GAP-STATE DEFECTS IN HYDROGENATED AMORPHOUS SILICON-CARBON ALLOYS STUDIED BY PHOTOTHERMAL DEFLECTION SPECTROSCOPY

By using Photothermal Deflection Spectroscopy (PDS), defect gap states have been optically investigated in hydrogenated amorphous silicon-carbon alloys (a-Si1-xCx:H). The density of stable defects and metastable dangling bonds induced by white and 1.17 eV laser tight were measured for carbon concentrations varying from 0 to 45 %. There is a gradual enchancement of the density of stable defects in the alloy with carbon concentration. The density of photo-induced defects presents a small fraction of the stable defects in the low carbon content material and equals the density of stable defects for x=0.45. The evolution of the different densities of gap states in a-SiC:H is essentially a consequence of stronger Si-C and C-C bonds compared to Si-Si and the tendency for carbon atoms to adopt a coordination number of three.