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Gogova, Daniela
Publications (10 of 18) Show all publications
Yakimova, R., Virojanadara, C., Gogova, D., Syväjärvi, M., Siche, D., Larsson, K. & Johansson, L. (2010). Analysis of the Formation Conditions for Large Area Epitaxial Graphene on SiC Substrates. In: Bauer, AJ; Friedrichs, P; Krieger, M; Pensl, G; Rupp, R; Seyller, T (Ed.), SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2. Paper presented at 13th International Conference on Silicon Carbide and Related Materials (ICSCRM2009), Nurnberg, GERMANY, OCT 11-16, 2009 (pp. 565-568). Trans Tech Publications Inc., 645-648
Open this publication in new window or tab >>Analysis of the Formation Conditions for Large Area Epitaxial Graphene on SiC Substrates
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2010 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2 / [ed] Bauer, AJ; Friedrichs, P; Krieger, M; Pensl, G; Rupp, R; Seyller, T, Trans Tech Publications Inc., 2010, Vol. 645-648, p. 565-568Conference paper, Published paper (Refereed)
Abstract [en]

We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2010
Series
Materials Science Forum, ISSN 0255-5476 ; Vol. 645 - 648
Keywords
sublimation; high temperature; Ar pressure; ARPES; LEEM; DFT
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58214 (URN)10.4028/www.scientific.net/MSF.645-648.565 (DOI)000279657600135 ()
Conference
13th International Conference on Silicon Carbide and Related Materials (ICSCRM2009), Nurnberg, GERMANY, OCT 11-16, 2009
Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2013-03-28
Yazdi, G., Vassilevski, K., Cordoba Gallego, J. M., Gogova, D., Nikitina, I. P., Syväjärvi, M., . . . Yakimova, R. (2010). Free standing AIN single crystal grown on pre-patterned and in situ patterned 4H-SiC substrates. In: Materials Science Forum, Vols. 645-648. Paper presented at ICSCRM2009 (pp. 1187-1190). Transtec Publications; 1999, 645-648
Open this publication in new window or tab >>Free standing AIN single crystal grown on pre-patterned and in situ patterned 4H-SiC substrates
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2010 (English)In: Materials Science Forum, Vols. 645-648, Transtec Publications; 1999 , 2010, Vol. 645-648, p. 1187-1190Conference paper, Published paper (Refereed)
Abstract [en]

Free standing AIN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AIN microrods, which evolve from the apex of SiC pyramids grown on the SIC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AIN single crystals with a thickness up to 400 mu m and low dislocation density.

Place, publisher, year, edition, pages
Transtec Publications; 1999, 2010
Keywords
Free standing; Hexagonal pyramids; AIN; reactive ion etching; physical vapor transport
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58215 (URN)10.4028/www.scientific.net/MSF.645-648.1187 (DOI)000279657600283 ()
Conference
ICSCRM2009
Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2013-10-02
Malinauskas, T., Aleksiejunas, R., Jarasiunas, K., Beaumont, B., Gibart, P., Kakanakova-Georgieva, A., . . . Heuken, M. (2007). All-optical characterization of carrier lifetimes and diffusion lengths in MOCVD-, ELO-, and HVPE- grown GaN. In: Journal of Crystal Growth, Vol. 300. Paper presented at ISGN-1 2006 (pp. 223-227). , 300(1)
Open this publication in new window or tab >>All-optical characterization of carrier lifetimes and diffusion lengths in MOCVD-, ELO-, and HVPE- grown GaN
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2007 (English)In: Journal of Crystal Growth, Vol. 300, 2007, Vol. 300, no 1, p. 223-227Conference paper, Published paper (Refereed)
Abstract [en]

The metrological capability of the picosecond four-wave mixing (FWM) technique for evaluation of the photoelectrical properties of GaN heterostructures grown on sapphire, silicon carbide, and silicon substrates as well as of free-standing GaN films is demonstrated. Carrier recombination and transport features have been studied in a wide excitation, temperature, and dislocation density (from ∼1010 to 106 cm-2) range, exploring non-resonant refractive index modulation by a free carrier plasma. The studies allowed to establish the correlations between the dislocation density and the carrier lifetime, diffusion length, and stimulated emission threshold, to reveal a competition between the bimolecular and nonradiative recombination, and to verify the temperature dependence of bimolecular recombination coefficient in the 10-300 K temperature range. It was shown that the FWM technique is more advantageous than the time-resolved photoluminescence technique for determination of carrier lifetimes in high quality thick III-nitride layers. © 2006 Elsevier B.V. All rights reserved.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38848 (URN)10.1016/j.jcrysgro.2006.11.014 (DOI)45864 (Local ID)45864 (Archive number)45864 (OAI)
Conference
ISGN-1 2006
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2010-12-13
Malinauskas, T., Jarasiunas, K., Aleksiejunas, R., Gogova, D., Monemar, B., Beaumont, B. & Gibart, P. (2006). Contribution of dislocations to carrier recombination and transport in highly excited ELO and HYPE GaN layers. Physica status solidi. B, Basic research, 243(7), 1426-1430
Open this publication in new window or tab >>Contribution of dislocations to carrier recombination and transport in highly excited ELO and HYPE GaN layers
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2006 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 7, p. 1426-1430Article in journal (Refereed) Published
Abstract [en]

