The concentration of hole-electron pairs in pure silicon at T = 350 K is 7 × 1015 per cubic meter. Antinomy is doped into silicon in a proportion of 1 atom in 107 atoms. Assuming that half of the impurity atoms contribute electrons in the conduction band, the factor by which the number of charge carriers increases due to doping (the number of silicon atoms per cubic meter is 5 × 1028) is

• A. 14 × 1015
• B. 0.5 × 1021
• C. 2.5 × 1021
• D. 1.8 × 105