Question

Mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an n-type semiconductor, the density of electrons is 10¹⁹m^–3 and their mobility is 1.6 m²/(V.s) then the resistivity of the semiconductor (since it is an n-type semiconductor contribution of holes is ignored) is close to: 

(1) 2$Ω$m 

(2) 0.4$Ω$m 

(3) 4$Ω$m 

(4) 0.2$Ω$m

Answer 1

Ans: (2) 0.4$\Omega$m

Sol: $j = \sigma E = nev_d$

$\sigma=ne{v_d\over E}$  

$=ne\mu$

${1\over\sigma}=\rho={1\over n_ee\mu_e}$

$={1\over10^{19}\times1.6\times10^{-19}\times1.6}$

$=0.4\Omega m$