Résumé
We report the results of a series of optical investigations performed on both 6H and 4H epitaxial layers grown at low rate (approximate to 1 mu m h(-1)) in a home-made cold-wall chemical vapor deposition (CVD) reactor. To keep the level of contamination as low as possible, attempts have been made to investigate the origin of residual dopants. In this way, we have found that aluminum comes only from the use of uncoated graphite susceptors. When using a SIC coated susceptor, we have found that the protection is only effective for about ten runs. (C) 1999 Elsevier Science S.A. All rights reserved.