Calculations were made of the Coulomb and piezoelectric fields that were associated with dislocations, in order to explain their effect upon the transport properties of junctions. It was noted that dislocation electric fields could affect transport since they were superposed upon the built-in and applied junction fields which controlled the currents. The screening of the fields in the neutral region was consistent with the small effect of the dislocations upon responsivity. Their effect within the space charge region was found to be significant, and was consistent with the non-linear dependence of performance upon dislocation density. The piezoelectric potential of a typical 60 dislocation in a sphalerite crystal, and the Coulomb potential of a dislocation which crossed a junction plane other than at 90, varied with angle in the junction plane. The angular variation of the potentials could be qualitatively interpreted in terms of an angular modulation of the potential barrier. Because of the non-linear dependence of junction currents upon the barrier (or junction potential), the angular variation of the currents did not vanish upon averaging. It was found that the range of the Coulomb potential was too short to account for much of the experimentally observed performance degradation, but could be responsible for a decrease in zero-bias impedance at cryogenic temperatures and low dislocation densities. It was therefore proposed that the longer-ranged piezoelectric potential could be important. It was also found that the superposition of the potentials of neighboring dislocations, because of the non-linear dependence of junction leakage current upon junction potential, could account for an observed non-linearity of performance degradation as a function of dislocation density; as measured by using etch pit techniques.

A.T.Paxton, A.Sher, M.Berding, M.Van Schilfgaarde, M.W.Muller: Journal of Electronic Materials, 1995, 24[5], 525-32