The incorporation and activation of impurities is governed by a number of physical and chemical laws. It is essential to know and apply them in order to predict experimental functional dependencies of impurity incorporation. For example, the incorporation of many impurities depends on the epitaxial growth temperature. How does the electrical activity, compensation, etc. depend on this growth temperature? How are the impurity characteristics influenced by the V/III flux ratio? These are some of the questions that are of interest. Furthermore, some incorporation characteristics are found only for certain impurity elements. Autocompensation is prominent among group-IV impurities. In order to minimize autocompensation, it is desirable to know the functional dependences of amphoteric impurity incorporation.

Another example of impurity characteristics is the doping efficiency. This is defined as the ratio of the free carrier concentration and the dopant concentration. The doping efficiency is unity for an ideal dopant element and an ideal doping procedure. However, it can be quite low. For example, the doping efficiency of impurities incorporated by implantation can be below 10% before activation. The understanding of the principles governing the doping efficiency is therefore desirable.

Finally, very high doping concentrations become increasingly important as the spatial dimensions of semiconductor structures shrink. What are the highest doping concentrations achievable in III–V semiconductors? What limits the maximum impurity concentration? These are some of the topics and questions that will be addressed in this chapter.