Novel n-type conducting amorphous chalcogenide CdS · In₂S_x: An extension of working hypothesis for conducting amorphous oxides

Novel n-type conducting amorphous Cd-In-S chalcogenide have been prepared by extending a working hypothesis to explore transparent conducting amorphous oxide to chalcogenides. The dc conductivity of the as-deposited samples is ∼10^-4 S cm^-1 at 300 K and can be further increased to ∼10^-2 S cm^-1 by heat treatment at temperature less than crystallization temperature. The activation energy of dark conductivity was ∼0.3 eV in the as-deposited samples and ∼0.13 eV for the annealed samples. Both activation energies are much less than the half of the Taue optical band gap (∼2.2 eV). Variable-range hopping was observed in the annealed samples at temperatures below 40 K. The signs of Seebeck and Hall coefficients were negative, indicating that conduction is n-type and no sign anomaly was observed in the Hall voltage. We suggest that the Fermi energy is controllable by doping of carrier electrons via thermal formation of the anion vacancy as has been observed in amorphous ionic oxides such as Cd₂PbO₄.