| 1. |
- Paskova, Tanja, et al.
(författare)
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Effect of Si doping of metalorganic chemical vapor deposition-GaN templates on the defect arrangement in hydride vapor phase epitaxy-GaN overgrown layers
- 2000
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:10, s. 5729-5732
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Tidskriftsartikel (refereegranskat)abstract
- Two different types of dislocation arrangements have been observed in hydride vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor deposition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a network of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution result in essentially different surface morphologies, respectively: (i) low-angle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislocations. The Si doping of the GaN templates was found to enhance defect interaction in the templates and to enable a reduction of the dislocation density in the overgrown thick GaN films, although it does not lead to an improvement of the overall structural properties of the material. (C) 2000 American Institute of Physics. [S0021-8979(00)08422-X].
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| 2. |
- Paskova, Tanja, et al.
(författare)
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Hydride vapour phase homoepitaxial growth of GaN on MOCVD-grown 'templates'
- 2000
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Konferensbidrag (refereegranskat)abstract
- We report on an improved quality of thick HVPE-GaN grown on MOCVD-GaN 'template' layers compared to the material grown directly on sapphire. The film-substrate interface revealed by cathodoluminescence measurements shows an absence of highly doped columnar structures which are typically present in thick HVPE-GaN films grown directly on sapphire. This improved structure results in a reduction of two orders of magnitude of the free carrier concentration from Hall measurements. It was found that the structure, morphology, electrical and optical properties of homoepitaxial thick GaN layers grown by HVPE were strongly influenced by the properties of the MOCVD-GaN 'template'. Additionally the effect of Si doping of the GaN buffer layers on the HVPE-GaN properties was analysed.
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| 3. |
- Valcheva, E., et al.
(författare)
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Elimination of nonuniformities in thick GaN films using metalorganic chemical vapor deposited GaN templates
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:12, s. 6011-6016
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Tidskriftsartikel (refereegranskat)abstract
- Thick hydride vapor phase epitaxial GaN layers are grown on metalorganic chemical vapor deposited GaN template layers as well as directly on sapphire, with the aim of investigating the effect of the template on the strain relaxation and spatial distribution of free carriers in the overgrown GaN films. Spatially resolved cross-sectional micro-Raman spectroscopy, cathodoluminescence, and transmission electron microscopy show improved crystalline quality for growth on metalorganic chemical vapor deposited GaN templates. The highly doped and highly defective near-substrate layer composed of columnar domains, typically present in hydride vapor phase epitaxial GaN films grown directly on sapphire, is absent in the layers grown on templates. Consequently, this results in elimination of the nonuniformities of free electron distribution, a lower residual free carrier concentration (<1017 cm-3), and improved strain relaxation. © 2001 American Institute of Physics.
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| 4. |
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| 5. |
- Valcheva, E., et al.
(författare)
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Impact of MOCVD-GaN 'templates' on the spatial non-uniformities of strain and doping distribution in hydride vapour phase epitaxial GaN
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 35-38
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Tidskriftsartikel (refereegranskat)abstract
- Thick HVPE-GaN layers are grown on Si-doped and undoped MOCVD-GaN 'template' layers as well as directly on sapphire, with the aim to investigate the effect of the MOCVD template on the strain relaxation and spatial distribution of free carriers in the overgrown HVPE films. Spatially resolved cross-sectional micro-Raman measurements, cathodoluminescence and transmission electron microscopy show improved crystalline quality resulting in elimination of the non-uniformities of electron distribution, a low free carrier concentration (< 1017 cm-3) as well as a significant strain relaxation effect. © 2001 Elsevier Science B.V.
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