THERMAL MISMATCH STRAIN RELAXATION OF EPITAXIAL IV-VI SI(111) STRUCTURES ON MULTIPLE TEMPERATURE CYCLING TO CRYOGENIC TEMPERATURES/

Epitaxial narrow gap PbSe is grown by MBE (molecular beam epitaxy) ont o Si(lll) substrates with the aid of a BaF2/CaF2 buffer layer. The ten sile strain which builds up on cool-down after growth due to the therm al expansion mismatch is relaxed by creation and movement of misfit di slocations in the main glide system. The thermal mismatch strain relax es even at liquid-nitrogen temperature, and after many temperature cyc les between room temperature and 77 K. Even after more than 1000 such thermal cycles, no substantial number of new threading dislocations fo rms according to the observed widths (approximate to 150 are sec for 3 mu m 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 (approximate to 10(8) cm(-2)) of grown in sessile dislocations .