Thermal mismatch strain relaxation of epitaxial IV–VI/Si(111) structures on multiple temperature cycling to cryogenic temperatures

Abstract

Epitaxial narrow gap PbSe is grown by MBE (molecular beam epitaxy) onto Si(111) substrates with the aid of a BaF 2/CaF 2 buffer layer. The tensile strain which builds up on cool-down after growth due to the thermal expansion mismatch is relaxed by creation and movement of misfit dislocations in the main glide system. The thermal mismatch strain relaxes even at liquid-nitrogen temperature, and after many temperature cycles between room temperature and 77 K. Even after more than 1000 such thermal cycles, no substantial number of new threading dislocations forms according to the observed widths (≈ 150 arc sec for 3 μm thick layers) of the X-ray rocking curves. Some strain hardening is observed. Plastic relaxation occurs at each cycle, the cumulative plastic deformation after 1400 thermal cycles is as high as 400%. The strain is relaxed mainly by the threading ends of misfit dislocations, which move back and forth on each cycle, this despite a considerable density (≈ 10 8 cm −2) of grown in sessile dislocations.