Chemical (dis)order in a-Si1-xCx:H for x<0.6

We studied the local bonding structure of the hydrogenated amorphous silicon-carbon alloy system (a-Si1-xCx:H). The chemistry of the carbon incorporation in the alloys for 0<x<0.6 was analyzed by infrared and visible spectroscopies. The material was deposited in a controlled atmosphere of argon and hydrogen by rf cosputtering of Si and C targets. We found that up to x approximate to 0.2 the carbon atom prefers to bond in a chemically disordered configuration, i.e., homonuclear bonds are favored. Between 0.2<x<0.6 a tendency to chemical ordering is apparent. These results are consistent with the behavior of the optical gap, the Urbach energy, and the density of defects of the material as a function of x.