| 11. |
- Choubina, Tatiana, 1950-, et al.
(författare)
-
Slow light in GaN
- 2008
-
Ingår i: 16th Int. Symp. ¿Nanostructures: Physics and Technology,2008. ; , s. 257-
-
Konferensbidrag (refereegranskat)
|
|
| 12. |
- Choubina, Tatiana, 1950-, et al.
(författare)
-
The slow light in GaN
- 2008
-
Ingår i: ICPS2008,2008. ; , s. 647-
-
Konferensbidrag (refereegranskat)
|
|
| 13. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
Anisotropic strain and phonon deformation potentials in GaN
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195217-
-
Tidskriftsartikel (refereegranskat)abstract
- We report optical phonon frequency studies in anisotropically strained c -plane- and a -plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E1 (TO), E1 (LO), and E2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E1 (TO), c E1 (LO), and c E2 are determined. A distinct correlation between anisotropic strain and the A1 (TO) and E1 (LO) frequencies of a -plane GaN films reveals the a A1 (TO), b A1 (TO), a E1 (LO), and b E1 (LO) phonon deformation potentials. The a A1 (TO) and b A1 (TO) are found to be in very good agreement with previous results from Raman experiments. Our a A1 (TO) and a E1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations, while b A1 (TO) and b E1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented. © 2007 The American Physical Society.
|
|
| 14. |
|
|
| 15. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
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
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:10, s. 103513-
-
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.
|
|
| 16. |
|
|
| 17. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
On the lattice parameters of GaN
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:3, s. 031911-
-
Tidskriftsartikel (refereegranskat)abstract
- The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy (HVPE) on (0001) sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c=5.18523 Å and a=3.18926 Å, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested. © 2007 American Institute of Physics.
|
|
| 18. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
Phonon mode behavior in strained wurtzite AlN/GaN superlattices
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:11, s. 115329-
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied phonons in AlN/GaN superlattices with different periods but a constant well-to-barrier ratio using a combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The strain evolution in the superlattice structures is assessed by high-resolution x-ray diffraction and reciprocal space mapping. We have identified E1(TO), A 1(LO) and E2 localized, and E1(LO) and A 1(TO) delocalized superlattice modes. The dependencies of their frequencies on in-plane strain are analyzed and discussed, and the strain-free frequencies of the superlattice modes are estimated. A good agreement between theory and experiment is found in the case of GaN localized modes, while large deviations between theoretically estimated and experimentally determined frequency shifts are observed for the AlN localized modes. The delocalization effect on the A1(TO) and E1(LO) phonons, as well as the free-carrier effect on the E1(LO) phonon are also discussed. ©2005 The American Physical Society.
|
|
| 19. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
Phonons in strained AlGaN/GaN superlattices
- 2007
-
Ingår i: 6th International Symposium on Blue Laser and Light Emitting Diodes,2006. - Physica Status Solidi, vol C4 : WILEYVCH Verlag GmbH & Co. KGaA. ; , s. 170-
-
Konferensbidrag (refereegranskat)
|
|
| 20. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
Strain and compositional analyzes of Al-rich Al1-xInxN alloys grown by MOVPE : impact on the applicability of Vegard's rule
- 2008
-
Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. ; , s. 1859-1862
-
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)
|
|
