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Tungasmita, Sukkaneste
Publications (10 of 15) Show all publications
Paskova, T., Paskov, P., Valcheva, E., Darakchieva, V., Birch, J., Kasic, A., . . . Monemar, B. (2004). Polar and nonpolar GaN grown by HVPE: Preferable substrates for nitride-based emitting devices. Physica status solidi. A, Applied research, 201(10), 2265-2270
Open this publication in new window or tab >>Polar and nonpolar GaN grown by HVPE: Preferable substrates for nitride-based emitting devices
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2004 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 10, p. 2265-2270Article in journal (Refereed) Published
Abstract [en]

We report on hydride vapor phase epitaxial growth of thick nonpolar GaN films on r-plane sapphire in comparison with polar GaN films on c-plane sapphire substrates with AlN buffer layers, aiming at developing of their quasi-substrate application. Both the thick films and the buffers were identified to have single crystalline structures. The microstructure of the films was studied by transmission electron microscopy. High resolution X-ray diffraction mapping and photoluminescence measurements were employed to characterize the strain present in both polar and nonpolar GaN films. In contrast to c-plane GaN, which is always characterised by isotropic in-plane properties, the a-plane GaN shows a strong in-plane anisotropy of the growth rate, morphology and strain distribution. Different defect, impurity and free carrier concentrations were observed in the polar and nonpolar material.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46187 (URN)10.1002/pssa.200404818 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Darakchieva, V., Schubert, M., Birch, J., Kasic, A., Tungasmita, S., Paskova, T. & Monemar, B. (2003). Generalized infrared ellipsometry study of thin epitaxial AlN layers with complex strain behavior. , 340-342
Open this publication in new window or tab >>Generalized infrared ellipsometry study of thin epitaxial AlN layers with complex strain behavior
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2003 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The effect of film thickness on the strain and structural properties of thin epitaxial AlN films has been investigated, and a sub-layer model of the degree of strain and related defects for all films is suggested. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sub-layer model has been successfully applied to the analysis of the ellipsometry data trough model calculations of the infrared dielectric function. © 2003 Elsevier B.V. All rights reserved.

Series
PHYSICA B-CONDENSED MATTER, ISSN 0921-4526 ; 340
Keywords
AlN, Infrared ellipsometry, Phonons, Strain
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46349 (URN)10.1016/j.physb.2003.09.059 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2011-09-19
Darakchieva, V., Paskov, P., Paskova, T., Birch, J., Tungasmita, S. & Monemar, B. (2002). Deformation potentials of the E-1(TO) mode in AlN. Applied Physics Letters, 80(13), 2302-2304
Open this publication in new window or tab >>Deformation potentials of the E-1(TO) mode in AlN
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2002 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, p. 2302-2304Article in journal (Refereed) Published
Abstract [en]

The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47892 (URN)10.1063/1.1465105 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Seppänen, T., Radnoczi, G., Tungasmita, S., Hultman, L. & Birch, J. (2002). Growth and characterization of epitaxial wurtzite Al1-xInxN thin films deposited by UHV reactive dual DC magnetron sputtering. Materials Science Forum, 433-4, 987-990
Open this publication in new window or tab >>Growth and characterization of epitaxial wurtzite Al1-xInxN thin films deposited by UHV reactive dual DC magnetron sputtering
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-4, p. 987-990Article in journal (Refereed) Published
Abstract [en]

Ternary Al1-xInxN thin films were grown by dual target direct current (DC) reactive magnetron sputtering under UHV conditions. The film compositions were determined to range from 0.30

Keywords
AlN, AllnN, cathodoluminescence, epitaxial growth, HREM, InN, magnetron sputtering, thin films, XRD
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48568 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Tungasmita, S., Persson, P., Seppänen, T., Hultman, L. & Birch, J. (2002). Growth of epitaxial (SiC)(x)(AlN)(1-x) thin films on 6H-SiC by ion-assisted dual magnetron sputter deposition. Materials Science Forum, 389-3, 1481-1484
Open this publication in new window or tab >>Growth of epitaxial (SiC)(x)(AlN)(1-x) thin films on 6H-SiC by ion-assisted dual magnetron sputter deposition
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 389-3, p. 1481-1484Article in journal (Refereed) Published
Abstract [en]

