The understanding of the defects within these materials was, and still is, absolutely essential for the development of modern semiconductor microelectronics. The idiosyncracy of germanium and silicon against foreign atoms was scientifically converted into the viable and indispensable method of doping. Conductivity can thus be controlled over huge ranges, an absolute prerequisite for electronics usage. Long lifetimes of injected carriers enable transistors to function. Measurements of lifetime are easy, yet they provide an incorruptible index for crystal purity and crystallographic perfection.
Many defects are vital, on the other hand.
The controlled substitution of a host atom by a specific foreign atom is the key idea of semiconductor materials engineering. Profound knowledge of the physics and chemistry of the defects yields the basis for these applications. The article by Queisser and Haller cites many examples for this research and its technical consequences. A multitude of experimental techniques are today available for the characterization of defects. The detailed atomic structures are nowadays clearly resolved, using techniques such as electron microscopy or tunneling microscopes.