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Structural and elastic properties of InN and InAlN with different surface orientations and doping
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Group–III nitrides, InN, GaN, AlN, and their alloys, have revolutionized solid state lighting and continue to attract substantial research interest due to their unique properties and importance for optoelectronics and electronics. Among the group–III nitrides, InN has the lowest effective electron mass and the highest electron mobility, which makes it suitable for high–frequency and high power devices. InxAl1–xN alloys cover the widest wavelength region among any semiconductor systems with band gaps ranging from 0.6 eV (InN) to 6.2 eV (AlN). Thus, InxAl1–xN is promising for light emitting diodes and laser diodes in a wide spectral range from infrared to deep ultraviolet, as well as for solar cell applications. InxAl1–xN thin films are also extensively studied in relation to their application for Bragg reflectors, microcavities, polariton emission and high electron mobility transistors. Despite the intense research, many of the fundamental properties of InN and InxAl1–xN remain controversial. For example, the material lattice parameters, stiffness constants, structural anisotropy and defects in nonpolar and semipolar films, effect of impurities and dopants are not established. Furthermore, to fabricate InN based devices, reliable n– and p–type doping should be achieved. At present, control and assessment of p–type conductivity using Mg doping of InN is one of the most outstanding issues in the field.

This thesis focuses on: i) Establishing the structural and elastic properties of InxAl1−xN with arbitrary surface orientations (papers I to III); ii) Studying structural and free-charge carrier properties of non/semi-polar and zinc-blende InN (papers IV and V) and iii) Establishing the effects of doping (p and n) on lattice parameters, structural and free-charge carrier properties of InN (Papers VI and VII). The work includes ab initio calculations and experimental studies of InN and InxAl1−xN materials grown in world−class laboratories in Japan, Europe and the USA.

The first part of the thesis includes general description of the basic material properties. Next, the structural and elastic properties and defects in InxAl1−xN and InN are discussed. The experimental techniques and relevant methods used to characterize the materials are described, as well as details on the ab initio calculations used in this work are provided. Part II consists ofseven papers.

In Paper I we present the first theoretical analysis on the applicability of Vegard’s linear rule in InxAl1−xN alloys in relation to strain related elastic and piezoelectric properties. We derive the elastic stiffness constants and biaxial coefficients, as well as the respective deviations from linearity by using ab initio calculations. The stress−strain relationships to extract composition from the lattice parameters are derived in different coordinate systems for InxAl1−xN with an arbitrary surface orientation. The error made in the composition extracted from the lattice parameters if the deviations from linearity are not taken into account is discussed for different surface orientations, compositions and degrees of strain. The strain induced piezoelectric polarization is analyzed for InxAl1−xN alloys grown psudomorphically on GaN. We establish the importance of the deviation from linearity in the extracted strain values in respect to the piezoelectric polarization.

Paper II reports the lattice parameters of InxAl1−xN in the whole compositional range using first-principle calculations. Deviations from Vegard’s rule are obtained via the bowing parameters, which largely differ from previously reported values. The paper discusses for the first time the implications of the observed deviations from Vegard’s rule on the In content extracted from x-ray diffraction.

Paper III discusses the lattice parameters and strain evolution in Al−rich InxAl1−xN films with composition. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x−ray diffraction (XRD). It is suggested that strain plays an important role for the observed deviation from Vegard’s rule in the case of pseudomorphic films. It is found that Vegard’s rule in the narrow compositional range around the lattice matching to GaN may be applicable.

Paper IV reports the first study of structural anisotropy of non-polar InN and semi−polar InN grown on sapphire and γ-LiAlO2 substrates. The on−axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a−plane InN films is suggested. The semipolar InN was found to contain two domains nucleating on zinc−blende InN(111)A and InN(111)B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. We found that a− and m−plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free−standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN−based devices.

Paper V reports the development of appropriate methods based on X-ray diffraction and Infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende InN and quantify their phase ratio. Detailed analysis on the formation of the cubic and wurtzite phases is presented and their evolution with film thickness is discussed in detail. The free-charge carrier and phonon properties of the two phases are discussed together with the determination of the surface electron accumulation.

Paper VI studies the effect of Mg doping on the structural parameters and free−charge carrier properties of InN. We demonstrate the capability of infrared spectroscopic ellipsometry to identify p−type doping. The paper provides important information on the effect of Mg doping on extended defects and lattice parameters, and also discussed the relationship between doping, defects and carrier mobility.

