Charged Impurity Effects on the Deformation of Dislocation-Free Germanium

Acceptor or donor impurities in the concentration range 10¹⁹/cm³ have a marked influence on the deformation behavior of germanium. Gallium raises the upper yield stress σM, while arsenic lowers it, in comparison with the value for undoped germanium. The behavior of σM is a direct consequence of the variation of dislocation velocity with doping. Direct measurements of dislocation velocity show that doping with arsenic raises dislocation velocity, while gallium lowers it, compared with the velocities for intrinsic germanium. The change in velocity or σM is not observed until the impurity concentration is comparable to the intrinsic carrier concentration at the test temperature. Neutral impurities in the range of 10¹⁹/cm³ do not influence either σM or dislocation velocity. The net change in the σM or velocity parameters over the intrinsic values increases with decreasing temperature of test. From the dependence of dislocation velocity and maximum stress on impurity concentration, it appears that these parameters which control the deformation behavior are directly related to the electronic properties of germanium.