| 1. |
- Roder, C., et al.
(författare)
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Strain in a-plane GaN layers grown on r-plane sapphire substrates
- 2006
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Ingår i: Physica Status Solidi (A) Applications and Materials. - : Wiley. - 1862-6300. ; 203:7, s. 1672-1675
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Tidskriftsartikel (refereegranskat)abstract
- The strain in a-plane GaN layers of different thickness grown on r-plane sapphire substrates by hydride vapor phase epitaxy was studied by X-ray diffraction. The layers are found to be under compression in the growth plane and under tension in the growth direction. Therefore, the symmetry of the GaN unit cell is no longer hexagonal but orthorhombic. With increasing layer thickness the strain relaxes and the curvature of the wafer increases. Wafer bending is proposed to be the major strain relaxation mechanism. The anisotropic in-plane strain relaxation is attributed to the elastic and thermal anisotropy of GaN and sapphire. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
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| 2. |
- Roder, C., et al.
(författare)
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Stress and wafer bending of a -plane GaN layers on r -plane sapphire substrates
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:10
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Tidskriftsartikel (refereegranskat)abstract
- The stress and wafer bending of (11 2- 0) a -plane GaN layers of different thicknesses grown on (1 1- 02) r -plane sapphire substrates by hydride vapor phase epitaxy were studied by high-resolution x-ray diffraction and photoluminescence and photoreflectance spectroscopies. The layers are found to be under compression in the growth plane and under tension in the growth direction. The elastic and thermal anisotropies of the GaN and the sapphire crystal result in an in-plane stress and a wafer curvature, both of which are different in the two in-plane directions parallel and perpendicular to the GaN c axis. The GaN unit cell is no longer hexagonal but orthorhombic. The stress relaxes with increasing GaN layer thickness while the curvature of the wafer increases. Different stress relief mechanisms are considered, and the stresses in the layer and the curvature of the wafer are calculated using standard models on wafer bending. The results suggest that the wafer bending is the dominant stress relief mechanism. In addition, the redshift of the near-band-edge photoluminescence and the free exciton photoreflectance peaks with increasing layer thickness is correlated with the strain data determined by x-ray diffraction. © 2006 American Institute of Physics.
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| 3. |
- Litwinski, C., et al.
(författare)
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Photophysical properties of gallium hydroxyl tetratolylporphyrin and 13(2)-demethoxycarbonyl-(gallium hydroxyl)-methyl-pheophorbide alpha
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 418:4-6, s. 355-358
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Tidskriftsartikel (refereegranskat)abstract
- Two metal tetrapyrroles containing gallium, gallium hydroxyl tetratolylporphyrin and 13(2)-demethoxycarbonyl-(gallium hydroxyl)methyl pheophorbide a (Ga-(OH)-chlorin), were synthesized from their respective free bases using Ga(III)-acetylacetonate in a phenol melt. Their photophysical properties were investigated and the quantum yields of different monomolecular deactivation processes were determined. For Ga-(OH)-porphyrin S-2-fluorescence was observed and quantified. In contrast. for Ga-(OH)-chlorin no S-2-fluorescence was observed. Both compounds should be useful as efficient photosensitizers in photodynamic therapy. (c) 2005 Elsevier B.V. All rights reserved.
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