Interfacial properties of AlN grown on m-plane sapphire by plasma-assisted MBE have been investigated in the context of achieving high-quality GaN/AlN heterostructures with reduced internal polarization. We investigate ~200 nm-thick epilayers deposited either directly on m-sapphire or after 30 min of sapphire nitridation at the growth temperature (~720^oC). The active nitrogen flux was tuned to obtain a growth rate of 0.3 ML/s (~280 nm/h) under Al-rich conditions. AlN was synthesized under a III/V ratio of ~0.95 to achieve two-dimensional layers. High-resolution transmission electron microscopy (HRTEM) identified the dominant film orientation as (11-22) semipolar, with the AlN basal planes aligned parallel to the (1-104) plane of sapphire. This result is consistent with in situ RHEED observations and x-ray diffraction studies. An interfacial zone comprising additional AlN nanocrystals with the m-plane orientation was observed. In the case of growth without nitridation, the average m-plane nanocrystal size was 30 nm, but it was increased significantly in the case of nitridated sapphire, with some nonpolar crystallites exceeding 100 nm. A good epitaxial relationship with the substrate was observed both for the case of semipolar as well as for nonpolar AlN, comprising patches of regularly spaced misfit dislocations which were characterized using circuit mapping. However, the periodicity of the interfacial structure was perturbed by interfacial roughness comprising nanofacets on the (1-104), (1-10-2) and {1-210} sapphire planes. Often these nanofacets were found arranged in v-shaped formations, and were correlated to the introduction of misoriented nanocrystals. The nonpolar and semipolar orientations are interrelated by a 90^o<11-20> relative rotation leading to the formation of low-energy grain boundaries between them.

Acknowledgement: Work supported under the 7th European Framework Project DOTSENSE (Grant No. STREP 224212).

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/18428 must be provided.

1. Plasma-Assisted MBE of III-nitride semiconductors: From two-dimensional layers to nanostructures
2. Epitaxial growth on porous substrates
3. Epitaxial growth on porous substrates of III-V semiconductors
4. Inter-subband optics at 1.55 µm in GaN-based nanostructures - Physics and applications
5. Morphological, structural and optical properties of high-quality InN on GaN-template films deposited by RF sputtering
6. The microstructure and properties of InN layers
7. Non-linear absorption measurements of InN/InGaN multiple-quantum-wells structures at 1.5 µm using the Z-Scan method
8. Electron microscopy of InGaN nanorods spontaneously grown on Si (111) substrates
9. Microstructure of InN grown on Si (111) by plasma-assisted MBE using a double buffer layer
10. The (10-10)/(2-1-12) grain boundary in nonpolar GaN:Atomic structure and influence on defect introduction
11. Structural models of GaN quantum dots in semipolar AlN
12. Structural properties of quaternary InAlGaN MQWs grown by plasma-assisted MBE