The astounding success of microelectronics rests on a simple materials principle : creating a highly purified and perfected , spatially ordered semiconductor matrix , whose electrical and optical properties may be selectively adjusted by local substitutions of host atoms by dopant atoms. This unique materials utilization differs remarkably from all earlier technologies , because the controlled, almost imperceptibly small disorder by doping (rather than the ordered host ) dominates the relevant properties ! Defect control is thus a major concern for semiconductor technology. Homogeneity is an absolute necessity for this strategy, but only a few of the semiconductors can be made so homogeneous as to suppress the strong deleterious effects of inhomogeneity. Recent advances are summarized : atomic resolution of defect analyses, multiatom reactions and hope for applications,contactless measurements, gettering as well as detailed theory of simulations. The emergence of novel quantum devices, with both reduced dimensions and reduced dimensionalities heralds a paradigm change, since the quantizing small geometries exert stronger influences than defects do; nevertheless, materials perfection and interface control remain prerequisites for these structures.