Some Effects Occurring in Dislocated Tellurium

Dislocation densities as small as 1000 cm−2 are sometimes found in carefully produced single crystals of tellurium, but since the material is very soft a quite mild stress can introduce 106 dislocations/cm2 or more. Dislocation etch pits of sharply geometric shape can be developed on the cleavage (101̄0) planes by the slow attack of sulphuric acid; their planar surfaces correspond to (11̄00), (101̄3), (011̄1), and (01̄11̄) faces. Effects are noted on faces exposed by cleavage at 77°K which suggest that even at this temperature the material can suffer localized plastic damage, for brief etching of such faces produces small flat-bottomed pits; these may be interpreted by supposing that the mild stress of cleavage at 77°K generates shallow dislocation loops. The flat-bottomed pits disappear when a surface layer ≥25 μ is etched away. A marked increase in electron-hole recombination rate is noted in plastically deformed crystals. If the additional recombination occurs through the dislocations themselves, then each has a capture radius of some 4×10−8 cm at 300°K. Dislocated crystals also show more prominent trapping effects at low temperatures than structurally pure samples, and contain additional readily ionizable acceptor sites; these may be derived from the dislocations themselves or from other defects created or activated by plastic flow.