Nitride-based devices are reaching maturity. The next development stage could start by using AlN wafers as substrate. First companies are going to commercialize this material. Nevertheless, there are some open issues to be solved on the way to success. Basically, it is still a problem to prepare surfaces without damage layer. A solution of this problem is important not only for device application but also for seeding in bulk crystal growth.

This contribution will show in detail the structural consequences of different AlN surface preparation methods on the quality of AlN bulk crystals grown on it. Moreover, the practical effect on the overall growth concept will be discussed taking into account the cost-benefit ratio.

For this approach c-oriented seeds were prepared from spontaneously grown AlN crystals by sawing, lapping, and mechanical polishing of the N-polar (000-1) face using 2 µm diamond slurry. The seeds were further processed by chemical etching, thermal annealing, Ar-ion milling or chemical-mechanical planarization (CMP) to achieve structurally perfect surfaces. After that, the finished seeds were used in short time growth experiments at constant growth conditions (T=2150 °C, p=600 mbar N₂, t=1 h, grown layer thickness ~200 µm). All samples have been characterized before and after growth by X-ray rocking curve measurement, atomic force microscopy, and Nomarski microscopy.

In contrast to the well known thermal reconstruction of mechanically treated SiC surfaces, AlN does not show a comparable behavior. Maximum FWHM values of 60 arcsec have been found for Ar-ion milling and mechanical polishing. Thermal annealing and CMP led to the best FWHM values of about 15 arcsec. Large-area layer growth via well defined step flow was only observed after chemical etching or CMP finishing.

A detailed analysis of the defect situation of AlN bulk crystals grown on differently finished seeds shows that due to its enormous efforts in preparation time, CMP finishing is not the most cost-effective seed preparation method. The findings are compared to homoepitaxial MOCVD deposition results on AlN wafers with different surface finish.

• 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/29515 must be provided.

1. Growth and properties of bulk single crystals of selected transparent semiconducting oxides (TSOs): β-Ga₂O₃, In₂O₃ and SnO₂
2. Sublimation growth of AlN crystals on {111} TaC seeds
3. XPS and AFM investigations of buffer layer between Si(100) and 3C-SiC, created by interaction with C₂H₂