Misfit dislocations between boron‐doped homoepitaxial films and diamond substrates studied by X‐ray diffraction topography

Boron‐doped diamond epilayers grown over diamond substrates have a different lattice parameter from the undoped diamond substrate, which introduces a lattice mismatch between substrates and epilayers. This can generate misfit dislocations at the interface when the epilayer reaches a certain critical thickness. For a boron concentration of about 1 × 10 20  atoms cm −3 , the calculated lattice mismatch is about 1.3 × 10 −4 and the critical thickness is of the order of 0.2 µm. In the epilayers studied, grown over high‐pressure high‐temperature 1b (001) substrates, the lattice mismatch and the epilayer thickness are 1.3 × 10 −4 , 30 µm and 6.5 × 10 −4 , 4 µm. The epitaxial strain has been relaxed by the generation of two orthogonal misfit dislocation systems. These are edge dislocations parallel to the [100] and [010] directions with a Burgers vector making an angle of 45° with the (001) interface. Their lengths are 40–60 µm and their lineal densities 200–240 cm −1 . They are heterogeneously nucleated, propagated in the form of half‐loops along the slip planes (011) and (101), respectively, and related mainly to ⟨111⟩ threading dislocations emerging from octahedral growth sectors. Another kind of half‐loop originates from the substrate growth sector boundaries. Limited X‐ray topography has been demonstrated to be a very useful tool to discriminate between substrate and epilayer defects when their lattice mismatch is not sufficient to separate such defects in conventional Lang topography. X‐ray section topography has confirmed the presence of [001] dislocations in the epilayers and the misfit half‐loops related to threading dislocations propagating from the interface.