Propagation of threading dislocations in heteroepitaxial diamond films with (111) orientation and their role in the formation of intrinsic stress

摘要

In the present study, systematic correlations were revealed between the propagation direction of threading dislocations, the off-axis growth conditions, and the stress state of heteroepitaxial diamond on Ir/YSZ/Si(111). Measurements of the strain tensor ε by X-ray diffraction and the subsequent calculation of the tensor of intrinsic stress σ showed stress-free samples as well as symmetric biaxial stress states for on-axis samples. Transmission electron microscopy (TEM) lamellas were prepared for plan-view studies along the [111] direction and for cross-section investigations along the [112] and [110] zone axes. For samples grown on-axis with parameters which avoid the formation of intrinsic stress, the majority of dislocations have line vectors clearly aligned along [111]. A sudden change to conditions that promote stress formation is correlated with an abrupt bending of the dislocations away from [111]. This behaviour is in nice agreement with the predictions of a model that attributes formation of intrinsic stress to an effective climb of dislocations. Further growth experiments under off-axis conditions revealed the generation of stress states with pronounced in-plane anisotropy of several Gigapascal. Their formation is attributed to the combined action of two basic processes, i.e., the step flow driven dislocation tilting and the temperature dependent effective climb of dislocations. Again, our interpretation is supported by the dislocation propagation derived from TEM observations.