On Ag-doping in amorphous Sb2S3 thin film by HeNe and HeCd laser exposures and its optical characteristics

The metal photodoping effect and material characterization in the system of Ag (10 nm)/a-Sb2S3 (300 nm)/Si-substrate have been investigated using a HeCd laser (λ=325.0 nm) and a HeNe laser (λ=632.8 nm). The Ag thin film is optically transparent for the HeCd laser light. Although an optical-bandgap shrinkage (negative ΔEop or darkening) due to the Ag-doping is observed in the all films exposed to each laser, the ΔEop dependency on photon dose and the Ag-doping profiles are distinctly different. While the maximum value of ΔEop in Sb2S3 films exposed to HeCd laser saturates at about −0.08 eV, the ΔEop in Sb2S3 films exposed to HeNe laser is not saturated and the maximum is a relatively large value (about −0.25 eV). The doping front (with a peak Ag concentration) on the Ag depth profiles always exists at an interface between the chalcogenide and semiconducting substrate. In the case of films exposed to HeNe laser, however, the Ag at the chalcogenide surface is completely depleted and the peak shape appears to be broadly distributed with the doping front as a symmetry center. On the other hand, the films exposed to HeCd laser exhibit a relatively uniform Ag distribution without a surface depletion and with a sharp peak shape. Of course, these differences in Ag-doping phenomena can be ascribed to the differences of optical energy for two types of lasers (above-Eop and sub-Eop exposures). However, we believe that it is also important whether the Ag layer absorbs optically an incident laser power or not, i.e., thermally.