Nonequilibrium carrier dynamics has been investigated in ELO and HYPE grown GaN layers in a wide temperature and excitation range by using the time-resolved picosecond FWM technique. Carrier lifetime in the samples at 300 K increased up to 2.8-5.1 ns in accordance with the decreasing threading dislocation density from 4 x 10(7) cm(-2) (ELO) to mid 106 cm(-2) in HYPE layers. At T < 100 K, the hyperbolic shape of FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased at lower temperatures to a few hundreds of ps. The dominance of bimolecular recombination in HVPE layers at 10-40 K was demonstrated by the exposure characteristic of FWM, that has shown a sublinear growth of carrier density with excitation, N proportional to I-1/2. Numerical fitting of the set of FWM kinetics at various T confirmed the temperature dependence of bimolecular recombination coefficient B proportional to T-1/5 and provided its value B = 2 x 10(-11) cm(3)/s at 300 K and 3.2 x 10(-9) cm(3)/s at 9 K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8-1 mu m at 300 K and its dependence on dislocation density and temperature. (c) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46012 (URN)10.1002/pssb.200565139 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Gogova, D., Talik, E., Ivanov, I. G. & Monemar, B. (2006). Large-area free-standing GaN substrate grown by hydride vapor phase epitaxy on epitaxial lateral overgrown GaN template. Physica. B, Condensed matter, 371(1), 133-139
Open this publication in new window or tab >>Large-area free-standing GaN substrate grown by hydride vapor phase epitaxy on epitaxial lateral overgrown GaN template
2006 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 371, no 1, p. 133-139Article in journal (Refereed) Published
Abstract [en]

In this paper, the potential of the high growth rate hydride vapor phase epitaxy technique and laser lift-off for the fabrication of large-area (2?) free-standing GaN substrates is revealed. Structural and optical properties of 250-µm-thick GaN layer grown on a MOVPE epitaxial lateral overgrown GaN template have been investigated employing different analytical experimental techniques. A low value of dislocation density of ~1×107 cm-2 on the Ga-terminated face of the free-standing material was determined from AFM images. X-ray diffraction (XRD), Raman scattering measurements, and low-temperature photoluminescence (PL) were exploited to assess the structural and optical quality of the GaN. The full-width at half-maximum value of XRD ?-scans of the free-standing GaN material was determined to be 264 arcsec for the (101¯4) reflection. The XRD and low-temperature PL mapping measurements consistently proved the good crystalline quality and lateral homogeneity and small residual stress inside the material. Hence, the free-standing GaN achieved is highly advantageous for a lattice-constant and thermal-expansion-coefficient matched substrate for additional strain-free homoepitaxy of III-nitrides-based device heterostructures. © 2005 Elsevier B.V. All rights reserved.

Keywords
Bulk-like, ELO, Free-standing, GaN, GaN substrates, HVPE
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50313 (URN)10.1016/j.physb.2005.10.122 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Kasic, A., Gogova, D., Larsson, H., Hemmingsson, C., Ivanov, I. G., Yakimova, R., . . . Heuken, M. (2005). Characterization of crack-free relaxed GaN grown on 2″ sapphire. Journal of Applied Physics, 98(7), 73525
Open this publication in new window or tab >>Characterization of crack-free relaxed GaN grown on 2″ sapphire
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2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 7, p. 73525-Article in journal (Refereed) Published
Abstract [en]

