The role of EL2 centres in infra red images of defects in GaAs materials

Careful measurements of the changes induced by photoquenching in the infra red transmission image of GaAs wafers at Liquid Nitrogen temperature shows an important enhancement of the mean light level and disappearance of the usual fourfold feature; but it also shows that the contrast of the pattern (cell structure) is not affected at all. The contribution of EL2 centres to the image is questioned; it is deduced from these results that photoquenchable EL 0 2 centres are slightly more abundant in the cells than in the walls. In large cell materials an intermediate zone is found surrounding the cells and containing higher EL 0 2 densities. This sheds new light on the role of the dislocations; these results are discussed and compared with etching and luminescence images.