Structural Studies Of Amorphous Semiconductor-Metal Alloys

It is well known that a semiconductor to metal transition may be induced in amorphous semiconductor-metal alloys by increasing the metal concentration above a critical limit. However, without a knowledge of the atomic scale structure of the alloy it is difficult to ascribe a mechanism to this process. Three alloy systems (a-Si1?xNix---H, a-Ge1?xAux and a-Si1?xSnx---H) have been prepared as thin films by rf reactive co-sputtering over pertinent composition ranges. The micro-structure of these alloys has been investigated using EXAFS. Both a-Si1?xNix---H and a-Ge1?xAux appear to consist of two separate phases, regions of an amorphous Ni---Si alloy and a crystalline Ge---Au alloy being embedded in an amorphous matrix provided by a-Si and a-Ge, respectively. In contrast, however, Sn atoms are substituted randomly into the a-Si tetrahedral random network.