Paper VII presents the first study on the effect of impurities on the lattice parameters of InN using first principle calculations. We considered both the size and the deformation potential effect for Mg0, Mg, Si+ and O+ and Hi+. The incorporation of H on interstitial site and substitutional O leads to expansion of the lattice. On the other hand, incorporation of Si or Mg leads to contraction of the lattice. The most pronounced effect is observed for Si. Our results indicate that the experimentally observed increase of the in−plane lattice parameter of Mg doped InN cannot be explained neither by the size nor by the deformation potential effect and suggest that the growth strain is changed in this case. The reported size and deformation potential coefficients can be used to elucidate the origin of strains in InN epitaxial layers and the degree of electrically active impurities.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 79 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1485
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-85567ISBN: 978-91-7519-754-8 (print)OAI: oai:DiVA.org:liu-85567DiVA: diva2:571712
Public defence
2012-12-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2012-11-23Bibliographically approved
List of papers
1. Elastic constants, composition, and piezolectric polarization in InxAl1-xN: From ab initio calculations to experimental implications for the applicability of Vegards rule
Open this publication in new window or tab >>Elastic constants, composition, and piezolectric polarization in InxAl1-xN: From ab initio calculations to experimental implications for the applicability of Vegards rule
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2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 15, 155310- p.Article in journal (Refereed) Published
Abstract [en]

We present a theoretical analysis on the applicability of Vegards linear rule in InxAl1-xN alloys in relation to strain related elastic and piezoelectric properties. We derive the elastic stiffness constants and biaxial coefficients, as well as the respective deviations from linearity (Vegards rule) by using ab initio calculations. The stress-strain relationships to extract composition from the lattice parameters are derived in different coordinate systems for InxAl1-xN with an arbitrary surface orientation. The error made in the composition extracted from the lattice parameters if the deviations from linearity are not taken into account is discussed for different surface orientations, compositions and degrees of strain in the InxAl1-xN films. The strain induced piezoelectric polarization is analyzed for InxAl1-xN alloys grown pseudomorphically on GaN. The polarization values are compared with those obtained from our experimental data for the lattice parameters. We establish the importance of the deviation from linearity to correctly determine the piezoelectric polarization and also a smooth, not particular piezoelectric response at GaN lattice matched conditions.

Place, publisher, year, edition, pages
American Physical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85295 (URN)10.1103/PhysRevB.86.155310 (DOI)000309777900004 ()
Note

Funding Agencies|Swedish Research Council (VR)|2010-3848|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program|2011-03486|FCT Portugal|PTDC/FIS/100448/2008|Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||

Available from: 2012-11-19 Created: 2012-11-15 Last updated: 2017-12-07
2. Lattice parameters, deviations from Vegards rule, and E-2 phonons in InAlN
Open this publication in new window or tab >>Lattice parameters, deviations from Vegards rule, and E-2 phonons in InAlN
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 26, 261908- p.Article in journal (Refereed) Published
Abstract [en]

The lattice parameters of InxAl1-xN in the whole compositional range are studied using first-principle calculations. Deviations from Vegards rule are obtained via the bowing parameters, delta(a)=0.0412 +/- 0.0039 A and delta(c)=-0.060 +/- 0.010 A, which largely differ from previously reported values. Implications of the observed deviations from Vegards rule on the In content extracted from x-ray diffraction are discussed. We also combine these results with x-ray diffraction and Raman scattering studies on InxAl1-xN nanocolumns with 0.627 <= x <= 1 and determine the E-2 phonon frequencies versus In composition in the scarcely studied In-rich compositional range.

Keyword
ab initio calculations, aluminium compounds, crystal structure, III-V semiconductors, indium compounds, nanostructured materials, phonon spectra, phonons, Raman spectra, X-ray diffraction
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16526 (URN)10.1063/1.3056656 (DOI)
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2017-12-14
3. Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire
Open this publication in new window or tab >>Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire
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2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 10, 103513- p.Article in journal (Refereed) Published
Abstract [en]

