The intrinsic concentration of electrons and holes (i.e. concentration of e-h pa

Question

The intrinsic concentration of electrons and holes (i.e. concentration of e-h pairs) in Si at room temperature is approximately 1x1010 cm-3.
Given the density and atomic mass of Si to be 2.33 g/cm3 and 28.06 g/mol, determine the ratio of ionized to
unionized Si atoms in the lattice.
Answer
A.
5.00x1022
B.
6.02x1023
C.
2.00x10-13
D.
4.00x10-10
E.
1.00x10-18
F.
2.00x10-10
G.
5.00x10-10
2 points
Question 2

At room temperature the intrinsic carrier concentration for InSb is 1.6x1022 m-3 and the electron and hole mobilities are 7.7 and 0.07 m2/V-s, respectively. Compute the conductivity of InSb at room temperature.
Answer
A.
200 (?-m)-1
B.
2x10-2 (?-m)-1
C.
2 (?-m)-1
D.
2x104 (?-m)-1
E.
20 (?-m)-1
F.
2x103 (?-m)-1
G.
2x10-4 (?-m)-1
2 points
Question 3

Calculate the resistivity of Si doped to a concentration of 2x1018m-3 boron (B) atoms given that the mobilities for electrons and holes
in silicon are 0.14 and 0.05 m2/V-s, respectively.
Answer
A.
62.5 ?-m
B.
0.016 ?-m
C.
22.3 ?-m
D.
0.061 ?-m
E.
16.4 ?-m
F.
0.045 ?-m
G.
32.0 ?-m

Explanation / Answer

I agree with question 2 having the solution of 2x10^4 (ohm-m)^-1

But question 3 I don't believe is correct because when I calculated the conductivity

conductivity=concentration*e*(mobility_electron+mobility_holes)

                  = 2*10^18*1.6e^-19(0.14+0.05) =0.0608

Then, since conductivity= 1/resistivity

1/0.0608 =16.4 ohm-m

If anyone can confirm these two solutions being true and possibley a hint for question 1, please share :)

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