Nitrogen-polar growth of AlN on vicinal (0001) sapphire by MOVPE
| Autor: | Pampili, Pietro, Pristovsek, Markus |
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| Rok vydání: | 2024 |
| Předmět: | |
| Zdroj: | J. Appl. Phys. 135, 195303 (2024) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1063/5.0202746 |
| Popis: | 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{\deg} 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{\deg}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 ${\mu}$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{\deg} and 2{\deg} offcut sapphire substrates. Comment: 14 pages, 10 figures |
| Databáze: | arXiv |
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