CHEMICAL (DIS)ORDER IN A-SI1-XCX-H FOR X-LESS-THAN-0.6

We studied the local bonding structure of the hydrogenated amorphous s ilicon-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 v isible spectroscopies. The material was deposited in a controlled atmo sphere of argon and hydrogen by rf cosputtering of Si and C targets. W e found that up to x approximate to 0.2 the carbon atom prefers to bon d in a chemically disordered configuration, i.e., homonuclear bonds ar e favored. Between 0.2<x<0.6 a tendency to chemical ordering is appare nt. These results are consistent with the behavior of the optical gap, the Urbach energy, and the density of defects of the material as a fu nction of x.