Conductive strontium titanate layers produced by boron-ion implantation

The ion implantation of boron has been found to be an effective method for increasing the conductivity of strontium titanate. A highly conductive layer was formed by implantations at doses of 3.6×1016 to 1.0×1017 ions/cm2, using an accelerating voltage of 100 kV, corresponding to a boron range of about 300 nm. The conductivity of the implanted layer was found to be further enhanced by about four orders of magnitude after annealing at 225 °C. The surface resistivity attained was typically 1000 Ω/square at room temperature. The resistance increased with rising temperature between 77 and 500 K. All samples were found to be n type, as determined by Hall-effect and thermoelectric measurements. The measured Hall mobility range was from 100 cm2/V sec at 77 K, decreasing to 5 cm2/V sec at 300 K. The existence of several defect energy levels can be inferred from the electrical data.