Al- and N-polar AlN layers grown on c-plane sapphire substrates by modified flow-modulation MOCVD

M. Takeuchi, H. Shimizu, R. Kajitani, K. Kawasaki, T. Kinoshita, K. Takada, H. Murakami, Y. Kumagai, A. Koukitu, T. Koyama, S. F. Chichibu, Y. Aoyagi

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67 Citations (Scopus)


We report the growth of N- and Al-polar AlN layers on c-plane sapphire by flow-modulation MOCVD (FM-MOCVD) with some flow sequence modifications. Surface polarities were decided by pre-treatment for sapphire substrates prior to AlN seeding layer growth. Low-temperature nitridation (620 °C) was done for the N-polar samples, and no-nitridation was done for the Al-polar. To avoid strong vapor-phase reaction between TMA and NH3 and to enhance the surface migration of Al atoms, FM-MOCVD technique was used. The flow sequence was modified for optimization of each N- and Al-polar growth. The surface features were completely different between the N- and Al-polar AlN layers in atomic force microscope images. The former had domed structures and the latter atomic steps. The dislocation densities were counted from plane-view transmission microscope images to be about 3×1010 cm-2 for the N-polar layer and about 1×1010 cm-2 for the Al-polar. Secondary-ion mass spectroscopy measurement revealed oxygen- and carbon-incorporation into the layers. Band-edge and impurity-related emissions were observed from only the Al-polar layer by room-temperature cathodoluminescence, whereas the N-polar one did not emit.

Original languageEnglish
Pages (from-to)360-365
Number of pages6
JournalJournal of Crystal Growth
Issue number2 SPEC. ISS.
Publication statusPublished - 2007 Jul 15


  • A1. Crystal morphology
  • A1. High-resolution X-ray diffraction
  • A3. Low-pressure metalorganic vapor-phase epitaxy
  • B1. Nitrides
  • B2. Aluminum nitrides
  • B2. Semiconductor aluminum compounds


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