XVI. Scattering of electrons by charged dislocations in semiconductors

Abstract

Abstract Experiments suggest that dislocations in germanium act as rows of closely spaced acceptor centres. In n-type material a dislocation accepts electrons and becomes a line of negative charge surrounded by a cylindrical region of fixed positive space charge. An array of parallel dislocations will have relatively little effect on electron mobility parallel to the dislocations. The mobility normal to the dislocations will be reduced because: (1) The space charge cylinders deflect electrons and scatter the electron momentum normal to the dislocations; this reduces mean free time. Dislocation scattering is characterized by a mean free path that depends on direction. (2) Even when the dislocations are far enough apart that the mean free time is not affected, the macroscopic mobility may be reduced because the electrons cannot drift parallel to the applied field; instead they follow curved paths winding between the space charge cylinders (which in typical cases are the order of a micron in diameter). This ...