Propagation and annihilation of threading dislocations during off-axis growth of heteroepitaxial diamond films

Threading dislocations in heteroepitaxial diamond films deposited on Ir/YSZ/Si(001) substrates with an off-axis angle of 4 towards [100] have been studied by cross-section transmission electron microscopy using the weak beam dark-field (WBDF) technique for Burgers vector identification and large-angle convergent beam electron diffraction (LACBED) in order to facilitate a precise crystallographic determination of the local growth surface. Close to the diamond/iridium interface the films contain a high density of dislocations of both 90 and 45 types. Within the first micron of film growth their density decreases drastically by annihilation or mutual interaction resulting in a preference for 45 type dislocations. Vicinal growth surfaces cause a tilt of the dislocation line vector away from the crystallographic [001] axis in the step-flow direction. Tilting is influenced by gas phase impurities. With 100 ppm nitrogen in the feed gas, step bunching produces a structured surface consisting of an alternating sequence of terraces with reduced off-axis angle crystallographically close to (001) and risers with increased off angle. The dislocations with lines close to [001] during terrace growth abruptly tilt by more than 20 at the transition to riser growth. The appearance of several discrete tilt angles during nitrogen free growth without pronounced step bunching is attributed to the corresponding Burgers vectors which cause either effective climb for the lower angles or effective glide for the higher ones. The present observations are of high relevance for improved strategies towards a further dislocation density reduction and an efficient control of intrinsic stress formation. (C) 2016 Elsevier B.V. All rights reserved.