The electrical properties of dislocations in semiconductors

According to the theory of Read, closely spaced acceptor sites occur at dangling bonds along dislocations in semiconductors and lead to the formation of space-charge tubes which scatter electrons. In order to test Read's theory, parallel arrays of dislocations have been introduced by plastic bending and extensive electrical and galvanomagnetic measurements have been made on n-type germanium crystals. The experimental results are not in agreement with Read's theory; however, it is shown that Read's basic model is applicable but it must be modified by the assumption of non-specular electron scattering at the edges of the space-charge tubes—the electrical and galvanomagnetic consequences of the theory plus modification are worked out and good agreement with experiments obtained. The following quantities are derived: conductivity (σ), Hall constant (R), and magnetoresistance (MR) for current both parallel (‖) and perpendicular (⊥) to the long axis of the tubes with magnetic field (H) at right angles to the current. The quantities R, σ_‖ and σ_⊥ were measured versus temperature from 78°K to 300°K and MR was measured at 78°K as a function of the angle between H and the normal to the neutral plane (N). It was found that the variation of the electrical properties in the sample, particularly along the N direction, is so great that to obtain valid data one must use small samples cut from bent crystals; data are presented for whole samples, as well as small samples, in order to illustrate this effect. The dislocation acceptor level in n-type germanium is found to lie at ～0.50 ev below the conduction band edge. By using the above theory one can determine values of the dislocation density (N) from the result of electrical measurements on semiconductors; this was done in order to determine, on deformed n-type germanium, variations in N from region to region of bent samples as a function of temperature and time of deformation and annealing. In addition, other experiments were performed on plastically bent indium antimonide; it was found that the electrical effects of dislocations, although considerably different from those in germanium, can also be explained by the theory presented here.