Study of in-gap defects in intrinsic and B-doped a-Si(1-x)Cx : H by photo-induced optical absorption and photoluminescence

The infrared (IR) absorption dependence on visible light illumination has been measured in doped and undoped hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films grown by plasma enhanced chemical vapour deposition. The measurements were made by a highly sensitive technique which exploits properly designed a-Si1-xCx:H/ZnO test waveguides for lengthening the interaction region between the IR and visible (VIS) radiations in the material. Experimental data show that boron doping strongly enhances the VIS light induced variation of the IR absorption, whereas the increase in carbon content has a quenching effect on the phenomenon. The a-SiC:H films have been also characterized by photoluminescence measurements. The spectra are dominated by a photoluminescence band, ranging between 1.4 eV and 1.9 eV. This band is enhanced by the increase in carbon content, while is strongly quenched with increasing B-doping level. On the basis of these results, a correlation is found between the measurements of optical absorption, photo-induced absorption and photoluminescence. The type and the density of defects induced in the films by the different growth conditions have been recognized as the origin of the different behaviors observed.