Pipe-diffusion-enriched dislocations and interfaces in SnSe/PbSe heterostructures

Dislocations provide fast diffusion pathways for atoms in semiconductors which can alter compositional profiles of finely tuned heterostructures. We show in model lattice-mismatched IV-VI semiconductor heterostructures of SnSe/PbSe on GaAs substrates that threading dislocations are highly enriched with group IV species of the neighboring layer, with artifacts that reflect the dynamic nature of dislocations when growing dissimilar materials as well as altered bonding properties at the dislocation core. Using atom probe tomography, we characterize one-dimensional nanometer-wide Sn-enriched filaments, which extend downward from SnSe through threading dislocations in the PbSe layer and infiltrate the remote PbSe/GaAs interface through the misfit dislocation network in the short time of growth. Local Sn compositions of only 6%--8% around the dislocations are significantly lower than the 30% Sn expected in bulk PbSe. We estimate the diffusivity of Sn atoms along threading dislocations to be ${10}^{--14}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{--1}$ at 300 \ifmmode^\circ\else\textdegree\fi{}C, approximately three orders of magnitude larger than the lattice diffusivity. In contrast, Pb atoms from PbSe either do not diffuse upward into the orthorhombic SnSe layer or do so only a short distance as one-dimensional filaments before abruptly stopping, likely due to the nature of SnSe on PbSe epitaxy involving lattice mismatch. Beyond compositional anomalies, we detect elevated multiple-atom evaporation events that are spatially correlated to the dislocation, over and above an already high baseline in the matrix. In mixed-bonded IV-VI materials, where previous work has linked such events to the nature of bonding, we find that dislocations show up as distinct from the matrix.