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Strain-related structural and vibrational properties of group-III nitride layers and superlattices
Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-8112-7411
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This PhD thesis is focused on strain-related phenomena in group-III nitride layers and heterostructures. Key issues in material properties as phonon mode behavior, structure and lattice parameters of AlN, InN and GaN, as well as of AlN/GaN superlattices are addressed in order to give answers to some open questions. The research is motivated by the enormous technological application potential of the group-III nitride materials for optoelectronic devices and high temperature, and high power devices. Due to the lack of native substrates, the group-III nitrides are typically grown on foreign substrates resulting inbuilt-in strain in the films, as well as, in misorientation and defect formation. Substantial efforts have been concentrated on the research of strain-related fundamental properties of group-III nitrides. However, some of the strain-related structural and vibrational properties of these materials remain unclear and this gap has to be filled in order to fully explore the possibilities for applications.The thesis contributes to the knowledge of the strain-related phenomena ingroup-III nitrides by concentrating on the following: i) lattice parameters and strain relaxation in GaN, AlN, InN films with different thicknesses, as well as free-standing GaN quasi-substrates; ii) phonon mode behavior and deformation potentials of AlN and InN; iii) structural evolution in AlN and GaN; iv)phonon mode behavior and strain evolution in AlN/GaN superlattices. The layers studied were grown by a variety of growth techniques and nucleation schemes aiming at establishing of a comprehensive understanding of the material properties.

The thesis is organized as follows: In the first part a general description of the basic properties of group-III nitrides is given with a special emphasis on the structural and vibrational properties. The vibrational properties of lowdimensional group-III nitrides are also reviewed. After that, basic concepts of strain phenomenon in group-III nitrides, as well as the strain effects on phonons and on structural properties are discussed. Finally, the experimental techniques used are introduced.

The second part of the thesis consists of six papers providing informationon specific strain-related structural and vibrational properties of III-nitride layers and superlattices.

The lattice parameters of GaN films grown by two different techniques on a-plane sapphire are the subject of Paper I. We have determined two different values of the in-plane lattice parameter of the GaN layers in contrast to only one in the case of films grown on c-plane sapphire. We suggest that the observed distortion of the hexagonal symmetry can be attributed to the presence of anisotropic in-plane strain in the films. A new approach to determination of lattice parameters has been proposed.

Paper II deals with the lattice parameters of GaN quasi-substrates grown by hydride vapor phase epitaxy using two nucleation schemes. The lattice parameters of both, Ga- and N-polar faces of the quasi-substrates were determined and compared. The strain relaxation phenomena in such free-standing layers and the concept of strain-free lattice parameters are discussed.

Papers III and IV are devoted to the deformation potentials of the E 1 (TO)mode in AlN, and the E1 (TO) and E2 modes in InN, where a combination of infraredellipsometry, infrared reflection, Raman scattering and x-ray diffractionstudies was used. The reported results in Paper III present the first experimentalvalues for the E1 (TO) deformation potentials of AlN and the results for the InN deformation potentials in Paper IV are the first ever reported.

The strain evolution and its effect on the structural and vibrational properties of thin epitaxial AlN layers with different thicknesses have been studied in Paper V. A model of the strain evolution with film thickness and related defect structure is suggested and it is successfully used in the infrared ellipsometry data analysis.

Paper VI is focused on the strain evolution in AlN/GaN superlattices withdifferent periods and its effect on their phonon properties. The presence of phonons originating from the superlattice constituents was revealed and their nature is discussed.

Place, publisher, year, edition, pages
Linköping: Linköping University , 2004. , p. 69
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 891
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-179291Libris ID: 9615849ISBN: 9185295256 (print)OAI: oai:DiVA.org:liu-179291DiVA, id: diva2:1595053
Public defence
2004-09-24, hörsal Planck, Fysikhuset, Linköpings universitet, Linköping, 14:15
Opponent
Note

All or some of the partial works included in the dissertation are not registered in DIVA and therefore not linked in this post.

Available from: 2021-09-29 Created: 2021-09-17 Last updated: 2023-12-28Bibliographically approved
List of papers
1. Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
Open this publication in new window or tab >>Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
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2003 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 5, p. 703-705Article in journal (Refereed) Published
Abstract [en]

The lattice parameters of GaN layers grown on a-plane sapphire were investigated. The hydride vapor phase epitaxy and metalorganic vapor phase epitaxy were used for the determination of parameters. The strain anisotropy was found to have different values in the films and obtained values of parameters were grouped around two values.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46727 (URN)10.1063/1.1542931 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2023-12-28
2. Deformation potentials of the E-1(TO) mode in AlN
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: 2023-12-28

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