DISLOCATION ETCH PITS IN LPE-GROWN PB1-XSNXTE (LTT) HETEROSTRUCTURES

Heterostructures of Pb1-xSnxTe grown by LPE were studied by an etch technique. A consistent pattern appeared in which the lattice-mismatched heterostructure exhibits a high etch-pit density (?1×107 cm-2) at the interface and in the heteroepitaxial layer. The greater the lattice mismatch, the higher is the defect density. A mismatch as small as ∼2×10-4 is already sufficient to generate defects at the interface. A low-etch-pit-density substrate does not moderate the defect performance in the interface and the epilayer. Homostructures show preservation of dislocation etch-pit density throughout the whole thickness of the epilayer without a substantial decrease, contrary to other reported results. Some differences were found with respect to the opposite heterostructures Pb1-xSnxTe/Pb 1-ySnyTe and Pb1-ySnyTe/Pb 1-xSnxTe. A high growth temperature (?600 °C) causes a decrease in etch-pit density and the disappearance of some defects. Enhanced nucleation, annealing of dislocations, and bulk diffusion are believed to take place at the high temperature. Some defects disappear and others diminish upon slow cooling, but the basic mismatch character remains.