The Atomic Arrangements and Radial Distribution Functions of Amorphous Silicon and Germanium

Abstract

Experimental scattering measurements of the radial distribution function (RDF), g(R), of amorphous silicon^1,2 and amorphous germanium,^1,3 plotted in Fig. 1, show that these substances preserve the local tetrahedral structure of their crystalline forms with peaks representing four first-neighbors at R_O and twelve second neighbors at (8/3)^1/2 R_O, where R_O is the crystalline first-neighbor distance. The short-range crystalline and amorphous RDF are, of course, quantitatively different. The first- and second-neighbor peaks in the amorphous RDF are somewhat broader than the corresponding peaks in the crystalline RDF. Thus, the local tetrahedral structure is somewhat distorted in the amorphous forms. However, it is only at larger values of R that qualitative differences between the crystalline and amorphous RDF become apparent. For example there is no peak in the amorphous RDF at the third-neighbor distance, (11/3)^1/2R_O, of the crystal.