured.
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| 4. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Sublimation epitaxy of AlN on SiC : Growth morphology and structural features
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 273:1-2, s. 161-166
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the development of individual AlN crystallites, sublimation epitaxy of AlN was performed on 4H-SiC, off-axis substrates in an inductively heated setup. Growth process variables like temperature, extrinsic nitrogen pressure and time were changed in an attempt to favor the lateral growth of individual AlN crystallites and thus open possibilities to prepare continuous patterns. Scanning and transmission electron microscopy and cathodoluminescence were used to obtain plan-view and cross-sectional images of the grown patterns and to study their morphology and structural features. The growth at 1900°C/200mbar results in AlN pattern consisting of individual single wurzite AlN crystallites with plate-like shape aligned along [1 1̄ 0 0] direction. The only defects these AlN crystallites contain are threading dislocations, some of which are terminated by forming half-loops. Because of the uniform distribution of the crystallites and their high structural perfection, this AlN pattern could represent interest as a template for bulk AlN growth. Alternative growth approaches to AlN crystallite formation are possible resulting in variation of the final AlN pattern structure. From a viewpoint of obtaining continuous patterns, the more favorable growth conditions involve applying of increased extrinsic gas pressure, 700 mbar in our case. © 2004 Elsevier B.V. All rights reserved.
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| 5. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Superior material properties of AlN on vicinal 4H-SiC
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:3
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure and optical properties of thick (>100 nm) AlN layers grown by hot-wall metalorganic chemical vapor deposition are characterized by infrared spectroscopic ellipsometry, cathodoluminescence, and transmission electron microscopy. The choice of substrates among the available SiC wafer polytype modifications (4H/6H) and misorientations (on-/off-axis cut) is found to determine the AlN defect interaction, stress homogeneity, and luminescence. The growth of thick AlN layers benefits by performing the epitaxy on off-axis substrates because, due to stacking faults, the propagation of threading defects in AlN layers is stopped in a narrow interface region. © 2006 American Institute of Physics.
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| 6. |
- Lundskog, Anders, et al.
(författare)
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InGaN quantum dot formation mechanism on hexagonal GaN/InGaN/GaN pyramids
- 2012
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Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 23:30, s. 305708-
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Tidskriftsartikel (refereegranskat)abstract
- Growing InGaN quantum dots (QDs) at the apex of hexagonal GaN pyramids is an elegant approach to achieve a deterministic positioning of QDs. Despite similar synthesis procedures by metal–organic chemical vapor deposition, the optical properties of the QDs reported in the literature vary drastically. The QDs tend to exhibit either narrow or broad emission lines in the micro-photoluminescence spectra. By coupled microstructural and optical investigations, the QDs giving rise to narrow emission lines were concluded to nucleate in association with a (0001) facet at the apex of the GaN pyramid.
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| 7. |
- Lundskog, Anders, et al.
(författare)
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Unexpected behavior of InGaN quantum dot emission energy located at apices of hexagonal GaN pyramids
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- InGaN quantum dots (QDs) have been grown at the apices of hexagonal GaN pyramids. The pyramids were selectively grown on a (0001) oriented GaN template through circular apertures in a SiN mask positioned in square arrays. The emission of the InGaN QDs was shifted towards higher energies when the center-to-center distance of the pyramids was increased, while the emission from InGaN quantum wells located on the {1101} facets of the pyramids was energetically shifted towards lower energies. No energy shift was observed for (0001) truncated pyramids with truncation diameters larger than 100 nm.
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| 8. |
- MacMillan, Mike F., et al.
(författare)
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Infrared Reflectance of Extremely Thin AlN Epi Films Deposited on SiC Substrates
- 1998
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Ingår i: Materials Science Forum Vols. 264-268. ; , s. 649-652
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Konferensbidrag (refereegranskat)abstract
- The room temperature reflectance of thin (£ 1000Å) AlN epi-films deposited on n type 6H SiC has been measure. These epi-films are too thin to produce interference fringes, from which epi-films thickness is often extracted, within the measured spectral region. However, features from the AlN reststrahl reflectance band can be clearly seen for AlN epi-films as thin as 250Å. Thicknesses are extracted from the measured spectra by comparing them directly to calculated spectra with the epi-film thickness being the only fitting parameter. The accuracy of these thickness determinations is confirmed by comparing them to thickness measured on samples studied by cross sectional TEM.
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| 9. |
- Palisaitis, Justinas, et al.
(författare)
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Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:3, s. 034302-
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Tidskriftsartikel (refereegranskat)abstract
- The early stages of InGaN/GaN quantum wells growth for In reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated STEM–VEELS spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (>20 nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots may act as carrier localization centers inside the quantum wells.
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| 10. |
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