| 1. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
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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
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:10, s. 103513-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Darakchieva, Vanya, et al.
(författare)
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Lattice parameters, deviations from Vegards rule, and E-2 phonons in InAlN
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:26, s. 261908-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Darakchieva, Vanya, et al.
(författare)
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Role of impurities and dislocations for the unintentional n-type conductivity in InN
- 2009
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Ingår i: PHYSICA B-CONDENSED MATTER. - : Elsevier BV. - 0921-4526. ; 404:22, s. 4476-4481
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Tidskriftsartikel (refereegranskat)abstract
- We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.
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| 4. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
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Strain and compositional analyzes of Al-rich Al1-xInxN alloys grown by MOVPE : impact on the applicability of Vegard's rule
- 2008
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. ; , s. 1859-1862
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Konferensbidrag (refereegranskat)abstract
- We have studied composition and strain in Al1–xInxN films with 0.128≤ x≤ 0.22 grown on GaN-buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x≤ 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub-layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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| 5. |
- Darakchieva, Vanya, et al.
(författare)
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Unravelling the free electron behavior in InN
- 2008
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Ingår i: Optoelectronic and Microelectronic Materials and Devices, 2008. - : IEEE. - 9781424427161 ; , s. 90-97
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Konferensbidrag (refereegranskat)abstract
- Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.
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| 6. |
- Olsson, Fredrik, et al.
(författare)
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Epitaxial lateral overgrowth of InP in micro line and submicro mesh openings
- 2007
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Ingår i: 2007 International Conference on Indium Phosphide and Related Materials. ; , s. 311-314
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Konferensbidrag (refereegranskat)abstract
- Towards achieving a large area of InP on silicon, a study of ELOG of InP on InP has been undertaken on lines with different orientations and with openings that are 100 mu m long and 10 gm wide. This knowledge has been transposed on sub-micro mesh structures. By this method we have obtained 2 gm thick InP on a mesh patterned InP. The layer exhibits room temperature photoluminescence (PL) with a full width half maximum of 24 nm. We propose that this intensity can be increased if nano-sized openings are used.
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| 7. |
- Olsson, Fredrik, et al.
(författare)
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Epitaxial lateral overgrowth of InP on Si from nano-openings : Theoretical and experemintal indication for defect filtering throughout the grown layer
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:9, s. 093112-1-093112-6
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Tidskriftsartikel (refereegranskat)abstract
- We present a model for the filtration of dislocations inside the seed window in epitaxial lateral overgrowth (ELO). We found that, when the additive effects of image and gliding forces exceed the defect line tension force, filtering can occur even in the openings. The model is applied to ELO of InP on Si where the opening size and the thermal stress arising due to the mask and the grown material are taken into account and analyzed. Further, we have also designed the mask patterns in net structures, where the tilting angles of the openings in the nets are chosen in order to take advantage of the filtering in the openings more effectively, and to minimize new defects due to coalescence in the ELO. Photoluminescence intensities of ELO InP on Si and on InP are compared and found to be in qualitative agreement with the model.
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| 8. |
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