Doping effects on indentation plasticity and fracture in germanium

Abstract

Vickers micro-indentation tests have been performed in the temperature range 20 to 420° C on the {0 0 1} surfaces of germanium crystals of three different dopings: “intrinsic”, heavily doped p-type and heavily doped n-type. Indentation sizes, dislocation rosette sizes and median/radial crack lengths were measured. Rosette sizes were found to depend strongly on doping, being respectively larger and smaller than in intrinsic material for n-type and p-type specimens, over the temperature range 20 to 420° C. This result correlates well with dislocation velocity measurements in germanium. Indentation size (hardness) was found to vary with doping above ~ 300° C, hardness increasing from n-type through intrinsic to p-type material. Crack lengths, as a function of temperature, showed a sharp transition (to much shorter crack lengths) at a well-defined temperature; this ductile/brittle transition temperature was found to depend on doping, being lowest for n-type (~ 290° C) and highest for p-type (~ 400° C). This is the first observation of a relation between a fracture parameter and bulk electronic doping.