Nitrogen-polar growth of AlN on vicinal (0001) sapphire by MOVPE
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arXiv
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| Formato: | Preprint |
| Publicado: |
2024
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| author | Pampili, Pietro Pristovsek, Markus |
| author_facet | Pampili, Pietro Pristovsek, Markus |
| contents | We report about metalorganic vapour phase epitaxy of smooth nitrogen-polar AlN templates on vicinal (0001) sapphire substrates. The influence of V/III ratio, growth temperature, growth rate, as well as sapphire-nitridation time and temperature were studied. With 4° offcut sapphire, step-flow growth was possible only with V/III ratios below 2. However, optimal V/III ratio required precise adjustment, possibly dependent on reactor history and geometry. A rather narrow temperature window of less than 40°C existed for smooth surface morphology. Reducing the temperature affected adatom mobility, eventually disrupting step-flow growth; increasing the temperature favoured the formation of high-aspect-ratio defects on the epilayer. A low thermal-budget nitridation step with a short nitridation time of 15 s proved to be effective in controlling polarity without inducing excessive surface damage on the sapphire substrate. Growth rate also influenced surface morphology, with an increase in RMS roughness and step-bouncing for faster growths; however, at growth rates of 1.4 $μ$m/h or higher step-flow growth could no longer form. Finally, we developed a V/III ratio fine-tuning procedure, whereby the reactor-specific value that induces optimal growth is inferred by growth-rate variations. With this method, N polar AlN templates with sub-nanometre RMS roughness were demonstrated for both 4° and 2° offcut sapphire substrates. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2402_03180 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Nitrogen-polar growth of AlN on vicinal (0001) sapphire by MOVPE Pampili, Pietro Pristovsek, Markus Materials Science Applied Physics We report about metalorganic vapour phase epitaxy of smooth nitrogen-polar AlN templates on vicinal (0001) sapphire substrates. The influence of V/III ratio, growth temperature, growth rate, as well as sapphire-nitridation time and temperature were studied. With 4° offcut sapphire, step-flow growth was possible only with V/III ratios below 2. However, optimal V/III ratio required precise adjustment, possibly dependent on reactor history and geometry. A rather narrow temperature window of less than 40°C existed for smooth surface morphology. Reducing the temperature affected adatom mobility, eventually disrupting step-flow growth; increasing the temperature favoured the formation of high-aspect-ratio defects on the epilayer. A low thermal-budget nitridation step with a short nitridation time of 15 s proved to be effective in controlling polarity without inducing excessive surface damage on the sapphire substrate. Growth rate also influenced surface morphology, with an increase in RMS roughness and step-bouncing for faster growths; however, at growth rates of 1.4 $μ$m/h or higher step-flow growth could no longer form. Finally, we developed a V/III ratio fine-tuning procedure, whereby the reactor-specific value that induces optimal growth is inferred by growth-rate variations. With this method, N polar AlN templates with sub-nanometre RMS roughness were demonstrated for both 4° and 2° offcut sapphire substrates. |
| title | Nitrogen-polar growth of AlN on vicinal (0001) sapphire by MOVPE |
| topic | Materials Science Applied Physics |
| url | https://arxiv.org/abs/2402.03180 |