Lightly Al-doped Ta2O5: Electrical properties and mechanisms of conductivity

Lightly Al-doped Ta2O5 films (10;15 nm) obtained by rf sputtering have been studied with respect to their dielectric and electrical properties. The formed metal–high-k dielectric–semiconductor capacitors have been characterized by capacitance–voltage and temperature-dependent current–voltage characteristics. It was established that the introduction of small amount (5 at.%) Al into the matrix of Ta2O5 improves dielectric constant, introduces negative oxide charge, suppresses deep oxygen-vacancy centers in Ta2O5 but creates shallow traps and changes the dominant conduction mechanism in the stacks. The doping produces more leaky films at room temperature and lower current at high temperature as compared to the case of pure Ta2O5. It is concluded that the strong contribution of tunneling processes through shallow traps in the conductivity of doped films could explain the observed current degradation at room temperature and its improved temperature stability at high temperatures. The energy levels of the traps responsible for the current transport are estimated.

► Lightly Al-doped Ta2O5 high-k films deposited, (5 at.% Al). ► Al introduces negative charge in Ta2O5 and creates shallow traps. ► Тunneling through shallow traps results in current stability at high temperatures.