The lattice parameters and strain evolution in Al1-x In x N films with 0.07≤x≤0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard's rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1-x Inx N films with low degree of strain or partially relaxed, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. © 2008 American Institute of Physics.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-42505 (URN)10.1063/1.2924426 (DOI)65159 (Local ID)65159 (Archive number)65159 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
4. Structural, free-charge carrier and phonon properties of zinc-blende and wurtizte polymorphs in InN epitaxial layers
Open this publication in new window or tab >>Structural, free-charge carrier and phonon properties of zinc-blende and wurtizte polymorphs in InN epitaxial layers
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present a comprehensive study of the structural, phonon and free electron properties of zincblende InN films containing inclusion of wurtzite InN. Appropriate methods based on X-ray diffraction and Infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende InN and quantify their phase ratio are developed and discussed. Thorough analysis on the formation of the cubic and wurtzite phases is presented and their evolution with film thickness is discussed in detail. The freecharge carrier and phonon properties of the two phases are discussed together with the determination of electron accumulation at the zinc-blende InN (001) and wurtzite (10̅11) surfaces.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85554 (URN)
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2015-03-09Bibliographically approved
5. Structural anisotropy of nonpolar and semipolar InN epitaxial layers
Open this publication in new window or tab >>Structural anisotropy of nonpolar and semipolar InN epitaxial layers
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2010 (English)In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979, Vol. 108, no 7, 073529- p.Article in journal (Refereed) Published
Abstract [en]

We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) gamma-LiAlO2, respectively, and semipolar (10 (1) over bar1) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(111) A and InN(111) B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. Both, a- and m-plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free-standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN-based devices.

Place, publisher, year, edition, pages
American Institute of Physics, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-61185 (URN)10.1063/1.3487923 (DOI)000283222200053 ()
Note

Original Publication: Vanya Darakchieva, Mengyao Xie, N Franco, F Giuliani, B Nunes, E Alves, C L Hsiao, L C Chen, T Yamaguchi, Y Takagi, K Kawashima and Y Nanishi, Structural anisotropy of nonpolar and semipolar InN epitaxial layers, 2010, JOURNAL OF APPLIED PHYSICS, (108), 7, . http://dx.doi.org/10.1063/1.3487923 Copyright: American Institute of Physics http://www.aip.org/

Available from: 2010-11-05 Created: 2010-11-05 Last updated: 2013-05-01
6. Effect of Mg doping on the structural and free-charge carrier properties of InN
Open this publication in new window or tab >>Effect of Mg doping on the structural and free-charge carrier properties of InN
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 16, 163504- p.Article in journal (Refereed) Published
Abstract [en]

We study the structural and free-charge carrier properties of two sets of InN films grown by molecular beam epitaxy doped with different Mg concentrations from 1x1018 cm-3 to 3.9x1021 cm-3. We determine the effect of Mg doping on surface morphology, lattice parameters, structural characteristics and carrier properties. We show that infrared spectroscopic ellipsometry can be used to evidence successful p-type doping in InN, which is an important issue in InN. High resolution X-ray diffraction, combined with atomic force microscopy measurements reveals a drastic decrease in structural quality of the film for Mg concentrations above 1020 cm-3, accompanied with a significant increase in surface roughness. In addition, a decrease of the c-lattice parameter and an increase of the a-lattice parameter are found with increasing Mg concentration. Different contributions to the strain are discussed and it is suggested that the incorporation of Mg leads to a change of growth mode and generation of tensile growth strain. At high Mg concentrations zinc-blende InN inclusions appear which are suggested to originate from higher densities of stacking faults. Infrared spectroscopic ellipsometry analysis shows a reduced LPP-coupling, manifested as a characteristic dip in the IRSE data, and qualitatively different broadening behavior for Mg concentrations between 1.1x1018 cm−3 and 2.9x1019 cm−3 indicate the existence of a p-type conducting bulk InN layer for these Mg concentrations.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85564 (URN)10.1063/1.4871975 (DOI)000335228400017 ()
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2017-12-07Bibliographically approved
7. Effect of impurities on the lattice parameters of InN
Open this publication in new window or tab >>Effect of impurities on the lattice parameters of InN
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We study the effect of the most common impurities and dopants on the lattice parameters of InN by using ab-initio calculations. We have considered both the size and deformation potential effect and report results for H, O, Si andMg. The incorporation of H on interstitial site and substitutional O leads to expansion of the lattice. On the other hand, incorporation of Si or Mg leads to contraction of the lattice. The most pronounced effect is observed for Si. Our results indicate that the increase of the in-plane lattice parameter of Mg doped InN cannot be explained neither by the size nor by the deformation potential effect and suggest that the growth strain is changed in this case.a)Electronic mail: vanya@ifm.liu.se.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85566 (URN)
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2016-08-31Bibliographically approved

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