Spatial variation of activation energy in undoped high-resistivity bulk GaAs

Abstract

In undoped semi-insulating GaAs grown by the liquid encapsulated Czochralski or vertical gradient freezing technique mesoscopic electrical nonuniformities correlated to the cellular structure of dislocations exist which are mainly caused by the enrichment of the deep defect level EL2 in the dislocation-rich cell walls. In undoped GaAs crystals with a transition semi-insulating/medium resistivity in the transition region, the resistivity fluctuations between cell walls and cell interiors are much more pronounced (up to three orders of magnitude) and must be caused by different donors. A point contact technique developed for the detection of such nonuniformities was used to measure activation energies separately in cell walls and in cell interiors. In this way, it could be shown that also other defects or impurities than the EL2 are accumulated in the cell walls so that different donor species dominate the electrical properties of cell walls and of cell interiors.