We demonstrate the growth of high-quality and virtually strain-free bulklike GaN by hydride vapor-phase epitaxy in a vertical atmospheric-pressure reactor with a bottom-fed design. The 300‐μm-thick GaN layer was grown on a 2″ (0 0 0 1) sapphire substrate buffered with a ∼ 2‐μm-thick GaN layer grown by metal-organic chemical-vapor deposition. During the cool down process to room temperature, cracking was induced in the sapphire substrate, thereby allowing the bulklike GaN layer to relax without provoking cracking of itself. The crystalline quality and the residual strain in the 2″ GaN wafer were investigated by various characterization techniques. The lateral homogeneity of the wafer was monitored by low-temperature photoluminescence mapping. High-resolution x-ray diffraction and photoluminescence measurements proved the high crystalline quality of the material grown. The position of the main near-band-gap photoluminescence line and the phonon spectra obtained from infrared spectroscopic ellipsometry show consistently that the 2″ crack-free GaN is virtually strain-free over a diameter of approximately 4 cm.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30711 (URN)10.1063/1.2064311 (DOI)16323 (Local ID)16323 (Archive number)16323 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Gogova, D., Kanev, S., Monemar, B., Ivanov, I. G., Yakimova, R. & Talik, E. (2005). Growth and characterization of free-standing HVPE GaN on two-step epitaxial lateral overgrown GaN template. Pennington, NJ: The Electrochemical Society, Inc.
Open this publication in new window or tab >>Growth and characterization of free-standing HVPE GaN on two-step epitaxial lateral overgrown GaN template
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2005 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Pennington, NJ: The Electrochemical Society, Inc., 2005
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30790 (URN)16415 (Local ID)16415 (Archive number)16415 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2009-11-04
Monemar, B., Larsson, H., Hemmingsson, C., Ivanov, I. G. & Gogova, D. (2005). Growth of thick GaN layers with hydride vapour phase epitaxy. Journal of Crystal Growth, 281(1), 17-31
Open this publication in new window or tab >>Growth of thick GaN layers with hydride vapour phase epitaxy
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2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, p. 17-31Article in journal (Refereed) Published
Abstract [en]

In this paper we describe recent experimental efforts to produce high quality thick (⩾300 μm) GaN layers on sapphire, the removal of such a layer from the sapphire substrate, and the properties of the so obtained free-standing GaN material. The growth process is described in some detail in the vertical reactor geometry used in this work. Defects like dislocations, micro-cracks and pits produced during growth are discussed, along with procedures to minimize their concentration on the growing surface. The laser lift-off technique is shown to be a feasible technology, in particular if a powerful laser with a large spot size can be used. A major problem with the free-standing material is the typically large bowing of such a wafer, due to the built in defect concentrations near the former GaN-sapphire interface. This bowing typically causes a rather large width of the XRD rocking curve of the free-standing material, while optical data confirm virtually strain free material of excellent quality at the top surface.

Keywords
characterization, computer simulation, defects, chloride vapour phase deposition, gallium nitride
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46086 (URN)10.1016/j.jcrysgro.2005.03.040 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Gogova, D., Larsson, H., Kasic, A., Yazdi, G. R., Ivanov, I. G., Yakimova, R., . . . Gibart, P. (2005). High-Quality 2'' Bulk-Like Free-Standing GaN Grown by HydrideVapour Phase Epitaxy on a Si-doped Metal Organic Vapour Phase Epitaxial GaN Template with an Ultra Low Dislocation Density. Japanese Journal of Applied Physics, 44, 1181-1185
Open this publication in new window or tab >>High-Quality 2'' Bulk-Like Free-Standing GaN Grown by HydrideVapour Phase Epitaxy on a Si-doped Metal Organic Vapour Phase Epitaxial GaN Template with an Ultra Low Dislocation Density
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2005 (English)In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 44, p. 1181-1185Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30713 (URN)16325 (Local ID)16325 (Archive number)16325 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Misheva, M., Larsson, H., Gogova, D. & Monemar, B. (2005). Positron annihilation study of HVPE grown thick GaN layers. Physica Status Solidi (a) applications and materials science, 202(5), 713-717
Open this publication in new window or tab >>Positron annihilation study of HVPE grown thick GaN layers
2005 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, no 5, p. 713-717Article in journal (Refereed) Published
Abstract [en]

Single-crystalline GaN layers with a thickness up to 330 µm were grown by hydride vapor phase epitaxy on basal plane sapphire at gallium stable conditions in a bottom-fed vertical reactor at atmospheric pressure. Positron annihilation spectroscopy experiments were implemented in order to identify native point defects in the as-grown non-intentionally doped n-type GaN. Comparatively low concentrations of Ga vacancy related defects in the order of 1016 to 1017 cm–3 were extracted from the positron annihilation spectroscopy data. The Ga vacancy defect concentration was related to the intensity of the yellow photoluminescence band centered at 2.2 eV. The influence of the growth rate on the Ga vacancy related defect concentration was investigated. A trend of decreasing of the defect concentration with increasing of layer thickness is observed, which correlates with improving crystalline quality with the thickness.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46094 (URN)10.1002/pssa.200461420 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-05-11
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