(SiC)(X)(AIN)(1-X) thin films have been grown epitaxially on vicinal 6H-SiC (0001) by low-energy ion assisted dual magnetron sputtering in UHV conditions. AES showed a decreasing Si and C content for an increasing magnetron power ratio, (P-Al/P-SiC). The epitaxial quality of the films was improved as the SiC fraction increased. Films containing less than 5% of Si and C show an evolution of domain width similar to the growth of pure AIN. HRXRD show a decreased c-axis lattice parameter for a film with composition of AINC(X) (0less than or equal toxless than or equal to0.1), indicating carbon substitution in AIN. CL spectra show defect-related peaks of similar to3.87 and similar to4.70 eV, corresponding to O and C impurities respectively as well as on un-identified peak at similar to3.40 eV.

Keywords
AlN, epitaxial, SiC, sputter, thin film
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48835 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Tungasmita, S., Persson, P., Hultman, L. & Birch, J. (2002). Pulsed low-energy ion-assisted growth of epitaxial aluminum nitride layer on 6H-silicon carbide by reactive magnetron sputtering. Journal of Applied Physics, 91(6), 3551-3555
Open this publication in new window or tab >>Pulsed low-energy ion-assisted growth of epitaxial aluminum nitride layer on 6H-silicon carbide by reactive magnetron sputtering
2002 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 6, p. 3551-3555Article in journal (Refereed) Published
Abstract [en]

Epitaxial aluminum nitride thin films have been grown on silicon carbide (6H-SiC) substrates by pulsed low-energy ion-assisted reactive magnetron sputter deposition (+5/-20 V of bias pulses), with ion-assisted energy (Ei)?22eV, under ultrahigh-vacuum conditions. Surface ion interactions during the negative bias pulse gave rise to enhanced surface mobility of adatoms with beneficial effects, which extended over the limit of ion repelling in the positive pulse as the film thickness increased. High-resolution electron microscopy shows that a large (>90 nm) AlN domain width can form on the substrate. Domain-boundary annihilation and domain suppression during film growth have been observed. The growth rate also increased by a factor of ~4 compared to growth conditions with no ion assistance (Ei=2eV) and by a factor of 2 from dc ion-assisted growth. This indicates that the supply of nitrogen is a limiting factor for AlN formation and that the reactivity of nitrogen is increased on the growing AlN film surface for pulse ion-assisted deposition. High-resolution x-ray diffraction shows a reduction in the full width at half maximum of the rocking curve from 1490 to 1180 arcsec when pulsed ions are used. The cathodoluminescence shows high intensity of near-band edge emissions at wavelengths of 206 (6.02 eV) and 212 nm (5.84 eV) at a measured temperature of 5 K, with relatively low defect and oxygen and carbon impurity related emission, which is indicative of a high quality electronic material. © 2002 American Institute of Physics.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47064 (URN)10.1063/1.1448886 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Darakchieva, V., Birch, J., Paskov, P., Tungasmita, S., Paskova, T. & Monemar, B. (2002). Strain evolution in high temperature AlN buffer layers for HVPE-GaN growth. Physica status solidi. A, Applied research, 190(1), 59-64
Open this publication in new window or tab >>Strain evolution in high temperature AlN buffer layers for HVPE-GaN growth
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2002 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, p. 59-64Article in journal (Refereed) Published
Abstract [en]

High temperature AlN buffer layers are deposited on a-plane sapphire by reactive magnetron sputtering. The effect of the buffer thickness on the AlN structural properties and surface morphology are studied in correlation with the subsequent hydride vapour phase epitaxy of GaN. A minimum degree of mosaicity and screw dislocation density is determined for a 50 nm thick AlN buffer. With increasing the AlN thickness, a strain relaxation occurs as a result of misfit dislocation generation and higher degree of mosaicity. A blue shift of the E-1(TO) frequency evaluated by means of infrared reflection spectroscopy is linearly correlated with an increase in biaxial compressive stress in the films through the IR stress factor k(E1)(b) = 2.57 +/- 0.26 cm(-1) GPa(-1).

