CATHODOLUMINESCENCE STUDIES OF ORIENTED DIAMOND FILMS

Transport properties of highly oriented diamond films have shown a marked improvement over random polycrystalline material. Scanning cathodoluminescence microscopy has been used to determine the type of defects present in oriented films and the way in which they are distributed in the layers. Our results show that undoped films contain significant nitrogen and silicon impurities, which are homogeneously distributed across individual diamond grains. In contrast, boron-doped layers are characterized by intense blue Band A and intrinsic edge emission: these signals arise from localized regions which correspond to grain boundaries. Between these regions, cathodoluminescence emissions are reduced and are similar to the undoped film; however, free-exciton emissions are increased. These observations are discussed in terms of film structure and impurity incorporation, and it is suggested that compensation of boron by nitrogen impurities may explain the absence of green Band A and bound-exciton-related emission for these films.