Electrical Characterization of Cu and Al Doped Amorphous Semiconductor As2Se3
The electrical conductivity and thermoelectric power of an amorphous semiconductor As2Se3 in pure and doped forms were studied with temperature. The dopants used were 1 at. % Cu and 1 at. % AI. Measurements on electrical conductivity were performed in the temperature range 223-573 K and that of thermoelectric power in the temperature range 343-473 K. The effects of the impurities on the conductivity and thermoelectric power of amorphous As2Se3 are small. The samples showed conductivity activation energies. The electrical conductivity versus inverse temperature curves showed a break at low temperatures. The activation energy of conduction, E , above room temperature were found to be 0.77 ± 0.09 eV, 0.82 ± 0.09 eV, and 0.64•± 0.03 eV for pure , Cu doped, and Al doped samples respectively. The thermoelectric power varied linearly with inverse temperature and all samples were found to be p-type. The activation energy, ES' from thermoelectric power measurements were found to be 0.96 ± 0.06 eV, 0.87 ± 0.02 eV, and 0.84 ± 0.05 eV for pure, Cu doped, and Al doped samples respectively. Most of the above results have been explained on the basis of the CFO and the dangling bond models. The CFO model postulates a mobility edge and overlapping tails of localized states in the energy gap and in the dangling bond model, charged defects D+, DO, D-, exist in the energy gap, which act as traps to charge carriers.