An Electromechanical Effect in Semiconductors

Abstract

The resistance of semiconducting crystals to indentation deformation has been found to be lowered significantly (up to 60%) by the simultaneous presence of a small potential (0.05 to 10 V) between the indenter and the crystal surface. This electromechanical effect appears to be confined to the plastic strain region of a surface layer of material 2–3 μ deep. A large body of experiments of varied nature have established that the effect is real and not spurious. Similar effects are observed in a number of different semiconductors (Ge, Si, InSb and SiC) but not in metals or ionic crystals. The effect disappears at elevated temperatures but becomes enhanced below room temperature. It is not sensitive to the type of current carrier. The roles of surface preparation, crystallographic orientation, kind and concentration of charge carrier, geometry, and time have also been examined. Other and possibly related experiments show significant enhancement of the surface photovoltage (the Dember potential) by a longitudinal electric field. All of these experiments are extensively documented and discussed but no satisfactory model or mechanism has yet been conceived.