Microstructural development of directionally solidified Hg1−xZnxSe alloys

Abstract

Hg1−xZnxSe alloys have been studied as an alternative to Hg1−xCdxTe for the detection of electromagnetic radiation, because the shorter ZnSe and HgSe bonds have been predicted to improve lattice stability. Several ingots with x=0.1 were directionally solidified using a modified Bridgman-Stockbarger method; one was grown in an applied magnetic field, which greatly reduced radial compositional variations. A method was developed to reduce wetting. This, combined with the convex liquid-solid interface shape, produced boules that were single crystalline after growing ∼3.5 cm. Observed surface features indicated ampoule wetting was eliminated using a graphite getter. Microstructural characteristics were greatly improved over HgCdTe alloys. In six boules, a total of only one twin was observed. A method for polishing and producing dislocation etch pits was developed for these alloys, revealing dislocation etch pit densities one to two orders of magnitude less than HgTe-based alloys. A kink in the thermal profile during processing of one boule generated more dislocations than did lattice mismatch due to compositional variations. This alloy has improved microstructural properties and resistance to dislocation formation compared with similar II–VI alloys.