A study of distortions and related electrical activity in dislocated Si-Cz ingots

This work aims at contributing to increase the understanding of crystal defects and their induced distortions in dislocated silicon Czochralski ingots. A popped-out ingot (PO), which experienced a premature detachment from the melt during the tail pulling step and an ingot with grown-in dislocations (GID), were studied. In each ingot, two wafers, cut at different heights, were characterized by photoluminescence (PL) mapping and Rocking Curve Imaging (RCI). Distortions and misorientations between crystal domains were quantified on large surface areas (up to one fourth) on the wafers. Dislocation densities in the order of a few 10 5 cm −2 were estimated in both ingots. In PO wafers, slip bands were found to be the main distortion structure. Additionally, round-shaped dislocation cells of 100 - 300 μm in diameter were observed. Dislocation densities and misorientations were found to decrease further from the detachment front. Different defects were identified in GID ingots: cellular dislocation pattern (500 to 1400 μm in diameter), boundaries, sub-grains and dislocation sources. Smaller dislocation cells were observed in regions with the highest distortion values. A good correlation is obtained between the distortion level distribution and thermal excess stress distribution maps calculated in the literature. As defects propagate in the ingot, cell sizes decrease, associated dislocation densities increase and the misorientation between domains swiftly increases. While sub-grain boundaries have a known effect on the charge carrier lifetimes, our result reveal the unexpected impact of dislocations cells, which are not visible on PL maps, on carrier lifetimes.