Deep-UV nitride-based optoelectronic devices mostly base on layers grown by metal organic vapor phase epitaxy (MOVPE). Pseudomorphic growth on AlN for UV-C and homoepitaxial growth on GaN for the near UV-A region has been successfully applied for UV-LEDs. However, the lack of suitable substrates for applications in the UV-B region between 280 nm and 360 nm requiring Al_xGa_1-xN compositions around x = 0.5 still limits further progress in this field.

Suitable pseudosubstrates in this range thus are of great interest. To realize such pseudosubstrates, a hot-wall reactor was adapted for growth of Al_xGa_1-xN-layers on sapphire by hydride vapor phase epitaxy (HVPE). By varying the composition, the UV LEDs covering the complete UV-region can be grown pseudomorphic on transparent pseuodsubstrates. Patterned sapphire substrates (PSS) were applied to manage the strain in the thick AlGaN layers. Different substrate patterns like stripes and hexagonal cells were used to minimize crack formation. The use of a thin AlN seeding layer was found to improve the composition homogeneity and morphology of the subsequently grown Al_xGa_1-xN layer.

Parasitic growth of AlGaN on the sidewalls of the patterns on the sapphire substrates was found to be determined by the orientation of the {1-100} sapphire facets. Propagation of these parasitic domains to the growing surface leads to distortion that hinders the use as a substrate. In this work, growth studies comprising variation of reactor pressure between 200 mbar and 800 mbar, V/III-ratios between 5 and 40, carrier gas composition and growth temperature were carried out on (0001) oriented PSS to determine conditions for optimum coalescence of AlGaN layers at different compositions.

Coalesced layers in the composition range between Al_0.3Ga_0.7N and Al_0.5Ga_0.5N with thicknesses of 20 µm to 50 µm were successfully grown at growth rates of 10 µm/h to 20 µm/h. Growth results and recent progress will be discussed.

This work was supported by the German Research Foundation in the project RI1224/1-1.

• 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/30225 must be provided.

1. Effect of carrier gas on the optical and structural properties of GaN