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 (lambda = 325.0 nm) and a HeNe laser (lambda = 632.8 nm). The AE thin film is optically transparent for the HeCd laser light. Although an optical-bandgap shrinkage (negative DeltaE(op) or darkening) due to the Ag-doping is observed in the all films exposed to each laser, the DeltaE(op) dependency on photon dose and the Ag-doping profiles are distinctly different. While the maximum value of DeltaE(op) in Sb2S3 films exposed to HeCd laser saturates at about -0.08 eV, the DeltaE(op) 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-E-op and sub-E-op exposures). However, we believe that it is also important whether the Ag layer absorbs optically an incident laser power or not, i.e., thermally. (C) 2001 Elsevier Science B.V. All rights reserved.