Structure of hydrogenated amorphous silicon-carbon alloys as investigated by extended x-ray-absorption fine structure

We have studied the local structure of hydrogenated amorphous silicon-carbon alloy films, a-Si_1-x{C}ₓ$:H, by measuring the extended x-ray-absorption fine structure at the Si K edge. We find that first-coordination-shell average bond lengths are 2.35 A{} for Si-Si and 1.86 A{} for Si-C and are constant with concentration to within ±{}0.015 A{}. By comparing the composition of the first coordination shell around Si with the average concentration, we show that the alloy tends to be chemically ordered, in that heteroatomic bonds are preferred.