Strain relaxation and dislocation patterning in PbTe/PbSe (0 0 1) lattice-mismatched heteroepitaxy

Strain relaxation and dislocation formation for PbTe molecular beam epitaxy on 5.2% lattice-mismatched (0 0 1) PbSe substrates is studied using in situ reflection high-energy electron diffraction and scanning tunneling microscopy. For layers exceeding 1 monolayer (ML) in thickness misfit dislocations are formed along the fourfold in-plane 〈1 1 0〉 directions within the layer/substrate interface. These misfit dislocations are of pure edge type with a 12 [1 1 0] type Burgers vector parallel to the interface. At layers exceeding about 5 ML, remarkably regular square arrays of misfit dislocations are formed with a dislocation spacing of 10 nm and a high uniformity of the spacings of ±12%. This is due to the mutual lateral elastic repulsion between the dislocations as well as the fact that the (0 0 1) interface is a preferred dislocation glide plane in the lead salt compounds.