Electrical conductivity $\sigma$ of uncompensated Si: As has been measured in the temperature range 1.8-300 K, for a range of values of arsenic concentration $n_{\mathrm{As}}$ from 7.4×${10}^{18}$ to 10.5×${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The value of $n_c$, the critical concentration for the metal-insulator transition, is (${7.8}_{-0.5\mathrm{}}^{+0.3\mathrm{}}$)×${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ for Si: As. The ratio of $n_c$ for Si: As to $n_c$ for Si: P is about 20% higher than that given by a simple argument based on the difference in effective Bohr radii.

• Received 24 February 1983

DOI:https://doi.org/10.1103/PhysRevB.28.638