Metal-insulator transition in Si: As

Electrical conductivity σ of uncompensated Si: As has been measured in the temperature range 1.8-300 K, for a range of values of arsenic concentration nAs from 7.4×{}10¹⁸ to 10.5×{}10¹⁸ cm^-3. The value of nc, the critical concentration for the metal-insulator transition, is (7.8_-0.5+0.3)×{}10¹⁸ cm^-3 for Si: As. The ratio of nc for Si: As to nc for Si: P is about 20% higher than that given by a simple argument based on the difference in effective Bohr radii.