Subgap Absorption of Boron-Doped and Undoped a-SiC:H Detected by Photothermal Deflection Spectroscopy

Subgap absorption of boron-doped and undoped a-SiC:H alloys is studied by photothermal deflection spectroscopy (PDS). In undoped a-SiC:H, the PDS deduced mid-gap states density N_s shows saturation at 2-5% carbon flow ratio (C₂H₂/SiH₄), while Urbach energy monotonously increases with increasing carbon content. Doping with boron to a-SiC:H also increases N_s and Urbach energy, which tendency is similar to that of a-Si:H. There is no evidence of boron compensating the carbon-induced defects in a-SiC:H. The photoconductivity enhancement of a-SiC:H by doping boron must be attributed to the change of occupation in the gap states.