A new method of zone leveling for materials having distribution coefficients in the range of 0–0·6

Abstract

By doping an originally pure crystal at both ends and by subsequently melting it repeatedly back and forth, the calculated impurity distributions, as obtained after each pass, converge to a horizontal straight line. This is, therefore, a useful method for obtaining a uniform impurity distribution along a single crystal. In the last zone, however, the abrupt change in impurity concentration, due to the normal freezing cannot be avoided. The first doping of the crystal has to be done before the first pass and the second doping at the other end of the crystal after the first pass. Graphs are given for different values of k, for the length of the crystal in relation to the zone length and for the minimum number of passes needed to obtain a uniform impurity distribution. The results indicate that the method is extremely well suited for materials with values of k up to 0·6, while ordinary zone leveling fails for materials with a value of k between 0·1 and 1. In the new method the impurity content in any pass is proportional to the introduced impurity content at one end. Thus any desired uniform impurity distribution can be easily obtained.