Growth and fundamental properties of SiGe bulk crystals

Abstract

Czochralski growth of bulk crystals of Si x Ge 1− x alloys and their fundamental properties were reported. Full single crystals of large size, larger than 25 mm in diameter and longer than 40 mm in length, were obtained for the alloys of composition 0 < x < 0.15 and 0.73 < x < 1 . Single crystals of SiGe alloys ( 0.80 < x < 1 ) heavily doped with electrically active impurities with a concentration up to 10 20 cm −3 were also successfully obtained. The velocity for single crystal growth in the whole composition range was evaluated and discussed in terms of the occurrence of the constitutional supercooling. The study on the local atomic structure shows that most of the strain in SiGe alloys is accommodated by changes of both the bond length and bond angle. Electrical and thermal conductivities show the minima at the intermediate composition at x = 0.5 – 0.7 , implying the alloy scattering due to a distortion of the crystal lattice. Oxygen impurities, incorporating from a quartz crucible, occupy preferentially a bond-center site between Si atoms to make an Si–O–Si quasi-molecule. The mechanical strength of the alloys becomes temperature insensitive at elevated temperatures and depends on the composition, being proportional to x(1– x) over the whole composition range, which may be originating in the built-in stress fields related to microscopic fluctuation of alloy composition and the dynamic interaction between dislocations and solute atoms.