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48172 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Paskova, T., Valcheva, E., Birch, J., Tungasmita, S., Persson, P., Paskov, P., . . . Monemar, B. (2001). Defect and stress relaxation in HVPE-GaN films using high temperature reactively sputtered AlN buffer. Journal of Crystal Growth, 230(3-4), 381-386
Open this publication in new window or tab >>Defect and stress relaxation in HVPE-GaN films using high temperature reactively sputtered AlN buffer
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2001 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 230, no 3-4, p. 381-386Article in journal (Refereed) Published
Abstract [en]

The influence of high temperature buffer layers on the structural characteristics of GaN grown by hydride vapour phase epitaxy on sapphire was investigated. Strain relaxation as well as mismatch-induced defect reduction in thick GaN layers grown on AlN buffer was microscopically identified using cathodoluminescence and micro-Raman spectroscopy in cross-section of the films. The results were correlated with photoluminescence and Hall-effect data of layers with different thicknesses. These relaxation processes were suggested to account for the specific defect distribution in the buffers revealed by high-resolution X-ray diffraction and transmission electron microscopy. © 2001 Elsevier Science B.V. All rights reserved.

Keywords
A1. Crystal structure, A1. Defects, A1. Optical microscopy, A1. Stresses, A3. Hydride vapor phase epitaxy, B1. Nitrides
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47280 (URN)10.1016/S0022-0248(01)01264-7 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Paskova, T., Paskov, P., Darakchieva, V., Tungasmita, S., Birch, J. & Monemar, B. (2001). Defect reduction in HVPE growth of GaN and related optical spectra. Physica status solidi. A, Applied research, 183(1), 197-203
Open this publication in new window or tab >>Defect reduction in HVPE growth of GaN and related optical spectra
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2001 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 183, no 1, p. 197-203Article in journal (Refereed) Published
Abstract [en]

GaN technology is still based on highly mismatched heteroepitaxial growth on foreign substrates, and therefore needs to overcome a high defect density and a high level of stress in the epitaxial layers. Various attempts have been made to reduce the defects and stress in thick GaN layers. We here report a reduction of the defect density in thick GaN layers grown by hydride vapour phase epitaxy, using regrowth on free-standing GaN films, as well as introducing an AlN buffer and AlN interlayer in the growth sequence. Special focus is put on the optical properties of the material.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49387 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Paskova, T., Valcheva, E., Birch, J., Tungasmita, S., Persson, P., Beccard, R., . . . Monemar, B. (2000). Effect of Si doping of metalorganic chemical vapor deposition-GaN templates on the defect arrangement in hydride vapor phase epitaxy-GaN overgrown layers. Journal of Applied Physics, 88(10), 5729-5732
Open this publication in new window or tab >>Effect of Si doping of metalorganic chemical vapor deposition-GaN templates on the defect arrangement in hydride vapor phase epitaxy-GaN overgrown layers
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2000 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 88, no 10, p. 5729-5732Article in journal (Refereed) Published
Abstract [en]

Two different types of dislocation arrangements have been observed in hydride vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor deposition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a network of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution result in essentially different surface morphologies, respectively: (i) low-angle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislocations. The Si doping of the GaN templates was found to enhance defect interaction in the templates and to enable a reduction of the dislocation density in the overgrown thick GaN films, although it does not lead to an improvement of the overall structural properties of the material. (C) 2000 American Institute of Physics. [S0021-8979(00)08422-X].

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49550 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
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