| 21. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Photoluminescence study of near-surface GaN/AlN superlattices
- 2008
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 68940G1-
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Konferensbidrag (refereegranskat)abstract
- We report on the emission properties of GaN/AlN superlattices (SLs) grown by metalorganic chemical vapor deposition on a thick GaN layer. Nominally undoped and Si-doped SL structures with the well/barrier thickness ratio 3:1 and different SL periods are investigated. It is found that in these SLs without capping layer the energy position, intensity and linewidth of the emission are determined by the interplay of the built-in polarization field, the depletion field arising from the pinning of the Fermi level at the surface, and the screening of the electric field in the quantum well due to the both the polarization-induced two-dimension electron gas (2DEG) and the photo-generated carriers. A non-uniform equilibrium electron distribution and an electron accumulation at the bottom AlN/GaN interface are evidenced by the observed recombination of the 2DEG with the photo-excited holes occurring below the GaN bandgap.
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| 22. |
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| 23. |
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| 24. |
- Paskova, Tanja, 1961-, et al.
(författare)
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Characterization of mass-transport grown GaN by hydride vapour-phase epitaxy
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 273:1-2, s. 118-128
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive study of the morphological, optical and microstructural properties of mass-transport (MT) and conventionally grown GaN by hydride vapour-phase epitaxy is presented. Spatially resolved techniques have been utilized to reveal in a comparative way, the characteristics of the material grown either in predominant vertical or lateral growth modes. A strong donor-acceptor pair (DAP) emission is observed from the MT regions with a distinctive intensity contrast between the exciton and DAP emission bands from MT and nontransport regions. Secondary ion mass spectroscopy and imaging were employed to investigate the impurity incorporation into different regions. An increase of residual oxygen and aluminium impurity concentrations was found in the MT areas. In addition, positron annihilation spectroscopy showed a strong signal of Ga vacancy clusters in the MT grown material. The increase of the point defect concentrations of both Ga vacancy and oxygen impurity, most likely forming defect complexes, is related to the enhancement of the DAP emission.
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| 25. |
- Paskova, Tanja, 1961-, et al.
(författare)
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Defect and emission distributions in bulk GaN grown in polar and nonpolar directions : a comparative analysis
- 2008
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 68940D1-
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Konferensbidrag (refereegranskat)abstract
- We have investigated bulk GaN material grown by HVPE either in the conventional polar [0001] direction and subsequently sliced with nonpolar surfaces or grown in the nonpolar [11-20] direction. Spatially resolved techniques such as cathodoluminescence imaging and transmission electron microscopy, as well as profile measuring techniques such as positron annihilation spectroscopy and secondary ion mass spectroscopy were employed to directly visualize the extended structural defects, and point defect (impurity and vacancy) distributions along the growth axes. A comparative analysis of the results shows a distinctive difference in the distribution of all kind of defects along the growth axes. A significant decrease in the defect density in material grown along the polar direction, in contrast to the constant behavior of the high defect density in material grown along the nonpolar direction points out the low-defect superior quality of the former material and indicates the preferable way of producing high-quality GaN substrates with nonpolar surfaces.
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| 26. |
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| 27. |
- Paskova, Tanja, 1961-, et al.
(författare)
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Effect of sapphire-substrate thickness on the curvature of thick GaN films grown by hydride vapor phase epitaxy
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:12
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Tidskriftsartikel (refereegranskat)abstract
- The effect of sapphire-substrate thickness on the curvature and stress in thick hydride vapor phase epitaxial GaN films was studied by high-resolution x-ray diffraction at variable temperatures. The curvature was found to have the maximum value for comparable thicknesses of the film and the substrate, while the stress at the film surface decreases with increasing film thickness and increases with increasing substrate thickness, which is in very good agreement with the simulation results. The curvature at the growth temperature was found to be strongly influenced by the value of the intrinsic tensile strain, which is determined by the film/substrate thickness ratio. © 2007 American Institute of Physics.
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| 28. |
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| 29. |
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