Question:

Given that the mobility of electrons in Ge is 0.4 m²/Vs and electronic charge is 1.6 × 10⁻⁹ C. The number of donor atom (per m³) semiconductor of conductivity 500 mho/m is

8×10²¹

8×10¹⁵

5×10²¹

8×10¹⁶

Using, σ = neμe
Here, σ = 500 mho/m
e = 1.6 × 10⁻⁹ C
μe = 0.4 m²/Vs
∴ ne = 500 / (1.6 × 10⁻⁹ × 0.4) = 7.8 × 10²¹ ≈ 8 × 10²¹ m⁻³